ATL928

Hi, my 1982 has the following tire sizes:
Front- 255/55/16
Rear- 265/45/16

I found a recommendation for 36/44 psi for front/rear tires on 16" wheels, but these tires are obviously not stock and I am unsure how to ascertain the correct tire pressures. Does anyone have a formula for this, or does someone run this size on their car? It is a 1982. Thanks!

the flyin' scotsman

if you have a laser temp gun then run the car long so everything is well up to temp and measure inside, middle and outside tyre temps......if all are same then pressure is correct.

To low in middle increase the pressure; too high in the middle decrease pressure.

depami

Not sure about handling but for tread wear, the chalk method works well.

Put a heavy chalk line all the way across the tread and drive a few miles. Decrease pressure if chalk wearing in middle. Increase pressure if chalk wearing on outside. Just right if chalk wear even all the way across.

ATL928

Had not thought of that.

Petza914

So for those of you that have done the temp gun or chalk line, what pressures did you end up with?

jetson8859

36psi on 245/35 18 front
40psi on 285/35 18 rear

Ride not too harsh and tire wear is even after approx 4K miles on these tires

FredR

When you run a wider wheel generally speaking you should need less pressure to support the load that is distributed in a wider footprint. There are other factors in play such as how you intend to use the car/to what extent you want to push it and your local climate. If you do not work the tire too hard it will heat up less so more cold pressure needed.

If you check the small print on the sidewalls of your tire it will tell you the rated load of the tire and at what pressure it is rated. If you pro rate this to your corner weight [a bit less than 400kg] you may find the number it produces is something like 24 psig. The Michelin tire specialist for this part of the world was a friend of mine and he suggested I try this approach for one of our autocross events [low speed/tight twisty bends]. I looked at him cross eyed but took his advice and immediately went a second a lap quicker.

On high speed circuits different again - those chaps may well have a different take.

With your size tires I would suggest you start by targeting 33 psig front and rear warm and see how you go. Most folks seem to err more on the high side and this reduces the contact patch as you are then driving around on footballs that wear in the middle and no where else.

In short there is no simple one size fits all answer.

Rgds

Fred

depami

Everything Fred just said is absolutely correct. Great job explaining that Fred.

Start with that and use chalk. You may find one that suits all your needs or you may have several for different driving conditions and styles.

My Supra likes 28 cold. But that can vary by the tire.

the flyin' scotsman

I started with 36psi as its stock for GTS wheels and tyre size then went DOWN from there.

The 295s on the rear are 27psi fronts 30psi cold.............the rears run much hotter.

24 psi Fred? for what sizes?

ATL928

Great info! Thank you so much. Can apply this knowledge to my other cars as well

FredR

Malcolm,

That was with 265x35x18 on the front and 295x30x18 on the rear. I was running the Michelin Cup tyre- very strong sidewall- probably a bit atypical in the way they behave. I had problems getting the tyre up to temperature for the timed lap we were hitting. The load rating was 600kg at 36 psig so the logic was 400kg corner load try 24 psig. I figured the reason it might have worked for that particular set of conditions was that with slow tight & twisty bends with uneven surfaces the lower pressure allowed the tire contact patch to seat on the tarmac that much better- a bit like the way we lower the tire pressures [to 12 psig] for driving in soft desert sand in our 4x4s - if you have ever tried this.

For day to day street use I currently run 35 psig front and 33 psig rear for short journeys where the temp does not really get much higher. For a longer run I might drop the pressure a bit. I am having problems with rear traction from the lights but put that down to too much rear camber- no problem with cornering grip once I get going. Really I should try lower pressures once more I suspect albeit I am running Conti's these days.On the rears I have a sneaking feeling I would get better traction off the line with something in the region of 27 to 30 psig.

The point is circumstances as to how and where one is using the tire kick in and there is quite a bit of lattitude to find the optimal solution. We tend to default to numbers that are higher than we really need with safety in the back of our minds but if we have less grip we have less safety margin- a bit of a paradox.

Rgds

Fred

Adk46

I have the standard tire sizes, 225s and 245s. My first experience with the car was with new wheel sets I got from another member here, and at first I assumed the pressures were good as-received - 34 and 34, I think. The turn-in behavior was very strange, however, even in moderate driving (although I do live on twisty roads). Because of something I read on this forum, I tried the standard pressures - 36 and 44 - and the strangeness went away. I was very surprised at this sensitivity to pressure.

For what it's worth from this small experience, my advice is to carefully monitor handling as you fiddle with pressures. I'm interested in doing a chalk test, but I'm not sure it would make me change pressures.

Andre The Giant

This is all very interesting. I will have to purchase some chalk since I can use it for other instances. This has always been a concern on my side on what tire pressure should I use for my OEM 225/50R16 on a MY 85.

I will also verify the handling of the car to see if I notice any differences, the only problem is that I don't drive it enough !

Smudo

Hi, I have bridgestone adrenalin r002 tires in 225/50 size both front and rear. I prefer around 33 - 34 psi on the street and around 28 psi on the track.

MainePorsche

After riding on same tire for the last 3 changes and testing various pressures, my Y rated Potenzas and I like 34 all the way around.