[goram]

My 335d has 19s, and currently running with Pirelli P Zeros runflats, 255 35 96Y at the rear. They will need replacing come MOT time in a few weeks. The ‘standard’ spec suggests the load rating should be 92.

Anyone know if I would notice much difference if I swapped from 96 to 92? TBH I’d rather ditch the runflats completely, but struggling to justify the cost of 4 when the fronts have plenty of tread left.

[Techno 9000]

I have tried lower, but still compliant, Load Index tyres on a previous car, yes it makes a difference, but not chalk and cheese, every little helps though.

In regards to running run flat and non run flat at the same time, well I did until the other axle set wore down more, then changed those over.

[robbiep]

Originally Posted by Techno 9000

I have tried lower, but still compliant, Load Index tyres on a previous car, yes it makes a difference, but not chalk and cheese, every little helps though.

In regards to running run flat and non run flat at the same time, well I did until the other axle set wore down more, then changed those over.

Never, ever, run RFTs with non-RFTs, even if on different axle

As to the load index, you might just, possibly, notice a fraction more suppleness in the ride from the lower load index rating. Or it might all be because you're expecting to feel a difference.
I doubt if it'll make any real difference in everyday driving. If it was a track car, it might be a different matter

[sensible]

Originally Posted by robbiep

Never, ever, run RFTs with non-RFTs, even if on different axle

Exactly this ^

[goram]

Certainly won't be mix and matching run flats with non run flats. Don't even want to mix brands either. I've read (rightly or wrongly) of potential damage to the xDrive system.

[HighlandPete]

Originally Posted by goram

My 335d has 19s, and currently running with Pirelli P Zeros runflats, 255 35 96Y at the rear. They will need replacing come MOT time in a few weeks. The ‘standard’ spec suggests the load rating should be 92.

Just a quick thought. Are you running 96Y or 96Y XL? The 96 XL is an equivalent tyre to the 92Y, at the lower 2.5bar rating.

[mitch060708]

I am looking to get runflats put back on my 435 xd. They are 19”.

I think the front should be 225 40 19 89y

But what about the rear 255 35 19 ???

Any help please? Thanks

[robbiep]

Originally Posted by mitch060708

I am looking to get runflats put back on my 435 xd. They are 19”.

I think the front should be 225 40 19 89y

But what about the rear 255 35 19 ???

Any help please? Thanks

What does the label on the slam panel say ?

[Techno 9000]

Originally Posted by Techno 9000

In regards to running run flat and non run flat at the same time, well I did until the other axle set wore down more, then changed those over.

Originally Posted by robbiep

Never, ever, run RFTs with non-RFTs, even if on different axle

So where is the logic in saying that you should never run Run-flat and non run-flat tyres, even on a different axle?
To my thinking, where concerned by the possibility of damage to the X-Drive transfer box, the concern would be a mismatch in rolling circumference and this wouldn't be an extra factor invoked especially by having run-flat and non run-flat, it could happen with a variation in rolling circumference between any tyres, e.g. Heavily worn vs brand new tyre.
Where X-Drive isn't fitted then the debate goes to a variation in grip between different tyres and that could be bigger with say 'select your favourite big brand tyre make' on one axle vs 'linglong ditchfinders " on the other axle.
Interested to hear the views of the forum massive.

[HighlandPete]

Originally Posted by Techno 9000

So where is the logic in saying that you should never run Run-flat and non run-flat tyres, even on a different axle?
...
Interested to hear the views of the forum massive.

It's the difference between best practice and compromise.

Many wouldn't notice the difference in normal driving, but as we approach the limits, it's in the handling characteristics. Will be changing the understeer / oversteer balance, tyre slip angles are different for RFTs than non RFT. Grip levels can be different over the same surfaces. Lateral stiffness, a critical part of balanced handling will be very different. Unpredictable limits, depending on what axle has the RFTs and mixed with what other tyre.

Bridgestone even make the following statement for mixing RFTs.

Install Bridgestone Potenza S001 RFT tires in sets of four only.
Due to the traction and handling capabilities of the Potenza S001 RFT, Bridgestone recommends they be used in sets of four to provide the best handling characteristics and tire performance. Potenza S001 RFT tires may NOT be mixed with other tire models, such as the Potenza RE050 RFT, Potenza RE050A RFT, Potenza RE050A I RFT or Potenza RE050A II RFT.

I think we get the gist of why mixing can be a bad thing.

Any one who knows the history of the E46, will know that even mixing brands and specs on the 330ci, could result in very strange handling and snap oversteer. Even mixing Michelin PS1 & PS2 was a disaster, made for a very unpredictable chassis. Mixing Michelin with other brands on the other axle was also destabilising.

[Wills2]

TBF Bridgestone Potenza S001 RFT are quite possibly the worst tyre I've ever driven their disclaimer should read "Don't fit them"

[goram]

Originally Posted by Wills2

TBF Bridgestone Potenza S001 RFT are quite possibly the worst tyre I've ever driven their disclaimer should read "Don't fit them"

Seeing a lot of that on here, will give them a swerve for sure.