Replace 15" with 13" wheels?

[jamest]

Hi, I've just bought an R300 which currently has CR500's on 15" wheels. The car is going to be used for road and track although I will probably go for a track biased set up and I've heard that handling balance is much better on 13" wheels. The rear tyres are pretty much finished so I'm wondering whether I'd be better investing in a set of 13" wheels and tyres and then selling the existing ones. What is the accepted wisdom on this? Should i just stick with the 15's or move to 13's? Thanks.

[OJ]

I believe this is a bit of a moot point. I've only ever driven on 13" wheels in Race Cars. The fact that all Caterham race cars use 13" wheels probably answers your question though.

Conventional wisdom suggests that 13" rims would have larger sidewalls and thus be softer and more progressive as a result. I'd imagine putting 15's on would have a similar effect to stiffening the anti roll bars or putting stiffer springs on. The tyres will also be cheaper I'd imagine.

However, I think the 15's look much nicer, so I'd just drive the thing as it comes and leave them on it!

[Tango7]

I'd buy a spare set of 13" track wheels and get track tyres. Keep the 15" for the road and swap over at the track. If you haven't got a trailer to carry the track wheels, you can sort out a tyre rack that fits on the FIA bar and means you can carry 4 wheels with you.

13" tyres are very cheap and there is a plentiful supply usually from the race teams. Pay around £10-15 a tyre

[adamb]

Is there a significant ground clearance problem when running 13in wheels? I also have 15ins on my R400 and was considering swapping to 13's, but already the speed bumps outside my flat have to be taken very slowly to avoid scraping....

[jamest]

Thanks for the replies, I think I'll do as suggested and keep the 15's and buy a set of 13's in the future. Where can I buy the tyre rack from?

[Neal H]

Is it really as simple as just swapping 13" wheels for 15" when you get to the track, or are there other things that will need to be taken into account - what about the geo settings for example?? I would have thought that you would need to make a decision and stick with one or the other.

[Tango7]

James,

Have a word with Dave Morris about the last batch of tyre racks he had made and whether he has any left over. The thread on Blatchat is : http://www.blatchat.com/T.asp?id=145473

Alternatively, there was a very recent post about a more temporary solution which may also be worth hving a look at too : http://www.blatchat.com/T.asp?id=154635

HTH

T

[Tango7]

Neal,

I suppose it depends how serious you are about trackdays? The usual problem I encountered was ground clearance coming off 15" 50 series tyres and going onto 13" ACB10's or slicks with a much lower ground clearance but for track use, this is not really a problem.

With regards geo and the car's set up, inevitably the setup is going to be slightly compromised but this is more than offset by the additional grip and tyre performance you will have from the trackday tyres over the road ones.

Speaking to Jonny Leroux of Bookatrack, I questionned the use of crossply ACB10's and their very neutral/flat position on the road and being used on a road car with a radial setup (X degrees negative camber etc.) and his reaction was that for most trackday users, it would be of neglible detriment and most people wouldn't notice the difference.

Cheers
T

PS Actually there is a big downside I found using slicks : going off Oulton Park circuit to fetch fuel and forgetting I had them on...

[Neal H]

Also, if you are planning to fit 13" wheels so you can run slicks, there is also the expense of needing a dry sump - assuming you don't already have one!

Neal.