Home » Are Cross-Drilled Brake Rotors Worth Your Money?: Ask An Engineer

Are Cross-Drilled Brake Rotors Worth Your Money?: Ask An Engineer

Cross Drilled Ts2
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Dear fellow Autopians, welcome to another edition of Ask An Engineer. I got a question a while ago from one of our astute readers who wanted to know why some high performance cars and high performance brake upgrades have rotors full of holes. What’s the point of all these holes? Do they actually improve braking performance or are they only there to look cool? Let’s get into somer nerdy physics to discuss how brake rotors work, and then we’ll delve into whether cross-drilled ones are worth your time.

I’ve been thinking about this question myself for many years, and I figured this would be a good time to find the answers. I thought that rather than develop my own theories, I better contact some experts. I contacted Brembo North America, the North American arm of Brembo S.p.a., and they were kind enough to indulge my questions. And while I wasn’t able to interview any of their engineers directly, they did respond to my questions in writing.

Vidframe Min Top
Vidframe Min Bottom
Image (131)
Image via Mercedes

Why Cross Drill?

The term “cross-drilled rotor” refers to a brake rotor that has been drilled with a cross-wise series of holes. Most brake rotors have a smooth un-blemished surface where the brake pads sit:

Cross Drilled Rotors 4
Image via: Amazon.com: Centric Premium Replacement Front Disc Brake Rotor for Select Honda and Acura Model Years (120.40046) : Automotive

A cross-drilled rotor, on the other hand, contains a series of holes in this area:

Cross Drilled Rotors 5
Image via: Mercedes-Benz Brake Rotor (C63 AMG, C63 AMG S, CL600, E550, SLC43 AMG, 360x36mm, Front) 000421201207 by Fremax | Europa Parts

While the term “cross-drilled” suggests the holes are drilled into the disc after it is made, it is more common nowadays for the holes to be cast into the rotor as part of the casting process. Drilling holes can lead to cracks later in the life of the rotor, so most manufacturers create them as part of the initial forming process. This ensures the impact on the strength and durability of the rotor is minimized.

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Most car enthusiasts I talked to about this see cross-drilled rotors as a cool upgrade. Some race cars have them so they must be good for the street, right? But beyond the esthetics and the fact that some race cars use them, are there engineering reasons why you should put them on your car?

According to Brembo:

Among other things, cross-drilling provides a pathway for gasses created during the friction process to escape. As most would expect, there is often an accompanying reduction in weight as well. Where aesthetics are concerned, depending on your year of birth or simply where you land on the topic, it’s entirely possible that nothing looks cooler behind a wheel than a cross-drilled brake disc.

Fair enough, but I wanted to know more. Cross drilling is a lot of work and expense to go through just for looks and to let a few gasses escape.

To better understand the impact of cross drilling, we need to dig into some of the engineering behind brakes, and look specifically at the function of brake rotors.

Energy

At a very fundamental level, the entire braking system in a vehicle is an energy conversion device. Its entire purpose is to convert the energy of motion onto heat. All objects, when they are in motion, have what is known as Kinetic Energy. It goes back to Sir Isaac Newton’s first law of motion, which states: “An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.”

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The second part of that law is key here: An object in motion remains in motion… unless acted on by an unbalance force. By the way, don’t get weirded out by the words “unbalance force.” That’s just engineering speak for a force that pushes on the object in some way.

So, an object that is in motion wants to stay in motion because it has energy that wants to keep it that way.

Mathematically speaking, this “kinetic” energy is:

KE = 1/2 x Mass x Velocity²

Kinetic Energy is 1/2 the mass of the object times the square of its speed. You can think about it as the amount of energy it took to get it up to that speed. If something is heavy, it takes more energy to get it up to speed vs something that is light. And it takes more energy to get something up to a higher speed than a slower speed. Makes sense, right?

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Once you have an object in motion, if you want to change that motion, i.e. if you want to change the direction it’s moving in, or you want to speed it up or slow it down, you have to provide the “unbalance” force that Newton was talking about. There are many ways to do this. You could push on the object sideways to make it deviate from the “straight line” it is traveling on. This would be like steering the wheels on a car, causing the tires to generate a sideways force. Or you could push on the car from behind to make it go faster (in effect, increasing its energy). Lastly you could push on it from the front to slow it down.

Pushing on it from the side won’t change the amount of energy the object has, it just changes its direction, and pushing from behind would increase its energy and thereby its speed. Pushing from the front would slow it down. But, you say, the kinetic energy equation contains velocity, so if we slow an object down, aren’t we changing its energy? To which I say, “You are absolutely correct, grasshopper. Very astute of you.” Slowing something down does indeed reduce its kinetic energy because we have reduced its velocity.

But now we get into another fundamental area of physics which is governed by what is known as the Conservation of Energy law. This law states that energy can neither be created nor destroyed. Wait a minute. You’re saying that all the energy I had after drinking that cup of coffee (which has little caloric value) this morning was already there? What about when I get tired? What happened to all my energy? Well, the energy you had this morning came from the steak you ate yesterday, which came from the cow that gave up its life for your dinner. The cow grew from the grass it ate in the fields and the grass came from the sunlight and the rain that fell on it. The sunlight came from the fusion reaction happening in the sun which came from the hydrogen molecules in the sun.

Those molecules came from the gaseous cloud that created the sun a few billion years ago, which came from other stars that blew up a few billion years before that. Eventually, if you trace it back far enough you get to the big bang and maybe even before that. So, all the energy you had this morning and all the energy you will ever have in your lifetime has always existed and will always exist in one form or another.

But, I’m talking here about stuff like hydrogen molecules and grass and energy as if it’s all the same thing. Well, that’s because fundamentally they ARE the same thing, and as proof, I give you Albert Einstein’s famous Theory of Relativity which states:

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Energy = Mass x (Speed of light)²

This means that any object is actually nothing more than a bunch of energy, and if you could convert an object into energy, the Theory of Relativity tells you how much energy you could get.

Get To The Point Already

Well, that’s all very interesting, but this article is supposed to be about brake rotors, not high-level physics, so let’s get out of these weeds and back to the good stuff. You’ll see in a minute why we had to take this little diversion.

