Home » Our Suspension Engineer Talks About The Effects Of Wheel Spacers And Wheels With Different Offsets

Our Suspension Engineer Talks About The Effects Of Wheel Spacers And Wheels With Different Offsets

Wheelspacers Top

My fellow Autopians, you know those wheel spacers that people use to make their tires stick out to give the car a wider stance? Do you think those are a good idea? Let’s forget for a moment about the fact that, on many “stanced” cars, they are one pebble away from ripping those fenders off — let’s just talk about the offset. I’m not asking if you like it. I’m only asking if it’s a good idea. If you’ve read any of my previous posts you probably already know what my opinion is, but rather than throw opinions around, I want to talk about it using some real science and engineering.

Suspension Geometry

Screen Shot 2023 02 21 At 11.44.56 Am
Image: KSP Performance/Amazon

The geometry of a suspension, especially the front suspension, includes several parameters that depend on the location of the center of the wheel and the center of the tire contact patch. These parameters determine how the suspension responds to road impacts, like potholes, braking forces, and in the case of a driven axle, acceleration forces. The parameters I’m talking about here are the scrub radius, the kingpin offset, and the bearing load line. Here they are looking at a section through the wheel and tire from the front:

Wheel Spacers 1

The bearing load line is the vertical line going through the center of the wheel/tire assembly. We’ll get to that in a bit.

With a normal value between negative 15 mm and positive 15 mm. scrub radius is the distance as viewed from the front from the center of the tire contact patch to the point where the kingpin axis intersects the ground. The kingpin is the line from the center of the upper ball joint (or the upper spring mount in the case of a MacPherson strut) through the center of the lower ball joint. It represents the axis the suspension spins around when you steer the car.

If the kingpin/steering axis intersects the ground inboard of the center of the tire contact patch, the scrub radius is said to be positive. If the kingpin axis intersects the ground outboard of the center of the tire contact patch, then the scrub radius is negative. Many rear wheel drive cars have a small positive scrub radius while many front wheel drive vehicles have a negative scrub radius. A negative scrub radius is usually the result of pushing the kingpin axis as far outboard as possible in order to achieve as small a kingpin offset as possible. The kingpin offset is the distance as viewed from the front between the center of the wheel/tire assembly and the kingpin axis. (see above). Normal kingpin offset values range from about 50 – 100 mm. I’ll explain later why this is desirable.

The kingpin offset and the scrub radius are important parameters because braking, acceleration, and impact forces act through them to create torques (or “moments”) that try to steer the suspension. The larger the values for these two dimensions, the larger these moments. What keeps the suspension from actually steering in response to these moments is the steering system and the hands holding the steering wheel. As the moments get larger, the work those hands have to do also gets larger so you can see why suspension engineers try to keep the both the scrub radius and the kingpin offset as small as possible. Let’s look at how the acceleration, impact, and braking forces act through the scrub radius and kingpin offset.


In the case of acceleration, the forces push on the suspension at the wheel center.

Wheel Spacers 4

This may seem counterintuitive, since it is the tire contact patch that is accelerating the car, not the wheel center. However, it is important at this point to separate the wheel and tire assembly from the suspension and think only about what is happening to the suspension. We need to consider how the forces travel through the tire and into the suspension.

When the engine turns the wheel, the turning torque from the driveshaft or halfshaft is applied to the wheel and tire assembly, not to the suspension. As the tire tries to roll forward, the tire pushes on the suspension via the bearing. Imagine if the suspension weren’t there to hold the wheel assembly. The tire would just roll forward and the car wouldn’t move. But since the tire is attached to the suspension and the suspension is attached to the body, the force from the tire contact patch is able to travel to the body and move the car forward. But the loads first have to travel through the suspension, and it can only do that through the point at which the wheel and tire assembly is attached to the suspension, namely the bearing. So, the wheel and tire assembly pushes on the bearing and the bearing pushes on the suspension and it all happens at the point where the bearing sits, which is the wheel center.

