What tire pressure?

[gavs]

Personally I run 36 front and 38 rear but I also ignore the tyre placard. I have my own reasons for running the pressures I do

[Diesel_vert]

What pressure do the GTI owners run? I've been using 37psi, I heard its better to run higher for less tyre wear and less fuel costs

The car should have a sticker in the fuel flap that lists the manufacturer's recommended inflation pressures.

There's no pressing need to deviate from the manufacturer's instructions or specifications unless you wish to alter the car's dynamic behaviour.


The figures listed on the sticker are for "cold" tyres (i.e. tyres that are have been stationary for a few hours and at ambient temperature).

If inflating the tyres while they're warm, you should add an extra 2-4 psi to compensate, depending on how far or long they've been driven on.

[GTD_XU1]

I run my GTD at 40psi all round if I'm off for a highway run, which is often and 38psi around town for a little extra comfort for passengers. Present tyres are P7 Cinturato 225/45 on 17inch standard rims.

[MountainBikeMike]

What pressures would one recommend for some high speed flowy and tight corners on a mountain run? Or should I say, how many psi would be beneficial to differ from manufacturer/tire shop setting?

I take it that grip would be enhance with a few psi less, for the sake of additional tire wear, but at what point does it become unsafe, un-fuelly, and drastic tire wear?

Really I do want to save fuel, ESP on cruises, but YOLO More grip is more grip Running Michelin SP3's 235/40/18x8

[Diesel_vert]

What pressures would one recommend for some high speed flowy and tight corners on a mountain run? Or should I say, how many psi would be beneficial to differ from manufacturer/tire shop setting?

Accurately set the manufacturer's recommended inflation pressure, then fine tune to your liking.

... with a few psi less... at what point does it become... unsafe?

This will obviously differ from vehicle to vehicle, but generally, tyre underinflation becomes unsafe when:

- the handling and stability of the vehicle is adversely affected

- the inflation pressure is so low that the tyre cannot safely support the weight of the vehicle, since the load capacity [kg] of a tyre is proportional to inflation pressure (up to its maximum rated load capacity)

- the tyre overheats

All of which may lead to internal (cannot be seen unless the tyre is unmounted) or external structural damage.

Really I do want to save fuel, ESP on cruises, but YOLO More grip is more grip Running Michelin SP3's 235/40/18x8

If you want more grip, you should consider purchasing a set of road tyres that puts a disproportionately high emphasis on grip (at the cost of treadwear), such as the Bridgestone Potenza RE-11A, Dunlop Direzza II, Yokohama Advan AD08R or equivalent.

[MountainBikeMike]

Accurately set the manufacturer's recommended inflation pressure, then fine tune to your liking.



This will obviously differ from vehicle to vehicle, but generally, tyre underinflation becomes unsafe when:

- the handling and stability of the vehicle is adversely affected

- the inflation pressure is so low that the tyre cannot safely support the weight of the vehicle, since the load capacity [kg] of a tyre is proportional to inflation pressure (up to its maximum rated load capacity)

- the tyre overheats

All of which may lead to internal (cannot be seen unless the tyre is unmounted) or external structural damage.



If you want more grip, you should consider purchasing a set of road tyres that puts a disproportionately high emphasis on grip (at the cost of treadwear), such as the Bridgestone Potenza RE-11A, Dunlop Direzza II, Yokohama Advan AD08R or equivalent.

Cheers but that's all the obvious stuff. Why I'm getting at is; would I be wise to drop down 2-4 psi for a cruise day for a bit of extra safety, or would the differences likely be marginal.

As you said, to low + corners = un-supportive tire walls

I always keep thinking moto/mtb we drop the pressure to reduce rebound speed of the tire over bumps, and let them conform to the ground. And dragsters etc run low. Different for street cars I guess!

[Diesel_vert]

Why I'm getting at is; would I be wise to drop down 2-4 psi for a cruise day for a bit of extra safety

Unless I've misunderstood your statement, it's generally accepted that increasing a tyre's inflation pressure increases overall safety on paved public roads, not by decreasing it.

... or would the differences likely be marginal.

In terms of load capacity, you have a bit more leeway than usual, since you've fitted 235/40 R18 95W XL tyres (as opposed to the stock 225/40 R18 92W XL tyres).

