CHANGE OF RUNFLATS TO NON RUNFLATS

jaydon9269 · Post by **jaydon9269** » Wed Jun 30, 2021 1:55 pm

Just changed the 4 Bridgestone Potenza run flat tyres on my 2016 E89 Z4 to 4 Michelin Primacy non
runflats.
The technician was not sure of the tyre pressures but put 36 in each wheel (car has 17 inch alloys)
Can anyone advise me of the correct pressures to use
Thank you

fotodirk · Post by **fotodirk** » Wed Jun 30, 2021 2:12 pm

Hi there,

made a similar change some years ago on my E85 using the same pressure as before, 2,3 bar front and rear.
Enjoy the difference in tyres!

enuff_zed · Post by **enuff_zed** » Wed Jun 30, 2021 2:19 pm

jaydon9269 wrote: ↑Wed Jun 30, 2021 1:55 pm Just changed the 4 Bridgestone Potenza run flat tyres on my 2016 E89 Z4 to 4 Michelin Primacy non
runflats.
The technician was not sure of the tyre pressures but put 36 in each wheel (car has 17 inch alloys)
Can anyone advise me of the correct pressures to use
Thank you

Firstly, I would double check the pressures as in my experience the fitters don't always get it quite right.
Then you may find you have to experiment a little to find what suits you best but you don't have a bad starting point there.
Mine are 18" wheels, but I ended up with 34F & 36R. Others have found slight differences to that suit them better.
It does come down to driving style and how it feels through the seat of your pants too.
I would also suspect different tyres react to different pressures too.
In short, keep tweaking until you're happy.

sars · Post by **sars** » Wed Jun 30, 2021 2:21 pm

It really depends, let’s assume you have a square set up, that is 225/45 R17 all round so the pressures are the same front and rear. I would suggest you drive it for a while and alter them as necessary. There’s a mixed consensus on here some have dropped the pressure, I myself increased them by a few psi but that is possibly because I ran winter tyre on the 17” wheels and bought a set of 18” wheels for summer.

Jasonn · Post by **Jasonn** » Wed Jun 30, 2021 10:54 pm

I changed from RFTs to gooduear Assy 5 - fitter used the same tyre pressures as the RFT - i think im now on 32 front and 34 rear

Pbondar · Post by **Pbondar** » Wed Jun 30, 2021 11:02 pm

Here’s a table from Continental with suggested tyre pressures for various sizes..

I found their 18” asymmetric tyre pressures too high especially the rears..

Their 17” tyre pressures seem better but still a bit high ..

The main reason for the high pressures is the fact that if you insist on sustaining 155 mph you need a lot of tyre pressure..

I’ve yet to find any tyre manufacturer offering any specific adjustments for run flat vs non run flat tyres…

As others suggest starting at the 32/34 to 36/38 works for many,,

Nictrix · Post by **Nictrix** » Thu Jul 01, 2021 7:15 am

Are manufacturers tyre pressures not related to MPG figures also?
Do higher pressures not give less resistance on the road giving higher MPG?
Im sure I have heard this with push bikes where high tyre pressures make cycling easier as there is less resistance.

flybobbie · Post by **flybobbie** » Thu Jul 01, 2021 7:39 am

Nictrix wrote: ↑Thu Jul 01, 2021 7:15 am Are manufacturers tyre pressures not related to MPG figures also?
Do higher pressures not give less resistance on the road giving higher MPG?
Im sure I have heard this with push bikes where high tyre pressures make cycling easier as there is less resistance.

As a kid cycling on wet roads seemed easier, i assume less grip resistance.

flybobbie · Post by **flybobbie** » Thu Jul 01, 2021 7:41 am

My 18 inch non rft Asy, i run 38 front 40 rear and get even wear across tyres. When rears were 42, the crown wore more on previous tyres.

Pbondar · Post by **Pbondar** » Thu Jul 01, 2021 9:02 am

Nictrix wrote: ↑Thu Jul 01, 2021 7:15 am Are manufacturers tyre pressures not related to MPG figures also?
Do higher pressures not give less resistance on the road giving higher MPG?
Im sure I have heard this with push bikes where high tyre pressures make cycling easier as there is less resistance.

Not really..under pressurised by a significant amount does affect rolling resistance…

The manufacturer has to ensure at the maximum possible sustained speed that everything holds together when that speed is maintained for a significant period ie on an autobahn..

Tyres need much higher pressures to cope with that possibility…

Busterboo · Post by **Busterboo** » Thu Jul 01, 2021 9:52 am

Thank you very much, Pbondar, for the reassuring Continental data.

Pbondar · Post by **Pbondar** » Thu Jul 01, 2021 10:22 am

Busterboo wrote: ↑Thu Jul 01, 2021 9:52 am Thank you very much, Pbondar, for the reassuring Continental data.

I knew you would be pleased about that!-:)

I did follow its advice on my 18" Asymmetric tyres..however even two up the back was 'boing' around..so backed them off to 34/38 ..much better..but I'm not planning a cruise at 155 mph..

Busterboo · Post by **Busterboo** » Thu Jul 01, 2021 11:42 am

Pbondar wrote: ↑Thu Jul 01, 2021 10:22 am
Busterboo wrote: ↑Thu Jul 01, 2021 9:52 am Thank you very much, Pbondar, for the reassuring Continental data.
I knew you would be pleased about that!-:)

sars · Post by **sars** » Thu Jul 01, 2021 7:26 pm

Pbondar wrote: ↑Wed Jun 30, 2021 11:02 pm
The main reason for the high pressures is the fact that if you insist on sustaining 155 mph you need a lot of tyre pressure..

I would be interested in your reasoning of why you think this is so

Pbondar · Post by **Pbondar** » Thu Jul 01, 2021 8:56 pm

sars wrote: ↑Thu Jul 01, 2021 7:26 pm
Pbondar wrote: ↑Wed Jun 30, 2021 11:02 pm
The main reason for the high pressures is the fact that if you insist on sustaining 155 mph you need a lot of tyre pressure..

I would be interested in your reasoning of why you think this is so

Here you go…simple

https://www.tyreleader.co.uk/tyres-advi ... e-to-speed

Z4-forum.com

Z4-forum.com