Since the acceleration force pushes on the suspension at the wheel center, this force together with the kingpin offset creates a moment around the kingpin axis which tries to steer the suspension. The only thing stopping this steering action is the steering system and the driver’s hands holding the steering wheel.


In the case of impact forces, the situation is the same, but the direction of the force is opposite.

Wheel Spacers 3

Instead of pushing the wheel and tire assembly forward, impact forces actually push it rearward. And as with acceleration forces, impact forces together with the kingpin offset create a torque around the kingpin axis which is resisted by the steering system.


In the case of braking, though, the situation is a little different. Braking forces act on the suspension at the tire contact patch, trying to push the wheel and suspension rearward. In addition to a braking force, there is also a torque coming from the brakes which pushes on the suspension.

Wheel Spacers 2

The combination of a force and a torque has the effect of making the suspension act as if the force is being applied at the tire contact patch, not the wheel center.

Since we’re now talking about a force at the contact patch, it is the scrub radius, not the kingpin offset, together with the braking force that is creating a moment around the kingpin axis. As before though, the steering system is what resists this moment.

Now, this is where it becomes important to know if we have a positive or negative scrub radius, because the direction of the moment around the kingpin axis under braking will be opposite depending on which scrub we have. If the scrub radius is positive, the moment will be trying to toe the wheel out but if we have a scrub radius that is negative, the moment under braking will be trying to toe the wheel in. The vehicle dynamics under braking and the behavior of the suspension depend on maintaining the direction of this moment. It is what the engineers intended and designed the rest of the suspension around, and it is what the suspension tuning is expecting.

One thing to keep in mind in both the acceleration and braking cases is that under normal driving conditions, the forces are happening on both the left and right suspensions and they will pull or push on the steering system in opposite directions. If all goes well, the forces coming from the left and right will cancel each other out and the steering system won’t move, but if you are in a situation where the forces don’t balance, such as when one wheel is on ice or wet leaves, then the steering system will get pushed or pulled.

Bearing Load Line

Screen Shot 2023 02 21 At 11.29.05 Am
The bearings are part of the wheel hub, shown above. The hub mounts to the suspension, while the wheel/tire mounts to the hub via the six threaded studs you see here.

The bearing load line, shown below, is a line going through the center of the wheel and tire assembly, and shows where the majority of the load being carried by the bearing will be. For best bearing life, it is desirable to keep this line going in between the two ball bearing races of the wheel bearing. If the line passes through the bearing outside the races, the bearing will be carrying a moment, which can significantly reduce its lifespan.

Wheel Offset Effect

Now that we understand how these various forces push on the suspension, let’s look at the effect of wheel spacers. Remember that the forces act through the kingpin offset and the scrub radius, so if we change the size of these dimensions, we will change the size of the moments we get around the kingpin axis when we brake, accelerate, or hit a pothole. In the photo above, the car had two-inch spacers installed, which is about 50 mm. Here you see the same cross section as above but with a 50 mm spacer inserted:

Wheel Spacers 5

Compare this image to the one we saw before and you will see how the kingpin offset and scrub radius have increased significantly. If our scrub radius was 15 mm before, it will now be 65 mm: almost five times larger than it was. On the other hand, if our scrub radius was negative 15 mm then it is now positive 35 mm, meaning it has changed sign and now the moments around the kingpin axis generated by braking forces have not only increased but changed direction from what the suspension was designed to handle.

Similarly, if the kingpin offset was 50 mm before, it is now 100 mm, or double what it used to be.

The changes in the scrub radius and kingpin offset mean the forces the steering system, and the hands of the driver, need to resist have doubled or quintupled in strength and may even have reversed direction. That’s a lot more work the driver has to do and a much higher risk the wheel may be ripped from their hands. Don’t underestimate the impact this can have on the dynamics and handling of the car. These numbers are critical to the proper functioning of the suspension.

Imb Sx1jrb

Lastly, look at where the bearing load line now sits. It is way outside the ball bearing races and will cause a significant increase in the loading of the bearing — loading that it was not designed for. The life of the bearing will be reduced, and you can expect to have failures in a part that would normally last the life of the car.