As I stated before, I recommend accurately setting the manufacturer's recommended inflation pressure, then fine tune to your liking. I like to take a methodical approach to things (motoring enthusiasts are notoriously susceptible to confirmation bias), but that's just me.

But if you just want to see what a 2-4 psi reduction feels like, just deflate them, go for drive, and see if you like it (though preferably with no one else in the car to minimise your liability - just as a precaution).

[MountainBikeMike]

Unless I've misunderstood your statement, it's generally accepted that increasing a tyre's inflation pressure increases overall safety on paved public roads, not by decreasing it.



In terms of load capacity, you have a bit more leeway than usual, since you've fitted 235/40 R18 95W XL tyres (as opposed to the stock 225/40 R18 92W XL tyres).

As I stated before, I recommend accurately setting the manufacturer's recommended inflation pressure, then fine tune to your liking. I like to take a methodical approach to things (motoring enthusiasts are notoriously susceptible to confirmation bias), but that's just me.

But if you just want to see what a 2-4 psi reduction feels like, just deflate them, go for drive, and see if you like it (though preferably with no one else in the car to minimise your liability - just as a precaution).

What I'm getting at is that with less pressure there is a bigger patch of rubber touching the ground- potentially more grip. The 'spring rate' and rebound of the tire is also decreased meaning when a bump or object is hit it the air doesn't deflect the wheel as much, it absorbs. The harder the pressure in the tires the more the suspension will do the work absorbing, and vice versa.

Will do try. But I ask because the effects such as wear happen over time, not just in a trial period. By the the tires are fekukked.

But lets finish it and ill make it easy (higher or lower or tie for answer):

In general/on average, would people tracking their street cars run slightly more, less, or same pressures on the track than manufacturer spec?

[wai]

I take it that grip would be enhance with a few psi less, for the sake of additional tire wear, but at what point does it become unsafe, un-fuelly, and drastic tire wear?

Tyre pressures do not affect grip. Grip is controlled by the coefficient of friction between tyre and road. The tyre pressures will affect the feel as a low tyre pressure will allow the sidewalls to flex too much. Sidewall flexing will also increase the temperature of tyres. Low tyre pressures will also increase edge wear.

High tyre pressures are not preferred either as this can increase centre wear. The ride will also be harsher as there is no flex in the tyre sidewalls. The tyre sidewalls are a significant item in the vehicle suspension.

The ideal situation is where the entire tread is evenly in contact with the road. This will ensure the best ride and life.

One way is to inflate the tyres to a nominated pressure and then check the contact with the road. It is easily done, particularly after you have driven a bit. If you see darker edges on the tyres, then this means that the edges have not been in contact with the road surface. Drop the pressures so that the dark edge is not there or only just visible.

If you have to go really low for tyre pressure, then it is a clear indication your tyres are too wide for the load or "over tyred". Overheating of tyres is not really an issue on normal roads. Excessive flexing can cause de-lamination and separation of the tread from the carcass which is why you do not want to go for really low pressures.

Now that you know this, you will see the darker edges of the tread on just about every vehicle you see parked.

[MountainBikeMike]

Tyre pressures do not affect grip. Grip is controlled by the coefficient of friction between tyre and road. The tyre pressures will affect the feel as a low tyre pressure will allow the sidewalls to flex too much. Sidewall flexing will also increase the temperature of tyres. Low tyre pressures will also increase edge wear.

High tyre pressures are not preferred either as this can increase centre wear. The ride will also be harsher as there is no flex in the tyre sidewalls. The tyre sidewalls are a significant item in the vehicle suspension.

The ideal situation is where the entire tread is evenly in contact with the road. This will ensure the best ride and life.

One way is to inflate the tyres to a nominated pressure and then check the contact with the road. It is easily done, particularly after you have driven a bit. If you see darker edges on the tyres, then this means that the edges have not been in contact with the road surface. Drop the pressures so that the dark edge is not there or only just visible.

If you have to go really low for tyre pressure, then it is a clear indication your tyres are too wide for the load or "over tyred". Overheating of tyres is not really an issue on normal roads. Excessive flexing can cause de-lamination and separation of the tread from the carcass which is why you do not want to go for really low pressures.

Now that you know this, you will see the darker edges of the tread on just about every vehicle you see parked.

Good explanation. Will keep a lookout.