Tyre pressure question

[Sick Boy]

What pressure should I use in a 205/45 tyre, on a car that weights circa 1,100 kg?

Bar or lbs, it doesn't matter.

[TransAm]

There should be a maximum pressure on the sidewall - don't go over that, but that'll be quite high - much higher than you want to put in!

I would guess around 30-33 PSI, certainly no more than 36, and no less than 28.

Maybe someone else can advise a formula to work this out? My maths/physics is very rusty...

[T-Bird]

always go by the psi on the tire if it's aftermarket if it's stock demensions it should be the psi in your owners manual hell I would go by the owners manual no matter what.

[TransAm]

Originally Posted by T-Bird always go by the psi on the tire if it's aftermarket if it's stock demensions it should be the psi in your owners manual hell I would go by the owners manual no matter what.

Isn't the sidewall figure usually an absolute maximum? It's usually something like 60PSI!!!

I'm worried if he pumps them up cold, to the max PSI, then... :shock:

[T-Bird]

yeah it usually gives max psi but only an idiot would actually do that. the safest thing to do is to go to a tire shop and ask them. you can't be afraid of your local shops they can help.

[TransAm]

^ Good idea, I should have suggested that rather than give an estimate :roll:

[antonioledesma]

as I know, and told by an automotive professor, you should have at least 2 or 3 psi more of what your owners manual says
so, in my car, GM says I must have 28psi, but I use then at 33psi and the ride is way better

[Sick Boy]

Well, the tyre is not stock. In the wheel shop they told me between 28 or 30, so I guess they were right. My friend has the same tyres on his car and uses 33 psi. So...?

[antonioledesma]

use the pressure you like more.
surely your tyre will have a max pressure of... 50-60 psi, but those are maximum levels only achievable on highways, freeways, etc. and if you sometime reach that pressure on a highway, you'd better get out some of that hot air

use for one week a different pressure, start with the normal 28, then the next one use 35, and so on until you find yourself the best pressure for your riding needs

but pleas, remember that tyre pressure is only good if you've drove 1 or 2 kilometers. After that distance your tyre pressure will be scaled wrong

[coombsie66]

Trial and error basically, i used to run 32-34 psi in my 215/35/R18's and i was getting more wear on the outside edges than the centre, so i now run them at 36 psi and they are more or less even wear. May be a little hard for in the wet, but that just makes roundabouts more fun .
It'll be more about wear than friction performance on road car tyres as your not getting temperature into the tyre like with racing slicks, where the distribution of temperature across the tyre dictates the 'hot' pressure, from which you stick a valve cap on em and leave em to cool, which then gives you the 'cold' starting temp. The temp is ofcourse proportional to wear as well, so its all the same ball game.
Some pretty useless info there, feel free to sift through it!

[RC45]

Some folks eluded to this fact - but it may be avluable to clarify, all stated and recommended tyres pressures are "cold tyre" pressures.

So even driving donw to your corner gas station and the checking your tyres pressure is a false higher reading.

The main thing is that you get a feel for and recognise the heat induced pressure increase.

So if your drive way pressue is 29psi and your on the road temp is 34psi - just recognise this fact, and if you need to top your tyres up on the road, use this temp as a guideline.

On the road, the best bet is make sure you match left to right side temps - and you are better o topping the lower temp to match the higher one.

More useless info from the peanut gallery.

[ZfrkS62]

so in lazy man's terms, from what RC said. Figure your tires are going to gain between 4-6 PSI when hot.

Best way to figure it: Check your tire pressures before driving, write them down, and then when you stop to fill up for gas and you should have a fairly good idea as to which one gains what when hot.

4psi is about average, but depending on the condition of your tire, it could be higher or lower.

[ZfrkS62]

Originally Posted by Ronin005 in the winter i have them at 40psi, max on my tire is 44psi i believe. though this winter ill be getting winter only tires. and in the summer ill have it in the 30's, i change it every now and then.

That could be dangerous ronin. Having the tire over inflated means that all the contact area is in the center if the tire, which can be bad for winter driving since you've minimized your contact patch if there is alot of ice and snow. and in new england, there is definetly plenty of that

[LAMBOR]

DL and read the file below, i think you'll find important stuff in there.


http://www.tirerack.com/images/tr_ownersmanual.pdf

[TransAm]

Thsi thread made me check mine today - should be 33 PSI, they were 30 PSI - the last time I checked was January so I am pretty impressed (not with myself as you should check them a little more often :roll: , but with the tyres holding the pressure for 6 months :shock: )!