As we saw earlier, if we want to slow an object down, we need to reduce its kinetic energy. But we also learned that we cannot create or destroy energy. If we then want to reduce the energy of a moving object and we cannot simply destroy the energy it has, we need to do something else with it. We have to send it somewhere else. One thing we could so is transfer the energy to another object. This is what happens in a Newton’s Cradle children’s toy:

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Newtons Cradle Animation Book 2
Image via Newtons cradle animation book 2 – Newton’s cradle – Wikipedia Creative Commons: DemonDeLuxe (Dominique Toussaint)

The energy of one moving ball is transferred through the other balls until it finds the last ball and gives it motion. That ball then moves until gravity brings it back and the cycle starts over again.

Brake Rotors 101

We could reduce the kinetic energy of a car to nothing by running the car into a tree or brick wall. In that case, the kinetic energy is converted into twisted metal, broken bits, and noise. But that’s not very practical, so that’s where brakes come in.

The brake system takes the energy of motion and converts it not into the motion of another object or into destruction and mayhem, but instead into heat. Brakes slow down a car by taking the cars’ kinetic energy and using it to heat up the brake rotors. And this is where the design and configuration of the brake rotors plays such an integral role.

A car is a pretty heavy thing, and when you multiply even half of that by the square of its speed, that’s a LOT of energy. Converting that into heat means we get a LOT of heat, and that heat has to go somewhere. Normally, there are two places where we can get put heat: we can store it in some object, like the brake rotors, or we can send it into the air.

Storing heat in the rotors means their temperature goes up, which is fine but there is a limit to how hot we can let the rotors get because the hotter they get, the harder it gets to put more heat into them, and eventually they just melt anyway. So, the preferred method is to transfer the heat into the air as quickly as possible, and that’s what brake rotors are designed to do. But sending heat into the air takes time, and when you need to stop a car RIGHT NOW, you don’t have a lot of time. So, the first thing that happens when you hit the brakes is the rotors heat up, and then, as you drive further, the heat gets sent into the air and out the back of the car.

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Leaky Buckets

Think of it as pouring water into a bucket that has a hole in the bottom. You want to pour as much water (which is analogous to heat here) through that bucket as quickly as possible. As you pour water in, it starts to leak out the bottom, but if the hole is relatively small, there will come a point where you can’t pour any more water into it and you have to wait until some or all the water drains out the bottom. Brake rotors work the same way.

But there are ways to make the bucket bigger and/or make the hole in the bottom bigger, figuratively speaking.

Bigger Buckets

As you put heat into an object, like a brake rotor, its temperature will go up based on the formula:

ΔT = Q/(M x C)

The change in temperature (ΔT) is equal to the amount of heat you put in (Q) divided by the mass of the object you are heating up (M) times the specific heat of the material the object is made of (C). The specific heat of the material is something that is intrinsic to the material and doesn’t change, no matter how you design the rotor. For example, if the rotor is made of cast iron then the specific heat (C) is equal to 0.46 KJ/(Kg K). Don’t worry about the crazy units after the number 0.46. All you need to know is that this number is the same for all cast iron rotors. If your rotors are made of some other material, like carbon ceramic, this number will be different. The number represent’s the material’s capacity to absorb heat.

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What we need to understand about this formula is that if we increase Q, in other words if we increase the amount of heat we put in, the change in temperature will get bigger. Makes sense, right? But what we also need to understand is that if we make the object bigger, i.e., if we make the mass (M) bigger, then the change in temperature gets smaller. In other words, if we put a specific amount of heat into a small, light object, the increase in temperature will be bigger than if we put the same amount of heat into a bigger, heavier object. That also makes sense.

Basically, if we make the rotor bigger and heavier, we have made our bucket bigger because we can put more heat into it before the temperature gets too high and the thing can’t take any more or melts.

Bigger Hole

The other part of rotor design gets into the way we get rid of the heat once it is in the rotor. Remember how we said we couldn’t destroy energy? Since we can’t just destroy the heat that’s in the rotors, we have to send it somewhere else and that somewhere else is the air. We need to somehow get the heat into the air so it can be sent out the back of the car and away from our rotors. That’s where brake cooling comes in. We need to get as much of our brake rotors in contact with the air so the heat can pass from the rotors to the air as fast as possible. Doing this would be like making the hole in the bottom of our bucket bigger so more water can pass through it more quickly and our bucket drains faster.

Rotor Designs

Let’s take a look at some rotor designs. Cast iron brake rotors come in two basic varieties: solid and vented.

Solid Rotor
Solid Rotor. Image via BrakeBest Select Pro Brake Rotor 7771645 | O’Reilly Auto Parts (oreillyauto.com)
Vented Rotor
Vented Rotor. Image via NAPA Premium Brake Rotor NB 4885608 | Buy Online – NAPA Auto Parts (napaonline.com)

Notice how the solid rotor has a relatively thin single disc while the vented rotor has two similar thickness discs connected together by a bunch of short posts or fins. These posts form a gap between the discs (called the cheeks) that is open to the inside of the rotor, as you can see here:

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Vented Rotor Inside
Image via Subaru BRZ Disc Brake Rotor. Brake Disk (Front) – 26300SA001 | Suburban Subaru, Vernon CT

Having these gaps allows air to pass between the rotor surfaces and adds area to the back of each surface so more heat can transfer from the cast iron to the air.

Looking at these two different rotor designs, it is clear that the vented rotor contains a lot more material (i.e. is a much bigger bucket) than the solid rotor, and having the gap between the surfaces adds a lot of area (acting like a much bigger hole in the bucket) to transfer heat to the air.

Of course, the gap isn’t very useful if we can’t somehow provide a lot of air to the rotor so it can pass through it. In most street cars, this can be difficult to do since there are a lot of other things in the way: wheel bearings, dust shields, other suspension components. Getting lots of air into that area of the car can be difficult because we really want the air to pass smoothly over and under the car instead of up and inside the wheels.

Any time we divert air from moving smoothly over and under the car adds aerodynamic resistance, and we want to minimize that as much as possible for other reasons. Racecars, on the other hand, are much less sensitive to these aerodynamic problems, and you’ll find lots of methods used to direct air to the brakes to help cool them. This 1982 Lotus Formula 1 car used a plastic duct to direct air through the spindle to the inside of the brake rotors:

Cross Drilled Rotors 1

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Cross Drilled Rotors 2

Other times you may see large hoses used to direct air to the brakes:

Cross Drilled Rotors 3

While they are great in racing, these aren’t really practical in normal street cars because the space simply isn’t available inside the wheelhouse area. Racecars have a lot more options in this regard.

