Lower tire pressures improve acceleration/ straight braking?

[Jersey Tom]

Take a circle squash into an oval, the radius changes but the circumference doesn't.

For a material that doesn't compress at all, sure...

[Caito]

Would these lower tire pressures also work in the front tires for straight line braking?

Ask yourself this first... when was the last time you saw an F1 car lock the wheels in straight line braking? There's so much downforce that you're limited by the size of the brakes - not longitudinal braking traction (at least that's my understanding for typical behavior).

Then the driver with the strongest foot would be able to brake more?

[Jersey Tom]

Would these lower tire pressures also work in the front tires for straight line braking?

Ask yourself this first... when was the last time you saw an F1 car lock the wheels in straight line braking? There's so much downforce that you're limited by the size of the brakes - not longitudinal braking traction (at least that's my understanding for typical behavior).

Then the driver with the strongest foot would be able to brake more?

There are practical limits. You can always play with pedal ratio after all...

[Richard]

Forgive my ignorance, but I thought circumference was a distraction. The radius is the important dimension . The engine applied a torque to the axle. The resulting forward force applied to the vehicle is torque divided by lever arm to the road. So a smmaller tyre results in a bigger force (for the same torque).

Also, I've always thought the advantage of the floppy walls was the larger contact patch. I guess there is a small downside that distorting the walls absorbs some energy.

Anyway, isn't the floppy wall the result of trying to get around limits imposed by regs? What tyre would they use if given a free reign ? I guess it would be huge wide tyre like a dragster, I guess the aim is to maximise contact patch which would infer the car acceleration is traction limited?

[Greg Locock]

"It's debatable whether a squashed actually effects gearing or not."

easy. get your gps, measure the speed at a certain engine rpm in top gear. let the tires down a bit, repeat. continue until you get a measurable change. plot the results against psi and present them here. Instant stardom.

[bbq]

To my knowledge the dragster tires are actually designed to get bigger at high revs for a change in gearing.
Modern road and racing tires however are not really changing size, at least not intentionally.

I think most of the grip/tire pressure tradeoff is depending on the construction. You can very clearly feel a tenth or two in car balance, so there is an effect of pressure on the contact patch size.
Lower pressure gives you more grip in all directions. If you push over the limits, you will get to a point where the contact patch is caving in in the middle and loose area instead of gaining. There are very interesting videos of tyre pressure vs. water displacment filmed from below through a glass plate showing this (which I cant find right now ).

So: yes they do, but just in a small window. Recommended pressures are based on the construction of the tires and you can go a few tenths up or down. But don't expect it to be a huge difference.