::.. Tire Pressure

[Qube]

The stock suggestion of 29F/33R is too low for cars of this weight IMO. I'd run at least 32F/36R - maybe more. Just keep the 4PSI difference F/R. I run mine at 36F/40R and they are wearing squarely.

So really, what should we be running then? I agree that 29/33 feels low.

[NY535iManual]

I run the H&R sport springs, Bilstein Sports, and 18s wrapped with 235/40 Falkens, and have been very happy with 40f/42r. I have found that because of the wide, low profile tires, going any lower tends to make the car (particularly the front) "catch" on potholes and bumps, rather than ride (relatively) smoothly over them. I suspect that these pressures may lead to odd wear patterns as mileage builds though...

[joshua43214]

The drivers door will ave a sticker that gives proper tires and tire inflation, you can start with that number and adjust it to meet your needs. the recomendation will be compromise between economy and comfort.

[Anthony (M5 in Calgary)]

So really, what should we be running then? I agree that 29/33 feels low.

Where did that quote originate? Sounds like something I would have written...;)

[Spasso]

So really, what should we be running then? I agree that 29/33 feels low.
My 2500 lb Datsun 240Z runs 225/50-15's and my 3880 lb 530 Touring runs 225/60-15's

To get the performance and steering definition I run 28 to 30 psi max on the Datsun and no less than 40 psi on the Touring.

The Touring was vague and wallowed with 32 psi. The ride was smoother and road noise was quieter but the car handled like a drunken pig. 40 psi "almost" put it on par with my sedan.

Suspension geometry wears out the shoulders of the tire first. Lower pressures will accelerate the process.

Lower pressures allow the sidewalls to flex more (on a taller tire) generating excessive heat and premature failure. Google Firestone vs Ford and Explorer rollovers. The tires kept falling apart due to (as yet unknown) tires from a certain factory not being built to spec. Ford increased the frequency of failures by recommending a lower psi (why I'll never understand) which caused even more sidewall flexing and MORE HEAT and even more failures..

Rule of thumb, the heavier the car, the more psi you need. Tire size also determines pressure. The bigger it is above stock size the chances are you'll need less pressure for average driving.

Hope this helps.
DJ

[Qube]

My 2500 lb Datsun 240Z runs 225/50-15's and my 3880 lb 530 Touring runs 225/60-15's

To get the performance and steering definition I run 28 to 30 psi max on the Datsun and no less than 40 psi on the Touring.

The Touring was vague and wallowed with 32 psi. The ride was smoother and road noise was quieter but the car handled like a drunken pig. 40 psi "almost" put it on par with my sedan.

Suspension geometry wears out the shoulders of the tire first. Lower pressures will accelerate the process.

Lower pressures allow the sidewalls to flex more (on a taller tire) generating excessive heat and premature failure. Google Firestone vs Ford and Explorer rollovers. The tires kept falling apart due to (as yet unknown) tires from a certain factory not being built to spec. Ford increased the frequency of failures by recommending a lower psi (why I'll never understand) which caused even more sidewall flexing and MORE HEAT and even more failures..

Rule of thumb, the heavier the car, the more psi you need. Tire size also determines pressure. The bigger it is above stock size the chances are you'll need less pressure for average driving.

Hope this helps.
DJ

So in a nutshell, when I take these 235/45-17 on the track next week, I should stick to the labelled psi. MAYBE bump up one or two where a passenger is inside.

[Paul in NZ]

the factory pressure for 235/45/17 is 39f41r (or something very close to this)for the M5,its what i run on my 535 mtech suspension and 235 45 17

[Russell]

Best pressure stock tires? I currently use 30/34 for normal driving with one person in the car. However, it seems to handle a bit better at higher pressure but rides much rougher. I see even wear on tires as I rotate/balance every 5,000 miles

[Anthony (M5 in Calgary)]

the factory pressure for 235/45/17 is 39f41r (or something very close to this)for the M5,its what i run on my 535 mtech suspension and 235 45 17

38F/41R IIRC. The 29F is only for the 15" tires - 29 in a 45 series tire is asking for rim damage with a great big PLEASE.

[califblue]

I am running 32 psi F & 35 psi R on 225/60 15" Traction TA's ( V rated) handles awesome and sticks like glue

[Qube]

38F/41R IIRC. The 29F is only for the 15" tires - 29 in a 45 series tire is asking for rim damage with a great big PLEASE.

Gotcha. Will do :) I'll try from that benchmark.

[Zeuk in Oz]

I see even wear on tires as I rotate/balance every 5,000 miles
Even wear means you are running pressures that are too low.

When running correct tyre pressures, you should wear the centre of the tyres more than the shoulders.

The reason for this is that you should be running your tyres so that they run on the centre more than the shoulders when they are not stressed - you stress them when cornering or braking.

This is because if they are completely flat on the ground when just rolling normally, as soon as you stress them the centre loses contact with the ground as it gets sucked in.

Thus if you run your tyres with a slight over-pressure running more on the centres than the shoulders, as soon as you stress the tyre it sucks the centre in and the whole tyre is flat on the ground.

Therefore given that you drive many more kilometres without stressing your tyres, over a period of time the centres should wear a little more then the shoulders.

At least this is how it was explained to me 35 years ago and it certainly makes sense to me. :)

Edit : I run at least 36 psi all round on my 225/60/15 tyres. 40 on a long trip.

[Russell]

Even wear not good! First time I have ever heard that.

That said, Tire rotation every 5,000 tends to even out front outside edge tire wear and inside tire wear on rear. Even so, interesting theory. Think I will check with my tire store and others to see their opinion. I just may bump my pressures up a couple of pounds.