18x12 narrow body backspace?

I think you will find that 6.5" is all you can get with a 17" wheel. With my 17x11 wheels there is currently about 0.5" clearance between the lower portion of the upright and the wheel. I wouldn't want it any closer.

Mark
5481 & 5461

Thanks. I agree.

I'm looking at 18x12s and it looks like the larger inner diameter clears the upright and support shaft.

Also, I've seen reference to 20x12s with 6.75" backspace.

Check with Pantera East. They are experts on Pantera wheels and sell a lot of them. Excellent prices too.

Mike

Thanks. I sent them an E-Mail.

As for clearence, it should not be a problem. When I got mine 18 " x 11" with 295s on they was sitting too far in, but they did clear everything. They got spaced out 2" to sit right, and that means you could go up to 13" with on a 18" rim. Don't remember the backspacing on mine.

I'm running 18"x12 1/2" HRE's on the rear of my stock bodied Pantera with 7 5/8" backspacing. I do; however, have my brake rotors mounted on the outside of my hubs, which required an extra 3/8" of backspacing to compensate for the thickness of the rotors. I did have a slight rubbing problem at the rear (upper frame rail), due to too much wheel travel, which I solved by adding an extra bump rubber to each of my Koni shocks. Now it's perfect. Thanks to Dennis Quella for the extra bump rubber tip.

That's a good point. I guess that it's better to err on the side too much backspace, then use spacers to correct, if necessary.

I have stock brakes and intend to upgrade to a big brake setup in the next year or so. I've read concerns about brake hats offsetting wheels outward.

I'm planning 335/30-18s with a 26" diameter. That diameter clear the mufflers, but not the muffler hangers.

It sounds backspace of 6.5 to 6.75 is typical.

I previously had 17"x11"'s with 6.5" BS. The fit was perfect with a 335/35-17 tire. When I went to 18"x12.5", I simply split the difference and added 3/4" to the inside and the outside. The tread of the tire stayed in the same relative position but the sidewall is now straight with the wider wheels. I'm running 335/30-18 Hoosier tires. As I wrote previously, under full suspension compression, I was getting a little bit of rubbing on the upper rear frame rail, due to too much suspension travel, so I added a second bump rubber to my shock absorbers. It didn't affect the ride at all and I now have no rubbing problems anywhere (no, the muffler hangers aren't even close). Apparently, Pantera Performance in Colorado supplies all of their Koni shock packages with double bump rubbers.

Hi Dave,

Thanks for the clarification. On the last reply I came in from fighting with an ignition coil and wasn't all there. For my 18x12s, 7+" backspace makes sense.

I'll pull off the rear wheels tomorrow and measure more carefully. Also, my 350Z rears are 7" BS with the same bolt pattern. I'll test fit them too.

The wheels in your picture looks perfect. Since mine are ~0.5" narrower, it looks like I'll be close to the same.

After measuring rear wheel front and back clearance with a 26" tire, I found: Front = 5.25", Back = 8.25.

Looking at your 7.625" backspace, that makes 3/8" margin front and back. I'm going with 7.625.

I should see wheels in a week, so I'll document how to turns out.

Thanks for all of the help.

gen2pantera,

I'm concerned that 7 5/8" BS is too much for a 12" wide wheel. Remember, my 7 5/8" BS is effectively 7 1/4" BS because of my 3/8" thick brake rotor hats. I also had to modify my suspension to prevent rubbing on the inside sidewall of the tire. In essence, you have 3/8" more BS than I do, with a 1/2" narrower rim. Because your rim is narrower than mine, you'll have more sidewall "bulge" to deal with. If I were you, I'd have ordered 12" wide rear wheels with 7" or 7 1/4" (maximum) BS. If you're going to mount your brake hats outboard, you're probably OK, but if not, I'm worried your BS is too much. I hope you're not offended by my opinion. I'm just trying to help.

Hi Dave,

No worries. I appreciate the comments. I have stock brakes now, but intend to go to a big brake kit down the road. I figure that too much is better than too little. I can live with wheel spacers until I'm ready for brakes.

Since 17x11s are 6.5 BS, I figured I want the same outer fender clearance, so ~7.5" BS. I gave the builder the front and rear clearance numbers. I'll call in morning to confirm the plan. Thanks again for the help.

Just curious, what brake kit are you using?

Wheels - 20" x 12" HRE model 898R, 12 mm off-set
Tires - 325/25ZR20 Michelin Pilot Sport PS2
Brakes - Wilwood, hats mounted behind axle flanges in the oem location

Fit: Widest possible tire that wil fit with 12mm off-set, at the rear ride height my Pantera sits at. I had to roll the rear most section of the rear fender lip for clearance. I think I'd generally recommend 19mm off-set for 325/335 tires ... its absolutely a necessity for 335mm tires, at this ride height. Muffler clearance may become an issue with 335mm tires & 19mm off-set. I like the 325mm tires for the reason they give you just a little bit of wiggle room.

George,
12mm offset on a 12" wide wheel equals 7" backspacing. I used the same offset (or 7 1/4" BS) with a 12 1/2" wide wheel and 335/30-18 tire, which is about 3/8" shorter than your 325/25-20. I have absolutely no rubbing after performing the modification I described in my earlier postings but it's VERY tight. Oddly enough, I only experienced rubbing on the passenger side; the driver's side was fine. I didn't have any rubbing issues with the fender lips although rolling them is a good idea.

gen2pantera,
With the backspacing you're about to use, you'll have more fender clearance than the same tire on an 11"/6.5"BS rim because you're pulling the tire more to the inside. The centerline of the tire's tread, mounted on your proposed wheel, will be 1/2" further to the inside than the same tire mounted on an 11"/6.5"BS wheel. I hope this makes sense. I find that it's easier to visualize such things by thinking in terms of offset rather than backspacing.

David and George,

After your warnings/comments, I took a close look at the inner frame rail. Clearance there was just over 8". I was using 8.25" inner clearance previously. After early morning discussion with my builder, I'm going with 7.25" BS.

If there's an inner clearance issue, I'll live with 1/4" wheel spacers until I do big brakes. They recommend no larger than 1/2" spacers if necessary.

Even with the 25.9" vs. George's 26.4 diameter, I suspect that I'll need to roll inner fenders, per George.

Either way, thanks, as always, for the continued help and insights.

Brian

For the record, this thread was really helpful.

http://pantera.infopop.cc/eve/...044/m/6000004084/p/2

The tightest clearance area is not usually the subframe rails but the rear end of the upright's lower pivot shaft and its nylock nut. And in operation, tires deflect as much as 1/2" in hard cornering, as shown by fender-cams during pro races, even with 50 psi inflation pressures. One ex-Pantera owner carefully measured everything, bought new tires for his upgrade and managed to record 3.0 laps at a 'Vegas open track event before one tire sidewall moved enough to tear it open on "something", hurling the car off the track. Going home 550 miles on a flatbed trailer is not the way one likes to close a weekend event.... IMHO, 1/4" is not enough tire clearance, if the closest hard point has edges and you actually use those giant meats. Just a thought.

Bosswrench,

Thanks for comments. I think I'm OK with inner clearance. If not, wheel spacers will help until I do brakes. It's frontspace that concerns me. I really don't want to be in the market for GTS flairs right now.

At this point, I'll have to wait for delivery and tire mounting and hope this isn't a multi-pass process. Fingers-crossed.