420d M sport Run Flats on Front only

[bill j]

Car came with Bridgestone run flats all round, replaced rears only for non run flat Eagle F1. Noted typical improvements quieter, smoother etc but when on a run to Scotland last week and cornering firmly but Not Hard cornering the traction control cuts in, anyone had similar experiences just changing the rears?

[VerySideways]

Not a great idea to run runflats on one axle and not the other, grip levels will be very different, especially if it's cold, wet or bumpy.

Did you reset the TPMS after changing the rear tyres?

[bill j]

VerySideways said:

Not a great idea to run runflats on one axle and not the other, grip levels will be very different, especially if it's cold, wet or bumpy.

Did you reset the TPMS after changing the rear tyres?

Yes did all that, the tyres are 255/35/19 so wouldn't expect much side wall flex difference and grip levels should be similar I would guess.

[Monty Python]

bill j said:

Yes did all that, the tyres are 255/35/19 so wouldn't expect much side wall flex difference and grip levels should be similar I would guess.

Side wall behaviour will be quite different between an RFT and a normal tyre - on a RFT it's heavily reinforced so it has reduce flex in it, and it becomes more pronounced the lower the profile. I'd get the fronts changed to match the rears as soon as possible and sell the RFTs if there's much life left in them.

[Huskyman]

You really should change both axles to non run-flats as the handling could get interesting in certain conditions.. Also have you notified the insurance? I had to with my previous car, my E90 330d. There wasn't a change in premiums just a note on file.

[Slippydiff]

Ran my E90 335D MSport with NRF rears and RF fronts for a good 10k miles. The DSC light was rather active initially, but it all settled down as it adapted to the differing characteristics of the proper tyres. Though the tyre fitters at my usual tyre supply company looked at me like I'd walked out of spaceship when I told them to fit NRF's only to the rear
I drove the old girl hard, and never had a problem....... though the car was transformed when I finally fitted NRF's on the front too.

[bill j]

Yes if you look on the net there is lots of advice to keep same tyre types all round but I couldn't find any actual hard evidence or testing from tyre manufacturers when mixed. When you think about it the only difference is the side wall stiffness I couldn't imagine the compound being much different on the same tyre types if they are run flats or not so it must be that the slight lateral travel or compression differences of the normal tyre that effects the traction and traction control, interesting but it looks like the same tyres all round is the answer regardless. Thanks everyone.