Tyre pressure

[steve_spackman]

Does lowering the tyre pressure on the rear tyres on a RWD and front tyres on a FWD race car improve grip?

[Sonic]

You want the tires to be a the right temperature more than anything else so lowering pressures may bring them up to temp quicker but would soon move beyond the ideal window and be useless.

[Easy Drifter]

Steve: Tire pressures on a race car is a very involved and tricky subject. The pressure you run depends, to start with on the type of race car and the tire manufacturer and the compound. Race mechanics have a pretty good idea of where to start but for a newcomer you go to the tire Co. rep and tell him your tire type, compound and type of car. He then should give you the basic paremeters.
When you get to upper levels, like F1 or other major series tire Co. engineers work with the teams to optimize pressures utilizing the suspension set up data and checking tire pressues and temp across the tires after each run. That means inside edge, outside and middle on each tire. You then have to consider how quickly you could get the readings. F1 and some other series have constant pressure readings coming from the car while on track. Then you have to interpret all the data.
You use tire pressure alterations as one of many set up tools on a race car. It is far too complex to go into here but every suspension or areo change may require a slight pressure change at the upper levels of the sport.
There is no simple answer.
At any level of racing the final tire pressure depends on set up and weather can change the pressure you run. It is just one of the multitude of things that can affect a cars handling and the trick is to optimize them all.
Then you add in a set up that suits one driver but his teamate finds it hopeless!

[leopard]

I think yes, you will gain more grips from more surface of tyre on the road, by lowering the pressure to the level it is acceptable. But if the pressure is too low it will give you more disadvantage.

I prefer higher pressure than normal as it helps life of the tyres... :D

[Rollo]

I think yes, you will gain more grips from more surface of tyre on the road, by lowering the pressure to the level it is acceptable. But if the pressure is too low it will give you more disadvantage.

I prefer higher pressure than normal as it helps life of the tyres... :D

My learned colleague here is correct. By lowering the pressure of the tyre, the contact patch of the tyre to the road increases, therefore with a larger contact patch, grip goes up. This is true for all tyres in all circumstances.

It will also increase friction and therefore heat*. Increased friction also leads to decreased tyre life.

F1 and Top Fuel Dragsters typically run tyre pressures of about 1.1kg/cm² or 15-16psi. In my Ford Ka I run pressures of about 2.952kg/cm² or 42psi.

*heat also changes the equation subject to Charles's law and Boyle's law, but not Cole's Law.

[Mark]

Certainly in F1 tyre pressures are absolutely critical. Quite often you see a driver doing amazing lap times, then they pit, change their tyres and quickly fall back, and that's often because their tyre pressure was slightly off.

[wedge]

General motoring? Trackday? Racing/slicks?

Its true you're supposed to lower tyre pressures on the track because energy will be greater which will naturally increase tyre pressure.

Honestly, it depends really on what set up you're after. Tyres are unsprung mass which means you can use the sidewalls like springs via tyre pressure.

[driveace]

On a race car once the temperature of the tyres warm up then the pressure inside the tyre increases,so if you set off with temperature of say 40psi,after a few laps that pressure could have risen to 45psi.
Most race cars use filtered air or hydrogen in the tyres.

[Easy Drifter]

I believe it is usually nitrogen. At least that is what we used to use.
Pressure increases with air as it heats up and I would think Hydrogen too dangerous. You want something pretty much unaffected by heat.

[Rollo]

Hydrogen Gas H2 only has a specific density of 0.898g/L
Regular air a specific density of 1.292g/L
Nitrogen Gas N2 has a specific density of 1.251g/L

Hydrogen gas is physically smaller at a molecular level and would be more prone to leaking out of a rubberised container (the tyre) than either Air or Nitrogen gas would be.

Also, because N2 has a trivalent bond between the atoms, I would expect that Nitrogen gas is a) extremely stable b) has no obvious dipole and c) probably reacts better to changes in heat and pressure which is why they'd use it in tyres.

Though I could be wrong :s

[Daniel]

Yes it is nitrogen.

[Mark]

Hydrogen would be extremely dangerous! Of course nitrogen forms about 75% of air and is pretty much completely unreactable. Unlike oxygen which forms the other major proportion.

[donKey jote]

just make sure you don't have any water vapour in the mix, as it messes up the pressure-temperature dependence ;)

[Daniel]

just make sure you don't have any water vapour in the mix, as it messes up the pressure-temperature dependence ;)
Would you bother with nitrogen inflation on a roadcar donkey? There is a place near us which only fills tyres with Nitrogen and only fits Michelin tyres (It's a Costco) and curiosity always makes me wonder if it's really worth the bother. Michelin want stupid amounts of money for tyres for the Fiat so it'll have to be on Caroline's car :p She can be the guinea pig :p

[donKey jote]

No I wouldn't, just as I favour tap-water over bottled french eau - not worth the price hike... and if you're going to lose significant amounts of air it's way more likely to be through faulty valves or donkey driving than through diffusion :)

however, if you must try, make sure they give you orange Nitrogen, the molecules are slightly bigger than the blue type ;) :D :dozey: :arrows: