Jump to content
SAU Community

Tyre Pressures, And The Argument I Had With A Mate

Oddy man
 Share

Recommended Posts

Oddy man Collaborator

Oddy man

Posted
Posted

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?

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

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.

Duncan Grand Master

Duncan

Posted
Posted

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 Experienced

Stagea_Neo

Posted
Posted

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 Community Regular

pyro-ns

Posted
Posted (edited)

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 by pyro-ns
pyro-ns Community Regular

pyro-ns

Posted
Posted
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 :D

Jetwreck Grand Master

Jetwreck

Posted
Posted
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 :D. 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 Grand Master

pipster11

Posted
Posted

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 Grand Master

Stinky Rooster

Posted
Posted

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.

pipster11 Grand Master

pipster11

Posted
Posted
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

pipster11 Grand Master

pipster11

Posted
Posted
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

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Duncan
      Mistakes were made, my R34 Story

      By Duncan · Posted

      Have a look at that (shitty) pic I posted. You can see AN -4 braided line coming to a -4 to 1/8 BSPT adapter, into a 1/8 BSPT T piece. The Haltech pressure sender is screwed into the long arm of the sender and factory sender (pre your pic) into the T side. You can also see the cable tie holding the whole contraption in place. Is it better than mounting the sender direct to your engine fitting......yes because it removes that vibration as the engine revs out 50 times every lap and that factory sender is pretty big. Is it necessary for you......well I've got no idea, I just don't like something important failing twice so over-engineer it to the moon!
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      Yup. You can get creative and make a sort of "bracket" with cable ties. Put 2 around the sender with a third passing underneath them strapped down against the sender. Then that third one is able to be passed through some hole at right angles to the orientation of the sender. Or some variation on the theme. Yes.... ummm, with caveats? I mean, the sender is BSP and you would likely have AN stuff on the hose, so yes, there would be the adapter you mention. But the block end will either be 1/8 NPT if that thread is still OK in there, or you can drill and tap it out to 1/4 BSP or NPT and use appropriate adapter there. As it stands, your mention of 1/8 BSPT male seems... wrong for the 1/8 NPT female it has to go into. The hose will be better, because even with the bush, the mass of the sender will be "hanging" off a hard threaded connection and will add some stress/strain to that. It might fail in the future. The hose eliminates almost all such risk - but adds in several more threaded connections to leak from! It really should be tapered, but it looks very long in that photo with no taper visible. If you have it in hand you should be able to see if it tapered or not. There technically is no possibility of a mechanical seal with a parallel male in a parallel female, so it is hard to believe that it is parallel male, but weirder things have happened. Maybe it's meant to seat on some surface when screwed in on the original installation? Anyway, at that thread size, parallel in parallel, with tape and goop, will seal just fine.
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      How do you propose I cable tie this: To something securely? Is it really just a case of finding a couple of holes and ziptying it there so it never goes flying or starts dangling around, more or less? Then run a 1/8 BSP Female to [hose adapter of choice?/AN?] and then the opposing fitting at the bush-into-oil-block end? being the hose-into-realistically likely a 1/8 BSPT male) Is this going to provide any real benefit over using a stainless/steel 1/4 to 1/8 BSPT reducing bush? I am making the assumption the OEM sender is BSPT not BSPP/BSP
    • funkymonkey
      Jacks that fit under GTR lips that can reach the subframe?

      By funkymonkey · Posted

      I fashioned a ramp out of a couple of pieces of 140x35 lumber, to get the bumper up slightly, and then one of these is what I use
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      I wouldn't worry about dissimilar metal corrosion, should you just buy/make a steel replacement. There will be thread tape and sealant compound between the metals. The few little spots where they touch each other will be deep inside the joint, unable to get wet. And the alloy block is much much larger than a small steel fitting, so there is plenty of "sacrificial" capacity there. Any bush you put in there will be dissimilar anyway. Either steel or brass. Maybe stainless. All of them are different to the other parts in the chain. But what I said above still applies.
×
×
  • Create New...