rx7tt95

I managed to make it into the shop today to check on the status of the car and see if the 18x9.5" (45mm offset) Volk SE37A's would fit up front. As many may recall, I had 8.5's on the front, 9.5's on the rear. I would have preferred the 9.5's all around for obvious reasons, and with the car in the body shop, I felt it was the ideal time to make such a change.

There's nothing but good news. The 9.5's WILL fit in front, WITHOUT rolling the fender lip! If you have stock suspension, there may be a chance that the inside of the tire/wheel will contact the stock spring assembly. It seems that all the extra width was put on the INSIDE of the wheel (backspace?) not the outside. So...with 2.5" coil-overs going in, I will be fine. And that's with a 265/35/18 (Kumho) installed. A 285, if it's about the same OD, would fit as well. So theoretically, I can run 285's all around.

The rear fenders are being rolled and to be honest, it doesn't appear that there is anything to roll in the front. A friend did roll what little material was there on his car, but for now, I'll leave the fronts alone. I may, as Manny pointed out, remove the two fender lining screws just in case. I'll see how everything works with the car lowered a bit (.8" in front, 1.1" in rear, prelim, until the car is corner weighted).

But...thought you all might be interested in this info. Also, you "could" put a 5mm spacer in there and there would still be room. Might be a good setup with the stock suspension.

RISHIE! Check your hotmail account and your PM ASAP! Need to order two rims!

dclin

iTrader: (4)

That is so wierd - I had the urge myself this evening to stick my 18X10s +44 285/30/18s on front just for grins and they barely stick out past the fender. I reached back there with the suspension settled, and there was about 2 finger widths clearance - stock diameter springs up front. Of course, when the suspension compresses, the wheel tilts inward so not sure how it would work in the real world, hehe.

Anyways - Hmmm, can you say R-Magic wide front fenders?



Careful about putting 285/30s on 9.5in width wheels. Most tire manufacturers recommend a minimum size of 10in width for their 285/30s, including the Kuhmo Ecsta V700 that are slated for my track wheels.

Have fun with your new combo!

SleepR1

I still don't recommend this setup for real world use. If you plan to show the car (trailered to and from the show), then ok, but if you plan track it...I dunno, you might end up back at the body shop for front fender lip repair...my nickel's worth of opinion

rx7tt95

dclin-Yeah that looks to be a bit tight to say the least...the 9.5's give plenty of clearance of the outer fender. It could actually stand to be pushed out a few mm's. A +40 might be perfect with the stock suspension. I'll make sure to give a full report on the street manners of this setup. For now I'll stick to the 265's, although the Kumho 712's in a 275/18/30 look like they'd be closer to the stock rotating diameter.
Michel

GsrSol

So I guess it looks like my 17x9 +44mm offset will fit upfront.

Great news

ARD T2

iTrader: (22)

GSR, that will fit beautifully. I would suggest a 245/40/17 front and rear.

Rishie

red 7

hi guys, what about any of these sizes for the front. i have 2.5 inch i.d. eibach ers springs

18x9 +55
18x9.5 +50
18x9.5 +37 ??

thanks for any response
keep us updated on your volks rx7tt95

ARD T2

iTrader: (22)

Well from pure math, the +55 9's and the +50 9.5ers should work fine according to tt95's info with his stocker springs.

Rishie

SleepR1

No Text

SleepR1

With your suspsension setup, you could go 9.5 x 18 with 55 mm offsets with 265/35-18s with no clearance problems. For best results, raise the ride height at the left-front corner a bit.

msv

I've been running 18x10 at all 4 corners with 285/30-18's for quite some time. 53mm offset front and rear.

Mark
http://www.geocities.com/valspeed/

SleepR1

Public road or track setup?

Stock style springs or 2.5-inch skinny race springs?

Care to elaborate on the wheel and tire choice?

SleepR1

I bought a set of your R1 shocks a couple of years ago. Still have them, and they're performing very well with H&R springs.

Is the CWC big brake kit for fr/rr your creation?

rx7tt95

If I remember correctly (from viewing Mark's site), he was using Koni's with the GC 2.5" coil over conversion.