Cross Drilling

We saw earlier how adding a gap between the faces of the rotor adds surface area and allows better cooling. But what if we could increase the surface area even more? That would make the hole in our proverbial bucket even bigger. If we drilled a whole bunch of holes through the rotor, each of these holes would add more surface area and allow even more air to cool it. I asked Brembo if this was true:

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In conditions of heavy use, technically speaking cooling benefits of cross-drilling will increase or decrease relative to certain variables such as general disc design, the existence of vehicle ducted cooling, etc. In our years of racing experience, we have encountered certain applications where there has been evidence indicating measurable benefit with regard to operating temperatures. In other cases, we’ve not seen this. Again, any benefits realized tend to be application and usage specific. There are simply too many variables involved to have a “one size fits all” answer here.

But, drilling holes in our rotors removes material and we saw in our temperature formula how important mass is to helping keep the temperature down. I asked Brembo about this as well:

In general, high performance road going, street legal applications this is not a factor. On the other hand, if you have a vehicle which is set up for pure racing conditions while using OE sized brakes, an argument could be made that issues might be possible with a loss of thermal mass. Whichever application you have, it’s important to note that there is a right way (and several wrong ways) to cross-drill a brake disc. Details matter here – discs which have not been cross-drilled using the correct technique bring a level of risk regardless of intended usage.

So, cross drilling CAN be a benefit under the right circumstances. The added holes do add surface area, but that is only useful if we can provide the needed airflow so enough air can move through those holes to make a difference. In a racecar, there are many possibilities to make that happen but in a normal street car, we are stuck with the airflow we have, and it is usually minimal at best. The loss of mass in a rotor could, theoretically, be a bad thing, since mass helps absorb more heat, but experts don’t think that’s significant enough to matter in a street car. So the answer of whether cross-drilled rotors are useful clearly depends on the application.

Dust and Gasses

In the answer Brembo provided to my first question, they mentioned letting gasses escape. I wanted to find out more about this, and also about how the dust that is normally produced during braking is cleared away from the pads. Do cross drilled holes more effectively help clean this dust off the pads?

In our experience, pad life tends be overwhelmingly determined by things like temperature, speed, pressure, and time. That said, any disc which has been machined correctly and provides a pathway for friction dust and gasses to escape, will typically promote more consistent pad performance and overall life in high performance use.

So, cross drilling does help promote better pad life as long as it’s done correctly.

Cross-drilling isn’t the only way to help clear dust, though. Another way to allow gasses and dust to escape is by using slots:

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Slotted Rotor
Image via 126.61104SL StopTech Front Left Slotted Brake Rotor – Fits 2013-2017 Ford Fusion (napaonline.com)

I have used these in my suspension designs in the past and wanted to know which was better, slots or cross drilling?

For the vast majority of street legal vehicles, high performance or otherwise, if you’re looking at a “Brembo” disc I’d say you’re free to simply choose the one you like better. When you get to professional level, purpose-built race cars where all aspects of cooling, thermal capacities, etc. have been optimized, then we tend to find that different slotting designs offer us some level of control with regard to things like pad engagement, release, and overall life. This is why slotted discs tend to be more prevalent among certain realms of the racing world.

In summary then, cross drilling CAN be helpful under the right conditions and in the right suspension and vehicle environment. In general, though, these conditions do not exist in normal street cars so the question then becomes “does it hurt performance” and I think the answer to that is almost certainly: “no.” So it boils down to personal preference. Do you like the look of cross-drilled rotors? If you do, then go for it. You do you. But don’t expect to get a performance benefit. If that brake system upgrade you installed on your Mustang or BRZ with the cross-drilled rotors made the brakes feel better and stronger, it was probably due to some other change that came as part of the kit: bigger rotors or more aggressive pads, for instance.

But even if you didn’t get a performance upgrade, cross-drilled rotors do look cool!

Got a suspension question? Send it to AskAnEngineer@theautopian.com

[Editor’s Note: We made a little mistake (unrelated to the core of the article) in an earlier version. It’s gone now! Mistakes happen. Thanks! – JT]

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Der Foo
Der Foo
9 months ago

I used slotted rotors for probably 7 years on my Acura. The only negative was vibrations due to the slots. Not warped rotor feel, but buzzing from the slots. Not bad enough that I wouldn’t consider using them again.

Vetatur Fumare
Vetatur Fumare
9 months ago

Question: I have been told repeatedly that rear disc brakes are not much good for everyday drivers – drums providing all the braking power one needs away from the racetrack, with lower cost and much less maintenance. The calipers on the rear disc brakes on my neighbor’s car seized from disuse, so I think there is a good case for drums at the rear.
But perhaps with today’s porky vehicles, the math has changed?

Preston Tiegs
Preston Tiegs
9 months ago
Reply to  Vetatur Fumare

The absolute PITA of repairing drum brakes are enough reason for me to be on team disc

Phuzz
Phuzz
9 months ago
Reply to  Vetatur Fumare

You might need to replace brake shoes less than brake pads (although in my experience they tended to last a similar length of time), but changing brake shoes takes hours, will test your patience to the limit chasing those fucking springs across the garage for the fifth time, and will probably draw blood.
Discs all round isn’t a performance upgrade, it’s self care.

Unclewolverine
Unclewolverine
9 months ago
Reply to  Vetatur Fumare

Not sure, but drums offer less drag too, since the shoes are not in constant contact with the drum unlike pads.

Anthony Magagnoli
Anthony Magagnoli
9 months ago
Reply to  Unclewolverine

Modern cars manage the spring back and will even ensure the pads stay closer to the rotor when the wipers are on to keep the rotors from being wet when you first go to grab the brakes.

Vetatur Fumare
Vetatur Fumare
9 months ago
Reply to  Huibert Mees

Yeah, but the rear brakes do so little work that I don’t see them getting very warm.
From personal experience, I have never really had to do anything to the rear drums on any of the cars I’ve owned.

Jakob K's Garage
Jakob K's Garage
9 months ago

Nice explanation (thumbs up emoji)

Makes me wonder why more rims aren’t formed like turbines sucking in air for the brakes then?

And appreciate the underside disc brake cooling ducts on my old Citroën DS21, which I have always just found a bit silly really.

Could have used a little more on those escaping gasses though.

Anthony Magagnoli
Anthony Magagnoli
9 months ago

Rotors are natural air pumps through diffusion through the expansion area in the vanes from inside to outside.

