I have often pondered why modern performance cars have very low profile tyres fitted, when F1 cars have balloon tyres in comparison. I'd have thought if very low profiles offered even a slight advantage in roadholding, the F1 boys would fit them, or is it a rules thing? Perhaps I've missed the blindingly obvious. Any thoughts/ knowledge on this gratefully recieved.
Regards
Mike
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the original rationale and reasoning behind low profile tyres was that the tyre itself should take up a smaller percentage of the wheel diameter...
the thing that is so good about this is that it allows more space for bigger brakes, and in essential terms the wider you can make the brake disk etc, the better you can make the braking
now on road cars today there are ofen low profile tyres fitted, while the car itself has similar brakes to the less well speced cars in the same range..., with tyres that arnt quite so low profile, in these cases its just a better designed tyre youre getting
Are F1 brakes on the axle and not out at the wheel nowadays, carnt remember, i'll have a look and a think...
etc...
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I think you'll find F1 brakes are in the 'conventional' location.
Regards
john
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F1 use cross-ply tyres and are probably restriced in wheel diameter.
Modern (unconstrained) low-profile radial designs are aiming for ultimate roadholding, handling and braking (often at the expense of comfort/ride quality). Hence the large diameters to accommodate larger brakes and low profiles to reduce tyre slip angles.
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John is right, lower profile tyres do generate the same cornering force at lower slip angles. This makes the steering feel quicker. However, it is not neccessarily the case that lower profile tyres will provide higher maximum cornering forces. Lower profile tyres will approach maximum cornering force more progressively with increasing slip angle than a higher profile tyre of identical rolling radius. I have found that fitting 15" wheels as opposed to the 14" wheels the car had on it when i bought it has inproved the handling significantly. I think is due to the contact patch deforming less under hard cornering. The overall roll is less with 15" wheels.
However, fitting excessively large wheels suh as 17" ones on a mk.2 golf can ruin the handling and road holding, particularly in the wet. Additionaly the ride is terrible. This is because the suspension is not up to the job. Lower profile tyres require better suspension, as they are more responsive to camber and caster changes. That is why touring cars with there very limited ssupension travel and modifed suspension can run such wide low profile tyres, coupled with the fact that they run very low tyre pressures.
I do think some of the huge wheels i see new cars wearing are just fashion items. What surprises me most on new cars, and "modified cars" is what i think to be excessively wide tyres. I would think that the area of the contact patch would be related to the corner weight divided by the tyre pressure? Would anyone like to offer any other ideas? Wider tyres to me just means a shorter contact patch and less steering feel? I dont think tyres need to be wide for a car to have good handling and road holding, just look at the old Lotus Elan, it had bike tyres compared with some of todays "hot" hatches and sports models.
Ben
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Ben
Fitting very wide, low profile tyres does as you say result in a wide, short contact patch. This can lead to the problem in wet conditions you mentioned - the contact patch length on any tyre reduces in wet weather as the water builds up a wedge under the tyre. This effect is means that the wider tyres will aquaplane much sooner than the narrower tyres. I've seen road tests refer to this problem in some cars. You'll notice that rally cars use narrower tyres in wet, slippery conditions.
Regards
john
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Oh how I wish we could get away from the obsessive passion for speed and performance. You know the sort of thing - Top Gear twerps throwing cars all over the place and trying to convince ordinary people that's how they should be.
Please, motor manufacturers - give us back our comfort! Responses to my earlier thread suggest that a lot of you prefer (or at least fondly remember) cars that were comfortable. Low profile tyres may improve grip, handling, chuckability, image etc. but it is at the expense of comfort.
I'm a long time Citroen owner because of their capability of designing a car that will not shake my fillings out (or at least what's left of them at my age), but why did thay have to fit 15 inch low profile tyres to the Xantia HDi? My previous 94 TD had 14 inch "normal" profile tyres and the ride was superior (the handling was OK too, by my standards).
Grand Prix tyres belong on Grand Prix cars, and Grand Prix cars belong on a race track!
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I think it may be a rules thing, as for really low profile you should look at the sports racing machinery.
Although, the F1 car has very uncompliant suspension, to maintain ride height, and about half of the springing is in the tyres.
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Funnily enough, Stirling Moss is heavily against low profile tyres on road cars. They ruin the ride quality, are hopeless on road humps, lead to destroyed alloy wheels at the smallest pot hole and cost a fortune. Their only possible justification is to allow a bigger diameter wheel and hence a bigger diameter brake disc, but since brake disc composition will soon change anyway (ceramic or carbon fibre composites), even this is irrelevant. And, of course, if the roads get any worse, we'll all end up having to drive 4x4s or big tyred 2x4s anyway.
HJ
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Thanks to you all. i'd for gotten about the brake diameter, so thats probably one of the main reasons.
Cheers
Mike
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