Honestly, with the 18x9.5's on the front, I was surprised at just how much room there was. I've never called myself a wheel fitment "expert" by any means and I'm oft confused about the difference between backspacing and offset. My 17x8.5's, with a 33mm offset, were pushed way out. I could have gone with a wider width, maybe a 245 if I could find one in the appropriate OD. The 9.5's, with their 45mm offset, were actually pushed IN further than the 8.5's, meaning all the extra width came on the back side of wheel (using the flat mating surface between wheel and hub as the starting point for measurement). I'm assuming this is the backspacing. It "may" fit with the stock suspension in place as it was at full droop. None the less, with 2.5" OD coil-overs, I could run 285's without a problem. The offset would be the distance between the back of the mating surface and the front of the wheel where the lug nuts sit when tightened, correct? The "thickness" of that point denotes offset. On the 45 offset, there's less material than a 33? Am I thinking about this correctly, or is each forged with a specific offset in mind and not machined off later? Seems a rather expensive way to produce rims. There was more clearance for my 9.5's (45mm offset on the outside than on the inside of the wheel. So something with say a 40mm offset (pushed further out, not in) would work just as well, but a 50mm offset, would push the rims in even further unless the backspacing is different, no?
Michel

SleepR1

If I remember correctly (from viewing Mark's site), he was using Koni's with the GC 2.5" coil over conversion.

Honestly, with the 18x9.5's on the front, I was surprised at just how much room there was. I've never called myself a wheel fitment "expert" by any means and I'm oft confused about the difference between backspacing and offset

They're similar, but not the same. Back space is the dimension between the wheel mounting surface and the inboard side of the wheel rim. Offset is the dimension between the wheel's centerline and the wheel mounting surface

My 17x8.5's, with a 33mm offset, were pushed way out. I could have gone with a wider width, maybe a 245 if I could find one in the appropriate OD. The 9.5's, with their 45mm offset, were actually pushed IN further than the 8.5's, meaning all the extra width came on the back side of wheel (using the flat mating surface between wheel and hub as the starting point for measurement). I'm assuming this is the backspacing.

Correct, that is the back space.

If we do the calculation, you'll see why it makes sense:

8.5 inch wheel will be assumed at 9.5 inches in overall wheel width, 33 mm is 1.3 inches

(9.5/2) - 1.3 = 3.45 inches...this is the front space...the dimension between the wheel's mating surface and the outboard side of the wheel rim lip.

9.5 inch wheel will be assumed at 10.5 inches in overall wheel width, 45 mm is 1.77 inches

(10.5/2) - 1.77 = 3.48 inches front space. Lo and behold the front space is the same.

Logically the back space dimension changed, and that, plus the extra inche of rim widht (divided by 2) is where the 1 inch width was added, as illustrated in the following calculation:

8.5 (really 9.5) - 3.45 = 6.05 inches of back space

9.5 (really 10.5) - 3.48 = 7.02 inches of back space

There it is boyz!

It "may" fit with the stock suspension in place as it was at full droop. None the less, with 2.5" OD coil-overs, I could run 285's without a problem. The offset would be the distance between the back of the mating surface and the front of the wheel where the lug nuts sit when tightened, correct?

Let's go through the math (remember 45 mm is 1.77 inches). Assume 11 inches as your overall width with 285/30-18s on 9.5-inch wide wheels.

Also assume that the maximum back space clearance is 7.5 inches with 2.5-inch springs, and the maximum front space clearance is 3.5 inches in the front wheel wells.

(11/2) - 1.77 = 3.73 inches front space which exceeds the 3.5 inch by about 1/4-inch.

11 - 3.73 = 7.27 inches back space, which is within the clearance, but overall you will get rubbing of the fender lip. Definitely roll the fender lips like I suggested.

Offset is the measurement between the wheel's centerline (cut longitudinally down the middle, with equal halves inboard and outboard) and the wheel's actual mounting surface to the hub.

The "thickness" of that point denotes offset. On the 45 offset, there's less material than a 33?

No, there's a difference of 0.5 inches in offset from the center line. The wheel's centerline doesn't change, but the offset from the wheel centerline can change. The 0.5-inch difference in offset, PLUS the 0.5 inch greater rim width inboard (9.5/2), effectively pushes the wheel 1-inch more inboard when mounted on the hub...get it?

Am I thinking about this correctly, or is each forged with a specific offset in mind and not machined off later?

Custom wheels are built to the specs you provide. The wheel centerline is the reference point that offsets and back spaces are based on. It's unsafe to machine off material from the wheel's mating surface to the hub. This makes that metal thinner, and weaker, thus causing catastrophic wheel failure!

