Camber, Graining and Tire Pressure

[vonk]

Hello from USA.

Watching the beginning of Friday practice, the dark graining bands on tires were outboard of tread center for some cars and inboard for others. Eventually, they were all pretty much centered. One way to check camber setting.

Also, the width of the graining band appeared to vary some, probably as a function of tire pressure. Presumably, the wider band indicates lower pressure. The wider bands were usually less deep black implying less severe graining.

Since camber and tire pressure are not independ, teams must wind up with the best compromise of these variables for anticipated conditions in qualifying and on race day. They can’t change camber after qualifying, but can they adjust tire pressure on race day to accommodate changing weather? Lower pressure would result in a larger contact patch, better traction and less graining. But, how sensitive is handling to lateral tire compliance at that point. Where’s the limit? Probably different drivers are comfortable with different limits.

[Jersey Tom]

Lower pressure would result in [...] better traction.

Don't be too sure of that.

[marcush.]

Lower pressure would result in [...] better traction.

Don't be too sure of that.

I´d think the opposite is happening..with too much pressure only a middle section is
having real good contact to the pavement..and is overworked.
if you´d run excessive low pressure the hard worked areas would be the inner and outer extremes and the centre would be in better shape...?

Of course the graining will be minimised with a maximised contact patch but the question is if this alone could avoid the graining.

[vonk]

Lower pressure would result in [...] better traction.

Don't be too sure of that.

Please explain.

[Jersey Tom]

Basically what marcus was saying. Not dissimilar to having your road car tires under- or over-inflated. Sometimes taking air out gives you more grip. Sometimes it takes grip away.

Also.. I wouldn't say those dark bands are graining. Could just be worms for all I know (which I suppose could be misconstrued as graining).

[vonk]

Basically what marcus was saying. Not dissimilar to having your road car tires under- or over-inflated. Sometimes taking air out gives you more grip. Sometimes it takes grip away.

Also.. I wouldn't say those dark bands are graining. Could just be worms for all I know (which I suppose could be misconstrued as graining).

All other things being equal, a larger contact patch will result in a higher coeffitient of friction.

Whatever their name, the dark bands are the area of maximum contact stress.

[Jersey Tom]

All other things being equal, a larger contact patch will result in a higher coeffitient of friction.

All things are NEVER equal though, including just taking air out of the tire.

[riff_raff]

Jersey Tom is correct.

An under inflated tire will likely have an increased contact area initially, simply due to its lower structural spring rate. But the additional hysteresis losses it experiences within its carcass during use will also cause it to generate more heat, which will also likely cause its tread surface to overheat and lose grip.

The rubber compounds used in tire treads are designed to give optimum life and grip within a specific temperature range. That life and grip is also significantly affected by the way the tire rubber compound is heat cycled during its break-in.

riff_raff

[marcush.]

I doubt that graining and tyre pressure and Camber are really that much connected.
before talking about graining ,I think it is very important to actually define what we understand by graining.
To me this is tearing of the tyre tread surface without actually overheating of the tyre.The tyre sheds rubber at an alarming rate without building up grip.the tyre surfuce looks very coarse compared to the fine grain you normally see with a properly worked racing tyre.

a tyre not yet at working temperature may as well collect marbles from the track which can be incredibly difficult to get rid of again especially if your tyre pressures are low ,which is likely.

[vonk]

I doubt that graining and tyre pressure and Camber are really that much connected.

In my experience, even belted racing tires exhibit some convex “ballooning” within the range of proper running pressures. Therefore they would also exhibit some variation in contact patch size with pressure.

Regardless of what the dark bands really are, they do develop at the contact patch. Consequently, camber will have an effect on where they appear across the tread. That’s helpful, because I think the dark area should be centered for best traction and wear.

I believe these bands are stress caused and would, of course, reflect an average stress level while running.

[Jersey Tom]

That’s helpful, because I think the dark area should be centered for best traction and wear.

...this is based on...?

[vonk]

That’s helpful, because I think the dark area should be centered for best traction and wear.

...this is based on...?

A Goodyear guy once told me that, because of its thin tread structure, a slick racing tire's vertical compliance is softest at tread center where neither sidewall adds stiffness. This, he said, provides the largest and most flexible contact patch at a given load and pressure, thereby allowing the highest contact coefficient of friction and best tire wear. - Makes sense to me. Besides, I like symmetry.

[Jersey Tom]

Really depends on what you mean by the 'dark area' I guess, and when you're looking at it.

I'd say it's true that the middle of the crown area is going to be very vertically compliant.. but that's kind of a separate issue.

[marcush.]

talking about dark areas ,my aim would always to be to maximise contact patch area under load and this is ideally the whole tread width .
you just cannot afford to only work the centre.

[autogyro]

talking about dark areas ,my aim would always to be to maximise contact patch area under load and this is ideally the whole tread width .
you just cannot afford to only work the centre.

Surely one of the reasons for negative camber is to even out the load on the side walls during roll, to end up with an even force on the whole tread width at the limit of cornering?