Warrtalon

iTrader: (6)

Wasn't sure how to name the thread, but this is what I'm looking to discuss and is why I didn't include it in the large wheel/tire fitment thread...

My current setup is already chronicled in this thread: The Official Wide Tire Thread.
Year/Make/Model: 2005 GG MR
Wheels: 18X9.5 Enkei NT03+M +40 w/25mm spacers up front, no rear spacers
Tires: 285/30-18 Kumho Ecsta V710 (DOT slicks)
Suspension: Vishnu/Gerrard Ohlins
Alignment: -3.0f/-1.5r 1/16th toe-out front & 0 toe rear
Fenders Rolled or Cut: Heavy rolling front / minor rolling rear

I have two sets of old Kumho Ecsta V710 DOT Slicks, but I probably shouldn't use them due to age and being exposed to the elements (freezing/snow). In looking to purchase new slicks, I want to switch to Hoosier A6/A7 or Hankook Z214 C91. Here is where the problems arise:

• There's no problem getting 285/30-18 Hoosier A6s. This is probably the safe choice. It's also the most expensive choice, and I'm not sure if there would be a difference in ACTUAL size between the V710 and A6 that would cause any clearance issues. I'm hoping there wouldn't be.
• The Hankooks only come in 275/35-18 as far as I can tell (not 285/30-18), and I don't think 275/35 fits with my setup. I don't have a set to try and am not sure how to know/be sure/measure. If I could do the 275s, it would save me another .3 HP/WT points, thus allowing me to crank up the power a little bit.
• The Hoosier A7s only come in a max 245/35-18. I'm pretty sure that would fit/clear, but they are of course much smaller than my 285s. However, I gain .7 HP/WT points, so I can essentially go with max power/boost/tune at my lowest possible weight while having the new Hoosier rubber. Would 245 be stretched too much on a 9.5" rim? Would the lesser width combined with more power be a slower combo? I know some of these are impossible to know for sure.
• The more drastic change would be to get an entirely new set of race rims (and spacers) that have the necessary offset for running a 275/35-18 DOT Slick. I am not sure how to figure out the right one, though.

Any technical guidance on how to figure out the fitments would be helpful.

Separately, I'm interested in your opinions on what you might do or what you might recommend in this situation.

heel2toe

iTrader: (41)

While I can't answer all of your questions I have a couple comments and questions for you...first of all what type of racing will you be competing in? Are you solely looking to do NASA TT? How long are you looking for the tires to last?

There is a good discussion down in the motorsports section, I forget the title but it talks about optimum tread width, whp, weight, aero etc for a given setup. Think it might be worth checking out.

A 245 on a 9.5" rim will not be too stretched. I believe most of the STU guys are leveraging a 9.5" rim running 245's. I'm not sure how wide the new A7's run but typically the Hoosiers run a little wider than street rubber so keep that in mind as well.

Your wheels should be fine but I'm curious as to how you don't need any spacers in the rear? How is the rim not hitting your trailing arms?

Also, have you considered the BFG R1/ R1S to add to your list of possible tires?

At the end of the day there isnt a one size fits all solution. There are so many different variables to take into account and I think it would be nice to know where your car stands today? What is its current weight and is that HP figure current? Its a dyno dynamics so it'll read higher than a dynojet and that figure was also at elevation so I'd imagine its significantly higher than it appears.

Warrtalon

iTrader: (6)

Yes, NASA TT only and for short bursts, not long, extended sessions (or at least no expectation to maintain peak performance over the course of many laps). I don't have a specific amount of time I'd like them to last. If I can use the tires until they cord, that would be nice. I don't expect my tire choice to last a long time, though.

My rear rims have a different offset, but I failed to list it previously. From memory, I think the rear offset is +25.

I have considered the BFG. I would only use the R1S, but I am favoring the Hankook C91 currently (or the Hoosier A7 if they'd come out with larger sizes).

I'll know the new power numbers this week after getting the tunes/maps at sea level. I am expecting as high as 400whp a Mustang Dyno (440 for the NASA calculation), which would put me in TT1 at a min comp weight of 3275. Therefore, I plan to have a TT2 map that is capped at 375whp on the Mustang Dyno (412.5 for NASA) with a min comp weight of 3301.

That being said, if I went with the 245 A7s, I'd be able to run my max power and lowest rate and still be in TT2, but I'd be pushing smaller tires with more power.