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Originally Posted by akhbhaat
Well, let's look at the main "advantages" of runflats, point-by-point.
Runflats will prevent a crash caused by a high speed blowout.
Possibly, but the blowout alone is not the cause of the crash; driver panic is. A blowout will violently disrupt the car's balance for a moment and, of course, traction changes completely. Inexperienced and/or incompetent drivers (which do make up an enormous bulk of the US population) will tend to panic and react impetuously. This is what results in a loss of control leading to a crash. I myself have experienced a blowout at freeway speeds and was easily able to bring to car to a gradual stop without further incident. It's even been proven through testing that the vast majority of SUV rollovers caused by blowouts were due to the same reason.
Runflats are considerably more stable during blowouts due to the stiff sidewalls, but proper driver training with regular tires could ultimately give the same results. Of course, I'm not going to flat out deny that run flats AREN'T a benefit here - but a pricey one, and as I pointed out, a blowout with a regular tire doesn't have to result in a crash or loss of control unless the driver wants it to.
Runflats eliminate the spare and increase trunk room.
Statistically, the E90's trunk volume has increased by 16%, from 291.6 to 339.8 liters (10.3 to 12 cubic feet). Subjectively, this difference isn't really pronounced - the trunk opening hasn't enlarged (to accomodate bulky items) all that much, and some of the extra space is taken up by an otherwise useless storage tray. I consider this a wash. It's not as though 1.7 cubic feet is an enormous space even on paper.
Runflats eliminate the dangers and hassle of changing out a wheel along a busy shoulder or in a bad neighborhood.
Yes, but then you have less than 150 miles (is there any "and/or/whichever comes first" time limit attached to that figure? there'd almost have to be...) to find a reputable tire shop to repair or replace your blown tire! How is that ultimately any less of a hassle than the immediate (10-15 minute) inconvenience changing to a fully functional spare tire (which can essentially be used indefinitely)? I'd say it's more of a hassle! You could be at the shop for well over an hour, not including the time it takes to find one (though I'm sure the nav system has a built-in database of them :lmao: ), you could be unfairly charged if you're not familiar with the shop or its reputation...hell, they might not even have the right type of tire in stock, meaning you'll either have to replace it again later, or drive around for thousands of miles with a mismatched set of tires (dangerous, as they always have different grip/behavior properties).
As for finding a safe place to change the spare, there's nothing to stop you from slowly driving farther off the road, if on the interstate, or into a nearby parking lot if in a city climate. And I really don't know anyone who knowingly takes their $40,000 car through a neighborhood they wouldn't feel comfortable stopping in.
Oh, and if the tire cannot be repaired and needs to be replaced, have fun paying the $300+ fee for a new one (sport package owners get really screwed - thanks to BMW's unexplainable decision to use a staggered setup - which increases understeer considerably - the tires can't even be rotated and wear out at shorter intervals because of that, especially the wider rears which cost even more!). Note that if you decide to use most or all of the tire's effective post-flat/blowout range, the tire will effectively be destroyed with NO chance of successful repair.
Runflats eliminate the need to periodically check the tire pressure in the spare and/or inflate it if necessary.
Minor, minor inconvenience. Takes a minute once every month or two. Who cares?
Those are the supposed advantages. As you can see - at least from my point of view - none of them are really worthwhile and do not justify the cost. I'm not going to bother covering the glaring disadvantages in any detail (cost, ride quality, performance, etc) - those are already well documented.
Still gimmicky, I say, and for one main reason: price. If runflats cost the same as regular tires and were as easy to find as regular tires, I could ignore some of the flaws.
As it is, however, if I buy an E90, I'm going to toss the runflats as soon as they've worn out and replace them with regular performance tires and a steel spare in the trunk (at least for for highway hauls) and/or the M mobility kits used with the E46 M3. Anyone wanna take bets on whether the E90/E92 M3 has RFTs or not?
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