Tyre Pressures, And The Argument I Had With A Mate

[Oddy man]

Cue roadtrip, we meet bright and early at local BP for snacks and air.

I put 34psi in, for good firmness on open road driving (19s with a 35 profile)

Mate pulls up (r33) and puts 45psi in his (18s with 35 profile)

So after much bickering I ended up putting 38psi in my car and hoping to god I didnt have explosions on the highway, and all the while he's convincing me to put more in

I mean, christ, I'm usually a 32psi kind of guy, are my tyres going to explode? How much do you guys pump in?

[Oddy man]

I should add that additional cars Honda civic added 30, and Suzuki swift put 32 in.

Hmm

[KiwiRS4T]

32 would be fine. If I have 5 people plus their luggage i might put 36 in the back.

When i first went on the track I put 45 psi in my street tyres but they were still not up to it so i went to semi slicks and then slicks.

So no they won't explode if you put 45 psi in but there is absolutely no point in doing so. You will just wear out the middle of the tread.

[vic stagea mick]

34 psi

[66yostagea]

I run 36 with 17", but roads are very twisty up here. Federal 595s.

[Duncan]

I run about 38 normally...on most road tyres it wil improve handling at the cost of comfort. I don't agree that it is enough pressure to wear out the inside of a tyre, mine wears pretty evenly.

I have run tyres up to 45psi but that is specific tyres on the race track. Too high for general road use to me.

Also check the sidewalls, the tyres will hav a maximum allowable pressure which is generally 45....

[Stagea_Neo]

mine tyres rated to 40 or 45 psi.

on the old car which were rated to 34 usually ran 36, ride felt sooo much better and direct steering.

also better to be on the rating or slightly over inflated than under inflated, less chance of tyre blow out.

[pyro-ns]

can't remember what profile the girl's are, but they're 19's and we run 40 psi, checked weekly. totally even tyre wear so far.

Edited June 7, 2010 by pyro-ns

[HOWIROL]

Any idea what psi I should run? 225/30/20... Sorry for hijack!

[samkoek]

I put 40psi on my 245/45/18 on my S2 , also on my BMW 235/35/19 and 265/30/19, nothing happen and nothing wrong good grip on dry road and wet road as well. Plus I drive fast too, still grip.

[pyro-ns]

Any idea what psi I should run? 225/30/20... Sorry for hijack!

i'd put in around 36-40psi. it really depends on how much harshness you can tolerate and how the rubber reacts to certain tyre pressures. all you can really do is monitor the tread wear and make sure that it's even on all fours. all other things being neutral (camber, castor, toe), too much pressure will result in a bald spot right in the middle of the tyre and too little will result in baldness on the outside edges of the tyre.

if you find that extra pressure makes the ride too harsh (unlikely), then take a couple psi out and see how that goes. or if you've got coilovers, turn the dampner a few clicks towards soft

[Jetwreck]

Cue roadtrip, we meet bright and early at local BP for snacks and air.

I put 34psi in, for good firmness on open road driving (19s with a 35 profile)

Mate pulls up (r33) and puts 45psi in his (18s with 35 profile)

So after much bickering I ended up putting 38psi in my car and hoping to god I didnt have explosions on the highway, and all the while he's convincing me to put more in

I mean, christ, I'm usually a 32psi kind of guy, are my tyres going to explode? How much do you guys pump in?

What was his argument for putting 45psi in? I don't get why he would want 45psi on the street....more to the point why he would want it on the open road . I never put more than 36-38 psi in mine on the street...shit if i want more grip in the arse on the street I drop em down.

[pipster11]

if you run a lot of stretch you need high pressures but i never go over 40

mine are normally 36-38 for better fuel consumption (plenty of grip with the awd)

and as jetwreck said, if you want more grip on the street you would drop them down a bit, you dont really need stiff sidewalls on the street but you need more straight line grip

[Stinky Rooster]

I would be a little careful going over 40 psi on the open road due to higher running temps. Considering Chales Law of Thermodynamics (pressure is proportional to temperature in a given volume) if your tyre temps are likely to go up then you could easily end up with a tyre pressure approaching 50psi. Apart from the obvious lowering of grip, due to less sidewall deflection and reduced contact patch, the effects of a blowout will be much more pronounced. All that risk for a possible saving of 0.1% fuel mileage doesnt really add up IMO.

Try alternating the pressures fron to rear too - a difference of only 2psi can be felt quite easlily. If you want a little more direct feeling in the steering wheel while maintaining a rear grip bias, try going 2 psi higher on the front.

[Hanso]

I run 36-38 for regular day-to-day driving myself.

[Socrates]

What would you reckon for 195/70/14?

[pipster11]

I would be a little careful going over 40 psi on the open road due to higher running temps. Considering Chales Law of Thermodynamics (pressure is proportional to temperature in a given volume) if your tyre temps are likely to go up then you could easily end up with a tyre pressure approaching 50psi. Apart from the obvious lowering of grip, due to less sidewall deflection and reduced contact patch, the effects of a blowout will be much more pronounced. All that risk for a possible saving of 0.1% fuel mileage doesnt really add up IMO.

Try alternating the pressures fron to rear too - a difference of only 2psi can be felt quite easlily. If you want a little more direct feeling in the steering wheel while maintaining a rear grip bias, try going 2 psi higher on the front.

is that isothermal, adiabatic or polytropic expansion? haha

just studying for my thermal eng. exam as we speak

[Socrates]

i'll put my money on isothermal cause it is due to heat

[pipster11]

i'll put my money on isothermal cause it is due to heat

isothermal expansion the temp stays the same (p1v1=p2v2)

i dont think it really matters

195/70's i'd go with something normal 32-34 maybe

its a pretty high profile tyre

[Angus Smart]

13 psi in my Mojos