Abdominal Snoman
Abdominal Snoman
9 months ago

Having spent a couple 10’s of thousands of dollars on brakes for lemons and wrl race cars over the last decade, I’ve come to the conclusion that only 2 things seem to matter… First, buy a good pad that is appropriate to the car and track you’re going to be on and appropriate to the temperature the race will be held at. This makes 80% of the difference you’ll be able to notice. Second, ducting, as much of it as you can. This is key to our cars and not because the brakes overheat, but because there’s one other place the rotor can displace heat that’s not mentioned in this article that can make a huge difference in the life of other components. In addition to displacing the heat into the air, the rotor is also in contact with the hub, which is held in place by the wheel bearing. These really don’t like getting heated up to the same temperature as the rotor and we kept having constant wheel bearing and cv axle failures till we switched to 2 piece rotors so less heat from the surface area can be transmitted to the hub, and we went as overboard on cooling as space allowed. Never once did we notice any difference from a $25 rotor to a $250 rotor. It really boils down to be pick the right pad for what you’re doing, and keep that pad at the temperature range it works in. (Also change your brake fluid regularly, but that should be a given. Once a year on my street cars is more than enough IMO, and on the race cars it’s generally every 3 months or 2 races)

Anthony Magagnoli
Anthony Magagnoli
9 months ago

It’s been found, and we’ve confirmed, that good air DEFLECTION into the rotor area (and wheel bearing, etc), with backing plates removed, can have just as good or better results than running ducts to backing plates. This was on a GT350 racecar, even at high speed and/or high elevation tracks with high ambient temps (Road America, Utah Motorsports Campus @90+ F). You see many OEMs employing this solution.

William Sheldon
William Sheldon
9 months ago

The photog for the napa disk brake couldnt be bothered to rotate the disk so the large chip wouldn’t show? hahaha
Or maybe, perhaps it’s an accurate representation of the product?

James Mason
James Mason
9 months ago

I prefer cross-drilling my brake lines (thanks KaleCoAuto). It keeps that pesky fluid from building up pressure and having nowhere to go.

The Clutch Rider
The Clutch Rider
9 months ago
Reply to  James Mason

personally, i prefer cross drilled tires.

Shooting Brake
Shooting Brake
9 months ago

Interesting article. 6 years ago I installed Power Stop brand Front and Rear Carbon Fiber Brake Pads with Drilled & Slotted Brake Rotors on my 2011 Volvo C30 and after performing the break in procedure provided by the manufacturer I noticed right away that the brakes grabbed much better than the OEM brakes. I’d say that with applying 30%(W.A.G.) less brake pedal force ,the new brakes stop quicker than the OEM and I no longer have any brake dust.

I am still driving on them today, 6 years and 40K miles later.

Last edited 9 months ago by Shooting Brake
lastwraith
lastwraith
9 months ago
Reply to  Shooting Brake

Couldn’t that easily be due to the materials change and not necessarily the drilling or slotting?

Shooting Brake
Shooting Brake
9 months ago
Reply to  lastwraith

Yes, of course, the new pads are Carbon Fiber whereas the old ones were metallic. So I am happy with shorter stopping distances and NO BRAKE DUST .
( which I hate cleaning)

Stacheface
Stacheface
9 months ago
Reply to  Shooting Brake

Power Stop came to mind for me too, since I found them a few years ago I put them on my cars and truck. Compared to a premium ceramic brake pad, theirs are MUCH better in braking distance (I initially got them for better braking when towing). Maybe the drilled and slotted rotors help, or maybe it is just their carbon fiber ceramic vs regular ceramic pads, but they do work. And, they sure look cool, especially on cars you wouldn’t expect – 2000 Beetle and a newer Forester.

Shooting Brake
Shooting Brake
9 months ago
Reply to  Stacheface

I would do It again, I have been happy with the results.

Manuel Verissimo
Manuel Verissimo
9 months ago

Dang, another cool topic scooped up by Huibert. No rush to finish my draft on brakes then.

Crank Shaft
Crank Shaft
9 months ago

I recall that Mercedes Benz said that the reason they started using them as standard equipment on the S Class is because cross drilling improved initial bite.

Paul B
Paul B
9 months ago

I thought e=mc^2 was how you put bubbles in beer.

Hoonicus
Hoonicus
9 months ago
Reply to  Paul B

Surely you can’t be Yahoo Serious. Hadn’t thought of that fascinating documentary of Einstein’s early years in Australia for a long time- which is relative you know.

pizzaman09
pizzaman09
9 months ago

I’ve been consistently disappointed in cross drilled and slotted rotors and always pleased with smooth rotors. I’ve always found that cross drilled and slotted rotors can be noisy at times, vibrate at times and trap ice making them useless. One my cars with smooth rotor brakes I’ve never had this issue.

Of course I am not a hard breaker, I’ve never worn out a set of pads on any car, but have consistently ruined, warped or justed needed to replace many sets of rotors. Doesn’t matter the car, Oldsmobile 88, BMW E36, Jeep Comanche, Mini R56, all have had similar issues to what I describe above.

Sklooner
Sklooner
9 months ago

Having just spent 5 hours beating the rusted rotors off my XC60 I wonder is sledge hammer divots improve braking or not

Paul B
Paul B
9 months ago
Reply to  Sklooner

Coated rotors are the bee’s knees in salty climates.

It’s amazing how tiring beating off the rotors is.

121gwats
121gwats
9 months ago
Reply to  Paul B

Also can grease the back of them after sanding surface rust

Sklooner
Sklooner
9 months ago
Reply to  121gwats

Yeah they were shiny where the studs were it was all around the edge where it was rusty- never had any that stuck before even in Montreal where the roads are paved with salt

PaysOutAllNight
PaysOutAllNight
9 months ago
Reply to  121gwats

Don’t use grease, use anti-seize compound.

Also, modern Toyotas have one or more threaded holes in the top of the rotor hat. Run a bolt into that threaded hole and it pushes the rotor right off. I suspect many other brands have that, too, but I’ve only personally used it on a Toyota.

Last edited 9 months ago by PaysOutAllNight
121gwats
121gwats
9 months ago

While you’re correct, and I do use anti-seize when it’s close by, grease works just as well for rotors if you change them an a regular interval. 20 years, haven’t had an issue. The point is, don’t go in the rain without a coat.

