Trye pressures

[qaz]

What pressures on f/ford Avon ACB10 for wet and dry races would you recommend please?

[StephenRae]

I was waiting for those who know better to enlighten us... for what its worth 16 front and 18 rear is a good place to start. The object is to run at the optimum pressure of 20lbs all round so if its cold and wet they will hardly 'pump up' in use. Check the pressures straight off the track, then when they cool down and adjust accordingly.

[Mackmot]

check the tyre temperatures, if they are hotter in the middle than the inside then reduce the pressure, if they are hotter on the inside and outside than the middle reduce that pressure. If they are hotter on the inside only then reduce the camber and if they are hotter on the outside then increase the camber. Thats the very basic idea but because on ACB10s you should be running with pretty much all the tyre working.

[R59]

I was just about to make some comments about suspension setup, then I read again to see F.Ford. If you have your cambers set right, therefore you have maximum surface contact at full speed and thus the temperature should be even if the pressures are right. You can check that by inside to outside temperatures, as well as outer/centre temps.

And yes, the 16/18 split is a good start on those. Fill 'em with nitrogen too, it's more stable than air as the tyres warm up.

Rob.


Rob

[Pug620]

Is the nitrogen thing a wind up or does it really efect the tyre pressures when hot?

Marty

[tyrrellf1]

Originally posted by hawkesfire
Is the nitrogen thing a wind up or does it really efect the tyre pressures when hot?

Marty

I'm pretty sure that the F1 teams use nitrogen. I just don't know how to convert my foot pump!

[DSM]

Nitrogen filling does reduce the increase in pressure due to heat and the temperatures are also more stable. However, normal air is mostly nitrogen anyway (78%) and there is a school of thought that says the real benefit comes from the fact that the tyres are inflated with DRY nitrogen, as opposed to air with quite a lot of moisture content.

[greenamex2]

Nitrogen ONLY improves consistency due to the fact that it is a dry gas as a result of it's manufacturing process.

All the stuff about it expanding less etc etc etc is going against one of the basic laws of pyhsics.

Pressure is directly proportional to Temperature divided by volume in a sealed container. This is true for ALL gases.

Where Nitrogen scores over common or garden compressor air is it is a gas rather than compressor air which is a gas generally mixed with at least some water, if not oil and all sort of other junk that doesn't obey the above law.

In short, use it if it is available but don't expect a massive difference unless you (or your tyre fitter) haven't drained your compressor recently.

[R59]

Have you been watching those Open University programmes on BBC2 again Denis?

It's not just the F1 boys that use it. Most hypercompetitive slick shod people use it. There is less of an increase in pressure, and therefore more consistancy.

For those of you who watched the F1 from Spa, you'll remember seeing the pics of Schuey's front tyres wibbly wobbly after the safety car period. So, yes, the pressures do still change with temp when you use N.

And as for your compressor, not just draining the tank, it's whether you have a drier fitted (that works) to the air line too....

Rob.

[dtype38]

Don't want to rain on anyones parade here, but I'm afraid the air vs nitrogen thing is all a great piece of hype with no foundation in reality. Fact is that for a constant volume (like a tyre) the relationship between pressure and temperature is related by the equation P1 = Po.(1 + b.T1) where Po is the pressure at 0 deg C, T1 is the temp in degrees above zero, and b is pressure coefficient of the gas in question. Unfortunately, the reality of the situation is that for dry air the coefficient is 0.0036744 and for dry Nitrogen the coefficient is also 0.0036744. So to five significant figures, it makes no difference which you use. I think that Denis has it right when he says its more to do with how "dry" it is rather than which one you use.

[Pug620]

Even better as i could have got nitrogen if needed but my tyre infating rig is two breathing air cylinders with a regulator so this air is dry and oiless .

Then i just refill it at work .

Marty

[Onlooker]

Originally posted by dtype38
Don't want to rain on anyones parade here, but I'm afraid the air vs nitrogen thing is all a great piece of hype with no foundation in reality. Fact is that for a constant volume (like a tyre) the relationship between pressure and temperature is related by the equation P1 = Po.(1 + b.T1) where Po is the pressure at 0 deg C, T1 is the temp in degrees above zero, and b is pressure coefficient of the gas in question. Unfortunately, the reality of the situation is that for dry air the coefficient is 0.0036744 and for dry Nitrogen the coefficient is also 0.0036744. So to five significant figures, it makes no difference which you use. I think that Denis has it right when he says its more to do with how "dry" it is rather than which one you use.

See there is a great example of the numbers not supporting the reality it makes a difference, particually if you remove all gasses from the tyre with a vacume pump and use medical grade Nitrogen. The change is quite signicficant. As air is contains an element of water in it, i would have thought that you would have to add the reletive coeffiects for the water as well? and find this ratio prior to comencing the calculation, you know with this sort of info you could save a company like Williams or McLaren a fortune and more than pay for your position there, doing nothing, whilst the dopey engineers got on witht he less obvius stuff, like thermodynamics and fluids, of which some of them would be reasonabley smart
Cheers

[Pug620]

So whats best??

Dry air or nitrogen

cheers

Marty

[Tim Falce]

Having read all the above posts I have decided to fit a set of Yokohama fork lift truck tyres to my car. These are cut in the same pattern as 032Rs so the grip will be at the same level but being solid they wont suffer from any difference in pressure as they heat up. The only problem is actualy heating them up, so I have decided to install an oven in the back of my Land Rover to pre heat them.
I will let you all know how I get on.

[StephenRae]

Falcemob...hard to believe but there is a flaw in your plan. Whilst you are not actually wrapping your Land Rover/oven around the tyre I think it will still be classed as a tyre warmer and as such is not allowed!
You could heat them up outside the circuit..but then the car will glue itself to the transporter floor so you will have to fork lift it out but you can't 'cos the ******* fork lift is back at base, up on bricks.
I don't think you've thought this through..and I'm not helping.

[Revracing]

Since Air consists of 73% Nitrogen there should be little difference between Dry Air and Nitrogen, since as has already been stated it is the water content that causes the trouble.

[Tim Falce]

Originally posted by StephenRae
Falcemob...hard to believe ............I don't think you've thought this through..and I'm not helping.

Aha, this is where plan B comes in....trouble is I haven't thought that through either

[Chris Y]

Fill the tyres with helium - reduce your unsprung weight

[StephenRae]

...or hydrogen...go out with a bang!!!

[dtype38]

Originally posted by Onlooker
See there is a great example of the numbers not supporting the reality ....bah....blah... Williams or McLaren ...blah...blah... some of them would be reasonabley smart
Cheers

OK, so that was a simplification, but I couldn't be bothered to get out my psychiometric charts and my Kaye and Laby, then cross check using a decent pressure transducer and pyrometer.

But I do know how to spell vacuum, and that if I pumped all the air out of my tyres they'd collapse and probably pop off the rims ... but I hope to watch you do that in the paddock one day.

Do you do everything on your car that the F1 boys do?? If so can I have some money for a set of Yoko 008s for my car... I promise to fill them with nitrogen.... honest