Backspacing explanation from DISCOUNT TIRES.com...interesting

allcarfan · Dec 15, 2003

As many of you have read, my new wheel/tire combo ended up not fitting. Even after I did extensive research for the perfect backspacing and tire width.

Well, I broke out the ruler and straight edge and measured the backspacing of the wheels that were sent.

(SEE PIC that I got from GP001s thread)

When I measured this way, I found out that the backspacing is actually 5.75 backspacing rather than the 5.5" that discount tire.com had told me they were. I had to wait until this morning to call them. I get one of their reps on the phone and explain the situation. This is what he told me:

"The wheels you have ARE, INDEED, 5.5" backspacing, but once the factory installs the 1/2" mounting surface and offset is adjusted, it comes out to be closer to 5.75" of backspacing. What you need is a 22mm offset. With this offset, and the 1/2" mounting surface added from the factory, it should give you about 4.65 (or.87 - I dont remember) total backspacing. We will see if we can order some ZERO offset wheels that will give you 4.5" backspacing because they dont have the extra mounting plate on them"

Ok...the good news is, it looks like they will exchange the wheel/tires for what I need. I will probably have to pay shipping...but, hey, thats only $30. bad news is, they think they are going to have to order them and it may take 6 weeks! Good thing my car isnt road worthy...good thing I kept my old wheels and tires too!!

The part that gets me is the explanation on backspacing. When I ordered, they said they had 4.5 and 5.5" backspacing. To me...that means...the distance from the wheel mounting surface to the top of the inner wheel lip (see pic). According to these guys....that is PRIOR to the offset/mounting surface, etc is installed on the wheel from the factory.

has anyone heard of this before? I thought that I was right in the way that I was measuring.

Shane

zookeeper · Dec 15, 2003

I'm not buying their explanation, everywhere else in the world, you lay your wheels face down and measure from the rear edge to the mounting pad to determine backspace.

rbohm · Dec 15, 2003

i agree with zookeeper, i think they screwed up.

allcarfan · Dec 15, 2003

thats what im thinking.

Someone can call them and verify...see if they give the same explanation. Its toll free.

Shane

gp001 · Dec 15, 2003

Yup, they're full of it. Backspace and offset can only be measure once everything is in place, not measures then readjusted. That makes no sense. Here's a few explanations I pulled off google to make sure I didn't give anyone bad info

http://www.thebensons.org/blkntan/backspacing.htm
http://www.jeepmadness.com/backspacing.html
http://www.wheelvintiques.com/measure.html

gp001 · Dec 15, 2003

From Discount tires site

http://www.discounttire.com/dtc/brochure/info/helpDeskWheelOffsets.jsp

Using this it give you a backspacing of 4" + .866" (22mm) = 4.866" ?
A zero offset wheel would give you a 4" backspace, right? Becasue the mounting surface would be at the wheel center. Where do they get 4.5". Since the offset is measured to the "hub mounting surface" the thickness should not matter. Am I missing something here?

allcarfan · Dec 15, 2003

gp001 said:
From Discount tires site

http://www.discounttire.com/dtc/brochure/info/helpDeskWheelOffsets.jsp

Using this it give you a backspacing of 4" + .866" (22mm) = 4.866" ?
A zero offset wheel would give you a 4" backspace, right? Becasue the mounting surface would be at the wheel center. Where do they get 4.5". Since the offset is measured to the "hub mounting surface" the thickness should not matter. Am I missing something here?

NO GP, you are not missing anything. What you are saying is what I thought....what you are quoting and questioning is exactly what they said. I dont even know if it is worth it to send them back. It doesnt sound like they know what they are talking about. I can add a 1/4 wheel spacer and be done with it, ya know? The only thing I dont like about that is...I will have a 1/4" wheel spacer and a 3/4" wheel spacer on there. Blah.

Shane

gp001 · Dec 15, 2003

allcarfan said:
NO GP, you are not missing anything. What you are saying is what I thought....what you are quoting and questioning is exactly what they said. I dont even know if it is worth it to send them back. It doesnt sound like they know what they are talking about. I can add a 1/4 wheel spacer and be done with it, ya know? The only thing I dont like about that is...I will have a 1/4" wheel spacer and a 3/4" wheel spacer on there. Blah.

Shane

I hear ya shane. Frustrating dealing with slow or special people. Maybe you should reference them to their own site

good luck

allcarfan · Dec 15, 2003

I have come up with a solution.

Forget Discount Tire.

My wheelspacers are 3/4" thick..aluminum and have pressed-in studs. I am having a machine shop fab up a 1/4" thick piece of aluminum that I can weld to the back of the spacer...giving me a 1" spacer and the needed backspacing for my setup (nothing is ever easy).

What is good about adding this fabbed up plate to the back of the adapter is...the pressed-in studs will NEVER...EVER fall out because this plate will be holding them in!!