Thomas Metcalf
Thomas Metcalf
9 months ago
Reply to  Sklooner

I anti-seize the crap out of the mating surface when I put new rotors on a car.

Taargus Taargus
Taargus Taargus
9 months ago
Reply to  Thomas Metcalf

Yeah, I’ve replaced rotors a few times and I goop anti-seize on there like crazy. Someone out there is enjoying a stress-free rotor change thanks to me getting rid of all my cars before I see the benefits, lol.

PaysOutAllNight
PaysOutAllNight
9 months ago

I’ve found that a light coat on both surfaces is more than enough; more than that makes a huge mess when going back later.

If you’re getting rid of the car before seeing the benefits, you’re also getting rid of the car before you see that you’re using too much.

Taargus Taargus
Taargus Taargus
9 months ago

This is true.

I am sort of exaggerating the use, but I’m definitely not shy with the stuff. And honestly, I hope both of those cars survive long enough to see another rotor replacement. Especially the SX4.

SonOfLP500
SonOfLP500
9 months ago

Many, many moons ago I read or heard somewhere that drilling discs puts turbulence into the flow of any surface water, and increases the time for discs to dry when braking in very wet conditions…? So long ago I can’t remember either where or when, and, as I type it, it sounds more and more like BS.
And don’t the fins in vented discs work like the blades of a centrifugal turbine to suck cooling air through the disc from the centre?

B85S5DSG
B85S5DSG
9 months ago

“The specific heat of the material is something that is intrinsic to the material and doesn’t change”

Not quite correct. Specific heat of a function of temperature and goes to 0 as you approach 0 Kevin.

B85S5DSG
B85S5DSG
9 months ago
Reply to  B85S5DSG

I meant Kelvin, not Kevin. Damn autocorrect.

Thomas Metcalf
Thomas Metcalf
9 months ago
Reply to  B85S5DSG

Ah yes, the Kevin scale. Invented by Lord Kevin himself!

SteamTroller45
SteamTroller45
9 months ago
Reply to  B85S5DSG

I feel like if your brakes are approaching 0 Kelvin you have bigger issues.

Grampa Thug
Grampa Thug
9 months ago

There’s a lot variables for an average driver to consider when making a call on drilled rotors. I can certainly appreciate the science and numbers and I see a bunch of qualified commenters here but I’ll base my call on 60 years of auto work, and still going, much of it as Master Tech and certified automotive machinist. The only broken rotors I’ve ever seen were drilled rotors. I’ve seen only three of these on street cars and there were chunks of rotor missing. I understand the technology may have improved but I won’t use them. I’ll stick with a maximum mass and surface area disc for my spirited driving and leave the drilling to the ‘how do my drilled rotors look’ crowd. There’s too many other options for performance.

Doctor Nine
Doctor Nine
9 months ago
Reply to  Grampa Thug

I’ve seen vented rotors break when they are used way past their in-spec thickness. But yeah, much more likely with cross-drilled. Especially if they are the kind that aren’t designed as cross-drilled from the get go, but modified stock. Never really liked those.

Oldskool
Oldskool
9 months ago

Never used drilled or slotted rotors. But the way I see it, is all those holes add up to a lot of reduced surface area. Surface area that could be used to increase pad to rotor friction and therefore stopping power. Same reason pitted rotors won’t stop as well. Slots wouldn’t be as bad in that department, but still, rotors with an unmolested surface are going to be more reliable against cracking. I’ll take that choice any day. Even if drilled or slotted rotors do happen to stop a little better, the increased risk of catastrophic failure isn’t worth it to me. Especially drilled rotors. An emergency stop transmits a ridiculous amount of torque from the pad grip area to the hub. Reducing that steel section with a bunch of holes is a no-go to me.

Last edited 9 months ago by Oldskool
Manuel Verissimo
Manuel Verissimo
9 months ago
Reply to  Oldskool

The amount of contact surface has no impact on stopping performance.

F_tan = F_norm * mu

Mu being the coefficient of friction of the two materials.

Matt Smith
Matt Smith
9 months ago

Why do drag cars use wide tires for more traction? Is it possible that your fundamental level of physics is a little too simplified for this. In reality the coefficient of friction will change with a change in surface area. Anytime adhesion exists sliding force is proportional to contact area. Not to mention coefficient of friction itself also changes with temperature and contact pressure (both functions of area). Its not a constant value at all conditions.

Manuel Verissimo
Manuel Verissimo
9 months ago
Reply to  Matt Smith

Tires have a coefficient of friction dependant of their loading, while to the best of my knowledge brake pads do not. Their mu coefficient is indeed dependant on temperature and manufacturers often provide the graphs, which I’ve sifted through extensively to try and fix my fading issues at the track.

To the best of my knowledge, decreasing the contact area on a brake pad will not impact stopping performance, I’ve even found slotted disks to have a better feel on track. Also, keep in mind that stopping power is hardly ever an issue as the tire is usually the weak link in the system, that’s why it’s challenging to prevent lockup when braking on track.

Increasing contact surface has other advantages regarding thermal loading of the pad and pad life though, that’s why you want big brakes on race cars.

Last edited 9 months ago by Manuel Verissimo
TheHairyNug
TheHairyNug
9 months ago

yo, what’s the coefficient of friction of empty space? I’m gonna guess that it’s less than that of a rotor surface

Manuel Verissimo
Manuel Verissimo
9 months ago
Reply to  TheHairyNug

It’s nothing, as there is no contact, but where contact do occur, only the normal force and the mu coefficient matter. You will just increase the stress and thermal loading in the rotor but will achieve the same stopping power when reducing the contact area.

Last edited 9 months ago by Manuel Verissimo
Black Peter
Black Peter
9 months ago
Reply to  Oldskool

You can’t consider the total area of the rotor, only the area of the pad. If there is an X% reduction of contact area but an XX% reduction in heat related fade, you made the right decision right?

Jack Trade
Jack Trade
9 months ago

So perhaps a dumb Q compared to those of rest of the commentariat, but I’ll ask anyway – which OEMs besides Porsche offer the “cross-drilled” rotors these days? And are there any we’re they’re stock/not higher-level options?

Last edited 9 months ago by Jack Trade
Hoonicus
Hoonicus
9 months ago
Reply to  Jack Trade

My 2010 MB C300 sport 4matic specs. them for the front, and I gladly paid a little more for coated. Spent a few years working part time in a hot rod shop, and saw many totally clogged with rust cooling veins. I suspect the holes promote more airflow.

