Conti Challenge Z34 Wheel sizes
 

I can see from the IMSA specification document that the Doran Conti Challenge cars are running 275/35R18 tyres.

Can anyone confirm the wheel size and offset are used please

My Z34 build runs to slightly more relaxed regs, BUT I cannot flare the guards and I am interested in Conti-spec wheel size/offset and how much space might be available under front/rear guards.

I am intending to run a 280/655R18 Dunlop slick for dry and 265/650R18 for a wet.

The dry tyre really needs an 11" wheel but am dubious about fitting this under the front guard as I cannot flare the guard (I can roll the lip though). I could come back to 10.5 or even 10 a pinch but that is less than ideal.

RB

I'm 99% sure they are forced to run OEM size in both wheel and tire. Maybe not offset but I know 245/40 and 275/35.

Id just get 10.5. I run +15 square and it's a slight issue that I can't lower ride height but I'm also only at -2.9 camber. It works for me.

Best bet is just to PM BJ and ask. His user name is dwnshift

I don't know the answer either, but I do know that up to 295/40-18 on 18x10+34 fit with proper race camber.

315/30-18 on 18x10 +30 will fit up front

So bad ***.

and fyi they are RPF1's in 18x10.5 +15. only 19lbs. crazy light but not as light as the 17.4lbs fronts i used to run in 9.5".

I have PM'd BJ, but his PM Box is full .... if anyone is local, can they please mention this thread in passing, so he can reply if he has the time.

I have trial fitted an 10.5 x 18 ET15 on the front and they "poke" about 15-20mm which is enough to get a fail at scrutineering ("tech").

At this stage, I am thinking 18 x 10.5 ET30 all round but run a 7mm spacer on the rear. That way, all wheels are identical which only means I need 1 spare rim rather than 2.

I have an 18 x 9 at ET47 in the shed which has the same amount of rim (with 2mm) inboard of the hub that I can use to check clearances on the spindle and suspension arms etc as I run through steering lock and suspension sweep, so we'll see.

Measure twice before ordering I think .... will need two sets of rims pls a spare so cost is "non-trivial".

I have noooo idea what our offset is
We are 275 front and rear (as of Watkins glenn 2014)
I can say this about slicks and side walls... When we ran the Pirellis for what ended up being a test day last year ;(
305 /680/18 killed the acceleration on the car.
If it would have been the old tire that was 305/640/18 it would have been waaay faster.
It killed the car.


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Is why I am sticking with 650/655mm diameter tyres. I can also do a 310/655R18 in Dunlop.

Whilst our local Pirelli Motorsport dealer lists the 305/640R18, he does not import them and requires a special order. Since they are then air-freighted, I get worried about chemical changes in the rubber given that aircraft holds are not heated and the rubber sees -50degC for 20-odd hours between Italy and Australia which cannot be good for it.

RPF1's 10.5 are +15 With a 285/35/18 tire, and about -3.0 or greater camber in front, they clear just fine if that helps. Judging by Doran's specs, with proper camber, +5 or +10 would probably be in there and work fine. My fenders are not rolled, but my front right wheel does sometime catch my fender a little tiny bit and sort of "self rolls it" I think it is more of a ride height issue though. Once the tire tucks inside under compression it's fine.

Any more tire height than that though you better be 400+ whp. I think that is what BJ is getting at. The rolling radius of the rear tires makes a big impact on the acceleration of any car, it needs to match the HP/FD ratio. That's why FI drag cars and all big horsepower cars run really big radius tires.

Remember, I have a sequential box with 1:1 6th gear, with choice of 3.9 or 4.08 FD, so rolling radius is slightly less of an issue, and yes, I am expecting ~480-500hp at the crank (14:1 on E85 with C12/RZ1 profile cams).

I have a set of 18 x 9.5 PF01 at ET35 and run 0.5" spacer in front (effectively ET22), with 1.0" spacer at the rear (effectively ET10) and with 275/35R18 R-Specs, I have 2-3mm of poke at current ride height on -3.0 degrees. This is about all I can get away with at tech, any more poke and I get defected.

If there is sufficient room to extend the inner rim half the full 25mm, then the equivalent in 10.5 wide should be ET35, which is why I'm confused that a 18 x 10.5 ET15 will fit on the front (I'm less concerned at rear fitment).

Here are photo's of trial fitment of 18 x 10.5 ET15 on the front at ride-height (is fitted with 295/30R18 Dunlop DZ03G which is "about" the same size OD as my planned slicks).

To clear tech, I am going to need bodywork changes based on these photo's which is going to bump me out of my planned class and into GT3 territory and I'd like to avoid that because F458GT3, Gallardo GT3 and 997 GT3 are just too bloody fast !!!

I cannot imagine there is any LHD/RHD differences in play, nor the fact that our cars down-under are manufactured in Japan and the US cars in Tennessee, so I am a little confused at present.

Clearly, some more research is required.

I'll get there but is chewing up some time.

Not sure the opffset, but the wheels are square with the rear spaced. Here they are from the A.M. Performance days.

http://www.the370z.com/attachment.ph...1&d=1439757819

i don't know how you would do it, but if you could get them shipped as a live animal, they would keep them in the heated compartment