Time difference between 14" & 15" R specs

tbro · Postby **tbro** » Thu Oct 22, 2009 8:38 pm

Hi all,
Has anyone used 14" R spec tyres and then gone to 15" R specs without any other changes?

I realise that 15" with the lower profile ratio will handle track work better but I'm interested in finding by just how much?

I'm in the position of needing either 2 x 14" Dunlops or spending the extra money and buying 4 x 15" Toyo's or Dunlops,
as next year is going to be first year doing a full series and not having any experience driving other than club days, I'm not sure if spending the extra $800 is really necessary or if I'm better off running what I've got and getting used to the car and racing ( at the back), and spending time learning from others the correct lines etc.

Thanks

Terry

lightyear · Postby **lightyear** » Thu Oct 22, 2009 9:24 pm

I had 185 x 14 yokohama's r spec tyres and went to 205 x 15's r888's. I did go a bit faster with the 15's, it was noticable out of corners where it had more grip. But even after spending about $3,000 on upgrading to 15x8's and nb8b brakes and a retune with another 20kw's. The times only went from 1:57 to a 1:55 at phillip island. Even now after taking more weight out of it and driving a bit better i have only dropped another 2 seconds to 1:53. So it takes a fair bit to make a difference to your lap times. Not just slightly bigger tyres.

tbro · Postby **tbro** » Thu Oct 22, 2009 11:22 pm

Thanks for that info Lightyear.

I think I'll keep my money in my wallet and just get some experience with the car the way it is.

Terry

manga_blue · Postby **manga_blue** » Fri Oct 23, 2009 10:55 am

Good idea. I think I would have been much better off starting on 185r14s. Cheaper, lighter and much less fuss. Going to R-Specs gives you 1 or 2 seconds, much better control and fewer heat problems. Varying the size of the R-Spec only gains you a tenth here or there.

project.r.racing · Postby **project.r.racing** » Sat Oct 24, 2009 4:58 pm

wheel diameter has nothing to performance specs. overall tyre diameter and width is what you need to concern yourself with. and matching that tyre width with the rim width.

14x6 w/ 185/60r14 tyres vs 15x7 w/ 205/50r15 tyres... even though the tyre diameter is increased effecting accelleration, the extra rubber on the track from the wider rubber allows higher speeds thru corners. it's all a balancing act really.

and as above, going for the 14s tyres is most likely the better option. the smaller the tyre, the cheaper it is.