Jack Trade
Jack Trade
9 months ago
Reply to  Hoonicus

Interesting…what are they coated with, exactly?

Doctor Nine
Doctor Nine
9 months ago
Reply to  Jack Trade

Modern Mercedes rotors use a polymer UV coating. I think you can still get aftermarket cadmium plating in some countries, although it’s illegal (heavy metal) a lot of places. Zinc is still available, and theoretically is useful in high salt road conditions. Although, I’d prefer the polymer myself.

LTDScott
LTDScott
9 months ago

Anecdotally, having raced in the 24 Hours of Lemons for the last 15 years has shown that drilled rotors are usually more trouble than they’re worth due to rotor cracking issues. Most of the winning teams are using standard blank rotors, usually with air ducts added.

My E30 race car has stock brakes other than upgraded pads and hoses and I can usually get 3-4 races out of one set of front rotors before they start to heat crack, which isn’t that much of an issue on solid rotors compared to drilled. Air ducts help a lot here.

Anthony Magagnoli
Anthony Magagnoli
9 months ago
Reply to  LTDScott

People scoffed, but I ran slotted rotors front and rear on my SpecE30, including when I won the 2012 NASA National Championship. I felt that the brake torque was more consistent through the brake zone. For sprint racing, the slight pad wear increase was barely noticable. For endurance racing, I’d stick to solid rotors, as you’re doing.

Last edited 9 months ago by Anthony Magagnoli
LTDScott
LTDScott
9 months ago

Yeah, for short races I can see slotted rotors being the way to go.

Cheap Bastard
Cheap Bastard
9 months ago

“The sunlight came from the fusion reaction happening in the sun which came from the hydrogen molecules in the sun.”

Correction: There are no molecules of any kind in the fusion core of sun. There aren’t even atoms. What you got there is a big ass ball of superheated plasma, e.g. nuclei and electrons free roaming like it’s a 1970s swingers party. Plasma is a fundamental form of matter distinct from solid, liquid or gas. Its also by far the most common form of matter in the universe. Fusion is a process of joining nuclei to create new atoms. Sticking atoms together to create molecules is chemistry.

Thomas Metcalf
Thomas Metcalf
9 months ago
Reply to  Cheap Bastard

When you describe it that way, the uncontrolled fusion reaction happening 8 light minutes from us is pretty nasty.

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Thomas Metcalf

Fun fact: The photons that hit your eyeballs may have left the sun 8 minutes ago but the fusion event that generated the energy they contain occurred between 100,000 to 1 million years ago. It takes light that long to reach the surface.

https://openstax.org/books/astronomy/pages/16-3-the-solar-interior-theory

Good thing too. The photons generated by fusion are high energy gamma rays. They need to be split up several times to make millions of lower energy visible light and IR photons.

The sun may be hot but the energy density is low. Per cubic foot the solar fusion core puts out about the same amount of energy as a turtle!

I got that gem from a book by James Mahaffey:

https://www.goodreads.com/author/show/7476706.James_Mahaffey

If you have any interest in nuclear power his books are worth a read. An excellent fair and balanced presentation of the facts.

I was skeptical so I did the maths myself. It checked out. The solar core puts out as much energy as an equivalently sized pile of space turtles.

Thomas Metcalf
Thomas Metcalf
9 months ago
Reply to  Cheap Bastard

Very interesting. Thanks!

Hoonicus
Hoonicus
9 months ago
Reply to  Cheap Bastard

For the calculation, was it a googolplex of garden variety box turtles, or a googol of toddler toting capable Galapagos giant tortoise?

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Hoonicus

I think my final model was a green sea turtle. That took a while. You’d be surprised how hard it is to find information on the caloric needs of ANY kind of turtle.

(I did make sure it was some kind of a turtle, not a tortoise. I like to keep it real).

Bizness Comma Nunya
Bizness Comma Nunya
9 months ago

So basically don’t get cross-drilled rotors.

SarlaccRoadster
SarlaccRoadster
9 months ago

No, basically it doesn’t matter for a street car.

When you take your car to the track, then it starts to matter.

You’re not gonna overheat your brakes on the street . Outside a track the only scenario would be something like maybe driving down a mountain with an overloaded car while riding the brakes.

Last edited 9 months ago by SarlaccRoadster
Bizness Comma Nunya
Bizness Comma Nunya
9 months ago

So…basically don’t get cross-drilled rotors…

Andy Individual
Andy Individual
9 months ago

Your excellent discussion about energy conversion leads right into something I have been puzzling. As the world is getting overtaken by big EVs and giant cartoon wheels, I get that one justification is the need for bigger brakes to stop these heavier vehicles, but isn’t that what regen is for? Shouldn’t EVs actually need smaller brakes?

Tarragon
Tarragon
9 months ago

Not an auto engineer but my understanding is: In a lot of cases EVs could get away with smaller brakes. But there’s an important case where they can’t. When the battery is full, (like a long down hill slope), or disconnected (some failure) then the motors have no where to put the energy, or when the battery is cold it can accept less charge. Either way the motors can’t push energy, or as much energy, into the batteries. At that point all braking is with the mechanical brakes.

Jeremy Aber
Jeremy Aber
9 months ago
Reply to  Tarragon

Exactly. For day-to-day applications, the regeneration does the vast majority of the breaking by converting the kinetic energy as electricity. But you still need traditional brakes to fully stop the vehicle and stay in place like while sitting at a red light for example. And given that large batteries are very heavy, having large physical brakes may also be necessary for safety in case of an emergency situation where the regenerative braking can’t function properly.

Cryptoenologist
Cryptoenologist
9 months ago
Reply to  Jeremy Aber

Regen can fully stop the car, and will hold in place at a stoplight unless you are on a grade. But it definitely does not have the capacity to stop as quickly as conventional brakes especially below a certain speed.

VanGuy
VanGuy
9 months ago
Reply to  Jeremy Aber

Yeah, (based on my knowledge, not an engineer) regen does do a lot of work–but for “oh shit oh shit oh shit” sudden stops, or the battery at MAX capacity, or for the last few MPH above a stop–you need mechanical brakes, and the car is heavier, hence the need for heavier-duty brakes.

Supposedly, for most Priuses, when you’re in neutral it disables the regenerative braking altogether. Great way to test the sound/feel of the mechanical brakes.
I’m approaching 150k miles on my 2012 Prius v (heavier than the regular Prii) and it had its rear brakes replaced before I got it at 116k and I just replaced the front brakes fairly recently.

