Home » Watch This Vintage Safety Ad Demonstrate Why Split Rims Are So Dangerous

Watch This Vintage Safety Ad Demonstrate Why Split Rims Are So Dangerous

Split Rims Topshot

If you ever want a tire shop to tell you “absolutely the fuck not,” ask them to mount and balance tires on split rims. Perhaps unsurprisingly, vehicles and their components used to be designed with safety somewhere way down the list of priorities, and that mindset led to the potentially lethal contraption known as the split rim. You may have heard them referred to as widowmakers or suicide rims, and may have even heard stories of people being killed by them. Today we’re going to explore why split rims are so dangerous.

Split Rims 3


The split rims that are considered as hazardous as small explosive devices aren’t anything like the multi-piece wheels you occasionally see on passenger cars. Multi-piece wheels are bolted together, gaps between components are sealed, and tubeless radial tires are typically run. The most common type of split rim was designed to be run with inner tubes and has outer bead seats that are completely separate from the wheels themselves, with nothing holding them on aside from the power of friction. These wheels were popular on older heavy-duty trucks, motorhomes, and agricultural equipment, although you don’t really see them as often nowadays because of how incredibly dangerous they are.

If you aren’t familiar with wheel terminology, the bead seat is what holds the tire onto the wheel. They’re subject to an immense amount of pressure between vertical and lateral load, so they’re normally fixed parts of a wheel. I’ve mounted radial tires on one-piece wheels before and can tell you firsthand that getting a tire over the lip of a wheel and on the bead seat can be a bastard of a job. It’s a tight fit because you absolutely do not want a tire to debead and suddenly lose all pressure.

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Think of split rims a little bit like snap rings. Each one is stretched over the edge of a wheel, then very carefully seated in place by going slowly, using a tire cage, hearing protection, and a very long air chuck to pump in five PSI at a time. Some people tap the rim at each interval with a hammer to seat, but the general rule is never going higher than 40 PSI to seat. However, even while going slow, it’s still entirely possible for the rim to pop off of the wheel with enough force to kill anyone in the immediate vicinity during the inflating process. Here’s what Ireland’s Health and Safety Authority has to say about these wheels.

Split rim wheels are different from standard one piece wheels. Spilt rims are multi-piece wheels, where the tyre is held in place by a locking ring. Split rims are not normally used on cars or light vehicles. They are however found on a number of larger vehicle types. This type of wheel configuration is commonly associated with lorries, tractors, forklifts, and other heavy vehicles used in the construction and mining sectors.

A failure to put in place the necessary safety control measures when working with split rim  and multi piece wheels can give rise to serious hazards, as there is a risk of failure of the multipiece wheels. Failure of multipiece (Split Rim) wheels can result in violent separation, the explosive release of high pressure air and the ejection of component parts. The rapid release of explosive force from a ruptured tyre / tube or violent separation of the component parts of the wheel can result in serious injuries including fatalities.

It certainly doesn’t sound like these wheels have any tolerance for lack of caution. In case you find it difficult to imagine the sort of devastation these wheels can cause, here’s a visual example of what can happen if someone tries to seat a tire on a split rim without following proper safety procedure.

Well, that dummy just vaporized. By now, you’ve probably realized that these things are far, far more terrifying than coil springs. All that pressure in the tire means that these rims in 20-inch sizing can whiz off at up to 130 mph according to the BC Forest Safety Council. Even after you seat the rim on the wheel, the tire could still suffer a zipper failure while inflating to the high pressures these tires are run at, resulting in spectacular failure. What’s more, tires on these wheels can’t simply be reinflated if they’ve been driven on with less than 80 percent of specified tire pressure. You need to take the wheel off, put it in a cage, and pray to your deity of choice.

While we often take for granted the passive safety built into modern vehicles, we should take a moment to be thankful that split rims aren’t nearly as common as they used to be. While tire mounting failure on a one-piece wheel can still have serious consequences, split rims were a very risky way of doing things and are mercifully mostly items of the past.

(Photo credits: Ken-Tool, Health and Safety Authority)

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30 Responses

  1. Last tyre related death I know about happened about 10 years ago in a neighbouring village.
    Chap was under a farm trailer welding with an oxy acetelin torch, and got careless where he put it, managing to burn a hole in the tyre.
    It exploded, and blew him from under the trailer, 10 metres across the workshop and headfirst into the wall.
    Wife and neighbours heard the bang and rushed out, but there was not much of his head left.

  2. Ah, my father spent much of his career managing a reseller of wheels and tires for agriculture and industrial vehicles (and lots of other stuff but the main business was wheels and tires). So he was very familiar with this danger and had to scold the floor employees a number of times to keep things safe.

