Low profile vs High profile tyres (a car thread!)

[hertsbiker]

Would I be right in thinking that *in general* a low profile tyre will give more grip in a corner due to reduced sidewall flex... but a higher profile tyre will give better grip on acceleration & braking due to deformation?

And if not.. why not? I'm trying to work out the best tyre for all conditions.

Had to drop a car-tech related subject into the forum with all these O/t posts going on !

C

[mondeoman]

Thats about right ......

Drag cars have bog all pressure in them and loads of deformation on kick-off, maximising grip

Racers have low sidewalls to minimise flex, reduced "springing", to give them better control of suspension movement using springs and dampers .....


Mind you, I might be talking out of me ar$e here of course!

[aww999]

That would certainly be my understanding of it . . . but it all goes out of the window when you look at F1 cars though??? Big squidgy low pressure tyres on them (relatively speaking).

[mondeoman]

aww999 said: That would certainly be my understanding of it . . . but it all goes out of the window when you look at F1 cars though??? Big squidgy low pressure tyres on them (relatively speaking).

Forced on them by regulation to limit cornering speeds - and you've seen how they have crap grip on acceleration from standstill, but overall a reasonable compromise.

[ehasler]

I may be wrong, but aren't dragster tyres actually designed to expand a huge amount when they rotate to give a higher drive ratio, and thus higher speed? If you watch a standing start, the tyres go from an F1-style wide and short tyre to a tractor-style thin and tall tyre.

Also, even at the relatively low pressures that F1 tyres run at, they don't appear to distort much at all even under massive load.

[Fatboy]

Part of the reason F1 tyres are so tall is that they form a major part of the suspension in that they do a lot of the bump absorption.

[trackdemon]

Absolutely, tyres contribute perhaps as much as 50% of an F1 cars overall handling balance, with the rest coming from suspension and aerodynamic . Hence the reason the manufacturers need to spend so much cash on them. Massively sensative to pressures and loads, and very light but they are the main means of bump absorbtion. The slow-mo's at somewhere like Hockenheim give a very good view of what goes on with an F1 car when cornering fast.

[aww999]

Dragsters run really low pressure in the rears (like ten psi or something) to maximise the tyres footprint on the ground so they squidge out as you describe. Then as the tyre starts to rotate centrifugal force turns it into a circle again so you see the car climb up at the back. If one side climbs up before the other ("tyre shake") the car can easily go out of control though. It's not really a design feature, it just happens because the tyre has been optimised for maximum grip in that first tenth of a second.

[andyvdg]

I think F1 sidewalls are defined by the regulations. I'm not sure they are allowed to use low profile tyres like the BTCC.

In terms of acceleration / cornering grip I suspect it all depends on how flexible the lateral versus longitudinal movement is.

There was a debate in sprint recently about grip from tyres and tyres pressures etc. which seem to boil down the chemical reaction of the rubber with the road was the most significant factor. Rolling frictional forces (related to the tyre pressure) was relatively small. So the surface area in contact with the road was most important versus the pressure exerted by the car on the road.

I expect someone like GreenV8s to come along and tell us all what's going on

Cheers,

Andy.

[Simonelite501]

The slick tyres used in dry weather straight line drag racing differ from the tyres used in F1 in that they are designed purely for optimum transfer of power in the forward direction. Their sidewalls are significantly thinner and softer, and they are usually run at lower pressures. There are different tyres for each requirement within drag racing, fast, powerful light cars need a different tyre from a steel bodied bracket racer. In general, the heavier car will require a stiffer sidewallrun at around 18psi, Super Gas cars run around 5-7psi, Pro Mod cars run around 5psi, and Top Fuellers run around 3-5psi. The stiffer wall aids reaction and 60ft times, moving the heavier bracket cars more quickly and consistantly. With a heavy car, getting moving is of prime importance. The more flexible tyre walls on Top fuel cars help because they tend to wrap up and cushion the sudden force of aceleration, in addition they have a sling shot effect that although marginally dropping reaction time, reduces elapsed times. The soft sidewall also allows for tyre growth at high rpm providing an artifialy higher gear ratio.The down sides of soft tyre walls and low pressures are, firstly, that the rims tend to spin inside the tyres as the tremendous grip overcomes the BHP,this is why you will often see drag cars tyres bolted to the rims. Second is that the sidewalls only stay ridgid under power and after crossing the finish line cars can become very unstable. Drag racing is one of the most exhilerating forms of motor sport on the planet, its also more technical than most people think, 99% techinlogical know how, 1% horse power, and seeing that a Top Fueller runs about 5500BHP thats alot of Know how

[hertsbiker]

excellent ! thanks chaps. That goes some way to settling a long standing "discussion" with a mate of mine!

C