rodybmw

In the old days when car manufacturers did not use crumple zones in the front and read of the car the damage from an accident did not look that bad (no crumpled/bent hood, etc.). However, that just meant that a high level of the impact energy was transferred to the occupants. To solve this problem they started designing cars that would bend and crumple to a great degree, but by doing so a lot more of the impact energy was absorbed by the hood/etc. and not transferred to the occupants.

To me it seems that RFT's should work the same way. When there is an impact the energy from it HAS to be absorbed by something. If the sidewalls flex more and absorb more energy (in normal tires), then less of the impact energy is transferred to the wheel. On the other hand, if the sidewall is VERY stiff and does not flex nearly as much (RFT tires), then there is nothing to absorb the impact energy before it gets to the wheel. So in my opinion RFT's may cause more bent wheels than normal tires.

pennetta

The impact pressure will first be absorbed by the most flexible components (rubber tire, cars suspension)and then move on to the less flexible components (Aluminum wheel). As long as the RF sidewall is more easily deformable than the wheel, then its aiding in saving your rim. If a conventional tire doesn't absorb enough impact energy before it touches the wheel, then it will transmitt more energy to the wheel and thus bend the rim easier.

pedrollo

I too have damaged Volvo rims without (always) terminating the tyre.

If the sidewall is soft (I was amazed how thin they are), the load gets spread across the wheel by the air pressure. If it is too bad then the tyre can completely collapse and allow the impact to directly damage the rim.

I have seen photos on here of rims split in two right round the circumference, this has to prove that the stiff RF sidewalls are transmitting loads not previously seen onto the edge of the rim.

I have ordered the spare wheel and 172s with non-RFs, no doubt in my mind.

pennetta

Just remember that the runflats are lower profile (ie. 35 & 40 series) which always transmits more energy to the wheel than non-runflats (50 series) regardless of tire construction type. In a 275/35-18 tire, the sidewall height is 40% of the tire width of 245- which equals 96 mm or about 3.8 inches. In a 225/50-17 the sidewall is 113 mm or about 4.4 inches. So the non-runflat has 16% more absorbing distance than runflat tires.

rodybmw

It's true that the OEM 17" tires have higher sidewall heights than the OEM 18" RF tires. However, most people get the non-RF tires to replace their 18" 35 and 40 profile RF tires while keeping their OEM wheels, or they are getting new 19" or 20" wheels with 25, 30, or 35 profile non-RF tires, which have even lower sidewall heights than the OEM RF's. So in cases like these the non-RF's would have the same or lower sidewall heights than the OEM 18" RF's.

katheikia

I had a bent rim after hitting a pothole the first week I had my car. The SA at the dealer confirmed that the run flat tire contributed to this. It makes perfet sense, if you fell flat on your ass, would you rather have a harder material on your behind or a softer material ??????

pedrollo

Rody is correct, I havn't had a sidewall bigger than 45 for years, so am comparing apples with apples.

anlauf

I know the N. Cal. roads are terrible...but in 7000 miles of driving I have bent 4 of the 18" wheels. I called BMWNA today to express my displeasure....I have never bent a wheel in all my 47 years of driving....now 4 in 7 months of e60 ownership?

Any suggestions....non RFTs? Different wheels? Move to Hawaii?


__________________
Anlauf
2006 530 Sport Manual, Silver Gray/Black, Premium, Nav, Sirius, Split Rear Seats, Shades, Al Cube interior trim

gatemaster

... you've read the posts about split wheels etc ?

how about just a marginal wheel design ? Not happy about this but it could be reality.

I'm of the opinion that the really really bad potholes/seams in the road have collapsed the r/f tire sidewall to the extent that it has "bottomed out". i do have 3 bent rims ("egg shape") and i can think of several bad potholes or seams that i swore should have caused a blowout. maybe the r/f tire survived (good) but at the expense of the wheel (bad) ?

-mike

BetterMakeWay

I agree. IMO the rf tire, and as much as i hate them, really protect the wheel better than a non-rf tire of the same size. Forget about shock absorbing and stuff like that, if you hit a pothole that badly to actually damage the rim, then rf tires are better because they don't allow because of their stiff tire walls, they don't allow the concrete lip to hit the rim. Because non-rf tires don't have the stiff walls, those tires indeed at 1st thought tend to absorb the force of the impact, but just slightly, if the pothole is a bit bigger you'll end up with a tire bump (dunno if it's the correct term) since the tire wall gets distorted so fast and so powerfull that then metalic inserts from the tire snap. And if the pothole is huge enough than it simply won't absorb too much and act directly as a cotton. It's like hitting with ur fist a wall that's been patched with 1cm cotton.YOu will simply feel the wall with your knuckles regardless you hit 1st the cotton. I dunno if this was a good example but i think you got the ideea. And the fact that rf tire don't aborb so much that doesn't mean it's 100% taken by the rim. A big impact like that will therefore be absorbed more by the suspension than by thr rim itself.