    To his credit there was no split rim-related injury or death on his watch although there was one event where the lip shot away from the wheel vertically AND through the warehouse roof.

  3. Perhaps off topic (holy cow, those exploding tires are damn scary, especially with the way they deform the heck out of those tire cages) but there are some pretty cool vintage trucks in that video. What the heck is that ten-axle rig??

  4. Ok, a little bit of terminology needs to be clarified. A widowmaker is a specific type of split rim wheel. Both locking ring and ‘Widowmaker’ fall into the split rim category.

    A widomaker was specifically manufactured by Firestone and carried the designation of RH-5. They are different because it two separate pieces that join together in the center of the rim. They are basically two pieces that are roughly the same size that ‘lock’ together with a sort of ‘two hands clasping’ arrangement.



    This is what makes them so dangerous. If the two parts are not seated exactly right, they WILL explode. And there’s no good way to definitively determine if everything is perfect before inflating them.

    Locking ring split rim designs are dangerous as well but not nearly as much. The important things are that the rim and rings are clean and nothing is damaged or bent. We had a inflation cage that we used but there are other methods for field service such as placing tire bars through the wheel, wrapping a chain through the wheel, or inflating it on the truck in the outside dual position so that if the ring blows off, it hits the inside dual and is contained.

    I worked in a tire shop in high school in the late 90’s. We serviced split rims regularly. I did 40 or 50 while I worked there and never had one let go but I also ALWAYS followed the proper procedure and inflated them in the cage. I don’t recall ever doing a widowmaker but I do remember seeing at least one set. I think we turned them away.

    1. I also worked at a tire shop in the late 90’s during high school. I would have been fired on the spot if I did something remotely unsafe with a split rim. They took it VERY seriously.

    2. Beat me to it by a long while.
      And yes. Firestone is very much the poster child for a company that has continuously, repeatedly, and deliberately engaged in unethical acts, outright crimes, and deliberate negligence in the name of profits since the day it was founded.
      And no. Bridgestone hasn’t been any better.

  5. Not sure if its still there, but for a while the Heavy Equipment shop at one of the bases I was stationed at had a patch in the roof from a split rim popping.
    When I was there, the hole was there but the civilian worker that caused it was long since retired.

    I was told the story went something like: one of the guys was working in the back of the shop and the bell rang for lunch. He stopped work, put most everything away, and went to eat lunch. Midway through there’s this god-awful BANG. He looks up and goes “fuck! the wheel!” and runs off.
    Turns out he had hooked up a machine to air it in 5PSI increments, and was going to just watch it from a safe distance and turn it off when it seated or when it reached a certain pressure. He somehow forgot it was airing and let it go during lunch until it had reached shop PSI which (due to requirements for some of the air tools working on heavy equipment) was something ungodly high.

    If not for the patch and the imprint of a semi-circle on the roof, I’d say it was bullshit. I know it reads like bullshit.

    I do know that I personally experienced one blowing while in the cage. When I was there they had a dedicated tire shop and we did split rims semi regularly. The tire cage wasn’t even in the shop, it was outside and all the controls for the air to the cage were inside. Had to roll the tire outside, put it in the cage, hook up the air line, come inside and close the door, then you could manipulate the air pressure. I did a couple dozen split rims when I was assigned to the tire shop, the procedure got annoying as hell until about two weeks in and one blew in the cage. It damned near gave me a heart attack. People from different buildings came to check on us to see what the noise was.
    Never bitched about the procedure after that.

  6. Reminded me of how much I loved doing tire replacements when I worked at a neighborhood gas station/garage back in my teens/20s. When they were big steel wheels with sloppy sidewalls, things went pretty smooth – they’d pop in place pretty easily. When lower profile tires came in ….look TF out. Nothing quite like the fun when the tire’s aired up to spec PSI and the thing hasn’t completely seated on the bead yet, and you’re standing there …..just…. waiting…..

  7. I have a family connection with these. In the early 70s my father was one of the lawyers representing Firestone in product liability lawsuits for multi part wheels among other things. I got a bunch of decals and an Airforce Museum book while he had to fly to Dayton.
    As DavidBowieKnifeSpooney mentions these split rims are distinct from the more modern cast spoke wheels found on old dump trucks and the like. The “Dayton” style have nuts and wedges that positively clamp the rim in place. These wheels survived on heavy equipment and construction trucks because the removable bead meant you could change a tire with a wrench and a couple of pry bars rather than tire machine.

  8. About 10 years ago, my Dad was airing up a split rim tire from an old tractor. It was one of the smaller front wheels and he had it lying flat on the ground. The rim let go and flew straight up in the air, luckily missing his face by inches, but it took off the first joint of his right index finger where he was holding the air hose. He counted himself a very, very lucky man.

