Tyre Pressure

benm7 · Post by **benm7** » Thu Sep 08, 2005 10:28 am

Hi guys,

I remember seeing this in a post somewhere but have searched and searched but cannot find it!

What are the recommended tyre pressures for a GPX with standard wheels?

Cheers,

Ben

FTO338 · Post by **FTO338** » Thu Sep 08, 2005 11:00 am

I use 36psi all round for normal road use, itâ€™s not the most comfortable, but it is the safest, as the tyres have more surface contact on the road, therefore you feel all the hums & bums. But it is recommended by lots of advance driving school.

Remember there are no such things as a "comfortable accident".

shue · Post by **shue** » Thu Sep 08, 2005 11:37 am

what would u use with 18s and low profile tyres

scarecrow · Post by **scarecrow** » Thu Sep 08, 2005 12:56 pm

I run about 40psi in mine. That's 17's, medium profile.

ph3var · Post by **ph3var** » Thu Sep 08, 2005 2:19 pm

I too would like a recommendation for 18s with 35 series low profiles.

SchumieFan · Post by **SchumieFan** » Thu Sep 08, 2005 5:01 pm

32psi in my stockies

HiRAEdd · Post by **HiRAEdd** » Thu Sep 08, 2005 5:20 pm

I run 36 PSI in my 17's with...I guess you'd call them medium profile (45's).
I really need 40's though, I get some hella rubbing over big bumps and two people in the car hehe.

Blondy · Post by **Blondy** » Thu Sep 08, 2005 7:02 pm

You guys are using way to much pressure, the standard pressure is 32psi for the front and 28 for the rears. The general rule is up the psi by 2 for 17" alloys, 4 psi for 18" alloys.

So 16" wheels
32psi front
28psi rear

17" wheels
34psi front
30psi rear

18" wheels
36psi front
32psi rear

But have a play with the pressures see what you prefer, I wouldn't go as much as 40psi though.

Anubis · Post by **Anubis** » Thu Sep 08, 2005 11:19 pm

HmmmMMM ... ok so 36 and 32

... Thanks for that ... I was just about to ask that question as well ...

scarecrow · Post by **scarecrow** » Thu Sep 08, 2005 11:40 pm

Tyres are rated for 44psi before they start to bulge, 40 is perfectly conservative even for hot days. 32psi and 28psi is whats recommended by car manufacturers to ensure a smooth ride, it has nothing to do with performance/safety. Give 'em a bit more i say

Blondy · Post by **Blondy** » Fri Sep 09, 2005 12:45 am

It is going to be based on all factors performance, safety and a smooth ride.

40psi seems far to high in my opinion but if the handling suits your driving style then keep it at 40.

RichardH · Post by **RichardH** » Fri Sep 09, 2005 1:15 am

Blondy wrote:You guys are using way to much pressure, the standard pressure is 32psi for the front and 28 for the rears.

Not necessarily. It all depends on the tyre, the driver, the application.

You can run 32 front and 28 rear on stock tyre sizes if you absolutely must have a soft soft ride. However, check the pressure twice a week. ANY lower than that and your ability to cope with any situation other than "trundling down the road" will be in jeopardy. In wet conditions, your tyres will be cold, therefore lower pressure, therefore the centre won't be so inclined to stick to the road, risking the horrors of aquaplaning. In the dry, cornering hard with lower than 32psi in the fronts could roll the tyres badly under the rim, and feel as sloppy as hell. And your fuel consumption won't be spectacular, as the rolling resistance will be high.

Running stock tyres at 40psi front and 36 rear? I did that for a year or two on Pirelli P7000 (stock size). It was great while I was using the same tyres for both street and motorkhana, because I wasn't good at switching my driving between road and performance (I'm now able to do that, and have extra stock rims with r-comp tyres fitted, hehe). By the time those Pirelli tyres were dead, the centres were indeed worn more than the edges... but not excessively. At those pressures, your fuel consumption will be excellent! ...but it's a bit of a jiggly ride, and unless you're cornering like a psycho on the road, a little unnecessary IMHO. But every day felt a bit like a track day, hehe.

