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15" to 13" wheel size switch?
kurt - 20/10/07 at 05:37 PM

Which 13" tyre size will give me the same diameter as a 195/50 15 that I'm running now. I'm thinking of switching to 13" wheels and don't want to wreck my speedo calibration.

athoirs - 20/10/07 at 05:54 PM

Well how did it go Kurt???

I have 13" wheels on my Indy. If you have a speedohealer then re cal using that. Much better than compromising your choice of rubber, which I would stick out my neck and say is one of the most important things on your car

mangogrooveworkshop - 20/10/07 at 06:00 PM

i back you up on that one andy

stevebubs - 20/10/07 at 06:32 PM

This may help...

britishtrident - 20/10/07 at 06:38 PM

Seven look a lot better on 13" wheels

kurt - 20/10/07 at 06:49 PM

Never a truer word was spoken Andy! On my third session, my fuel tank breather spilled out fuel and I suspect onto my tyres causing me to spin and have a shunt with the armaco. Luckily it was low speed and only smashed my nosecone. Having no trailer, I gaffer taped it back together and drove it home since there was no chassis, suspension or steering damage. Lucky escape really. All the sevens were runnign 13" wheels with Toyo Proxes R888s so I fancy getting a set for track days. A crash ain't gonna stop me!!!!

athoirs - 20/10/07 at 07:57 PM

Dohhhhh.

I have had (along with loads of others I suspect) the same problem with fuel leaks. something like this is required;

http://www.merlinmotorsport.co.uk/FUEL-SYSTEMS-Tank-Breather-Valve/c26_215/p3555/BREATHER-VALVE-1/4-IN-LINE/product_info.html?osCsid=7765673068dec5712

This one is a bit expensive but it is two way. there are some cheaper ones on e-bay which are one way.

If your are going for new 13" wheels go for the compomotive CXrs they are light, do any offset and colour you want!

Andy

hobbsy - 20/10/07 at 10:51 PM

I don't know why everyone raves about the CXR's in 13x6 they are the same weight as an OZ Superleggera in 15x7 (just under 5Kg)

If only they made a 13" Superleggera!

gazza285 - 21/10/07 at 12:36 AM

Perhaps it's because the tyres that you use are much lighter on 13"s.

kurt - 21/10/07 at 07:32 AM

Thanks for the advice. My Dad is into building model steam engines and I'm sure he's talked about non-return valves he has turned up on his lathe, so hopefully it will soon be sorted.

Cheers, Kurt

hobbsy - 21/10/07 at 11:56 AM

quote:
Originally posted by gazza285
Perhaps it's because the tyres that you use are much lighter on 13"s.


Not sure if thats a reply to my post but if it is I was talking about just the wheel weights with no tyres.

IIRC the only big advantage you get with 13" CXR's is that you can fit ACB10 or other lightweight tyres. If you're fitting A048's or R888's I bet they aren't that much lighter as a complete package than my 15's Ultraleggeras with R888's (about 15Kg, 5Kg is wheel 10Kg is tyre!)

That said I've got some CXR's in 13x6 and with 185/50-13 ACB10's they weigh approx 10Kg all in but those tyres are also physically a LOT smaller than 195/50-15's so you'd expect a lower weight (5kg vs 10kg) anyway but its their crossply rather than radial construction that saves most the weight.

10kg vs 15kg a corner (and rotational and sprung weight) is well worth having. 20Kg in total off your car!

I'd be interested to know what a 13" CXR wheel with an A048 or R888 weighs

EDIT: Also handling advantage with 13" with more sidewall, more compliance arguably a smoother break away etc.

I'm not saying I don't like 13's its just that everyone goes on about CXR's for being mega light and they aren't really. They are probably quite strong though so useful for the sometimes rough racing in RGB etc!

I wish I hadn't sold my Mike Barnby R500 magnesium split rims, about 3.7Kg's each!

[Edited on 21/10/07 by hobbsy]

Schrodinger - 22/10/07 at 03:49 PM

quote:
Originally posted by athoirs
Dohhhhh.

I have had (along with loads of others I suspect) the same problem with fuel leaks. something like this is required;

http://www.merlinmotorsport.co.uk/FUEL-SYSTEMS-Tank-Breather-Valve/c26_215/p3555/BREATHER-VALVE-1/4-IN-LINE/product_info.html?osCsid=7765673068dec5712

This one is a bit expensive but it is two way. there are some cheaper ones on e-bay which are one way.

If your are going for new 13" wheels go for the compomotive CXrs they are light, do any offset and colour you want!

Andy


I'm not too sure about one way as they have to stop fuel escaping but allow air in and out.