Tyre pressures...

Since pressure is expressed as 'per square inch' I can see no reason why the pressure should be varied according to tyre size.

The rule of thumb was to start at the same pressure or higher. You don't tend to notice the detrimental effects of higher pressures with a low profile tyre but it helps retain its shape better.

There isn't an official line, though, unless the car can take those tyres...

One of my previous cars took 155/70/13s, 165/65/13s or 165/60/14s as standard. The 155/70/13s had higher pressures than the other two. I ran

185/60/13s just to be awkward, ultimately running slightly higher than the 165/65/13 pressures up front and materially higher at the back for more balanced handling.

Some people ran 195/45/15s or 195/40/16s. Some numpties ran 195/45/16s too and buggered their arches. :)

No one fitted big rims then :-) ?

Whatever it says on the sidewall of the tyre + 2-4psi depending on how hard you are going to be driving it.

Fraser

... really?

Only that's not what you do with the standard tyres - the max figure on the sidewall is far higher than the amount you're advised to put in in the handbook relating to the car.

I'm only asking this question as the Golf felt really soggy with the standard pressures in the 17s... so I upped them a bit, and a bit more... and all seemed well but on the TDI forums they advised sticking a bit more even than that in, which I tried earlier... and the resulting spinnage in second (admittedly on greasy roads and overly adjusted tuning box in place) meant I dropped the pressures back a bit.

Just wondered if there was an official rule of thumb for a happy medium, or do I just need to keep using trial and error.

If your tyres are marked like mine, jesus christ don't get anywhere near the max pressure... Mine says 70psi or summet mad!

Hehe... well my 17s are marked up as 50psi max... 38psi (cold) was enough to create the above spinnage in spades... 33psi which is about what standard rims need makes it feel a bit too spongy and prone to tramline... so 36psi seems to be a happy medium in this weather.

I can get that at 32psi on factory sized tyres on my "flatspot as wide as a bluewhale's c*ck" Octavia 2 litre.

There's no rule of thumb, as the 'ideal' pressure will vary according to the make and type of tyre, as well as what car they're fitted to. Trial and error is the way to go. Start with the recommended tyre pressures, then experiment with tyre pressures. Just a pound or two or three, either way, until you achieve a result satisfactory to you. Keep an eye on the wear pattern of the tyres from then on, as you might have to compromise a little on your 'ideal' pressures in order to keep the tyre wear reasonably even across the tread. Wear in the middle, reduce the pressure, if on the outer edges, increase it. Mike.

Less pressure in wider tyres. Not sure how you work it out mind. EG: My road bike runs 23mm tyres at 100psi. My mountain bike runs 2.25 inch tyres at around 35psi...

Have a look at this:

Possibly, but not as a rule. My car has 255 x 40 17's on the rear axle. Recommended pressures 35.6 psi Std tyres are 225 x 60 on 15's. Recommended pressures, rear axle again, 32.7 psi. Mike.

I don't think the wheels can be blamed for that... ;-)

No chance on this - at the same pressures as set for the standard rims, it generally feels soggy and tramlines like a bitch.

Ta... yet another yank claiming full pressure the tyre is rated to -10% is good.

It doesn't exactly enhance traction anyway - may be a different story with something with a bigger profile.

Heh. There's slow as standard, slow, slow and and slow as in modified with a loud exhaust, induction kit and big wheels, 22 second quarter mile compared with Kermy's low 19s.

Yebbut it's really boring... innit.

That's how boring. If I want to more than crawl from a standstill it spins. If I want to overtake, I need to make arrangements with the driver in front to slow down and the driver approaching to stay at home. Just so I can get a run up.

I don't find it boring.

I don't get that with mine - maybe you need to stop buying remoulds.

now if it was RWD you wouldn't complain bout the wheel spin :)

Not remoulds. Continentals I think. Can't remember which ones but sure they are Contis. They were on the car when bought and changing tyres because I don't like them isn't something I can consider normal. Not before they wear out anyway.