I have been autocrossing on Kumho 710s, size 205 50 15 on 15 x 6 wheels. I would like to switch to a 225 45 15 (Hoosier is the only autocross tire I have found in this size). What width rim should I run? Any other comments about the different set-ups, fitment issues, performance, etc.?

Any and all comments would be appreciated.

Len

 

I would recommend an 7.5-8" width... Hoosier probably recommends a 7-8.5" rim. I would shoot for a +40 offset, otherwise you may run into some rubbing on the outside (easy to fix with a Dremel!).

With an O.D. of about 22.9", I think you're going to have a LOT of fun on 225/45R15's... IIRC, I think Toyo makes the RA-1 in the same size (albeit a 2nd tier R-comp, great for track days but not the "best" for competitive AX).

 

Len,

If you keep the 15x6 rim it would work best with 205/50-15 tires.

What class do you autocross in?

If on a budget, I'd suggest keeping the 15x6" rim and keeping 205/50-15 in either Kumho V710 or Hoosier A6. How did you like the V710 and how long did they last for? Which 15x6 rim are you using?

Non stock classes allow any rim so a light weight 15x7 or even 15x8 rim would work better with 225/45-15 tires (Hoosier A6 or Avon Tech Ra). For 15x7 rim about +38mm offset will work and for 15x8 rim +36mm offset.

It is possible to fit wider tires on narrow rims or narrow tires on wider rims but it is not recommended for best results. 205/50-15 take rims 7-9" wide while 225/45-15 tires fit rims 7-9" wide.

There are two approaches to tires. Go light and sticky like 205/50-15 in V710 or Hoosier A6 or go wide and sticky like 225/45-15 in Hoosier A6.
To make best use of any tire you'll need enough front negative camber about -2 degrees or more (front camber plates if legal in your class).

Another approach is to go with a larger rim like 16x7 or wider and 205/45-16 in Hoosier A6.

 

Thanks for the responses guys.

Minihune - I appreciate your response here and in my LSD/Clutch/Flywheel thread. I run SM and have a pretty good amount of the standard drivetrain and suspension mods (My MCS is a 15% + 2% car, GIAC, Alta intake, UUC exhaust, short-shifter, H-Sport springs, adjustable lower control arms, and IE fixed camber plates).

I was mistaken about rim width, realized it shortly after posting - the rim is an inexpensive Flik Wasp in 15x6.5 weighing 12lbs.

I am a pretty competitive person and have had some good results and some just OK results. I got a FTD in one event last year on a tiny course, and won SM class in each of the events I was able to do in my local region (Chattanooga) in 2006. A couple of guys in my region have upped the ante in SM and in the first two events of 2007 I have been beaten. In some relatively nearby regions (Atlanta and East Tennessee/Knoxville) I do OK overall, but rarely a trophy position in SM. Two of the strong Atlanta SM cars are early MCS cars with Quaifes installed, running (you guessed it) on 225 45 15 Hoosiers.

I do all of these events with my 12 year old son, and while we do them for fun, its fun to do well. I'm looking for those little things that can help in that regard.

Len

 

Len,

Ok that info helps. 15x6.5 isn't the best choice for 225/45-15. If you want to be correct then 205/50-15 is best for that rim and either Hoosier A6 or Kumho V710 will work. Hoosiers are pricey and don't last so you'd have to take care of them. Next time you see some try touching the rubber tread, it's soft like hard eraser rubber when new. Kumho V710 don't cost nearly as much and are about 1/3rd longer wearing and are slightly heavier in the same size and not in 225/45-15.

To make use of 225/45-15 you really need 15x7 or up to 15x9. 15x7 are easier to find and Kosei K1 TS is about 12.6 pounds each. The 949racing 15x8 are 13.1 pounds or so for similar prices.

Using the stock shocks and H-sport springs means ride height is non adjustable and your front fixed plates have locked you into -2 camber so rears could be adjusted to -1 to -1.2 degrees if you want.
Your competitors will have fully adjustable shocks with adjustable and lower ride heights. Be aware that after about one year your stock shocks will likely be worn out when using H-sport lowering springs. Koni Yellows are a good replacement if needed and coilovers are not being considered.

With a light 15x7 rim (+38 to +40mm offset) you can choose from 205/50-15 or 225/45-15. Once you go 15x8 you should use 225/45-15. 225/50-15 will also fit but has a larger tire diameter and heavier weight which is not so good for autocross.

If you work backwards you'd be better off choosing the tire first with 225/45-15 being highest on the list then choose a rim that is wide as possible and light. Tirerack.com probably has the best selection in that respect. Talk to Alex@tirerack.com for more info.

Other size tires are also possible in 16" and 17" but compared to 225/45-15 few will be wider and lighter with a minimal outer tire diameter which helps with lowered gearing.

Comparing upgraded tires and wheels with LSD, clutch and flywheel for me the tires and wheels make more difference and are relatively durable albeit they have a finite life.

 

Thanks Minihune - and one more edit to my posts above. The wheels are Flik Fuels, not Wasps. The Wasps are my 17" street wheels.

Len