Do run flats crack the alloy?

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JonnyP2468

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I was just wondering what the effect would be on a standard tyre to that of a run flat tyre faced with a pothole.
Am I right in saying that the shock would crack the inside of the alloy on a run flat tyre rather than buckling?

And

Would the standard tyre allow the alloy to bend due to the edge of the pothole connecting with the rim?

Thanks!
 
A properly inflated tyre of either type would react the same. If the pothole is severe enough it will damage the rim.
Whether it cracks or buckles is going to be random, maybe micro cracks already in the rim material ..
 
I've seen both buckles and cracks in both MB and BMW rims after hitting potholes.
 
The potholes are to blame not the tyres (although a sidewall profile of 200 may help):)
 
All my cars in recent years had 16" wheels and 60 or 55 profile tyres.

Never ever had any issue with rim damage (other than kerbing).

I am pretty sure that the pot hole damage if a direct result of having large rims (17"-21") and low profile tyres (45-35).

I don't think that the tougher sidewall of the ranflat tyres would make a significant difference.
 
I've found that run flats tend to cause more damage to rims than their low - medium load rated counterparts. They have a lot less give in them so tend to exaggerate the impact.

Have a look at the issues BMW had with rims when most of their cars were fitted with run flats. A disproportionately high amount were being damaged when compared with standard tyres and, coincidentally the ride was much harsher with every bump being felt.

When I had my silly Jeep (SRT-8) I found that two rims had cracks on the inside edges. It was also very unforgiving over bumps due to the inflexibility of the sidewall.

I'd love to say that any damage could be avoided by careful and observant driving but this is not an easy thing to achieve with the current state of most roads, especially in the wet or snow.
 
I worked at a BMW MB dealer and the amount of warranty wheels we changed because of cracks caused by what was obviously crashing over bumps was ridiculous.
Even advising customers to try and avoid potholes didn't help.
And the ride from BMW RFT is abismal.
Think about it logically, each tyre is required to support the weight of each corner when deflated, no wonder the sidewalls had no give in them. And have you ever compared the weights of RFTs against normal tyres!
 
Interesting. If anything, I would have expected that the softer sidewall of the non-runflat tyre will be quicker to yield when hitting a pot hole, and allow road-to-rim contact that will crack the rim.

The idea that the rims crack not as result of actual contact with the pot hole, but as result of the shock being transferred to the rim via the runflat tyre's harder rubber is interesting, but not what I would have expected.
 
When I had our first new A210 I accidentally hit one of those ramps where they had plained off the top surface of the road prior to resurfacing. I hit it at 50 and bent and cracked all four AMG rim's. The tyres were fine though.
The sidewalls will give slightly but only to a finite degree.
RFT have virtually no give effectively giving the suspension more work to do.
 
The RFT ( Run-Flat-Tyre ) has been the desire of the tyre industry for 30yrs or so and in all that time they have been nothing more than a nemesis.

The current build has been adopted mainly by the German marque but the fact AMG and the BMW M series do NOT fit RFT's speaks volumes?

BMW has struggled to satisfy their promise to the customer base promoting the RFT as a safety feature, the main failing being the cost, noise, handling, durability, and damage to the wheels.

The RFT has an armored sidewall hence it's ability to hold the weight of the car but!... In order to keep the unsprung weight down the alloy is made from lightweight composites. As a result road shocks are transmitted directly to the rim cracking them. Often I see BMW wheels with several cracks.

I bought my wife a BMW because of the RFT's but she is disabled, so despite the fact, I despise the RFT they do have a place in this world for some?
 
I bought my wife a BMW because of the RFT's but she is disabled, so despite the fact, I despise the RFT they do have a place in this world for some?

I think so, knowing that when my wife is out with my girls, the tyres wouldn't go bang and she wouldn't have to wait for recovery for hours on the dangerous hard shoulder, I think it's worth the money.
 
The RFT ( Run-Flat-Tyre ) has been the desire of the tyre industry for 30yrs or so and in all that time they have been nothing more than a nemesis.

