Question Regarding Wheels and sizes
Discussion
Got an email from a freind and i was wondering if anyone can help with the below questions:
"
I’ve based my track and wheelbase on other similar sportscars and kit cars (i.e. WB= 2350mm, Track= 1470mm for front, rear depends on wheels and tyres).
The problem now is wheel and tyre sizes. The book I have suggests 13” wheels with 8” and 10” widths front and rear respectively but this is for a pure hill climber or sprint, non-road legal.
Looking at other cars again I can see the Caterham CSR uses 15” front and 15” by 10” rear, Westfield Megabusa uses 13” x 7” front and 13” x 8” rear. I’ve seen a busa engined kit car online with 17” rims that looked fine too!
Now I’m lost. The rolling circumference of the tyre is vital too in order to design the suspension. What I need as wheel and tyre sizes that:
Are not specialist sizes i.e. wheels and tyres are readily available
Makes most sense for high torque rear wheel drive car that is more quick than it is fast (~130mph top speed, 400-500kg full)
A range of possible sizes as I’ll also have to look at what torques and speeds each tyre will produce given a gearbox output speed and differential final gearing!
Any chance of asking ur contacts/looking up ur car websites for similar cars?
"
I was wondering if anyone has any input this would be greatly appreciated.
Regards
Rob
"
I’ve based my track and wheelbase on other similar sportscars and kit cars (i.e. WB= 2350mm, Track= 1470mm for front, rear depends on wheels and tyres).
The problem now is wheel and tyre sizes. The book I have suggests 13” wheels with 8” and 10” widths front and rear respectively but this is for a pure hill climber or sprint, non-road legal.
Looking at other cars again I can see the Caterham CSR uses 15” front and 15” by 10” rear, Westfield Megabusa uses 13” x 7” front and 13” x 8” rear. I’ve seen a busa engined kit car online with 17” rims that looked fine too!
Now I’m lost. The rolling circumference of the tyre is vital too in order to design the suspension. What I need as wheel and tyre sizes that:
Are not specialist sizes i.e. wheels and tyres are readily available
Makes most sense for high torque rear wheel drive car that is more quick than it is fast (~130mph top speed, 400-500kg full)
A range of possible sizes as I’ll also have to look at what torques and speeds each tyre will produce given a gearbox output speed and differential final gearing!
Any chance of asking ur contacts/looking up ur car websites for similar cars?
"
I was wondering if anyone has any input this would be greatly appreciated.
Regards
Rob
Not that it will help much, Rob, but do you have any further details of the car he's designing? Is it a 'Seven' type? What will he be using it for?
This is a really complex subject, because lots of factors are inter-related. It's therefore impossible to say that you need a certain wheel/tyre combination without having full details of the car (including weight, spring rates, ARB rates and suspension geometry) and, even then, doing a certain amount of testing to find the optimum.
As a general rule, wheel diameter will be governed by available tyres, gearing requirements and brake sizes, but within those constraints should be kept as small as possible to minimise rotational inertia (18" wheels with rubber-band tyres are pure bling unless you need the brakes from an endurance racer).
Wheel width will be governed by mainly by weight distribution and spring/ARB rates (though, again, tyre availability can be a big factor). The idea is to make each tyre work equally hard; tyres at the heavier end of the car are naturally worked harder, but different spring/arb rates front and rear can be used to make the car 'lean' more heavily on one corner as it goes round a bend, hence working that tyre harder. You might also choose to make the tyres at the driven end of a powerful car larger, to give better traction, in which case other factors might need to be adjusted to bring everything back into balance. Again, the fashion for very wide tyres is often counter-productive (Caterham freely admit that their cars would work better with narrowed rubber, but have to pander to customer preferences, and check out the front tyre width on an S2 Elise is you want to see a car that's been designed to work rather than to look good).
Then there's ride comfort and compliance... low profile tyres give better grip on perfectly smooth surfaces, but taller profiles often work better in practice and give a more progressive breakaway when they do reach the limit of their grip.
Sorry, but this is a really, really complicated 'how long is a piece of string'-type question without knowing a lot more detail.
This is a really complex subject, because lots of factors are inter-related. It's therefore impossible to say that you need a certain wheel/tyre combination without having full details of the car (including weight, spring rates, ARB rates and suspension geometry) and, even then, doing a certain amount of testing to find the optimum.
As a general rule, wheel diameter will be governed by available tyres, gearing requirements and brake sizes, but within those constraints should be kept as small as possible to minimise rotational inertia (18" wheels with rubber-band tyres are pure bling unless you need the brakes from an endurance racer).
Wheel width will be governed by mainly by weight distribution and spring/ARB rates (though, again, tyre availability can be a big factor). The idea is to make each tyre work equally hard; tyres at the heavier end of the car are naturally worked harder, but different spring/arb rates front and rear can be used to make the car 'lean' more heavily on one corner as it goes round a bend, hence working that tyre harder. You might also choose to make the tyres at the driven end of a powerful car larger, to give better traction, in which case other factors might need to be adjusted to bring everything back into balance. Again, the fashion for very wide tyres is often counter-productive (Caterham freely admit that their cars would work better with narrowed rubber, but have to pander to customer preferences, and check out the front tyre width on an S2 Elise is you want to see a car that's been designed to work rather than to look good).
Then there's ride comfort and compliance... low profile tyres give better grip on perfectly smooth surfaces, but taller profiles often work better in practice and give a more progressive breakaway when they do reach the limit of their grip.
Sorry, but this is a really, really complicated 'how long is a piece of string'-type question without knowing a lot more detail.
Gassing Station | Kit Cars | Top of Page | What's New | My Stuff