18's Vs 19's - Thick Or Thin

[Bourbon Boy]

Just took off my Axis 19" shoes and put back the stock 18" originals.

I drive everyday and I can't affiord to keep replacing pinctured tyres before a track day... My intentions are to make these 19" rims dedicated track rims.

Originally I was going to use the originals as track rims but I think they're too thin (8 wide - currently wearing 235s all around)... but I could be wrong. Let me know.

My question is what are the Pros and Cons if I run:

- 19" x 8.5-9" (F) and 19" x 10" ® OR sell these to get

- 18" x 8.5-9" (F) and 18" x 10" ® OR

- My stocky rims

Obviously Cost is a factor and also looks wise (for me) would be the 19"s but what else? Trackwise\Performance-wise??

I know there are some smart engineers in here that like to talk physics, so if it helps throw it in there.

Edited January 19, 2011 by Bourbon Boy

[djr81]

The smaller diameter track tyres will be cheaper - quite a bit cheaper. Also 19's have somewhat limited availability due to fewer people running them. First step is to figure out what tyre you want (eg Bridgestone RE55, Toyoa RA1 Yokohama etc etc) then find out if you can get them in the size you want then find out how much they are.

From a performance point of view the rim diameter is down the bottom of things to worry about.

[R31Nismoid]

In terms of performance - any gains, and i mean if any, are not really justified when you think about the pricing difference.

Unless you are running an dedicated track car, just get 17s or 18s and put semi's on those.

19s are just far too pricey

[numleg]

18s in the same widths as the 19s would make better track rims in my opinion.

Smaller rim = lower rotational mass and unsprung weight = faster

Also keep in mind that your tire wall does actually form part of your cars suspension. Have a look at pretty much any well developed race car, they will all have a decent profile tyre.

You may even be able to run a slightly oversize tyre on the rear, I've run 245s on 8 inch rims without problems you just need something with a nice stiff side wall.

I would be keeping the 19s for street use and looking for a pair of wider rear 18inch rims + 18 stock wheel on the front with some semi-slicks.

Hope that helps.

[djr81]

18s in the same widths as the 19s would make better track rims in my opinion.

Smaller rim = lower rotational mass and unsprung weight = faster

Actually the tyre as often as not weighs the same or more than the rim it attaches to. So the unsprung weight differential betwwen say a 17" & an 18" rim (assuming they are good rims not chrome rubbish) is minimal. As an example a rim + tyre is of the order of 20kg in a 50kg corner.

You may even be able to run a slightly oversize tyre on the rear, I've run 245s on 8 inch rims without problems you just need something with a nice stiff side wall.

I would be keeping the 19s for street use and looking for a pair of wider rear 18inch rims + 18 stock wheel on the front with some semi-slicks.

More tyre width equals more grip (generally). So a fatter tyre on the rear will promote understeer. Which is pretty much what Skylines do anyway. I would strongly recommend the same size tyre on both ends as it will help the balance and allow them to be rotated to even the wear out a little.