Tarragon
Tarragon
9 months ago
Reply to  VanGuy

but for “oh shit oh shit oh shit” sudden stops

It’s a tangent but this is why I don’t like vehicles that allow one pedal driving down to a complete stop. The emergency process, stomp the brakes, should be a variation of the the normal process, stop at a light.

I worry that folks who learn on and only drive that one-pedal system will not have the reflexes to stomp the brake for an emergency stop.

VanGuy
VanGuy
9 months ago
Reply to  Tarragon

That’s an interesting thought! I have mixed feelings on that.

I at least recall from Regular Car Reviews that one of the cars they had reviewed, at the highest regen setting, was decelerating even going down a steep hill. That makes me think that in an emergency, your reflex would still involve very quickly taking your foot off the pedal–at which point you’d still possibly be decelerating quickly, at which point, applying the mechanical brake would still be….”logical”? If not necessarily “automatic”.

Cryptoenologist
Cryptoenologist
9 months ago
Reply to  Tarragon

Hmm, this is interesting. I drove my EV this morning from 100% charge for the first time. Regen was exactly as strong as it is any other time. Obviously some capacity was used to get the car moving at first, and there is undoubtedly a bit of reserve top end capacity. I wonder if there is a capacitor involved.

What does the car do if the battery is full and you are headed down a mountain? Hopefully it overrides the regen setting and just lets the car freewheel.

Tarragon
Tarragon
9 months ago

I occasionally hit the battery limit in my PHEV:

  • On a cold winter day
  • The battery is fully charged
  • I haven’t pre heated it, which warms the cabin and batteries
  • I turn left out of my sloped sloped driveway
  • onto a road which is about a 1/2 mile gentle down slope with a stop sign at the bottom
  • I drive gently, which is basically coasting instead of accel / brake repeat

Even trying to make it happen I can only get the effect about 50% of the time. I totally feel the difference in braking. The first time it happened I thought I was sliding until I pushed a bit harder and the mechanical brake bit

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Huibert Mees

Not necessarily. The energy can be dissipated via the electric motor by resistor packs. That’s how diesel electric locomotives do it and they have a LOT more mass to stop.

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Huibert Mees

Not regenerative braking but rheostatic braking.

https://en.m.wikipedia.org/wiki/Dynamic_braking

Rheostatic braking offers a mechanism for an EV or hybrid to convert velocity into heat that doesn’t use a friction surface nor putting that energy into a perhaps already full battery via regenerative braking. Cooling systems powered by the electricity generated would aid the braking.

I dunno how the reliability of rheostatic braking compares to friction braking but I’d expect its at least comparable as it has fewer moving parts and no wear.

Andy Individual
Andy Individual
9 months ago
Reply to  Huibert Mees

Thanks for clarifying, but…

“And since brakes are safety critical systems, you won’t find any EV companies scrimping on them just to save a few pounds”

I have the distinct feeling there are some EV companies scrimping on critical safety systems. /s

Bassracerx
Bassracerx
9 months ago

on the street maybe in an emergency no. Electric vehicles also are heavier so they need bigger brakes to start with anyway. Brakes don’t slow you down your tires slow you down. All your brakes are doing is locking the wheels from spinning so the tires can do their job and slow the car down. also an ev is brake by wire so you still need a foolproof redundant system.

The Bonnie Situation
The Bonnie Situation
9 months ago

On the EVs I’ve driven, regen is disabled during ABS events. Important for the friction brakes to handle the full job during an emergency stop event.

Anthony Magagnoli
Anthony Magagnoli
9 months ago

EV’s can’t rely on regen. If you’re at full charge and need max braking, there’s nowhere for that energy to go. You can also overheat motors and batteries and need the brakes sized to do the full job, even if they’re underutilized 99.9% of the time.

World24
World24
9 months ago

I thought about getting the Slotted & Drilled rotors from Power Stop for my Jeep since 80% of my driving is done in a town where driving laws are optional, and I believe I generate a lot of heat because of all the braking I have to do around town.
This makes me think I’m good with their coated rotors that I bought instead. Ever since I got those coated rotors, I feel like they’re the best daily option in the salt belt.

SNL-LOL Jr
SNL-LOL Jr
9 months ago

The wood is converted to ashes and heat, but as you know, ashes weigh a lot less than the log you started with. The difference in that mass is equal to the heat energy that came out of the fire, and you can calculate it using Einstein’s formula.”

Not sure if serious or just trolling.

Jason Torchinsky
Jason Torchinsky
9 months ago
Reply to  SNL-LOL Jr

Ooops. Huibert is a suspension engineer, not a chemical engineer or a physicist! We all make mistakes sometimes! Right? Sure we do.

SNL-LOL Jr
SNL-LOL Jr
9 months ago
Reply to  Huibert Mees

“There are no more ferocious keyboard warriors than bored engineers pretending to work.”
Source: Me

Cryptoenologist
Cryptoenologist
9 months ago
Reply to  SNL-LOL Jr

Why are so many of us engineers pretending to work though? I like my job, I have things to do, and yet I’m here again, pretending to work. My only thought is that if I actually worked all the time I’m at work I would either run out of things to do or get burnt out.

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Huibert Mees

Mixed messages dude. You gotta be careful with your trolling else you’re going to come across as a nitwit or ignoramus.

Ian McClure
Ian McClure
9 months ago
Reply to  SNL-LOL Jr

That said, if you could recover 100% of the gasses emitted in the fire and cooled back to room temperature combined with the ashes, the remaining weight *would* still be infinitesimally less than the starting weight. E=mc^2 does apply to the loss of potential energy in purely chemical reactions, it’s just that the energies involved are so tiny they are practically immeasurable.

Last edited 9 months ago by Ian McClure
Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Ian McClure

The products would weigh considerably more than the starting weight unless you are extra careful to account for the mass of the air consumed as well.

Ian McClure
Ian McClure
9 months ago
Reply to  Cheap Bastard

True. Forgot to account for all of the inputs to the system.

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Ian McClure

You wouldn’t be the first.

Angry Bob
Angry Bob
9 months ago

The mass lost from burning the log goes up the chimney as gasses and soot.

The atomic bomb dropped on Japan converted 0.6 grams of uranium into energy. There’s A LOT of energy in matter.