These days, I run the stock size road tyres at 36psi front, 32psi rear. They are Toyo Proxes T1-S. At that pressure, they have great road feel, wear evenly and feel well balanced in all conditions. Plus, if I forget to check them, some mild pressure loss will still see the pressures err on the side of safety.

Incidentally, the shops that sold me the last two sets of tyres (two different brands, two different shops) both warned against running the fronts below 35psi... Their main reason was so I could avoid damaging the tyre sidewall. If not inflated sufficiently under load, a tyre rolling underneath during cornering could, they said, cause cracks along the sidewall of the tyres I'd bought.

I couldn't ever recommend running the rears at the same pressure as the fronts though. There isn't a lot of weight at the back of an FTO!

One of the advanced driving courses I did covered tyre pressures in detail. They reckoned practically every car could benefit from bumping up the stated factory pressures by a good 4psi, and recommended everyone did so. At the risk of repeating stuff, their reasons included better fuel consumption, better braking/avoidance, reduced risk of aquaplaning, safety buffer to guard against under-inflation (a big killer).

Hmm. This posting is too damn long. Sorry to bore you senseless!!

- Rich

Blondy · Post by **Blondy** » Fri Sep 09, 2005 2:27 am

You raise some interesting points.

I spoke to my Toyo dealer about tyre pressures, he recommended increasing the pressure by an extra 4psi due to the T1-S tyres having weak sidewalls, the T1-R tyres are meant to have a stronger sidewall so they won't require as much of an increase.

I'm not sure how true the above statement is though.

I've played around with 36F 32R but settled on 34F 30R on 17" alloys.

RichardH · Post by **RichardH** » Fri Sep 09, 2005 2:50 am

That statement sounds pretty true. The T1-S relies on good inflation to do its job.

Interestingly, so did the competition spec Toyo Trampio R1-R. Even with 37psi, it still rolled over during turn-in, and wore the edges horribly quickly. Having said that, we're talking about a tyre with the consistency and durability of marshmallow!!!

Comp tyres like the Bridgestone RE-whatever are apparently engineered with a very heavy sidewall indeed. They weren't recommended by my tyre shop for my FTO, as it was quite a light car, and lacking serious grunt.

My T1-S are getting towards the end of their useful life. Damn good tyres, they were. Better all-round tyres than the Pirelli P7000. I should take a look at the T1-R then, I guess!

- Rich

HiRAEdd · Post by **HiRAEdd** » Fri Sep 09, 2005 7:34 am

scarecrow wrote:32psi and 28psi is whats recommended by car manufacturers to ensure a smooth ride, it has nothing to do with performance/safety. Give 'em a bit more i say

10% more than the manufacturer's recommendation is what I've been taught at defensive driving courses.
Of course if you're on bigger than stock wheels, ask the person who fitted them for you what they recommend.

Anubis · Post by **Anubis** » Sat Sep 10, 2005 5:35 pm

Ummm ... Im confused ... So I have 18" rims I put 40psi now? or? ... HELP!?!

FTO338 · Post by **FTO338** » Sat Sep 10, 2005 10:58 pm

Hmmm I can't remember if you are from the UK Blondy, if so your figure might not be applicable in Aus as UK has different type of road surface then Aus.

Post by **Bennoz** » Sun Sep 11, 2005 2:50 pm

Air is also colder & denser. Its also why we get differing dyno results...

RichardH · Post by **RichardH** » Sun Sep 11, 2005 4:08 pm

Bennoz wrote:Air is also colder & denser. Its also why we get differing dyno results...

Aussie dyno results are higher because we're upside down. So the car doesn't have so much rolling resistance between the tyres and the rollers.

- Rich

scarecrow · Post by **scarecrow** » Sun Sep 11, 2005 5:32 pm

Put whatever your comfortable with, i suggest somewhere between 34-38psi front and rear. I don't have a problem running with 40psi in em, and on advanced driver training days that's what they usually recommend you get them to. I assume it's for a good reason.