RFT (Run Flat Tyres)

[Tony]

As posted in wim before the RFT is an armoured tyre that can support the car even if completely deflated, since the tyre is armoured then the cars coils are down-rated so the drive remains comfortable, in addition the tyres perform so well deflated then the car must have a pressure sensor system to warn the driver that a tyre is deflated.

 

Due to the rigidity of the tyre sidewall i is impossible to determine if the casing is internally damaged so a deflated RFT is scrap.

 

The unexpected consequence is that easy to repair RFT's are being sold in the second hand tyre market (Legally) Recently i have had cars booked for Geometry's with dire handling problems only to find RFT's fitted to unequipped cars.

 

Since the RFT is to become mandatory in future cars this current situation is likely to grow with repaired units on the road, a worrying future for those not in the know.

[Mark H.]

So if you buy a 2nd hand car and it had came with run flats from the factory and you replace them with normal tyres will the car now be under damped and what will be the consiquence of this?

 

Will it be more wallowy and just provide a bouncier ride, or will it have other more critical safety issues?

[Tony]

So if you buy a 2nd hand car and it had came with run flats from the factory and you replace them with normal tyres will the car now be under damped and what will be the consiquence of this?

 

Will it be more wallowy and just provide a bouncier ride, or will it have other more critical safety issues?

It would drive like the dampers have been removed. Remember the tyre is able to support all the corner weight deflated and still appear/drive like inflated, you maths that ability into a down-graded coil, then add that rate into a conventional coil, then do the same with the tyres.....

[Paul TVR]

I have driven many miles in a Mini Cooper S equipped with run flats, and a friend S who fitted yokohama rubber which wasn't a run flat, I can say the car handled better on a track with the non run flat tyres and also gave better road manners.

 

Do the manufactures take the different tyres they fit into consideration when selecting the spring/damper rates? I noticed the S came fitted with Dunlop tyres originally but then move on to perrili, it seem the cars coming out the factory each week with different tyres, as the manufacturers tyre specs differ they surely don't spring the car to suit?

[Tony]

I have driven many miles in a Mini Cooper S equipped with run flats, and a friend S who fitted yokohama rubber which wasn't a run flat, I can say the car handled better on a track with the non run flat tyres and also gave better road manners.

 

Do the manufactures take the different tyres they fit into consideration when selecting the spring/damper rates? I noticed the S came fitted with Dunlop tyres originally but then move on to perrili, it seem the cars coming out the factory each week with different tyres, as the manufacturers tyre specs differ they surely don't spring the car to suit?

Hello Paul welcome to wim. The RFT is a package that includes down rated coils. On the cooper models not fitted with the RFT package then many tyre manufacturers compete to be the OE preference.

 

At Bridgestones European proving grounds STS was involved in a performance example for the RFT ver standard construction and although i dislike the RFT it did prove superior.

[Paul TVR]

Thanks for the welcome Tony.

 

I guess the yoke's were just a more grippy tyre, if fitting non run flats would you suggest a high tyre pressure to compensate for the side wall flex?

 

Seeing the Mini has a 40 profile tyre the sidewalls are very small and have little give in them even on standard rubber so I guess the RFT would make a bigger difference to high profiled cars.

[Tony]

Thanks for the welcome Tony.

 

I guess the yoke's were just a more grippy tyre, if fitting non run flats would you suggest a high tyre pressure to compensate for the side wall flex?

 

Seeing the Mini has a 40 profile tyre the sidewalls are very small and have little give in them even on standard rubber so I guess the RFT would make a bigger difference to high profiled cars.

The Rave4 is a perfect example.... shame no one can remove the tyres?.... We are all in a transition period with the RFT. The fitment over the pond will be mandatory on all new cars by 08 and here in the UK by 012 so this evolution is coming.... Personally i don't like the RFT but i will have to adapt and move on.

[Paul TVR]

Thanks for the welcome Tony.

 

I guess the yoke's were just a more grippy tyre, if fitting non run flats would you suggest a high tyre pressure to compensate for the side wall flex?

 

Seeing the Mini has a 40 profile tyre the sidewalls are very small and have little give in them even on standard rubber so I guess the RFT would make a bigger difference to high profiled cars.

The Rave4 is a perfect example.... shame no one can remove the tyres?.... We are all in a transition period with the RFT. The fitment over the pond will be mandatory on all new cars by 08 and here in the UK by 012 so this evolution is coming.... Personally i don't like the RFT but i will have to adapt and move on.

 

I take it that's only new cars by 2012?

 

I guess they are safer, a puncture at speed is very easy to control, having driven the mini with a flat at 40mph plus they certainly work.

 

I noticed you said they shouldn't be repaired though? I had a tyre repaired after it picked up a screw, was only a week old and didn't lose pressure but I noticed it in the tyre.

[Tony]

Thanks for the welcome Tony.

 

I guess the yoke's were just a more grippy tyre, if fitting non run flats would you suggest a high tyre pressure to compensate for the side wall flex?

 

Seeing the Mini has a 40 profile tyre the sidewalls are very small and have little give in them even on standard rubber so I guess the RFT would make a bigger difference to high profiled cars.

The Rave4 is a perfect example.... shame no one can remove the tyres?.... We are all in a transition period with the RFT. The fitment over the pond will be mandatory on all new cars by 08 and here in the UK by 012 so this evolution is coming.... Personally i don't like the RFT but i will have to adapt and move on.

 

I take it that's only new cars by 2012?

 

I guess they are safer, a puncture at speed is very easy to control, having driven the mini with a flat at 40mph plus they certainly work.

 

I noticed you said they shouldn't be repaired though? I had a tyre repaired after it picked up a screw, was only a week old and didn't lose pressure but I noticed it in the tyre.

 

The reason they cannot be repaired is not the procedure for the repair or the success but the fact the technician cannot fully inspect the tyre for sidewall damage. The RFT has a limited distance for safe deflated operation, since the deflated handling is so good then it's unlikely the owner could say exactly how far the tyre had been driven on flat, this is despite the onboard pressure censors?

[Paul TVR]

I see so a tyre such as the one I had repaired which hadn't lost any pressure should be ok.

[Tony]

I see so a tyre such as the one I had repaired which hadn't lost any pressure should be ok.

The method for repair is not in question, the RFT is the same as any other tyre.... Problem is commercial liability? Since the tyre is violated when driven on flat most tyre shops cannot guarantee the internal structure is still safe.

The area between the base compound and the sidewall reinforcement could be compromised, since unlike normal tyres there would be no visual or physical clues the deflated RFT must be concluded as scrap.

[Tony]

I see so a tyre such as the one I had repaired which hadn't lost any pressure should be ok.

The method for repair is not in question, the RFT is the same as any other tyre.... Problem is commercial liability? Since the tyre is violated when driven on flat most tyre shops cannot guarantee the internal structure is still safe.

The area between the base compound and the sidewall reinforcement could be compromised, since unlike normal tyres there would be no visual or physical clues the deflated RFT must be concluded as scrap.

Bump

In various meetings with Bridgestone representatives they now openly say the tyre can be repaired "once" assuming the repair falls within normal parameters. Yesterday a very well known customer to STS had a puncture in his "RFT" 265/35-19. The injury was in the middle of the tyre and only deflated for a few miles.. All the management team debated weather or not to repair the tyre and the decision was NO! The reason for this is there is no "written" proof to say the tyre can be repaired, so due to commercial liability it was scraped.