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[1230vani]

Hi guys,

Just installed non-RFT Michelin PS2 tyres (19" 255/30/19 (rear) & 225/35/19 (front). The current pressure setup (with GAS) is 2.8 rear and 2.5 front. The ride feels softer and a bit wobbly. My question is what would be the ideal pressure for my car. Please help, I asked the guys at the shop who had them fitted, but I do not think they are such experts when it comes to non-RFTs on a E92.

Thanks a lot!

[R1000K3]

The ride SHOULD be softer with non-RFT. If you feel wobble it is probably a tyre issue (e.g. poor balancing). I'm using 2.5 rear and 2.3 front on 255/35/18 and 235/40/18. The car runs fine. These pressures provide good grip and comfort. The razor-sharp turn-in with RFT's is of course lost with non-RFT, but the total outcome is a big win. The car is less nervous and more comfy with ordinary tyres. I'm using Hankook V12's.

[1230vani]

Originally Posted by R1000K3

The ride SHOULD be softer with non-RFT. If you feel wobble it is probably a tyre issue (e.g. poor balancing). I'm using 2.5 rear and 2.3 front on 255/35/18 and 235/40/18. The car runs fine. These pressures provide good grip and comfort. The razor-sharp turn-in with RFT's is of course lost with non-RFT, but the total outcome is a big win. The car is less nervous and more comfy with ordinary tyres. I'm using Hankook V12's.

Thanks a lot for your reply! Thought this thread is not really visited. My issue is when I go into turns at higway speeds and hit some uneven surface, almost feel like the tyres are going to slide of the wheels. that is what i actually meant by wobbly. Do you experience that also? Your setup is even at lower pressure, do you have gas in the tyres also? The dude at the tireshop told me that the gas is lighter then the normal filling and that the pressure should be 2.8 rear and 2.5 front. am thinking of increasing it to 3.0 and 2.7 but am afraid it might be too much. I would just hate to regret switching to non-run flat.

[R1000K3]

I use ordinary air :-) I know aircraft may use some gas (nitrogen perhaps) to avoid tyre expansion when they become very hot, but this is not a real issue for cars.

RFT's have extreme good turn-in behaviour, so it may take some time to get full commitment to non-RFT's. Especially since the chassi is designed for RFT's. It is however just good if the tyres moves a bit, to keep grip on uneven surfaces.

I have a M-sport chassi and non-RFT's works real fine with it. Others have changed to M3 suspension when going to ordinary tyres. No problems for me to slide on dry tarmac with good control, the V12’s are great, as your tyres should be. The first impression with the non-RFT's is that they may bounce a bit in potholes, instead of being totally stiff as the RFT's.

[nicks3]

I have it from a reliable source that 2.6 bar all round is the way to go. That is what I am running and all seems well.

[1230vani]

Originally Posted by nicks3

I have it from a reliable source that 2.6 bar all round is the way to go. That is what I am running and all seems well.

Thanks!

I did some research and I have found the same (that all tires should be the same, on the pressure I keep finding different values). What you mean is that all 4 tyres should be 2.6?

[1230vani]

Originally Posted by R1000K3

I use ordinary air :-) I know aircraft may use some gas (nitrogen perhaps) to avoid tyre expansion when they become very hot, but this is not a real issue for cars.

RFT's have extreme good turn-in behaviour, so it may take some time to get full commitment to non-RFT's. Especially since the chassi is designed for RFT's. It is however just good if the tyres moves a bit, to keep grip on uneven surfaces.

I have a M-sport chassi and non-RFT's works real fine with it. Others have changed to M3 suspension when going to ordinary tyres. No problems for me to slide on dry tarmac with good control, the V12’s are great, as your tyres should be. The first impression with the non-RFT's is that they may bounce a bit in potholes, instead of being totally stiff as the RFT's.

Thanks a lot for your feedback. Did some crazy driving today, to see what the car can do, only at first the front tyre seems to slide just a bit, it does not effect when turning much but it is still a very obvious change from the run-flats. I think my car would def behave better with the sport suspension, but i am not getting that (too late for that one). Am considering the comment above to set them the same, or to increase the front pressure a bit as it only feels like an initial slide on the front wheels.

[1230vani]

Originally Posted by Croatian

Thanks!

I did some research and I have found the same (I do not have the sport suspension). What you mean is that all 4 tyres should be 2.6?

Is this research relating to Gas filled tires, or normal air (2.6 all round).

THanks!

[jadatis]

I once got hold of the formula the car- and tire-manufacturers use to determine the advice pressures.
Worked it out first for campers and later for normal cars and learned myself Excell to make spreadsheets for it.

Translated a few from Dutch to English to go worldwide with it.
http://cid-a526e0eee092e6dc.skydrive...0tyre-pressure
In this map the spreadsheet and examples to re-calculate advice pressures when you have other then original tires on the car, and to check the original and see if you can savely go lower in sertain conditions.
Collect the data asked on the first opening sheet and fill in .
Let me know if you used it and what the outcome was

[R1000K3]

Originally Posted by Croatian

Thanks a lot for your feedback. Did some crazy driving today, to see what the car can do, only at first the front tyre seems to slide just a bit, it does not effect when turning much but it is still a very obvious change from the run-flats. I think my car would def behave better with the sport suspension, but i am not getting that (too late for that one). Am considering the comment above to set them the same, or to increase the front pressure a bit as it only feels like an initial slide on the front wheels.

I think the front will slide more with high pressure, since the contact path is best with about 2.2 Bar front. Perhaps you are coming too fast into corners? The right way is not to overload the front, go in "easy" and let the rear grip push the car thrue the turn as son as possible.

[1230vani]

Originally Posted by R1000K3

I think the front will slide more with high pressure, since the contact path is best with about 2.2 Bar front. Perhaps you are coming too fast into corners? The right way is not to overload the front, go in "easy" and let the rear grip push the car thrue the turn as son as possible.

It feels at very low speeds as if for a split second the tire is moving from the front wheels. It could be that I feel like it is doing that, but perhaps it is just a loose feel that non-RFTs have. M PS2s have reinforced sides, but I thought they may not be reinforced enough (like those of RFT) for my car, so adding pressure might help. Then again, I might be imagining the whole thing as they just cannot be the same as the RFTs. The thing is I feel unsure to go in a high speed turn precisely thinking that the tire will fall of the front rims. Am going in circles with this topic. Thanks to all for their comments!

[johnnydad]

I swapped from RFT RE050As to non-RF PS2s recently. At first I experienced the same feeling as you - a slight softness initially, then grip, then more softness as the grip goes. I'd been running 2.6 all round on RFT's (17's, M-sport) so increased to 2.7 F/2.8 R. This really made little difference.

However, after 2000km of driving, they are wonderful - the bite has improved so they are almost as sharp, no longer feel soft and have limits that are much higher in wet and dry conditions.