Last edited 9 months ago by Angry Bob
David Tracy
David Tracy
9 months ago
Reply to  Angry Bob

Yeah, we uh…

…We made an adjustment.

Jb996
Jb996
9 months ago
Reply to  Angry Bob

I scurried down here to pedantically correct… Glad to see I’m not the first.

Burning is NOT mass conversion. The mass of the moisture and other particulate is lost up the chimney. Burning is just releasing molecular binding energy (electromagnetic energy between electrons and protons between different atoms, simplistically) into free photons (also electromagnetic energy). And then to molecular mechanical energy (heat) as those photons collide with and excite other molecules in the area. There’s a fair amount of energy stored chemically.
However…

Actual mass conversion releases a HUGE amount of energy
Converting the mass of a log (~2kg) into pure energy (some type of antimatter reaction?) would release 180 Peta-Joules (180×10^15), or 43 Megatons of TNT.
The largest nuclear weapon ever tested, Csar Bomba, was about 50 MT.

So, starting a small campfire would release a fireball 5-8miles in diameter and be visible 500-600 miles away.

And you would likely be banned from the smouldering ruin of that particular National Park.

Dar Khorse
Dar Khorse
9 months ago
Reply to  Jb996

Friendly neighborhood chemist here to turn up the pedanticity another notch. First, thanks to the editors for removing that erroneous example of energy conversion (now put all the “d”s back onto “unbalance”!).

“Burning is just releasing molecular binding energy”: nope nope nope nope! This is a very common misconception about chemical reactions and chemical bonds. Burning is a chemical reaction and chemical binding energy is NOT released when chemical bonds are broken. Let’s think about it a second: if you break a chemical bond (say, between carbon molecules in some wood), what do you need to do? You need to put energy INTO the bond in order to break it. But what happens next? New bonds (such as those between carbon and oxygen to make carbon dioxide) are formed, which RELEASES energy (as long as the chemical compound is more stable than the free elements, which is usually, but not always, true). So, the overall release of energy is due to the fact that the products of combustion (in this specific case) are more stable than the reactants were in the first place.

Otherwise, your points are accurately stated.

Last edited 9 months ago by Dar Khorse
Jb996
Jb996
9 months ago
Reply to  Dar Khorse

Man, there’s always someone more pedantic.
I love it!

I completely agree with you.
I knew that my “simplistically” statement was doing alot of heavy lifting.

I was saving words to get to the fun part. i.e. nuclear campfires.

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Jb996

“I was saving words to get to the fun part. i.e. nuclear campfires”

Yeah, about that…

The increasing failure of antibiotics to combat infections like multi-drug resistant Staphylococcus aureus has renewed interest in a long-forgotten treatment developed over 60 years ago in ex-Soviet Georgia. Tom Parfitt travelled to Tbilisi to witness the revival of bacteriophage therapy.
It was a fortunate, if curious, discovery —or so it seemed to the three woodsmen as they settled down to another bitterly cold night, deep in the forests of western Georgia.

Wandering through the snow, they stumbled across two metal canisters that were warm to the touch. Intrigued, the men picked up the tubes and took them back to their camp. There, they huddled around the canisters as if they were hot water bottles, hardly believing their luck. It turned out to be a near fatal mistake: the strange metal objects were the highly radioactive strontium-90 core of a long-abandoned radio-thermal generator, once used to power a navigation beacon for Soviet aircraft.

Within days, two of the men had severe radiation burns. They were rushed to hospital in the capital Tbilisi where doctors found the purulent lesions were deeply infected with an antibiotic-resistant strain of Staphylococcus aureus.

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(05)66759-1/fulltext

Mike F.
Mike F.
9 months ago
Reply to  Cheap Bastard

Good article – thanks for that.

Ian McClure
Ian McClure
9 months ago
Reply to  Jb996

E=mc^2 doesn’t only apply to mass conversion though. Any amount of energy in any form is equivalent to a quantity of mass, it’s just that in human-scale terms mass conversion via nuclear weapons is one of the only times it’s a big enough effect to be relevant. (Particle accelerators is the other). If you measure the energy output of a campfire and convert that amount into mass, you will get a (very tiny) value that reflects an actual, theoretically measurable, loss of mass between the starting and end components (assuming you could collect them all and measure them precisely enough).

Last edited 9 months ago by Ian McClure
Jb996
Jb996
9 months ago
Reply to  Ian McClure

I had, and deleted, a line about the infinitesimally small mass lost due to bond energies.

Last edited 9 months ago by Jb996
Cheap Bastard
Cheap Bastard
9 months ago
Reply to  Jb996

A couple of years ago I watched this craptastic Chinese movie about the Earth being moved out of its orbit into deep space for *reasons* using a ring of fusion rockets:

https://en.m.wikipedia.org/wiki/The_Wandering_Earth

Curious I estimated how much energy it would take to do that.

The answer? One Mt Everest + one Anti Mt Everest = one radiation blasted, deep frozen Wandering Earth snowball.

The movie has a prequel. I’m still debating whether to watch it. God I miss MST3k.

Dar Khorse
Dar Khorse
9 months ago
Reply to  Cheap Bastard

MST3K was the best. I have many fond memories of watching that show with my young kids.
Watch out for snakes!

SNL-LOL Jr
SNL-LOL Jr
9 months ago
Reply to  Dar Khorse

“If Godzilla is a parable for nuclear Holocaust, then Yongary is one for copyright infringement.”

David Davison
David Davison
9 months ago
Reply to  Cheap Bastard

In the days of my youth, I read a book by Larry Niven.
I believe it was “A World out of Time”.

Anyway, part of the book involved a scheme to enlarge Earth’s orbit.
If memory serves, it involved driving rockets down into the Earth’s atmosphere, with large scoops on the front to push air in the desired direction.

I haven’t seen the movie you refer to, but from the wiki, it sounds like they try to thrust against the Earth directly. If you do that, you are going to transfer all that heat into the Earth’s atmosphere.

Enough energy to move the Earth enough to get into an orbit that gets us out of within the red giant the sun will one day become would roast pretty much everything. And blast a fair amount of atmosphere into space.

Cheap Bastard
Cheap Bastard
9 months ago
Reply to  David Davison

IMO as far as a crucial need to suspend all sense of reality goes this was only seconded by “Moonfall”.

Yikes!!

Man With A Reliable Jeep
Man With A Reliable Jeep
9 months ago

Aha! I knew it!

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