What tire pressure?

[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

[wai]

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

Tyre compounds do play a part given that wheels rarely track dead true all the time. So where scrub is significant, a compound that allows the tyre to slide will reduce "rolling" resistance. Tyre pressures play a much greater part than compounds because when you look at it, an underinflated tyre had a greater contact patch and a smaller radius at the contact patch than the rest of the tyre, and so has to climb all the time. It is a bit like driving on an oval wheel. Now you have to overcome the vertical load on the tyre.

After all this, you do have to be very careful varying tyre pressures as the tyre sidewall plays a major role in a vehicle's suspension. The Holden Radial Tuned Suspension was not just marketing hype. If the tyre sidewall is stiffened and the rest of the suspension components are unchanged, you can end up with quite a degraded suspension system with steering affected and tyres bouncing and losing contact with the road.

At the moment, one of the reasons why the F1 teams do not want to go with 18" rims (as opposed to the 13" rims they currently use) is because the designers are going to have to make significant changes to the suspension components given that the tyres (sidewalls in particular) play such a large part in the suspension.

[kevinctr]

For tyres with stiffer walls like AD08, Dunlop ZII, etc, I lower the PSI by 2-3 PSI from factory specs.

[wai]

I should also say that a flexing sidewall or tread absorbs energy. Rubber has different characteristics on compression and then rebound. This is seen as heat, and this energy is absorbed from the car and so an increase in rolling resistance.

So, you don't want to under inflate your tyres as this can cause them to overheat, but you also do not want to over inflate them either as this can cause them to be too stiff and then end up with suspension issues.

[Diesel_vert]

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

Rolling resistance is mainly energy loss through internal friction of the tyre itself. An increase in inflation pressure will go some way in reducing RR, but that effect tends to decrease exponentially as you add more air. The choice of tyre (and how it's designed and constructed) will have a bigger effect on RR more than anything.

It is possible to create a tyre with high wet grip and low rolling resistance, at the expense of wear. Continental usually apply this design philosophy to their tyres, for instance.