Wheel backspace question

JPhil

Huh?
Joined
Mar 26, 2008
Messages
1,361
Location
Loveland, Colorado, USA
Will 4 1/2" backspace fit the front with a 17 x 8 wheel? '73 with OEM calipers.

I'm still trying to find new wheels and it's driving me mad. I've about decided on the American Racing Salt Flat (kidney bean) as the only one I can stand that is still made, but it only comes with 4 1/2" backspace per their catalog. They say it's a bolt on, but I don't entirely trust catalog specs. I'm going to mount 255/50 Nitto Invo tires.
I figure I could go 1/4" spacers if need be, but that's max.

(And I don't want to hear anything about "TTII"s or "1 1/2" adapters" and all that. I know. That's not my question.)
 
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On my '72 I have '89 vette wheels....17x9.5 all around, in front I have 255/50/17 tires, I restricted the steering a bit buy building up the limit blocks on the lower A arm.....kept tires off the frame/sway bar?.......

as you know they are flat faced wheels, and so I used adapters that netted out at 4.5" back space,

Which still don't say shit about the wheels you like hitting the calipers, so I only partial help....:hissyfit:
 
Backspacing is only one part of the issue: even with 3" backspacing the backside if the spokes can hit the calipper, it depends on how the inside of the wheel is shaped.
 
Well, this afternoon I went and did it-- ordered up a set of American Racing Salt Flat wheels, 17 x 8, 3.75" backspace.

http://assets.wheelpros.com/wheel_i...rican_racing_hot_rod_gray_vn470_salt_flat.png


The wheels are 'custom drilled' for lug dimensions, and back space has many options, so I opted for 3.75". Thanks for your advice all. AR said they'd fit my car, so we'll see when they show up. "4 to 6 weeks" but the guy at the tire shop said often it's much quicker than that.

Ordered a set of 255/50 Nitto Invo tires to go on them as well.

https://encrypted-tbn2.gstatic.com/...i_uhW9q1XBITV6bvLamt6bep8FceDJsbwKdpbS8-HfRCQ

$2000 total---sheeeit, blew my budget all to hell, but this is the last major investment in making the car 'roadworthy'. Engine, trans, driveline, brakes, suspension, steering all rebuilt & upgraded. It has reached the point where the tires are the weakest link now. There will always be stuff it needs, but this will let it handle like it should. I'm still a little in shock at how much I spent, but I know I'll have a big ol' shiteatin' grin on my face when they're in place.
 
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66534d4e30e17f9.jpg

Where's the emoticon for jacking off?

Even without the alignment yet, it feels so different. Those 15" Firestones were like driving on squishy balloons. Only small problem is the fronts rub on the bottom inside of the fender just a tad at near full lock. 2 minutes with a grinder to relieve a little fiberglass and that will be taken care of.

The rebuilt steering box Gary GTR1999 did for me at the beginning of the year makes an incredible difference too. Wow, now I can finally begin to feel this car handle like it was meant to.
 
It's been almost a couple weeks now and I have discovered a problem......

When I ordered the 3.75" backspace, I was worried about frame rub on the front at full lock. I forgot that with my bump steer blocks I lost some turning radius anyway and that would not have been a problem. Oh well it was too late, wheels were ordered.

The car is lowered enough that the tires are now hitting the top inside of the fender lip on full jounce. I have ground the inside of the fender lips as much as I dare, put spacers under the bumper blocks, set the rear spring to its stiffest setting and even raised the back about 3/4" (ugh!) but the rears still rub a little when it bottoms out. That 1/4" made a big difference. I may try to get 1/8" machined off the mounting face of the wheels.

I hate to remove the 1/2" spacer above the strut rod bracket to increase the camber change, but I may have to. Fender flares are not an option at this time.

Bummer. But they sure handle a hell of a lot better than the 15" Flintstones that it had before!
 
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Update.....

Figure I'll close out this thread.

I went through a number of options in my head to alleviate the fender rub problem.
Jack the car back up? I raised the rear almost 3/4" and bought some 1/2" front spring spacers. But I just couldn't do that, I couldn't.
Machine the wheels down? Most I could get would be 1/8", which would probably be enough, but not many machine shops can handle that job. Besides, it would be a cobble fix and I'm leery of doing that kind of thing to wheels.
Machine down the rotor hats? No, just no.
Smaller tires? Yeah, I could, but I don't want it to look like a Chicano low rider. Nothin' against them, but that's not how I've built my car.

So I just chanted ommmmmmm for a while, contemplated the zen of my error and accepted the only true and correct fix for the problem.

I went and ordered another set of wheels. 4" backspace.

The tire shop guy was sympathetic, said he would have insisted we test fit a like size wheel on his alignment rack, but "I sounded so knowledgeable" about it, he took my word for it on the specs. He gave me an even better deal than before on a new set, mounted & balanced for free. He felt bad for me.

These are just right. They fit & perform beautifully. I'm happy.

Hey, it coulda been a much worse mistake. I didn't grenade a motor, or kiss a mountainside--which I almost did yesterday but these new tires saved my ass.

(Anybody wanna buy an almost new set of wheels? Less than 500 miles, and they'll work fine if you haven't lowered your car.......I'll make ya a good deal...)
 
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Did changing to 4 inch backspace (from 3.75) fix rubbing at the front and the rear? Can you do me a favor and measure the distance from the outside of the fender lip to the tire sidewall (widest part of the tire) "D" and the height at the top of the wheel opening "H"?

453d57bd2b7ecb.gif
 
"H" = 27 1/2"

"D" = -1/4" (tire sticks out 1/4" past outside of fender lip)

Top of tire is 26 1/2" above floor (@32PSI), widest point is about 3" below fender lip.

Sidewall at top of tire is flush with fender lip.
I figure camber change is what allows it to clear on jounce, that 1/4" backspace was critical. I have about 2* camber in the fronts, when I reduce it it will be closer still.

Couldn't tell you if clearancing the bottom of the fenders was needed with these 4" BS wheels, I did it with the 3 3/4" BS wheels on it and haven't looked to see what the gap is now. These tires are big enough it probably still would, but I bet not as much.
 
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Didn't you have clearance problems with the rear tires also (that were fixed with the 1/4 added backspace)? Are those dimensions similar?
 
The back is jacked up to about 28" right now, but other than that yeah it's about the same. (Oh, and I meant -.2* front camber , not 2*.)

I had expected the tires would have hit the inside of the fender flare radius as well, but they never have.
 
My car is 29.5" in rear and 28.5" in front, it was an old show car that at one time had wicked flared on it, but got cut back to near stock, for a LATE shark, guessing 78+ it was born as a '72 I have '89 C4 wheels on it, with 2.5" adapters from VBP back in '95 when I bought the car the wheels were just about the first thing done, so told VBP what it took to put them on a C3.....

275/50/17 in rear, 255/50/17 in front, I had to limit the steering by building up the stop on the lower A arm.....still turn tighter radius than my '87 did....

:smash:
 
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