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... :lol:

[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]

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 :wink: .
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! :P

[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. :wink:

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

[ZfrkS62]

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 :twisted:

[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: )!

[gigdy]

I would not worry what the max pressure on your tire says it wont blow up at that pressure, you need a rediculous compressor or 2 to make a tire explode.

[T-Bird]

well you can take it to the gas station and leave it on there and trust me it will explode and very seriously injure you or possibly kill you. You ever notice some tire shops have cages they inflate tires in? that's mainly for the rims but it can happen. do you recall the firestone incident? tires can explode from excess heat (althought that was from a seperate cause)

[antonioledesma]

I would not worry what the max pressure on your tire says it wont blow up at that pressure, you need a rediculous compressor or 2 to make a tire explode.

:roll: you would think that twice. I knew someone who died because the tyre of a machine exploded (I think it is called sandblasting-something, which has a v8 detroit diesel engine)
here the tyres of big trucks have a metal ring called petitbone or something like that. Ok, the events were like these: of course a common hot day near the beach, ppl working and then BAM!! the tyre blew up and that ring hitted a person on the head :|

[ZfrkS62]

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: )!

And the sad thing is, you're still checking your tires more often than most people :? everyday i see at least 2 cars with damn near flat tires driving around like bats out of hell. I only hope i'm in the lane next to them when one of tires gives up :roll:

gigdy- a single compressor is more than enough to cause a tire to blow out. Most shop compressors are pushing 120PSI. I've seen tires egg the sidewall at 70psi. At that point you may as well be listening to a time bomb tick off the seconds because that's what the tire becomes.

[FoxFour]

Don't over inflate, it could permanently distort your tire. My suggestion would be to glance at the owners manual and go from there. Remember, 1 psi of air pressure can make a noticeable difference in how the tire, and the car as a whole; respond to the road, especially in handling. I know that you have a different tire size, but I do not think that the different size would make you alter your tire pressure.
For instance, my Mustang now as well as my old SVO Mustang, specified a 30psi front/ 30 psi rear, even though my SVO had a 225/50VR 16 tire versus my Cobra's 245/45 ZR17 tire. On both cars, I found that 34 front/32 rear was just about perfect for my street driven front-engine, rear wheel drive vehicle.

Also, when you fianally settle on a set pressure, keep a close eye on the wear pattern of your tires. If you see accelerated wear on the middle tread, that indicates over inflation. If you see wear towards the outer edge of the tread, that indicates under inflation. If you see that your sidewalls are showing wear, then that means your my kind of driver and you love the corners. :wink:

[rk331]

I've read all above and I hve something to say, thres a variable in all our life that is underestimate.... the temperature. If you can get a infrared non-contact thermometer you can read the temp of your tires, a low pressure tire gets an increase of temp (a delta respect the media temp of all the tire)in the sidewall because that zone has a periodical deformation, in the other hand a over pressure will make that the center of the tire that is in contact with the road increase the temp. I did a test in my car, driving 5 minutes and stop, take info and start again, the average temp of a tire (with an external temp of 27ºC) is aproximately 60ªC, if your tire gets over 80ºC you are in problems, in could explode. Try it, you can start at the pressure recomended for the dealer.

[graywolf624]

If you want to go to that level get a pyronometer and check the temperature and wear on the tread. That being said, personally I rarely ever use a gauge(except on the race car) that has a level of accuracy below 1-2 psi. Thus it really isnt worth it. Use the manufacturer setting and if it seems too stiff or loose add pressure accordingly. Watch the wear and dont exceed the max pressure and your good. The big thing with the street is its more feel then anything else, so its whats best for you.. On a track its whats optimal, but then you should also be using dehumidfied air, ect.