Putting wheel spacers on your car may look cool, but be aware that you are making changes to some of the most important parameters in your suspension and be prepared for the effects this will have on the handling and durability of your suspension.

[Editor’s Note: The degree to which these changes will affect your driving/ownership experience is obviously not something we can answer here. Who knows, maybe your bearings will still last long enough and maybe the handling and ride changes won’t be too noticeable. Huibert is an engineer, so he’s just telling you what’s happening from an engineering standpoint. Whether you can deal with that is a question only you can answer.

Also, as a few commenters have noted, a wheel that alters the offset/backspacing from stock can be modeled the same as an OEM wheel with a wheel spacer. Of course, it reduces the additional fasteners needed to keep a wheel spacer on, but physically, affects on handling/bearing durability are basically exactly the same. -DT].

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73 Responses

  1. Thank you for the article not written by an AI. Two things. It isn’t “kingpin” it is kingpin inclination or kingpin angle. A kingpin is a car part. My comment is pendantic mainly because the kingpin terminology was superceded my “steering axis inclination” about a million years ago.
    Second, if you study modern steering design you will find cars with the bearing load plane and the scrub radius all over the place. Literally sometimes 150mm apart. The manufacturers know they can cheat a bit just like the modders with spacers. As noted in other comments offset/spacer changes can often make things better, not worse. This especially true when the effective radius (rolling radius) or overall wheel width has changed. If course you wouldn’t know better or worse if you didn’t understand the technical details of your article. Thank you.

  2. I have a small complaint. Everything written is technically correct (the best kind of correct), but we’re not really talking about wheel spacers here, are we? We’re talking about changing the wheel offset. Spacers are only one way of accomplishing that. The same effects would be seen by using a wheel with a lower offset value if wheel and tire width remain constant. That said, by using a wider wheel/tire in conjunction with the spacers (or a wider wheel with lower offset), the suspension geometry in question can be largely returned to normal values, or at least mostly cancelled out.

    1. The key is to make sure the centerline of the wheel stays in the same place. So, if you have a wheel with a larger offset than stock and a wheel spacer that is the same thickness as the difference in offset, the centerline of the wheel will be back in the stock location and there will be no effect on the suspension.

    2. Agreed, this really needed a strong caveat that this is only accurate when identical/stock wheels are retained.

      As much as I hate the skateboard truck look (and accompanying reductionin usefulness), some of them commit this sin against their suspension and some of them design well enough to avoid it.

    3. Came here to say the same thing. I’m running wheel spacers on my car to “push out” high offset wheels so they sit in the same place as a lower offset wheel that’s the same as stock, so net effect compared to stock should be negligible. I’m not trying to “stance” my car.

  3. This is a really fascinating article with amazing technical explanations that slightly have gone over my head, but I do notice that the perspective it it is written from is rather like that of an OEM engineer:

    “Putting wheel spacers on your car may look cool, but be aware that you are making changes to some of the most important parameters in your suspension and be prepared for the effects this will have on the handling and durability of your suspension.”

    While I do appreciate that factory suspension setups in cars are built for longevity, comfort and handling stability, I’m curious to know more about if having a wider track can benefit handling and grip (at the expense of other factors), at what point a wider track stops being of benefit, or if there are actual ways to calculate the optimal performance-oriented setup for a particular car based on the figures explained above.

    Also, while a 50mm increase is massive and probably not beneficial, carmakers often fit wheels of different offsets and widths depending on the trim level, and most of the time the ‘sporty’ trim level has a wider track despite having the same suspension setup (save for lower springs and shocks). Does that mean the carmaker considers the different offsets for the base and sport models to be the minimum and maximum bounds for that value?

    1. If multiple offsets are available from the factory then the suspension and handling of the car have certainly been developed to deal with those offsets and there should be no problem using an aftermarket wheel with that offset.

    2. 100% it can help. How much it can help does also depend on the vehicle in question.

