Tyre Pressure

[BLACKGTR33]

Just wondering what tire pressure i should use for 18 inch rims with tires of 265 35 18 size. On a gtr r33 skyline.

Cheers

[blind_elk]

I run 36 in my 235/45x17s. The bigger the tyre diameter and the lower the profile, the more pressure you need to run. So, I would recommend at least 38, maybe even 40.

[bubba]

Experimentation..

As a starting point, with the 32 I used to run ~36psi with the 16" tyres, ~40psi with the 17" tyres and now with the 235/40/18's I run ~42psi. Same size tyres on the Stagea and I run 45psi in them.

[BLACKGTR33]

Would you have the fronts pressure the same as the back?

[Munkyb0y]

you could go 2 psi lower in the rear due to less weight.

i would try 40 front 38 rear.

edit: although not 100% sure on the gtr 4wd system, i expect front/rear pressure difference wont affect it.

[mickey]

I have stretched tyres, so I worry about it 'popping off' or something equally stupid. When they wear out I'll get proper sized tyres As such they are standard 18" 245/45's, so I run 35psi usually.

[Galois]

hey mate,

i have nankang ns2's on my r34 gtt, on the rear i have 265/35/r18's on 10" rims which i was told by the shop (tyrepower newcastle) should be at 40psi, on the front i have 235/40/r18's on 9" rims which apparently are supposed to be at 38psi.

i'm guessing the difference in pressure has something to do with the differing height, not sure, but the pressures have suited me okay.

the back is a handful in the rain though

[Munkyb0y]

^ a 235/40 and a 265/35 have the same height of sidewall.

[(OO)SKYLINE(OO)]

You all realise your tyre pressure will rise a few PSI after driving when the tyres have heat up...

[Brandon]

You all realise your tyre pressure will rise a few PSI after driving when the tyres have heat up...

Yea. I'm running 38psi "cold" (just driving from home to servo). I'm guessing it'll be around 40psi when hot?

[Galois]

^ a 235/40 and a 265/35 have the same height of sidewall.

ahh ok, what do the 35 and 40 refer to then?

You all realise your tyre pressure will rise a few PSI after driving when the tyres have heat up...

and even more for a track day or drags, or on a hot day or cold, or day and night. it'd hard to allow for all conditions tho.

back in my karting days we ran roughly 13 psi, but we'd adjust it till there was a 2 psi difference between hot and cold to find the ideal setup for the day

[Munkyb0y]

ahh ok, what do the 35 and 40 refer to then?

It is the height of the tyre sidewall as a percentage of the width. ie. aspect ratio.

265/40 would be a higher sidewall than 235/40. thats why the common size is 265/35. keeping the rolling diameter similar across the 18" range. u see?

[Galois]

It is the height of the tyre sidewall as a percentage of the width. ie. aspect ratio.

265/40 would be a higher sidewall than 235/40. thats why the common size is 265/35. keeping the rolling diameter similar across the 18" range. u see?

i do, thanks mate, i'm still on the steep side of the learning curve lol

[some_cs_student]

You all realise your tyre pressure will rise a few PSI after driving when the tyres have heat up...

My new tyre pressure monitoring system can see anything from 33psi to 39psi depending on weather / tyre temperature.

During warmer weather it was closer to 36 - 39psi.

[ClutchBurndout-:(]

whats the recomended psi for 255/35/R17?

[defari]

Just wondering what tire pressure i should use for 18 inch rims with tires of 265 35 18 size. On a gtr r33 skyline.

Cheers

i got 265 35 18's on the rear of my gtst - running 38psi (very minimal wear over the last 12 months)

[some_cs_student]

whats the recomended psi for 255/35/R17?

Depends on the tyre

I was recommended 38-40psi cold on a 255/40/17 by the seller for Federal 595RSR

[Galois]

before this thread gets out of hand with people asking what pressure they have for their tyre size (including myself!)

how much does a couple of psi matter? ok, so if we imagine the pressure is meant to be 40psi, for ease of numbers, and it runs at 38 psi. that's a difference of 5%, which would make fk all difference compared to other parameters, like temp, speed, cornering and driving style

and more importantly, how much does it vary between companies? because i'd imagine each company builds to it's own spec, which might vary by a few psi anyways

as a side note, my r34 was bought and after some dramatic events i checked the tyre pressure, it was 26psi, it was after that my worries about the prior owner began...

[getyayayaout]

There is no one answer to this question. Ideally you want to run a tyre pressure that balances the car and feels good when you drive it. Typically tyres heat up and expand when you drive, so if you stand on the throttle at every set of lights i'd expect the rear tyres to heat up a little bit, however its mostly the front tyres that heat up more than the rears because you have the load of the car thrown forward under braking and also the fronts are constantly working harder that the rears because the turn and slide (if only slightly). Also this is in theory what could happen, in reality it doesn't make a difference when you're stuck behind a bus.

Secondly, with a gtr, I personally think you should run all four tyres with the same pressure because otherwise it may trick the g sensor into thinking you've got wheelspin.

[(OO)SKYLINE(OO)]

Yea. I'm running 38psi "cold" (just driving from home to servo). I'm guessing it'll be around 40psi when hot?

Yep, pretty much and when the tyres have cooled down, it will go back to 38 psi.

and even more for a track day or drags, or on a hot day or cold, or day and night. it'd hard to allow for all conditions tho.

back in my karting days we ran roughly 13 psi, but we'd adjust it till there was a 2 psi difference between hot and cold to find the ideal setup for the day

Yes, true.

I just pump an all round 34 psi and seem fine.

My new tyre pressure monitoring system can see anything from 33psi to 39psi depending on weather / tyre temperature.

During warmer weather it was closer to 36 - 39psi.

WTF!

You got any pics of that, where did you get that?