Professor Helmüt Tester

...which allows the sidewalls to deform more, which allows them to bend more, which allows the horizontal centerline of the tire to drop.

If you measure the air pressure in your now-deflated tires when the load from the vehicle is applied, is it any different from that when the vehicle weight is removed ? No.

Red herring.

Nordschleife

I can't understand why you are telling me this

cherry picking what people say, out of context, and then quoting it back to them along with your own opinion hardly advances the sum total of knowlege.

my point is that how much the tyre is inflated can alter the shape of the contact patch.

Imagine a balloon half inflated, resting on a level surface, the contact patch is tiny. Now rest a weight on the balloon and the contact patch increases in size. Finally, increase the amount of air in the balloon and the contact patch will become smaller.

R+C

wanna911

What do you mean, both tires are AVO F3000,

there are two questions posed here, are you talking about same width wheel, different size tires, or wider wheel and tire?

Professor Helmüt Tester

I'm curious as to how you arrived at the conclusion that my response was cherry picking ? I quoted your entire post.

If you were referring to my initial reference to one item in the first "wanna911" post, then I still don't understand your point. If we're going to consider a 'real' tire, then #2 on his 'keep this in mind' list needs to be refuted. You won't get a proper analysis of the mechanical system know as 'tire' if one of your basic assumptions ("keep this in mind" sure does sound like a list of basic premises) is faulty.

weneversleep

DING DING DING! We have a winner!

I was actually just reading about this in Carroll Smith's "Drive To Win" last night... fabulous book...

Nordschleife

My point is that the amount of air in the tyre changes some of the physical characteristics of the tyre - with the tyre filled only to a very low pressure the contact patch is larger than it is at very high pressures.

Generally speaking, people who race cars prefer tyres which are as wide as allowed by the regulations and the limitations of their suspension system.

Having done this, efforts are devoted to finf´ding the best suspension set up in terms of camber, toe, ARB, spring and shock settings and tyre pressure, hot and cold.

My understanding is that the science behind what works and what doesn't work in tyre design is still imperfectly understood. Everytime I look at a race team budget I have to sit down before I look at the line called tyre testing.

Faux de mieux, design of GT cars is pretty damn simple, we make them as wide as possible with a long wheelbase, big overhangs and the widest tyres allowed. The Maserati is a good example. We then stick on the biggest wing allowed, twist the rules about the underbody and borrow a fork lift truck if any 'remodelling' is required.

At the same time it is most important to get on the most favoured customer list with the tyre supplier, remember X may supply 10 teams but only 3 will have the best tyres.

Most favoured status with the tyre supplier is really important, right up there with getting rid of drivers who crash the car and sponsors who don't pay.

I think that it is pointless getting theoretical about tyres when an empirical approach is adopted by the experts.

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jimculp

OK let's say you have a plane on a conveyor belt...

Nordschleife

as long as its the right conveyor belt

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Professor Helmüt Tester

On this we totally agree. My initial post in this thread was intended to make this point, but may have been somewhat clumsy.

Re: tire widths - I'll differ with you just a bit - 'as wide as possible' isn't always best. Low horsepower cars will struggle if they carry too much tire. Inability to get tires up to design temperature, excessive rolling resistance, etc. can conspire to raise lap times as tires get wider. Lack of access to tire manufacturers inner workings means that most of us have to 'run whatever's on the tire truck', and that means that we'll get compounds and constructions that aren't always ideal.

Nordschleife

I was forgetting about those, I haven't had to buy 'classic' racing tyres for some years lol

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Bull

I agree, which is why I said the same in post #8, just not as well and completely as Bill. Again, the key is "all other things being equal".

wanna911

So who can explain why, when done by a tire manufacturer, the contact patch was significantly bigger on a wider tire and rim?

Bull

The short answer is that they don't keep "all other things equal".

wanna911

Like what? The test clearly shows that the wheel diameter, tire type, Inflation PSI, and weight applied are the same. It was done to show this exact thing, so why would it be different, tire company had nothing to prove.

I think there are more factors with complex tire designs to be determined by a simple equation.

penguinking

perhaps it might be that as a tire's size increases, the way the tire deforms (to make the contact patch) is not linear.