Tyre Sizes?

[WildCards]

Two mates Wednesday night, both have got engineering degrees of some sort, both can be very anal and equally as boring talking about how things work.

My question, after discussing original Jag E-Type thin wheels/tyres was how could the car handle and grip well with it's small contact patch? Now i'm not saying grip well in todays world, but back when the E-Type was the daddy.

Long heated discussion later, one of them was basically saying that thin tyres have as much contact area and modern wide tyres due to pressures and some other technoflab that i glazed over at.

Does anyone here have any theories on this, just to set it right in my head :rolleyes4 /help (Isaac, possible be one for you)

[psbarham]

all a load of bolox , the e-type gripped well due to the excellent (for its time) suspension set up , get them in a ford pop and let them say it has loads of grip from the scrawney tyres

[mpau009]

don't know if its relevant, but i was watching WRC the other day, and they were discussing how by switching to a smaller width tyre they could get better traction when it rained and got a bit muddy. Could it be something similar?

From school physics, i seem to remember that traction was related to weight and friction, so maybe if the tyres are working within their limits (ie not smoking /Steeringw) then it doesnt matter too much?

But then, looking at those US topfuel dragsters, id have to say that they certainly believe that size makes a difference.... /yes

Any boffins got the answer..

[psbarham]

with rally cars they run thinner tyres to get through the sloppy cr@p on the surface , and find grip on the rock / stone/ shale underneath

[SGHOM]

gravel. snow, ice......... thin is good. /yes on tarmac, which I think most of us prefere to race on, fatter is better ! /Steeringw /yes

[WildCards]

This is what i thought. No prizes i'm afraid, but i'm glad i still know a thing or too about cars and i'm not going qwackers.

Ta

[zentac]

Suspension is the key, this is what Im finding out with the drag racing.

[Wodjno]

Suspension is the key, this is what Im finding out with the drag racing.

I agree the tyre has a lot to do with the ammount of grip a car has.. /yes

But as Richard says the key to good grip is in the suspension set up and also the chassis.. /yes A car can have the best tyres in the world, but if it has a crap chassis and suspension it's gonna struggle for grip.. Tyre pressure is very important aswell as this also acts as part of the suspension for the car.. To hard and it's gonna bounce or slide and to soft and it's gonna squelch all over the place .. It's finding the perfect balance between all 3.. /yes

[Rambaud]

IIRC, tyre contact area is basically a function of car weight and tyre pressure.

Therefore, all tyres have about the same same contact area (on the same car with the same tyre pressures), but the *shape* of the contact patch will alter depending on size and aspect ratio of the tyres.

[Pete M]

Going back to the original argument. The E-Type was (and is) a fantastic car, but on its original crossply tyres, it must have been a major handful, especially in the wet. As everyone else was on crossplies too, it really shone. Most of the E-Type owners I know in my Jaguar club are using 205 width radials, which are at least half as wide again as the original tyres and with all the advantages of modern radial construction. I don't think any of them would get away from me in the VR-4, though. My Series 3 XJ12 has similar horsepower to the VR-4, but is completely different to drive.