The current build has been adopted mainly by the German marque but the fact AMG and the BMW M series do NOT fit RFT's speaks volumes?

BMW has struggled to satisfy their promise to the customer base promoting the RFT as a safety feature, the main failing being the cost, noise, handling, durability, and damage to the wheels.

The RFT has an armored sidewall hence it's ability to hold the weight of the car but!... In order to keep the unsprung weight down the alloy is made from lightweight composites. As a result road shocks are transmitted directly to the rim cracking them. Often I see BMW wheels with several cracks.

I bought my wife a BMW because of the RFT's but she is disabled, so despite the fact, I despise the RFT they do have a place in this world for some?
I have always been of the opinion that by fitting RFTs, that's 1 less wheel (spare) for the factory to fit. Think a out the cost saving over a million cars! ;)
 
IF run flats give the wheel a hard time, think what it's doing to the life of the suspension joints.
 
IF run flats give the wheel a hard time, think what it's doing to the life of the suspension joints.
Yes I made this point earlier, it works the suspension so much harder
 
IF run flats are substantially heavier and the extra weight is not compensated for by the lighter wheels then ride would be worse irrespective of the tyres stiffness. There is no worse place on a car to add weight than the wheels. It increases unsprung mass and gives a double whammy effect on acceleration and braking i.e increases overall vehicle weight and increases rotational inertia. I would have thought heavier wheels is the last thing you would want on a sport oriented vehicle like a BMW.
 
Interesting.....is it worth taking he car to merc just to have a nosey and see if there’s any run out on them?
Also, does anybody know if warranty would cover a buckled rim? I guess not but it seems to be a very common issue, so I don’t really know if I’m honest.
 
The RFT has an armored sidewall hence it's ability to hold the weight of the car but!... In order to keep the unsprung weight down the alloy is made from lightweight composites. As a result road shocks are transmitted directly to the rim cracking them. Often I see BMW wheels with several cracks.

We've had two BMW 326M alloys crack. BMW not interested in replacement. The car doesn't do high mileage and isn't run over particularly bad roads (disproportionate amount of m'way mileage). Since replacing the 19" 326Ms with 18" non-OEM wheels a few years ago we have had one crack.

Hardly scientific though the car's usage patterns have been consistent year on year but my view is 326M 19" wheels are expensive and not of adequate quality for the price. The non-OEM wheels were 20% of the price and have managed a bit better (so far).

I bought my wife a BMW because of the RFT's but she is disabled, so despite the fact, I despise the RFT they do have a place in this world for some?

We looked at te option of switchign to non-RFTs. I took the view that while SWMBO is able-bodied being stuck on the side of a busy motorway or busy dual carriage way with no shoulder in rush hour possibly in twilight trying to change a physically large wheel or pump one up was something that bothered me.

RFTs have their place. But not on very low profile wide alloys.
 
Fair comment. I just see the distressed customer side of the RFT. Expensive, noisy, poor grip, harsh ride, cracked rims and none-repairable if punctured.
 
I do think we need a sense of proportion with regard to tyre punctures.

The mindset that tyres get regular punctures is completely out of date. think of all the other items that could leave your car stranded and compare them to a tyre. I had one of my cars for 5 years and in that time I NEVER had a puncture, however, I did blow-up 3 engines... No-one is suggesting we carry a spare engine (except Lexus, Toyota, Vauxhall, BMW etc on their electric cars), but it would have been more appropriate for me.

Flats are so rare these days, and the number of people who are likely to actually get out of their cars to look, never mind change them, is getting rarer, so waiting for a roadside rescue becomes the norm.

In this case we don't need a spare of any description.

Personally, I just carry a Fix-a-Flat aerosol... NO run-flat will ever disgrace any of my alloys!
 
The mindset that tyres get regular punctures is completely out of date.

Totally agree. Runflats are an answer to an almost non existent problem. I can't remember having had a flat in almost 50 years of driving that necessitated using the spare wheel out on the road. The odd nail and slow puncture yes but they never immobilised the car.
 

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