What tire pressure?

[Diesel_vert]

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.

That may be so, but on a public road, safety and liability concerns would normally place limits on what you can achieve through the adjustment of inflation pressures alone (especially underinflation, which affects the tyre's load capacity).

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.

Given your current tyre size, it's likely that nothing much will happen, but life often tends to throw a curved ball or two when you least expect it.

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?

The idea of lowering the recommended tyre inflation pressure on a road car fitted with road tyres on the track, is to counter the elevated operating inflation pressures experienced on the track caused by the sort of temperatures generated by constant maximum acceleration and deceleration loads, and consistently high speeds (centrifugal) and cornering (lateral) loads - forces which are generally beyond the envisaged operating scope of most road tyres.

On a track, you are aiming for a "hot" working inflation pressure, so for reasons of convenience, one may reduce the inflation pressure in the pit lane before joining the track proper (that is, if you have already experimented on previous sessions and know what the anticipated hot inflation pressure will be).

On a public road, you will generally not experience those sorts of elevated pressures and temperatures normally encountered on the track, so in your situation (mountain runs), there is no real justification of underinflating one's tyres.

Personally, I don't see any real pressing need for most people to deviate from the manufacturer's recommended inflation pressures, but again, if you feel the recommended inflation pressures are unsuited to your driving style, then start fine tuning.

It probably doesn't help to mention that one person's idea of "good" handling might not be the same as the next, but there we are.

[gavs]

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.

Not quite true wai. Yes, grip is controlled by the coefficient of friction over a specific contact patch but if you increase the given contact patch then you are afforded more grip. So many times I see this regarding 4x4's when people learn about tyre pressures and the amazing increase in grip you get. True, if you go too far then it becomes detrimental but a lower pressure does afford more grip.

[wai]

Not quite true wai. Yes, grip is controlled by the coefficient of friction over a specific contact patch but if you increase the given contact patch then you are afforded more grip. So many times I see this regarding 4x4's when people learn about tyre pressures and the amazing increase in grip you get. True, if you go too far then it becomes detrimental but a lower pressure does afford more grip.

Nah. If you increase the contact patch, there may be more tyre in contact with the road, but the contact pressure is reduced and they cancel each other out. Racing tyres are different to road tyres because they use softer rubber. They have to be wide to provide an adequate life. Narrow or wide, for the same rubber, there is the same grip.

A few decades ago, Alf Costanzo (hope I spelled that right) competed in the Alfa Sud series. Apart from using scrubbed road tyres, he used the narrowest tyres permitted as he wanted to get the tyres up to optimum operating temperature as quickly as possible. The commentators said he would be all over the track as he would have no grip. Well, he had as much grip as anyone as it was the same rubber compound. He actually had slightly better grip as the narrow tyres were up to optimum temperature sooner. Wear was not an issue as the races were less than 10 laps at a time.

I have done drawbar tests where an axle is fitted with different tyres (one wide and one narrow) with the same rubber compound, and the same surface. Both wheels have the same load on them. The axle is pulled from the midpoint, and both wheels unable to turn, will slip at the same time and by the same amount.

4x4's reduce tyre pressures as the tyre overpowers the ability of the loose surface to provide a stable base on which to drive. By increasing the contact area, the ability of the loose surface to provide a stable base is increased. Remember, that on a sealed road, it is the coefficient of friction between the tyre and the road surface that matters. In an off-road situation the tyre does not slip, but it is the unsealed road slipping internally. The loose road slips internally rather than the tyre not having traction on the surface which is why road material gets spat out.

[jeremy629]

I have been playing with my tyres pressures a little bit lately

Had them at 32psi. I measured how far I got from the tank of fuel to see how good it was. Then tried 35 psi. Another tank of fuel. Then lastly I have been driving at 40psi and surprise surprise (not) I get even better fuel economy. I am happy to have it set at 40 now though and not any higher. Also the car feels better over bumps. Maybe I have just been lucky not hitting any big ones?

[wai]

The higher the tyre pressures, the lower the rolling resistance. The trade off can be a harsher ride.

Just check that you are not too high as this will increase centre tread wear compared to edge tread wear.

[jeremy629]

Yeah will be keeping an eye on it :0) thanks wai

[MountainBikeMike]

Awesome. what were the differences in consumption?

[Diesel_vert]

I too was a fan of inflating the tyres above the specified values on the placard (for the specified load). In my own experience, it felt that the wear rate was reduced with no obvious centre wear pattern (a near-uniform wear pattern more or less, notwithstanding any alignment problems) and that less throttle input was needed to maintain momentum on the straights, though I didn't maintain accurate records to see if it made a difference to fuel consumption.

However, whilst it made the steering feel a little bit more responsive, it also felt that the tyres weren't able to hold the line in a corner as tenaciously and were more willing to slide. In addition, it felt as if the car would bounce over bumps on the road, making it a bit more twitchy when encountering mid-corner bumps. It made for a fun ride when pushing it, but somewhat disappointing, all at the same time.

I've also noticed that the ABS tends to engage earlier and/or more frequently during very hard stops, which was just disappointing and annoying.

Having said that, I'm also definitely not a fan of inflating the tyres below the specified values on the placard (in order to keep excessive wear at bay and maintain load capacity) so as a compromise... I just stick with the values listed on the placard - who would've thought, eh?

Well, FWIW, these are only my own (non-scientific) observations and experiences. YMMV.

[MrDeathLad]

i always thought it was the tyre compound that made a differnce to resistance not tyre pressure. sure, pressure makes a difference to the contact surface area but a softer compound = more resistance/grip = more fuel consumption? please correct if i'm wrong

[MountainBikeMike]

i always thought it was the tyre compound that made a differnce to resistance not tyre pressure. sure, pressure makes a difference to the contact surface area but a softer compound = more resistance/grip = more fuel consumption? please correct if i'm wrong

Hop in whatever pushbike you have at home right now, let the tires down till they sag a little under your weight, and come back from round the block a fit man you'll see it easier that way