I will let everyone know how it goes and take some pics...of course.

red65 · Dec 15, 2003

Careful welding to your aluminum spacers - assuming they start as 6061-T6 aluminum ("6061" being the alloy and "T6" being the heat treat), they'll end up as 6061-T0 after you're done welding (no heat treatment) - at least near the welds. 6061 in the T0 condition has roughly 1/2 the strength of heat-treated 6061-T6. I already told you I get heebie jeebies about wheel adapter strength -they turn into creepy crawlies when you compromise the strength by welding them... Just my .02. Careful!

allcarfan · Dec 15, 2003

red65 said:
Careful welding to your aluminum spacers - assuming they start as 6061-T6 aluminum ("6061" being the alloy and "T6" being the heat treat), they'll end up as 6061-T0 after you're done welding (no heat treatment) - at least near the welds. 6061 in the T0 condition has roughly 1/2 the strength of heat-treated 6061-T6. I already told you I get heebie jeebies about wheel adapter strength -they turn into creepy crawlies when you compromise the strength by welding them... Just my .02. Careful!

to be honest....welding really isnt necessary, im doing it as a precaution.

imshaggy2000 · Dec 15, 2003

allcarfan said:
to be honest....welding really isnt necessary, im doing it as a precaution.

Just have the company you bought them from send you 2 1" adapters, you will have peace of mind, dont turn it into a jumbled mess. Or see if they will take them all back in favor of 1" spacers. What ever works best for you. You dont want the wheel to fall off going around a sharp turn at high speed. Or if they wont take them back buy a new set and sell yours on e-bay!

imshaggy2000 · Dec 15, 2003

gp001 said:
From Discount tires site

http://www.discounttire.com/dtc/brochure/info/helpDeskWheelOffsets.jsp

Using this it give you a backspacing of 4" + .866" (22mm) = 4.866" ?
A zero offset wheel would give you a 4" backspace, right? Becasue the mounting surface would be at the wheel center. Where do they get 4.5". Since the offset is measured to the "hub mounting surface" the thickness should not matter. Am I missing something here?

No a 0mm offset on a 8" wide wheel will give you 4.5" backspacing. I know it seems like a bunch of BS, but read this. http://www.rsracing.com/tech-wheel.html

The basics are this, rim width is measured from with in the rim lips, and center line is measured on the out side of the lip to the center. Wheel center line from Wheel backspace give you the offset.

allcarfan · Dec 15, 2003

THat is a good piece of information there. Classic forums needs a wheel/tire sticky with a bunch of information.

As for ordering more spacers...well, they wont take the ones i have back. Adding a 1/4" to these spacers does not interfere with the integrity. Even if it wasnt welded, it wouldnt interfere with the integrity of the adapter. It will be easier to see when I post a pic.

Thanks for the helpful info.

67efivert · Dec 15, 2003

if u dont mind tell me what year is ur car and do u have the 3 or 4 bolt ball joints and what spindles r u using?
om only rinning .700 spacer behind my cobras with bout a 1/4 " to spare just trying to help

66P51GT · Dec 16, 2003

I wouldn't trust the double spacer route even if they are welded. Hub centric spacers are made to exact tolerances. Modifying these spacers is asking for trouble.

I doubt that setup would pass any SCCA or NHRA sanctioned event. $0.02.

-Chuck

gp001 · Dec 16, 2003

imshaggy2000 said:
No a 0mm offset on a 8" wide wheel will give you 4.5" backspacing. I know it seems like a bunch of BS, but read this. http://www.rsracing.com/tech-wheel.html

The basics are this, rim width is measured from with in the rim lips, and center line is measured on the out side of the lip to the center. Wheel center line from Wheel backspace give you the offset.

Thanks Shaggy! That explains the difference. It's all in the lips

347Fastback · Dec 16, 2003

I have a simple question guys. My 65 fastback I bought last Tuesday has a 9 inch lincoln rear. What wheel back spacing do I need to order for this car in the rear.??? I want to order some 17in wheels...

BobV · Dec 16, 2003

347Fastback said:
I have a simple question guys. My 65 fastback I bought last Tuesday has a 9 inch lincoln rear. What wheel back spacing do I need to order for this car in the rear.??? I want to order some 17in wheels...

If it's the Lincoln versailles rear, it's about 1" wider than the stock 8' (1/2" per side). Sooooo, you'd want a 17x8 wheel with approx. 5-1/8" - 5-1/4" backspace. Been there, done that!

BAD67FUN · Dec 16, 2003

I'll save you all from my opinion on dealing with wheel spacers. Some of you already know it . But I will concur that when dealing with wheels, the lips of the wheels are often overlooked. When a wheel size is called out, such as a 17 x 9.5 that is on the back of my car, those numbers are referring to the measurement taken on the wheel where the tire mounts. Just for the heck of it I measured my wheels before mounting them with tires. When measuring the overall diameter of the wheel it came out to 18.75"!! And the actual width (including lip) of the wheel measured 10.25". This is just info I thought I'd share because changing the wheel package on our cars seems to be at the top of most peoples lists. Good luck with whatever you choose. And furthermore... if you want to spend the extra dollar and like the wheels, call Vintage Wheel Works. They've dealt with this a thousand times I'm sure. Do you think they should send me a check for that plug???

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