Seems a rather expensive way to produce rims. There was more clearance for my 9.5's (45mm offset on the outside than on the inside of the wheel.

The position of the wheel/tire relative to the rim front fender rim lip shouldn't have changed with the 9.5-inch 45 mm offset, since the extra width and 0.5-inch more offset effectively added the extra inch on the inside.

So something with say a 40mm offset (pushed further out, not in) would work just as well, but a 50mm offset, would push the rims in even further unless the backspacing is different, no?

IMHO, if you're trying to fit 285/30-18s on a 9.5-inch wide wheel, you really should use a 2-inch (51 mm) offset and 7.5 inch back space. This will give just enough room to clear the suspension components, as well as clear the fender lip (just barely).

The math is as follows:

(11/2) - 2 = 3.5 front space, which is the max clearance.

11 - 3.5 = 7.5 back space, which is the max clearance WITH 2.5-inch OD springs

red 7

thanks guys for the info

Chadwick

iTrader: (12)

Guys, clearing the suspension is not the only problem, also remember that the wheel turns with steering input. If you have to much back space, the Tire and wheel can rub on the Lower A-Arm when making tight turns. Don't ask how I know this

Dan

Chadwick

iTrader: (12)

By the way, Nice post SleepR1, nice to see someone that understands offsets and backspacing!

Dan

red 7

you stated that a good combo for my setup in the front - 18x9.5 +55 265/35 18

my? what about the rear ?? width offset ??

i would like to run a 285/30 18 (there is a certan brand tire i want to use), is it ok to use a 9.5 in. wide wheel or do i need to use a 10 in. and also what offset do you suggest

im not planing to roll the fenders or anything i have the M2 trailing arms too

thanks for all the great input

SleepR1

you stated that a good combo for my setup in the front - 18x9.5 +55 265/35 18 my? what about the rear ?? width offset ??

Out of the choices you presented us, that was the only choice to run all the way around the car.

i would like to run a 285/30 18 (there is a certan brand tire i want to use), is it ok to use a 9.5 in. wide wheel or do i need to use a 10 in. and also what offset do you suggest. im not planing to roll the fenders or anything i have the M2 trailing arms too. thanks for all the great input

I recommend using a minimum of 10 inches wide for best results. 285 mm is 11.22 inches. With only 9.5 inches of rim width to support that much tire section width, the coverage only amounts to 85%. Generally you'll want 90% or more rim coverage for the best support of the tire's sidewall.

Offset would be anywhere from 51 mm to what Mark Valsikis recommends with his Tecnomags, at 53 mm. 55 mm might be a too much with a 10-inch wide wheel, as Chadwick points out. You'll run into trouble with clearing lower control arms, and in the case with the rear positions, the M2 rear trailing arms (despite the fact that the M2s are skinnier).

SleepR1

Thanks for the vote of confidence! I learned everything from Steve Cirian. His site is just great with regard to how he explains offset, back space, front space, etc.

red 7

thanks again SleepR1

now i have to find some rims with these offset that i like and are decent weight, because i know the tires i want to run

Wade

iTrader: (1)

Do all the math you want, there are no guarantees unless you go very conservative on the front.

We tried 255/40 tires on 17x9 45mm offset wheel all around, guess what, by the math it seems like it will work no problems...

Well... we got tons of rubbing on the top of the fender on the liner, the inside of the fender well at full lock, and even hit the lip, got it rolled later. No problems on the back of course.

It depends a LOT on the brand/model of tire and the ride height. If you have an adjustable suspension and don't mind adjusting your ride height based on rubbing in your front fenders, then fine... but if you want a certain ride height for looks or to corner balance your car, you better go conservative or you might have to jack your car up to look like a 4x4 to keep the wheels from rubbing.

IMO there is nothing that looks worse than a stock wheeled and ride height FD... except a stock ride height FD with bigger aftermarket wheels!

Has anyone else noticed that 94 and 95 models seem to ride higher? Wonder if that is just the age factor or if the rubber spring stops are harder or something.

Wade

GsrSol

Yes, my 94 sits up alot higher then everyone else car. I know most of them I compard to had 93's.

SleepR1

Wade,

Yeah, the 255/40-17 tire is probably responsible for the rubbing, especially the Yokohama A032Rs which tend to be taller than most other 255/40-17s.

I'd be conservative and mount 245/40-17s on 9 x 17, 45 mm SSR IA2s.