      Hell, some car sanctioning bodies have a width/height ratio rule (SCCA, I think?) and in certain instances within those bodies, a competitor just lowering one inch and adding 1″ spacers has done the work to get under that ratio.

      1. Many racing bodies do not permit wheel spacers though.
        The height ratio is another can of worms, the Government used to publish center of gravity figures on cars sold in the US and the SCCA used to use those, however for whatever reason the requirement was dropped and the SCCA and CASC went to the “Vehicle height must not exceed the overall track width of the tires” with no consideration of actual center of gravity.
        My Ford Fiesta was one of the SCCA black listed cars, fixed with the Ford Performance “Handling Package” IIRC it lowers the front by 3/4″ and the rear by 2 1/2″. The sad thing is this package was a “sport option” on the German made production car, but not offered on the made in Mexico version sold in North America.

    3. I only know about a few cars, but normally sport models get wider (and larger diameter) wheels and the increased offset is split, usually equally or at least close to the base model.

  4. Thanks for the indepth explainer. I always knew/suspected spacers were detrimental to bearings, and suspension components, but I didn’t know exactly why. As a JK owner, it’s crossed my mind a couple times as a shortcut solution to the poorly installed lift that came with my Jeep when I bought it. I’m glad I spent the time and money to get it fixed properly.

    I do have a question for Huibert, David, or anyone willing to answer me. Most desirable aftermarket wheels, steel or alloy, usually have a more aggressive-than-stock negative offset. Is there a certain threshold that’s safer to stick with I’d you want to branch out to different wheels? I think stock offset is something like 6.25” or so on JK 17″ rims…so I’ve been only considering options with an offset that’s 5.25” or greater. Does that help reduce the negative effects described or does it really matter?

    1. I would stick with options that are as close as possible to the original 6.25″ as possible but what you are talking about is actually called backspacing, not offset. Backspacing is the distance from the mounting face of the wheel to the inner edge of the rim and is affected by the wheel width as well as the offset. Two wheels can have the same offset but different backspacing if their widths are different. It’s confusing, I know, and probably a good topic for a future post.

    2. To piggy back on your comment another thing to keep in mind in the off-road world, a larger diameter tire will impact your scrub radius as well. At least in theory, you would need to move the wheel out (wider stance) to maintain the same scrub radius when you go to a larger tire.

      I can’t answer your question, but I know I have tried to keep my wheels centered between the bearings on my jeep. Once you get outside that envolope the load on the bearings goes up substantially which is even more deteramental if you are using the vehicle off road as it’s not uncommon to have most of the vehicle weight on only two tires.

  5. This article needs the comparative figures/drawings right next to each other, not separated by eight paragraphs and thus requiring scrolling back and forth.

  6. Uh, why the focus on wheel spacers?? All of this applies to aftermarket wheels with a negative offset. Assuming the wheel spacers are a high quality piece, there is no mechanical difference.

    1. I think there is a large difference between using a spacer to make up for aftermarket wheel backspacing in an attempt to get close to the original design and using spacers, or even double spacers to change the vehicles’ stance or be have incompatible wheels clear brake calipers. My take away is that small changes in suspension parameters can have an exponential effect on the vehicles natural handling characteristics.

      1. Yeah, but it doesn’t actually address anything about whether running wheel spacers is a good idea. I run some on my E30 because they take Miata-friendly wheels and get them back closer to stock offset. According to this article, that’s all good because I’m getting my suspension geometry back closer to stock… but says nothing about the safety of running wheel spacers and longer lugs to do it.

          1. Well in theory the shear forces between the wheel and the hub aren’t going through the lugs, so longer lugs won’t take any extra stress.

            However if you lengthen the lug, you need to increase the torque so that you get the same axial load on the lugs which press the wheel to the hub, otherwise you risk slippage between the wheel and hub, and then your lugs start seeing bending forces, which is bad for stress.

              1. Based on the fleets of some of the writers here, there has been a lot of long term testing going on. I’m sure David’s corrosion reports alone rival the AES archives.

