Rim/tire size choice for track

[fuscobal]

I am now running 225/45/17 on standard 7.5'' GTI rims wich was a much better setup for track than my first 235/35/19 Goodyear F1 Asymmetric street tires. However, in about 2 weeks I'll be installing 6POT 362x32mm AP Racing brakes wich will require 18'' wheels. As I'm gonna buy these anyway, I was thinking of going 8.5'' (instead of 8'') wich will allow me to run 235 and 245 tires as recommended by Toyo, Kumho...for semislicks.

The data to take into account for this choice will be :

1) 370HP/475NM
2) 1450-1500Kg including driver & gas
3) TT arms in front wich throw the wheels about 7-8mm out of the wheel arch with 235/35/19 on 8.5'' rims
4) 245 tires may cause rub on the rear

Tire sizes/recommendations from different manufacturers :


Tire size > Overall diameter > Overall width > Tread witdh > Optimum rim width > Rim width limits > Sidewall height (given by tyre calculators) > Difference in diameter from stock tire (recommended <3%)

Kumho V70a

225/45/17 > 628 > 224 > 207 > 7.5'' > 7'' - 8.5'' > 101.09mm > 0% (stock size)
225/40/18 > 631 > 229 > 212 > 8''    > 7.5'' - 9'' > 89.92mm   > 0.44%
245/35/18 > 624 > 251 > 234 > 8.5'' > 8'' - 9''    > 85.60 mm  > 0.89%

Toyo R888

225/45/17 > 635 > 231 > ? > 7.5'' > 7'' - 8.5'' > 101.09mm > 0% (stock size)
225/40/18 > 637 > 224 > ? > 8''    > 7.5'' - 9'' > 89.92mm   > 0.44%
235/40/18 > 648 > 244 > ? > 8.5'' > 8'' - 9.5'' > 93.98mm   > 1.70%
245/40/18 > 653 > 249 > ? > 8.5'' > 8'' - 9.5'' > 97.79mm   > 2.88%

Yokohama A048

225/45/17 > 632 > 226 > 223 > 7.5'' > 7'' - 8.5'' > 101.09mm> 0% (stock size)
225/40/18 > 635 > 231 > 216 > 8''    > 7.5'' - 9'' > 89.92mm  > 0.44%
235/40/18 > 645 > 244 > 226 > 8.5'' > 8'' - 9.5'' > 93.98mm  > 1.70%


Dunlop Direzza 03g is too expensive and I can find no sizes on the internet. As you can see, for 235 &245 tires, the optimum rim would be 8.5'' and the minimum 8''. As I said on point 3), my 235 tires on 8.5'' rims stick out of the wheel arch about 8mm due to the TT arms so running 235&245 tires with 8.5'' rim will require new wings (Kerscher wings are about 20-25mm wider so they give plenty of clearance for these tires). As the price of the 8'' vs 8.5'' rims will be the same (TD 1.2 pro race) and the 225 vs 235/245 tire will also be similar, the only added cost will be the Kerscher wings at 650 Euros + painting (another 200 Euros). The final question is if the added grip of 235/245 tires over 225 deserve the extra money for the new wings. Aslo, I would like to have enough sidewall to properly help the suspension over bumps (245/35/18 seem to lack sidewall here) but not too much to avoid flex (245/40/18 has the biggest sidewall but still smaller than 225/45/17)

PS : As you can see, for the same size, there are great variations in overall width and tread width between various manufacturers !

Hopefully you'll have the patience to follow this topic and will also help you guys in the future choosing tires/rims for our mk5 chassis !

[tony_danza]

225 track tyres are wider than 225 road tyres. Odd I know, but they are more like 240mm due to them being more square and having re-inforced shoulders.

I ran 235/40/18 on 8" ET48 rims. They rubbed on the arches under compression, but didn't poke out and didn't touch anything on lock. It was worth the rubbing for the grip. I thought these were ideal and it wasn't necessary to go any bigger.

Too much grip = less fun. You need a bit of slip.

[fuscobal]

Thanks for your input Tony. Please also vote in the poll. I was also thinking about 235/40/18 on 8x18'' TD 1.2 . It's weird you get poke as I don get it with 235/35/19 street tires on 8.5'' rims. My 225/45/17 V70a have 224 overall width and 207 tread width (as said in the table above) so they are not wider than street tires) !

[the bruce]

Did you still make any decision?

[fuscobal]

235/40/18 on 8x18'' TD 1.2 . This is the best I can think of that will increase traction/corner grip while avoiding fender/damper rub !

[the bruce]

 

ET?

[fuscobal]

45 !

[fuscobal]

Rims are here > TD 1.2 Pro Race in 8x18'', ET45 > the rim has 9.4Kg



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As the tires will be 235/40/18, I am now in the search for a good semislick. Kumho rule out as they don't do the V70A on that size, so I have several options :

1) Dunlop Direzza
2) Toyo R888
3) Yokohama A048
4) Michelin Pilot cup
5) Pirelli Trofeo
6) Nitto NT01
7) Others that don't come to mind now

What would be your recommendation knowing the car will have 1500Kg including driver (maybe some semis are better than others by just being lighter or having a stiffer sidewall). I do not really care about performance on wet or noise but do care about price and wear !

[the bruce]

Direzza 03G and Yoko 048 are pretty stiff.

[fuscobal]

For the moment, I only have prices for Toyo and Michelin and these will both be around 1000 Euros (normally the Michelins should be more expensive than Toyos but can get them for the same price). From what I know, Direzzas are probably the most expensive at about 1500-1800Euros/set so I wander how much better can they be to deserve such a high price. Don't have any price for the Yokohamas yet but heard many guys saying the rubber looses grip with each track day so their performance is inconsistent. Also, some say Toyo have a soft sidewall and don''t know if they are ok for my heavy car (also what compound would be best for me, hard or medium, knowing they should work well at 10-30deg celsius ?)

[the bruce]

http://www.goodtires.de/Sommerreifen/S2354018YMI228158/MICHELIN-PILOT-SPORT-CUP-MFS-235-40-R18-91Y.html

[fuscobal]

Thanks, about the same price I will get them ! Now, the main choice stands between R888, Cup and Direzza with Direzza being the most expensive by far and the other 2 about the same !

[Chalkie]

I run 18 x 8.5 with a 255/35/18 R888 or 255/35/18 Yokohama AD08, the wheels rub very slighy but only when I got a passenger in the back and I giving it beans...
arches have been rolled slighty...

[Chalkie]

I do not really care about performance on wet or noise but do care about price and wear !

I've found that Yokohama AD08's last almost 3 times as long as r888's and once youve got heat into the yoko's they are almost as  good as the 888's

[fuscobal]

Chalkie, what suspension have you got ? Any pics with the fenders/wheels ?