  9. Yes – these are dangerous but here’s something I never knew: Old Magnesium Wheels are as well.
    A local SCCA racer was killed when a magnesium wheel went to shrapnel as he was mounting tires for his Super V car. Following is an excerpt from the person who discovered the body:
    “He was getting wheels to put on the Super V so he could take it to the chassis dyno next week.I found out last night that the Mag wheel rim had split so a piece of it had hit Bob. He was using old tires for the dyno work and had new tires for racing. I still am not certain how much pressure we are talking about with this. He must have been trying to seat the bead and maybe the bead popped against the edge of the rim and caused it to brake (sic) off.” From what I gather the piece of rim must have severed his femoral artery and he bled out.

    The take away is…Magnesium wheels can corrode and fail. Old wheels should be used very carefully and probably not raced.

  10. There’s still a set of the original Widowmakers (Firestone RH-5 style mentioned in DavidBowieKnifeySpooney comment) on the back of my project 1950 Ford F3 in the garage. I learned about split rims when I took one of the front wheels in to get a tire put on it. Shop #1 couldn’t figure out how to get the thing apart, and shop #2, after an extended wait, told me they were willing to put a tire on it, but not inflate it since I was only going to use it to roll the truck around. After they kindly explained what it was needless to say I declined to have them do anything more. Anyway, the two on the back of my truck have been seated and holding air for honestly who knows, 30, 40, years at this point? I’ve kept them at low pressure 10-15 psi max, just so I could roll it around but the plan is to replace them this summer and do away with them completely.

  11. I worked for a law firm in the 1990s that handled a couple matters where a tire changing place had stopped using the cages and people had either been previously injured or killed. We had a big stack of standard production records that included all the diagrams, recommendations and so on that people absolutely needed to use a tire cage.

    I feel like I saw that video back in the mid 90s. I had no idea, so as a car nerd, I was pretty interested in the whole tire process for trucks. Since then, whenever I’ve passed a truck on my motorcycle, I absolutely do not dally alongside them.

  12. The instructor in our vo-tech auto shop also ran a Peterbilt with an over the road driver. We (16-, 17- and 18-year-olds) handled all the maintenance on the truck when it was home, including repairing/replacing tires on split rims.

    The instructor’s safety briefing before we were allowed to work on tires was intense, to say the least. No cage in the shop, so we wrapped a heavy chain around the tire. Never had one blow off. Proof that teenagers’ prayers are answered, at times.

  13. When dad had a 3/4 ton camper built for our ’64 F100 crewcab, additional leaf springs and slightly larger wheels were used for the additional load. When I got the truck from dad, it still had the 16.5″ rear split rim wheels on it. I had to take them to a few tire shops just to find one willing to demount the tires so I could recycle the tires. I still have the rims. Anyone interested in them? I replaced the overleaf springs with stock ones from a wrecking yard and eventually found stock rims.

  14. An older gentleman, who lives local to me, had a mobile tire repair shop in the 80´s, and within a few years, lost two of his brothers to incidents involving these types of rims. He called it quits after the second brother’s funeral.

  15. I not long ago replaced the split rims on our 2002 Nissan Patrol cab chassis with tubeless wheels. And it had nothing to do with the safety limitations of the rims themselves. The choice was made because I couldn’t get reasonably priced 7.50R16 tyres so had to run fatter 285/65R16 tyres which made the whole thing handle even more oddly than usual. Compounding this is that modern tyres no longer have smoothed faces on the inside of the carcass so the tubes I had inside the tyres were being abraded especially at the sidewalls…

  16. I changed split-rim tires as a ute before the cage laws came in. I knew of a local mechanic who was rendered into nearly a vegetative state when a split rim was being taken out of the cage. Just the impact of the tire hitting the ground caused the lock ring to pop off and hit him in the head.

    My cheapass boss wouldn’t pay for a new clip-on air chuck when the only clip-on chuck in the shop broke, so I had to hold the old chuck on, to air the tires. In a grim calculus, I only ever used my left hand to hold the chuck so I wouldn’t lose my useful hand.

  17. So I have a 1967 Nissan Patrol and they all came with 15″ split rims as far as i know. I’m not sure when this started, but I think maybe in 1967. Split rims are still used in areas like Australia and the middle east because they are easier to change in the bush.

  18. A few years ago when I bought my ’70 International 1200D from the original owner he mentioned that he still had the split rims for it in his shed even though he had replaced them with one-piece wheels a few decades previously. He offered them to me as part of the deal and I took them, of course, but now they’re just sitting in my shed…

    1. Depending on whether they also have removable centers, they make fine firepit liners. Just don’t cook food over the first couple fires.

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