                1. The blue VW in the video on this article used to be mine. Little baby brakes, huge wheels, 2 inch spacers! I also ran spacers on one of my Gambler 500 builds. I didn’t own either car long enough to see if the spacers hurt anything.

                  But I can say that the spacers survived the horrific beating on the Gambler 500 that the rest of the Gambler car could not.

      2. But as pointed out in the comments already, what this article is really addressing is changing the factory track width. Spacers are just one of several methods you can use to accomplish this. Conversely, you can use spacers to move high offset wheels back to the “stock” location, as I am on my car, where the net track width does not change and as such none of the things mentioned in the article would be valid.

      3. I’ve argued in long debates with people about gaining negative offset via wheel spacers vs an aftermarket wheel with a more negative offset. They argued the wheel spacer method has more bearing load on wheel bearing but the aftermarket wheel does not because it’s “one-piece”. I found all of the arguments silly. The scrub radius, bearing loads, etc will be identical.

        Wheel spacers get a bad name because of the cheap ebay spacers. A quality wheel spacer is fine.

    2. There is a mechanical difference when you get to talking about the bearings and the supporting structures of the suspension. All else being equal, you’re increasing the moment arm on those bearings by adding spacers.

      Quality spacers bolted up to quality wheels, yeah there shouldn’t be any issues with a component of the spacer or wheel failing, in that there’s no mechanical difference.

  7. I personally think this look is pretty silly, but as I’ve become more and more of an Old Man, I’ve consciously tried to avoid criticizing vehicular trends that appeal to younger people. Stereotyping a bit, but most people I see with spacers on their trucks or Jeeps appear to be in their 20s-early 30s.

    It’s not as if the mods that I enjoyed when I was younger kept engineering parameters within factory specs either! That’s the point.

    Whatever it takes to keep younger people interested in our hobby is worth celebrating, IMO. Be safe, be responsible, but be proud of your vehicle, whatever it looks like.

  8. Real question here, when we look at manufacturer built race cars based on production models, they often come with a wider track.

    How do they achieve this if not with spacers or different wheels? Are the control arms longer? That’d work well for a car with double wishbone all around but how about cars with a McPherson suspension like the Z4M race car for example? Wouldn’t that induce a huge camber?

    1. A lot goes into building a suspension for a race car, even one based on a production car. Many things can get changed, such as control arm lengths, beefed up bearings, etc. Also, don’t forget that race cars only need to last a few races at most. If bearing need to get replaced between every race because something about the suspension wears them out, that’s a cost most professional teams would be willing to accept.

    1. Bearing life would be affected but also performance. The change in wheel offset could change the way the suspension behaves during braking while in a turn, for instance, and change the understeer/oversteer behavior. In reality, it is most likely not as big a deal in the rear since the kingpin offset is often much larger to start with.

  9. This all makes perfect sense, but what I’d like to know is: is all this suspension geometry data published anywhere? If I want to go messing with my wheel offset, is there any kind of document, anywhere, that can allow me to make an educated guess as to whether I’m going to mess up my car by doing so?

    Barring that, are there any rules of thumb that are worth following? For instance, if I were to push my wheels out by like 20mm per side just to help them fill out the fenders a little better, what am I likely to experience? Am I going to ruin my wheel bearings doing that, or is my bearing load line still probably within the races? What if I want my steering wheel to be a little more communicative about what’s happening to the wheels?

    My priorities for my car aren’t necessarily exactly the same as the OEM’s. Is there any way for me, a member of the public, to make adjustments that’s better than a shot in the dark?

    1. You’re likely to experience: A better looking car, and maybe even more responsive handling due to a slightly wider track. That’s it.

      20mm spacers are nothing. It’s those 3-4″ monstrosities that brodozers are running that cause problems; you can modify almost any parameter on your suspension without detriment on a street car, as long as it’s not an excessive amount. MAYBE, MAYBE you would notice on the track, and it could be better or worse, slightly.

