CHANGE OF RUNFLATS TO NON RUNFLATS

[jaydon9269]

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]

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]

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]

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]

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

 

[Anonymous]

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]

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]

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]

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.

 

[Anonymous]

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]

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

 

[Anonymous]

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]

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

I knew you would be pleased about that!-

 

[sars]

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

 

[Anonymous]

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-advices/adjust-tyre-pressure-to-speed

 

[sars]

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-advices/adjust-tyre-pressure-to-speed

Simple, I think not, whilst I don’t disagree with what they say about reducing wall flex at higher speeds, really important on oval racetracks where cars run at high speed for long periods, they completely fail to mention that as the tyre flexes more, this results in more energy, more heat is generated and thus pressures increases. It’s usefulness to road cars in day to day applications I would say is somewhat limited, however I will ask my German colleagues tomorrow if they are advised to increase pressures if they’re going onto the autobahn

 

[Anonymous]

sars, I don’t disagree that in the UK it’s very hypothetical…

I’m merely trying to rationalise why on 155mph rated cars they all state those high pressures whereas for bouncing around the Scottish countryside less is more..

The kinetic energy of wheels rotating at 155 mph is 4 times larger than that at 75 mph

Another article

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=72

Coincidentally my Volvo XC70 has higher inflation pressure requirements for over 100 mph…

 

[SV8Predator]

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

Well every day is a school day! I never knew that.

Insufficient tyre pressure increases the contact of the tyre with the road. When the pressure level is too low, rolling resistance may increase even by 30%.

From:
https://www.oponeo.co.uk/blog/everything-about-tyre-rolling-resistance

 

[Pondrew]

Here you go…simple

Peter, your ability to Google facts seems to know no bounds. I would be interested to know your reasoning behind these "facts", as the website you quote is presuming, surely, that Boyle's Law is a fundamental factor in their calculations.

 

[Pondrew]

And Googling the answer is cheating