Wheel rim widths.

[RICHARD.T]

In Classic F3 we mostly run 8" front rims as that is what was used in period, but the rules now allow 8.5".
How much of an advantage (if any) would it be to use the wider rims?
Obviously the tyres have to be the same width.
Using split rims, it would not be that dificult to increas the rims to 8.5".

[SidewaysFeltham]

By changing the effective centres of the suspension verticals (either way), you are altering the carefully calculated design dynamics, unless the offset is identical to the original and any extra width is equally divided, left and right.

Fitting a tyre on an over-sized rim means that the walls are tensed outwards and you would be compromising the small adhesion patch and encouraging tread shuffle.

Rather than creating any advantage, it would normally promote disadvantage with the same width of tyre, unless you can source a specially manufactured tyre to suit the extra width.

I didn't realise how critical and interlinked steering and suspension geometry and tyres were until Jo Marquart kindly gave me some heavy advice about my car which he had designed!

(I was using, according to Jo, the "Wrong" tyres!)

[RICHARD.T]

Thanks sideways.
I have e mailed Julian Baldwin, of Avon Tyres, to see what rim size the tyres should be on in the first place and see his opinion, especially as he sometimes races his CF3 car.
Also, I was also going to ask if there was an advantage in the wet by increasing the track by about 1", by mooving the rim outers from the inside if the rim centres to the outside thus widening by half an inch each side. A wider track would give some advantages in the wet whilst the extra drag in the wet would not be a problem.

[SidewaysFeltham]

The critical thing is to (a) Promote the best grip (Obvious, I know!) which normally means super-sticky compound which doesn't overheat so quickly because of the far lower temps plus cooling effect of the rain and (b) Superior "Squeegee Effect to avoid aquaplaning.

In fact, we always used to use narrower tyres in the wet!

Moving the rim outers would again change the relative position of the critical contact patch to suspension upright dynamic, which may well adversely affect the geometry.

Seek the tyre co's advice throughout, but also seek the advice of other competitors racing the same chassis.