sooby

Simon,

In your explanation to question 4:

"If you increase the load, you increase the grip, but the grip per square inch remains the same. If you reduce pressures in order to increase the contact patch area, but the load remains the same, there will be more rubber on the road, but the load per square inch will reduce, meaning the overall grip stays the same."

In Drag racing, those big tyres have low inflation for more grip. If you take high speed pictures at the start of the race (after they've heated the tyres by burning them on the spot), you can easily see the tyres twisting under the load.

Not quite a road car - but hey!

Andy S.

Drag racing tyres have a very flexible construction, the Diameter of the tyre increases as you spin them up.

Most soft compound drag tyres do twist as well.

I know a couple of tyre technicians I will see if they will answer your questions

cheers Andy

elgordano

i don't understand half of the questions

Brit_in_Japan

1. B
2. C
3. A
4. B
5. A
6. B
7. B
8. B
9. B
10 B

Doh! Where did those answers come from ?

warrenm2

Read some of your answers and not sure I agree with them. I'll take you through my thinking...

First, an equation!

F=uN This is the (admittedly static) basic friction equation and it translates as "The sideways force (i.e useful cornering force) equals the downwards force (i.e. the weight on the tyre) times a fudge factor u.

Now the u term will depend on lots of factors - the tyre compound (stickier means higher u), the contact patch size, temperature (tyres get stickier as they get warmer - within reason), the state of the road surface, tyre deflection etc

Therefore what you are doing by fitting bigger tyres, assuming geometry and compounds etc are the same, is to increase the grip by increasing the contact patch area (the width that is). Now its true that by spreading the load over a wider area, this will lower the contact patch pressure (i.e the weight that is spread onto the road is spread over a greater area), and hence this will reduce the length of the contact patch (i.e front to back distance) by allowing the tyre to be more "round". However this will be influenced by tyre stiffness - which in itself is influenced by tyre pressure and tyre contruction. The thing to bear in mind is that the increase in width will increase the contact patch width by say 20% whereas the decrease in contact patch pressure will effect the contact patch length by maybe 3%? So overall you get a greater contact patch area by going to wider tyres and hence you get more grip with wider tyres (otherwise we'd all be putting 105's on our cars not 225s!). Its a similar trade off to compression ratios in engines - increasing the ratio will increase the energy used by the engine to compress the fuel/air mixture - however the resulting increase in bang more than offsets this, so within reason, high compression ratios are the way to go...

Also you can increase the length of the contact patch by increasing the outer wheel diameter - ie the diameter of the tyre at the tyre surface.

I dont have any proof of the figures other than bigger tyres grip better - reason? Bigger patch

Mark

prana

1. B
2. C
3. A
4. B
5. B - I dunno what a roll center is
6. B
7. A
8. A
9. B
10. B (mistake)

ex-webby

Hi Warren

Sorry, only just spotted this.

I'm going to get lost in all the formulae here, so will try to keep away from them!!

The performance of a tyre in what you could call "grip", does not conform to the standard solib body friction formula you quoted, unortunately. That's only part of the story.

The general rule of thumb is that *under normal operating conditions - load, temperature, etc* the grip a tyre produces (if you ignore compound) is a function of the load you put on it. This effectively (in isolation) means that the actual ammount of rubber on the road would make no difference to the grip.

Now, of course this never works out bang on in the real world, but it does mean that simply increasing the contact patch area does not necessarily increase the amount of grip you have. What it does do, is allow the strain on the tyre to be spread over a wider area, dissipating the heat quicker and better which means that (as long as you can get them up to temperature) the tyres will stay within in their optimum range for longer. They will also wear less.

Tyre stiffness does have a part to play in the contact patch area, but it is very minor, and certainly, the tyre will not be working as well if it is affecting the area of rubber on the ground. It will be at the wrong pressure, or just be a bad construction.

So in normal operating conditions, the only way you (again as a rule of thumb) change the contact patch area is by altering either the vertical load on the tyre, or the air pressure.

All the best

Simon

warrenm2

I disagree ;-)

n one

iTrader: (5)

Just did it, before I saw the answers, only got 3 right.

Dummy.