    2. 100% agree with this, I’ve been looking for info on scrub radius changes for the better part of two weeks and ultimately decided to “roll the dice” on a purchase without having any way to know if I’m going to regret it.

      I picked up a used set of Mini GP3 rims and plan to put them on my JCW Countryman shod in wider Summer tires. I’ll be going from 225 section rims on a 7.5″ rim with a 51mm offset to 235 section rims on an 8″ rim with a 39mm offset. Per Wheel-Size.com I’ll have a net change of 10mm in positive scrub radius but I have no idea what the hell that *means* in terms of real-world impact since there’s no way I can find to determine what the scrub radius was from the factory. 10mm doesn’t seem like much (certainly not 50mm!) but yeah… who knows.

      Well I guess I’ll find out!

  10. Yeah… .but like…. it looks better. Most cars have the wheel sunken inside the body a bit for MPG/drag reduction, which I get, gotta keep up the CAFE averages, but it just looks so bad. A mild drop to center the wheel inside the arch and spacers to make the face flush with the fenders = how things were supposed to look, design intent!

    1. The reason wheels and tires aren’t completely flush with the fenders is because the tire would hit the fenders under full load or build tolerance. Engineers need to make sure that on every car built in the factory, the tires will not hit the fenders so they leave room between the tire sidewall and the fenders to account for movement in the suspension and slight differences in the way each car is built. Some manufacturers are better than others at keeping the variation from car to car small and they can keep this distance small. Others aren’t as good and need to keep it large. All car designers I’ve ever worked with would prefer the flush look and this is always a discussion (sometimes heated!) between the design studio and engineering.

  11. Old-timer here. I remember when VW was advertising negative scrub radius as a selling point for one of their cars (I think it was the MkI Rabbit, née Golf, or could’ve been the Super Beetle, as it was one of the first VW’s with a MacPherson front suspension – I had both) and trying to explain the inherent safety of the design in layman’s terms. When I see a stanced car, I remember that ad.

  12. All I know is that in a tire shop they referred to the spacers as bearing killers. I remember the show Bangla Bangers where they would use spacers that looked like 30cm on some cars

  13. We should also talk about how incresing the track width, whether by spacers or wheel offset, also changes the wheel rate. That is, the effective spring rate at the tire. The tire is on a lever arm against the spring. If the length of that lever arm is increased, the motion ratio is decreased, making the spring less effective at the wheel.
    A strut type syspension has a very high motion ratio (usually around 0.97), but a divorced spring/shock setup like in the rear of many vehicles, can have a much lower motion ratio. I can attest to learning about this years and years ago when I put higher offset wheels on my SpecE30 (tire came inboard) and it gained excessive oversteer!

  14. This hurt my brain.

    All I know is I put Jeep JK wheels on my LJ and had to put 2 inch adapters/spacers on it to make it work. The factory JK wheels are 6.5 inch backspaced, and my 2 inch adapters took that backspacing down to 4.5 inches. I’d dearly love to find proper wheels that don’t require the adapters, but I would like to get that total backspacing down to 2 inches to get the stance I’d like.

    If spacers are bad, why are Jeep factory wheels backspaced so much?

    1. So wheels aren’t backspaced, they are offset. There is positive and negative offset That may feel pedantic, but its kinda important to have the correct terminology.

      Wheel offset is explained by Huibert in this article: https://www.theautopian.com/heres-why-car-wheels-are-so-flat-these-days-and-no-its-not-just-aerodynamics-and-styling/

      But at its heart it depends on the type of steering system you have (rack and pinion vs any of the more old school linkage styles) and is about reducing those factors that Huibert mentioned, scrub radius, kingpin distance, etc.

      1. While you’re correct to distinguish between wheel offset and backspacing, to be fair the Jeep world always talks in backspacing, not offset. Just last week I was cataloging a Jeep Wrangler lift kit my company is building and had to add a disclaimer for wheel backspacing.

