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Rally wheel backspacing (1/14)
 10/6/21 12:35pm
F4Gary
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
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So I want to replace my 50 year old 15 x 8  Rally wheels.  Can't seem to pin down the exact backspacing.

Various places list 4.0", 4.25", 4.5"....

Anyone know what it is supposed to be for my 72?

Also, anyone know of a good place to buy new Rally's at a reasonable cost?  I don't want the cheaper 10 hole universal fit Rally's.



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Re: Rally wheel backspacing (2/14)
 10/6/21 1:05pm
NorskyLifetime Member
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Twin Lakes, CO - USA

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Would think the specs would be somewhere in the Assembly Manual.

Bair's doesn't have any wheel specs on their site but MidAmerica does (1969-1982 steel rally wheel-15x8).



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Re: Rally wheel backspacing (3/14)
 10/6/21 4:43pm
F4Gary
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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.


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Assembly manual is just going to tell you how to bolt them on.

Again, I've seen different backspacing on different parts places.  I had see that at MAM.

I'm thinking 4.25 might be the right answer.

But if you look at their aluminum wheels, they have a 4.5" backspacing.

Confused.



|UPDATED|10/6/2021 1:43:12 PM (AZT)|/UPDATED|


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Re: Rally wheel backspacing (4/14)
 10/6/21 10:54pm
73shark
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Overland Park, KS - USA

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1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


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I just measured mine and from the wheel mounting surface to the inside edge of the bead flange is 3 1/2". That would equate to a negative 1/2" offset.



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1973 L-82 4 spd

Re: Rally wheel backspacing (5/14)
 10/7/21 6:45pm
manchestersharkLifetime Member
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Equinunk, PA - USA

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Greetings to those who may be interested.  The December 2021 issue of Corvette Magazine has a fantastic writeup on Roll Models, (wheels), for C1-C3 steel and aluminum wheels. It may answer All of your offset and back spaced questions. 

Re: Rally wheel backspacing (6/14)
 10/7/21 7:08pm
F4Gary
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Grapevine, TX - USA

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I don't get that mag anymore.



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Re: Rally wheel backspacing (7/14)
 10/7/21 9:22pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 698

The article says that the 15x8-in rally wheel had a -11 mm offset in a 3 1/2" backspacing. Basically what I measured last night.  Not sure why they mixed measurement systems but it is what it is.



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1973 L-82 4 spd

Re: Rally wheel backspacing (8/14)
 10/7/21 10:44pm
F4Gary
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Grapevine, TX - USA

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So that is 3.5 inches from the bead?  That would make it 4.0 inches from the lip....I guess.



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Re: Rally wheel backspacing (9/14)
 10/8/21 12:37am
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 698

It's from the inside vertical surface of the wheel that the bead rests against.  I used to measure from the flange to the mounting surface and that gave me 0 offset.  Need to measure the wheel and see where the 8"  measurement is.  Tomorrow's project.



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1973 L-82 4 spd

Re: Rally wheel backspacing (10/14)
 10/8/21 1:42pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 698

The 8-in measurement is from the inside of the flange across the wheel to the inside of the flange. So my previous measurements re: offset and backspacing are correct.  



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1973 L-82 4 spd

Re: Rally wheel backspacing (11/14)
 10/8/21 9:41pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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Re: Rally wheel backspacing (12/14)
 10/18/21 8:01pm
F4Gary
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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.


Joined: 8/26/2006
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So now I'm reading that I should have my wheels balanced lug centric and not hub centric.  That may be why I can't get rid of this little shake at 52-54 mph.

Also, in looking for wheels at all the aftermarket places, their backspacing measurements are all over the place.

I measured 3 of my wheels and from the bead it is 3 5/8" and from the lip it is 4".  The 3 5/8" goes along with Adams Apple's "B" measurement as the steel is probably about 1/8" thick.

Geez Louise.



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Re: Rally wheel backspacing (13/14)
 10/18/21 10:06pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 698

Have you considered a road force balance?



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1973 L-82 4 spd

Re: Rally wheel backspacing (14/14)
 10/18/21 11:32pm
F4Gary
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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1079

Yeah, I can do that, but with steel wheels, lug centric balancing is better than hub centric as the hole in the middle isn't as precise as a machined alloy wheel which is balanced with a cone centering the center hole.

What is annoying is Ecklers sells the Corvette 15x8 rally wheel with a "correct" 4.25 backspacing but then says a 1/4" spacer is needed.

Mid America sell the same factory "correct" rally with a 4.25 backspacing and never mentions a spacer.

And they are obviously measuring backspacing from the wheel lip and not the bead.

This is maddening.



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