305s on 370z 19x10 for now...345s to come. Fronts running 275

 

You can blame the wacky engineers at XXR for the weird sizing.

 

Looks like a G with 370 wheels. ? . ? I assume your 345-wish is with different wheels, as they are too big for the 370 wheel.

 

yeah 5mm in rear. might go 8, but im not 100% sure yet.

Yessir.

 

Alright, I've got the itch to go all out with my autocross setup once my current tires wear out. I'm going for 295F 315R x18 Hoosier A6, and I want the widest contact patch possible (widest wheels). I'm considering a 18x11 +28 front, 18x12 +36 rear. I'd rather overestimate the offset and use spacers to get it perfect. I used some of the setups in this thread and an online calculator to come up with what I think will work. Has anyone tried something similar? I have rolled fenders and will pull them slightly if I have to, but I want to avoid any major fender work for now.

BTW - I'm looking at the Forgestar F14. They're available in 18x10, 18x11, and 18x12, in a wide range of offsets. Similar weight to a RPF1, and less $$ than CCW, etc.

 

^^^

Do it man!

I like the F14s weight and the offsets they come in...dunno but can someone chime in on the qaulity of them compared to Enkeis as a track wheel.

 

With an 11 you will need it at +15 up front to clear the spindle. Easy way to check is off the offset calc , 9.5 +35 clears only by a few MM , 11 +15 has 1mm extra clearance. I would do 10.5 +20 up front if i was having custom made for widest tires.

Rear i would go 11.5 +25 , which is also going on know rear offsets to a close to clearing the inside.

 

I'd go 18x10 +25 front and 18x11 +30 rear and fit those tires under the fender. Your wheel idea isnt going to put all the tire under the fender anyway so why not run those sizes with 305 f 335 r?

The 18x11 +30 inner clearance



The 18x10 +25 inner clearance

 

Worth mentioning....every Forgestar F14 I have ever seen has been over the listed weight. I'd expect an 18x11 to be in the 22-23lb range. That's a good 4lbs heavier than the cheaper 18x10.5" RPF1.

 

Thanks SoCal07HR for the pics and measurements. That is extremely helpful.

I think the magic number for inner clearance on an 11" wheel up front is +16. The wheel would extend outward 1" more than the 18x10 +28(with spacers) RPF1 that has been used with a 305/30 tire. However, the 295/30 tire would be shorter and bulge much less on the 11" rim. Another calculator I used shows the 295 tire on an 11" rim extends 7mm more than the 305 on 10". I think that could be made to fit with only a slight fender pull, if even that.

In the rear, maximum offset for inner clearance of a 12" wheel looks like about +26. According to the calculator, the 315 tire on a 12" wheel will extend 17mm farther than the one in the below pic (315 on 18x10.5 +43). There is some space leftover there, and the rest could be handled by rolling flat and a slight pull. 2 degrees of camber will help too.


I know the safe bet would be a 10/11" stagger, but I don't think I will be satisfied unless I know the envelope has been thoroughly pushed to the limits. I'd probably end up spending money down the road on a wider setup. I've looked all over, and the only Zs I've seen with 11-12+ widths are the hardparking hellaflushers with 90 degrees camber and 225 tires.

 

I'm sure you have more experience than I do, but I based my statement on the weights from this link: http://www.forgestar.com/blog/?p=374. The weights listed are very comparable to advertised RPF1 weights in the same sizes. The 8.5 is actually lighter, and the rest are within 1 pound. I'm a big RPF1 fan, but they don't offer anything over 10.5", and the +15 offset isn't ideal for stuffing maximum rubber.

I talked to a vendor tonight who can get them for $1400 shipped. Wait time is 8-12 weeks, but they only require $700 down at the time the order is placed. I'm close to pulling the trigger.

 

I'm running a 19x11.5 with a 305 in the rear. Not gonna be hard parked at all 19x10 285 up front.

 

Looks like you've done your homework and this is what you want so I say go for it. It is gonna be a tight fit. I will be running the same setup eventually on my 10 and 11 inch staggered setup. good luck, post pics!

 

That's good data (about the 10" +28 with the 305) and a good picture (with data) - wonder where you got it? Glad it could all be useful. . .

Useless info without offsets! ! !

 

Rear:
19x11.5 +18 305/30/19

Front:
19x10 +19 285/30/19

Have Seibon CF front fenders which are +10mm wider than stock. Will be rolling/cutting rear fenders. Looking to run as little camber as ppossible.

 

I don't have any issue with the sizing in the front - even without the wider front fenders. I imagine you may even want to space the fronts out a bit with that front fender.

I am concerned about how you've made the rears fit, as I've had many sets of 10.5" wheels in various offsets rub with a smaller tire - even with rolled fenders and camber. Any pics of how it sits now?

 

In pieces. Going to body shop soon. A lot of changes this winter. Friend is running his Track purpose Z with 305s in the Rear and not running into big issues that I know of.

 

305 even 315 (like the picture above) are no biggie on the rear with the right offset. I was just surprised that your 11.5 +18 would work without some pull. Cheers.

 

If I searched and read correctly, I believe a +22 would have been an almost perfect offset with no more than -1.0 camber. I figured I would be close to -1 to -1.5.

What are your thoughts on this?