Tyre Pressure?

[Shibe]

My 07 S-GT is sitting on 215/45R17's all around. 

 

One thing I remembered to do yesterday was check my tyre pressure and adjust accordingly. When I check some one was sitting on 40psi, another sitting at 32 psi, one at 38 and basically it was all over the show. I put each tyre to 35psi to try an even balance and one thing I've noticed very quickly is that my fuel economy has dropped about a half kilometer per litre. 

 

I'm really lost with a general rule of thumb when it comes to tyre pressures since everyone has about a billion different answers. I'm thinking put each tyre at 38psi all round and just keep experimenting til i find a balance I like?

 

Any help is appreciated

 

[JGM]

I run 38 psi in both my 225/45R18 & 215/45R17 RE003s, lower profile and performance tyres are designed to be run at higher pressures and are certainly more fuel efficient when they are correctly inflated.

 

You obviously want to be careful how much pressure you run as you don't want to end up either, a) under inflating and wearing out the outside of the tread / side wall damage or, b) over inflating and wearing out the middle section of your tread.

 

38 psi is a personal preference, best you find the correct pressure and most economical for your tyre by doing the testing you proposed.

[Kj9024kr]

im on 215/45/18 all round and run on 38psi also. 

Maybe a little harsher ride, but i'd rather roll further and use less gas , since fuel tax is coming

 

[Batbaruman]

usually i just adjust the pressure according to what i want. if i know will be some more sporty driving and i'll be alone then will put it down to 35 cold pressure. if will be cruising around with passenger full of cars then 40-42psi. generally just sits around 38 for me. i feel as though i have less contact patch by a great deal when 'm just on my own in car and it's 42psi so that's very much so at the high end, atleast for my v7. in other cars have run different pressures front and back but not sure how critical that is with the subi awd system and if it messes with diff or anything if all 4 aren't even in that regard.

[Gripless]

What's the factory pressure written inside the drivers door sill by the lock catch?

Think factory there is a few psi difference front to rear due to the weight balance to keep the DCCD happy.

Somewhere between that factory pressure and the max psi rating on the tyre works.

 

Think im some thing like 38 front 36 rear on 45 profiles but it's the value on the door sill plus 2psi over winter.

you can run more on pure nitrogen as it won't expand as much with heat like the 21% oxygen content in the air. Which is only a benefit in traffic really where the tyres don't heat up.

 

Low pressure like 35 psi on 45 profile tyres won't be pretty at 100kph and a big pot hole.

Edited May 1, 2018 by Gripless

[Shibe]

9 hours ago, Gripless said:

What's the factory pressure written inside the drivers door sill by the lock catch?

Think factory there is a few psi difference front to rear due to the weight balance to keep the DCCD happy.

Somewhere between that factory pressure and the max psi rating on the tyre works.

 

Think im some thing like 38 front 36 rear on 45 profiles but it's the value on the door sill plus 2psi over winter.

you can run more on pure nitrogen as it won't expand as much with heat like the 21% oxygen content in the air. Which is only a benefit in traffic really where the tyres don't heat up.

 

Low pressure like 35 psi on 45 profile tyres won't be pretty at 100kph and a big pot hole.

 

Good point there. I didn't even think to check that. It's not sitting on factory wheels but this could probably still apply since I think the factory S-GT wheels are 17's.

[boon]

One thing to remember is that if you've just driven it a reasonable distance, wonky tyre pressures can be a sign of a S*** alignment, i.e one tyre is scrubbing a lot and getting much warmer than the others == higher pressure.

 

If you have one of the little gauges, take it for a decent drive then race around it and check all 4 corners.

[Shibe]

5 hours ago, boon said:

One thing to remember is that if you've just driven it a reasonable distance, wonky tyre pressures can be a sign of a S*** alignment, i.e one tyre is scrubbing a lot and getting much warmer than the others == higher pressure.

 

If you have one of the little gauges, take it for a decent drive then race around it and check all 4 corners.

 

Didn't actually think about this.. car is badly in need of a balance + alignment