Wheel sizes -- pros and cons

[alga]

What are the pros and cons of different wheel sizes? I know for a fact that smaller wheels with higher tyre sidewalls are lighter (my daily Civic's winter stamped steel wheels with 175/70R13 tyres weigh 9 kg each, whereas my summer 195/50R15 alloys weigh about 16 kg each!) Is that why Caterham uses 13" wheels? What are the benefits of bigger rims with lower tyres (except for looks)? As for cons, obviously they make the ride harsher.

On a related note, what about tyre widths? What does extra width give? School physics suggests that the friction is proportional to the force, so when the contact patch gets bigger, the pressure on it decreases, and the friction stays the same. This simple model misses something, as wider tyres usually have more grip. Any ideas?

What do you think are ideal wheel size and tyre width for a sevenesque roadster?

Ideal wheel and tyre sizes are those that Caterham use but the Roadster can't wear 13" alloy rims due to the rear upright. Not sure if steel wheels will fit either.

[flyerncle]

195/55/15 seem popular as they fit under standard arches and are similar in size to sierra wheels for the speedo ratio.

[alga]

Speaking of Caterham, according to their sales materials they use:

• the standard Sierra tyre size 185/70R14 on the more pedestrian Classic and Roadsport models (100, 125, 150 bhp)
• 195/45R15 (smaller diameter!) on Superlight, R300 and R400 (175 and 210 bhp), and the factory built (EU-type-approved?) CSR (260bhp)
• 6Jx13 fronts, 8Jx13 backs (tyres 175/55R13 and 205/55R13 according to some forums) on the race-focused Academy (125 bhp) and Superlight R500 (263 bhp) models. Apparently these are used with slicks.

But why? What are the tradeoffs?

Alga,

I have put 15" wheels on my T25 camper(standard wheel size is 14"), I worked out the rolling radius based on tyre sizes etc as didn't want to alter the gearing or affect the speedo BUT for some reason even though there is only a few mm difference in the sizes my camper now sits 25mm lower.
I was then expecting the old fella to rev out after seeing how much it had been lowered as obviously it must have changed the gearing way too much......but no, if anything it's better now as pulls away easier and flies up to a staggering 60mph and settles down rather than sat screaming it's head off...........


So Mr Alga maybe it's just fashionable to have low profile fat tyres....I really don't know

[3GE Components]

The 13" rims on a Caterham is down to the choice of tyres available, in 13" you have a vast range of tyres, from high performance road through to slicks for motorsport use.

Kind regards

John