I have read on this forum quite a few topics about members bent wheels and i am coming to the conclusion that the runflat tyres must be a contributing factor in these wheels becoming bent.The side walls are so hard that there is hardly any cushioning effect when you hit any size of hole in the road thus the shock wave going straight into the wheel. Any comments about this ?

 

No no, I would say that the RFT protects the rim more than a conventional tyre ! The tyre plays the role of fuse when riding on potholes !
As the tyre is lower, of course it's more risky if you use 19' or 20' rims, which are also far more expensive !
You don't have here complaints of people owning 16' rims, right ? Low profile tyres do NOT protect your rims !

RFT tyres are harder & make more noise, but they are better for your security.

And also always be sure to choose a tyre that protects the rim (out flank protection) against curbstones.

 

Logic says OliverB is right

 

However my experience, to my cost, says otherwise. I am 99% convinced that my 2 bent rims were caused by the RFTs after going over a particularly bad pothole. To be fair, they saved me changing a wheel at the side of the road, they got me home (slowly) but both rims were bent beyond repair.

I think the sidewalls are so stiff they don't cushion the blow in the pothole, so the force of the impact is transferred through to the rim. I know logic would say the rims are harder than even the stiff rubber sidewall, but something caused these rims to bend!

 

I agree with you about the security aspect but the harder the tyre wall then the greater the shock the wheel will have to take. The stiffness of the sidewalls will not allow the tyre to absorb much of the shock when you hit a pothole.

 

I'm with you.

If the tyre transmits more shock to the car due to stiff sidewalls, which we all seem to agree RFT's do.

Then more force must be being placed on the wheel structure.

 

Exactly !

 

The harder sports suspension won't help in these circumstances either.

 

Sorry guys, but I think it's all a matter of sidewall height and inflation pressure when it comes to wheel protection. Low profile tires simply are that: low profile. They do not mix with potholes, and in cold climates, you are asking for rim repalacement the lower the aspect of your rim to tire measurement, and the lower you allow your tires' inflation to become due to temp drops. Not uncoincidentally, ride is improved with higher aspect tires.

Some low profile tire manufacturers (Dunlop in particular) mould a substantial bead of rubber that surrounds the wheel's rim lip, (almost a "finger" wide) to help protect rims; why other manufacturers don't do this is beyond me.

But to address the original question, the firmness of the RF sidewall should protect rims to a slight degree, just as higher inflation pressure can protect, but, both transmit more vibration. However, that vibration is nothing like the shock of the edge of a pavement pothole or a curb. We're still talking RUBBER/air in RFT construction. It is the HEIGHT of the sidewall, and therefore how much there is to compress up against a pothol edge that is the measurement that really matters.

In part, this is why 21" rims are more popular in Southern California than the northeast--at least to anyone with common sense.

Cheers,
Ray Hull

 

I've bent rims on potholes with no damage to the mounted regular (non-run flat) tires twice on two different Volvos. Just replaced the rim and remounted the same tire. Seems the impact set up a pressure wave that bent the rim or perhaps the sidewall collapsed allowing direct transfer of the imact force, although this should have blown out or at least visibly damaged the sidewall. On the other hand I can envision the scenario where the sidewall does transfer the impact force in the case of a run flat. Either way I think it's as much cisrcumstance as anything else: velocity, the profile of the pothole, whether the car was braking at the time, the construction of the tire, the tire's profile, the temperature, whether it was an odd or even date, the phase of the moon, and the proximity of locusts.