Self Supporting Run Flat

Run Flat Tires (RFT’s) aren’t exactly new. In fact they’ve been around since the mid 1930’s when Michelin introduced a “semi-bullet proof” tire for the military. Although it performed as advertised, it was far too expensive to be considered for regular consumers. Over the decades, various types of RFT’s have been developed but they didn’t really take off until the last decade or so. Although, their popularity has dropped off somewhat of late, mostly because the perceived benefits are out-weighed by their very real downfalls.

Auxiliary Support Ring

There are two basic types of Run-Flat Tires; self supporting with thicker sidewalls and the auxiliary support setup, which had a special wheel equipped with an inner support ring that took the weight of the car if you got a flat.

The inner support ring took a lot of abuse though and if you got a flat you had to replace everything…the wheel and the tire. Most of these setups have become obsolete mostly because of the insanely high replacement costs. As such, the self supporting run-flat has become the most popular. Now I say “popular” rather loosely because Run Flat Tires only make up 1% of the entire market place.

From a consumer point of view, not having your trunk space wasted by a spare tire was a real bonus (especially since the likelihood of having a flat tire is pretty rare for most drivers). Most automotive manufactures though who adopted run-flats advertised them as a safety feature. Lets face it though, if a car company wants their consumers to adopt a new technology or feature of any kind, the best way to do is to market it as a safety feature. There are a couple ways that you could say it is a safety feature though in that if you get a puncture, and for whatever reason don’t realize it, the tire is less likely to fall apart, which could lead to difficulty controlling your vehicle. It also reduces the chance of you being stuck on the ride of the highway having to either change your tire or wait for your auto club to come get you. Being stuck on the side of the road certainly isn’t safe and regardless of if you change the flat tire yourself or wait for help, you’re going to be there for a while.

The downside though is that if you do lose air pressure in your Run Flat Tire, they have a limited range of about 50miles (or 80km) and must be driven at limited speeds of about 50mph (80km/hr) just like a good ole regular spare tire. Exceeding those limits could result in even more costly damage. This is why vehicles equipped with RFT’s needed to be equipped with air pressure warning sensors or the driver may not be aware that they had a flat (by design, it was rather hard to tell visually if your RFT was actually flat). Low tire pressure is actually pretty dangerous and that’s why all new cars are regulated to have an air pressure warning system equipped by the manufacturer.

This doesn’t sound all that bad though really. The tire will last a while so you can get off the road and to a service centre, you’re less likely to lose control of your car, and you have much more precious trunk space. But there is more to consider…they generally wear out faster and therefore need to be replaced far more often. This was such a problem that Honda and BMW had to settle out some class action lawsuits. They are very expensive to replace (30% or more expensive than regular tires) and they are also more stiff, often more noisy at highway speed, more prone to premature failures (in some cases anyway) and provide less fuel economy (again in some cases).

Ok…to me, this is starting to sound like more of a hassle. Honda seems to think so too and has stopped equipping their cars with Run Flat Tires altogether. Owners of Acura’s RL, and the Honda Odysseys claimed unreasonably low tire life and unexpectedly high tire replacement costs. This is becoming a common complaint especially for BMW and MINI owners because now all their cars come with RFT’s and ONLY RFT’s. They don’t even give you a choice anymore. Well, there is still a choice and that’s to not buy their vehicles unless they start offering the model you want with regular tires.

Now most people don’t drive too far outside of the city but I do and sometimes I end up much father away from a suitable tire centre than the limited range of a run-flat will allow for me to reach. So now I need an auto club membership. Sure most new cars come with roadside assistance but most of those only allow you to be towed to the nearest dealership. Well that could be hundreds of miles away and would totally destroy my road trip. It’s not like I can just drive to a Ma & Pa garage because they aren’t trained to handle a flat RFT. You can’t just fix them (for about $20 like a normal tire), you have to replace them (for about $500) and odds are, no small town service centre is going to be able to assist. Trip over…end of story.

Lots of consumers are way beyond fed up with the high replacement costs and premature wear of their run-flats and are looking to replace them with regular tires. Sure this can be done but in some cases, like those with BMW’s and MINI’s, the company claims that the suspension has been adjusted to compensate for the stiffer RFT’s and changing them to normal tires will void your warranty. It’s also important to note that if you lease your car which is equipped with run-flats, you are expected to return it with run-flats installed. However, many people who’s warranty has expired, and aren’t leasing, have changed them over to ‘normal’ tires and many have reported improved handling, performance, less road noise and more comfort. Nobody that I’ve heard about has stated that they’ve had any negative effects flipping over to none run-flat tires.

So why the hell is BMW insisting that ONLY run-flats be equipped on all their new cars? Because it’s more convenient for them…not you. Sure they say it’s safer and because you don’t have to carry a spare tire, that you save some weight. Yet they don’t tell you that RFT’s by design are heavier and decrease your fuel economy by 1% to 2%. Not all BMW’s come with only Run Flat Tires though, the exception is the “M” badged performance cars. Why? Simply because regular tires perform better.

As a long time BMW owner, I can’t say I’m happy about the direction that they’ve taken. I guess it will be a while before I buy a new 3-series…or I’ll have to save up so I can afford a new M3 🙂

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