Home page

Topic: Rally wheel backspacing

in Forum: C3 Handling Components

Back to top of thread


Already a Member? Click Here to Login
Not yet a Member? Click Here to Register for Free!
Re: Rally wheel backspacing (4/14)
 10/6/21 10:54pm
73shark
Limited Member
Send Private Message

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

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.



______________

1973 L-82 4 spd

Re: Rally wheel backspacing (5/14)
 10/7/21 6:45pm
manchestersharkLifetime Member
Lifetime Member
Send Private Message

Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 2060

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
Standard Member
Send Private Message

Grapevine, TX - USA

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


Joined: 8/26/2006
Posts: 1079

I don't get that mag anymore.



______________

Re: Rally wheel backspacing (7/14)
 10/7/21 9:22pm
73shark
Limited Member
Send Private Message

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.



______________

1973 L-82 4 spd

Re: Rally wheel backspacing (8/14)
 10/7/21 10:44pm
F4Gary
Standard Member
Send Private Message

Grapevine, TX - USA

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


Joined: 8/26/2006
Posts: 1079

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



______________

Re: Rally wheel backspacing (9/14)
 10/8/21 12:37am
73shark
Limited Member
Send Private Message

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.



______________

1973 L-82 4 spd

Re: Rally wheel backspacing (10/14)
 10/8/21 1:42pm
73shark
Limited Member
Send Private Message

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.  



______________

1973 L-82 4 spd

Re: Rally wheel backspacing (11/14)
 10/8/21 9:41pm
Adams' AppleLifetime Member
Lifetime Member
Moderator
Send Private Message

Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19866

 



______________
Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Re: Rally wheel backspacing (12/14)
 10/18/21 8:01pm
F4Gary
Standard Member
Send Private Message

Grapevine, TX - USA

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


Joined: 8/26/2006
Posts: 1079

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.



______________

Re: Rally wheel backspacing (13/14)
 10/18/21 10:06pm
73shark
Limited Member
Send Private Message

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?



______________

1973 L-82 4 spd

Re: Rally wheel backspacing (14/14)
 10/18/21 11:32pm
F4Gary
Standard Member
Send Private Message

Grapevine, TX - USA

Vette(s):
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.



______________

Our Sponsors help support C3VR