how to find correct tyre pressure for non oem size?

jej_knowles · 10 Mar 2014 at 22:20

Does anyone know of a calculation or a table of some sort to work out what the correct tyre pressure is for a non oem wheel/tyre combo?

Gibbo · 10 Mar 2014 at 22:24

Tyre pressures a lot of the time are set for a car because of its weight and weight distribution, so oem pressures is always a good starting point.

But post what car you've got and what your new wheel/tyre size is and people might be able to give you a rough idea.

jej_knowles · 10 Mar 2014 at 22:29

It's a 2003 corolla hatch with 215/35 R18 tyres.

Gibbo · 10 Mar 2014 at 22:33

jej_knowles said:
It's a 2003 corolla hatch with 215/35 R18 tyres.

What are the oem pressures and original sizes?

Front engine, reasonably light I'd try 30-32psi front cold and 29-30psi rear cold.

jej_knowles · 10 Mar 2014 at 22:38

I previously had 205/55 R16 and ran them at 34psi to keep the tyre wear even.

Gibbo · 10 Mar 2014 at 23:05

jej_knowles said:
I previously had 205/55 R16 and ran them at 34psi to keep the tyre wear even.

Well look at 30-34psi set from cold and monitor it, but that will be about right.

jej_knowles · 10 Mar 2014 at 23:16

Cheers gibbo ;-)

I'll try setting at 30psi
Tomorrow and see if the ride improves . Never had such low profiles before and feels very bumpy :-(

Gibbo · 11 Mar 2014 at 08:58

jej_knowles said:
Cheers gibbo I'll try setting at 30psi
Tomorrow and see if the ride improves . Never had such low profiles before and feels very bumpy

That's what happens when you go lower profile, less tyre wall for better turn in and improved handling, at the expense of a harsher ride.

More tyre wall for comfort and less noise, but at expensive of well sloppier handling.

jej_knowles · 11 Mar 2014 at 18:12

Wow! Amazing what difference dropping the tyre pressure just 2psi makes when you have such low profiles. Set it to 32 today and the ride and grip is greatly improved thanks for you input matey ;-)

Gibbo · 11 Mar 2014 at 18:24

jej_knowles said:
Wow! Amazing what difference dropping the tyre pressure just 2psi makes when you have such low profiles. Set it to 32 today and the ride and grip is greatly improved thanks for you input matey

Keep experimenting every car has a sweetpot as does type of tyre.

Example of this is, my 911 on Pirelli Pzero Corsa tyres is 29 front cold and 33 rear cold. On the Supersports I run 31 front and 35 rear cold. O.E. recommendation for my car is 33 front and 39 rear cold, I've always run less as the way I drive heats them up so much even on road.