Tyre Pressures on 18" wheels

Hey guys hope we are all ok.

Just a quick question about tyre pressures. I have a set of 18" wheels about to go on my car (currently running 17"'s) and I was wondering what pressures you guys are running as I assume that stock pressures will be too low due to the thinner tyre wall.

Any input will be greatly appreciated as always.

34 PSI all around

Daston - tyre pressures are determined as a factor of the vehicle weight and not the width/profile/size etc.

Start off with stock PSI and then adjust to get and even wear rate. This will obviously take some time to achieve best results as you have to monitor wear rate over a period of time.

Or if you have a tyre temp gauge (expensive motorsport item) you can see if you are getting an even temp distribution over the contact patch.

I run 32 all round.

You need to know the load rating of you tyres to work this out.

I run 36 all round, tried 38 but went back to 36

running eagle F1's if that helps

side wall will say 94Y or the like. If its Z rated it will have a max load e.g. 1440lbs,

they are ZR18's so guess that means they are Z rated?

Can someone give a definitive answer to this. I have just been out and checked mine and you don't want to know how low they were....

I haven't checked them since I had my wheels re-furbed....

I am going to go out later and put 35 in all round??

H.

used to run Eagle F1's at 36 psi all round

ZR's you wil see in small letters "max load 1440lbs" or similar. When I know this I'll give you a recommendation based on a formula I use (and aint sharing lol) to give you a pretty accurate "best" setting.

If you can find this info experimant between 34 and 36 psi. It will vary slighty according to the tyre you use.

I also run Eagle F1's (on 18's) and use 36psi all round... Tried it with less but it didn't feel quite right. I don't have any problems with uneven tyre wear either.

Not sure if my Halford digi tyre indicator is faulty but my 4 just read 27, 23, 23 and

17...... Although they don't feel low tbh!!

I will be checking them more regularly now!!

H.

I run 34 front, 32 rear.

17...... Although they don't feel low tbh!!

 

I will be checking them more regularly now!!

 

H.

Definitely check more regularly mate. My audi 80 went side-ways round a corner last week and i thought they were all fine....turned out my rear near-side was down to 17psi and the rest were normal.

get yourself a good pressure guage and test weekly

People expect a definitive answer, but the fact is that there is no absolute correct tyre pressure for each and every tyre size and car.

It depends on vehicle weight as the starting point (so start with manufacturers suggested PSIs), and then from there you change pressures due to suspension setups, grip balance, for preferred ride comfort or for driving style etc.

To find out a tyre pressure that will wear evenly throughout its life [which is the cost effective setup] then you need to measure the temperature spread across the contact patch.

This will give a quick result if you have a thermal gun... as you basically get the tyres warm after about 10mins of driving say, and then measure the inner, middle and outer tread to see if the temps are consistent.

If you don't have a thermal gun (like me) then the other way is to simply drive a few hundred miles for normal road driving or a few laps for track driving and accurately measure the tread wear.

Increasing or decreasing the pressures will affect which part of the tyre wears out fast than the other.

But to say it must be 36 allround or 32 allround or 35 front and 34 rear for examples then all these are compromises that suit that particular driver and car setup.

On my UK-spec I have found that 36 psi front and 34 psi rear wears my contact patch at an even rate.

For track driving I do a few laps to get them upto temp and then adjust them down to 38psi front and 35psi rear. For me this gives a good balanced feel of grip.

But I've now gone onto RS-R adjustable coilovers and I need to trial and error once again to see which pressures are best for each situation of driving.

I usually go 35 all around

Definitely check more regularly mate. My audi 80 went side-ways round a corner last week and i thought they were all fine....turned out my rear near-side was down to 17psi and the rest were normal.

 

get yourself a good pressure guage and test weekly

Yep mate! Learned a valueable lesson today....

I have had company cars for years and have become lazy on that front. We realised last week that I am always under the bonnet of the Supe, but we have had a BMW Coupe for 11 months and NEVER looked under the bonnet......

The car has been driving ok tbh. I wanted to check them at the meet I went to the other day in Leeds but didn't want to hold the rest of the convoy up.

Will check from now on!!

H.