        1. And to prove my point I just checked the article you linked to which talks about wheel offset. The ONLY reference to backspacing in the entire article? DT talking about Jeep Liberty wheels 🙂

  15. So here’s the rub.

    Wheel spacers are no different than running wheels with different offsets.

    Once they are bolted together with proper torque, it’s just a wheel with a different offset (now a lot can be said about the quality of materials of many wheel spacers and the studs used and what happens if you don’t use the proper style of spacers for the hub, wheel and lug nuts used – bad things, that’s what)

    The same effect on the suspension will happen if you use wheels with substantially different offsets.

    I don’t think that’s clear here. The title is misleading, the wheel spacer doesn’t change anything, the offset of the wheel does.

  16. I’ve run wheel spacers on my Mustang, initially because I couldn’t swing the money on aftermarket and now because I like my factory rims the best. I’ve never had an issue with them including spirited driving and a track day. While I know it’s not the ‘correct’ or ‘best’ option they’ve been fine for me!

    1. Similarly, I run adapters on my XJ to use JL Wrangler wheels and tires for a couple reasons:

      1. I like an OEM style wheel
      2. JK and JL Rubicon Take-Off wheels and tires are often cheaper than 5 33″ tires new
      3. I am lazy and like just buying a whole new set of wheels and tires that I can swap myself when I wear out a set

      I’ve ran this Jeep hard, including driving it to Moab and back from Houston with a week of wheeling in the middle and have not experienced failure.

      Maybe my unit bearings wear out quicker but the dirt can cause that as well. The important thing is if you buy these, buy high quality name brand parts, not the cheapo ebay ones.

      1. That’s rotational mass, not unsprung weight. However, regardless, I think the answer is it won’t matter much as spacers aren’t generally particularly heavy.

    1. Nice
      Maybe it’s the lack of caffeine this morning, but I got 2 comments past yours before I went, “Wait a minute there…‘negative offset’ ??” Good job!

  17. As other have said, but I feel compelled to restate:

    The issues arise because if you add spacers *without changing anything else* you are moving the scrub radius away from the wheel centerline. Anything you do to change this relative positioning will affect the handling of the car, and moving the scrub radius away from the wheel center will introduce additional mechanical stresses that *may* be bad for the car.

    If you also change other things that compensate for the change introduced by the spacers (i.e. use wheels with a different offset to bring the centerline back), those issues will be mitigated. In fact, that’s basically the real reason spacers exist: so you can use different offset wheels without screwing up your geometry.

  18. Pardon my ignorance, but are wheel spacing mods like this strictly cosmetic, or can they ever generate performance benefits?

    Huibert’s usual clear and concise explanation leads me to think it’s the former. But if so, it’s kinda unusual, as mods are often justified in performance terms, if only in theory (e.g. sure that giant aluminum spoiler *could* increase meaningful downforce as you rocket your Hyundai Scoupe around on the expressway in your best tank top + scowl).

    1. “Performance Benefits”. Maybe. I used wheels with less backspacing to keep the interior of my tire off of the frame. I did it in a way that the math mostly worked out.
      I went from a tire that was 10.4 inches wide to one that is 12.5 inches wide. On either side of the center of the wheel, that is .55 additional inches. The diameter increased from 31.7 to 34.8 inches, or a radial increase of 1.55 inches.
      So, stock, from the center of my tire (which is what I am measuring to avoid rubbing the frame rail) to the inner edge at any given point was 16.6812 inches. The new tire would be 18.4 inches.
      Now, I don’t have to move out the full 1.7 inches, as there is already room in the geometry. The stock tire doesn’t get right up on the frame at full lock, but it would if I didn’t get a wheel that pushed it out a little bit.
      So, yes? Performance? I can turn my wheel the whole way in almost both directions (full lock right rubs a hair) and not have problems. What I do have is a wheel and tire combo that works on my truck and makes me happy.

      1. Thank you – I learn something new here all the time. Sounds like there are definitely functionality benefits that can accrue.

        I guess I just wonder what the stanced guys (an extreme case I know) say when you ask them why? (not that I’m against whatever their reason is, I’m just curious).

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