Stock 15x8" wheel offset

Pacha

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Mar 13, 2009
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35
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Buenos Aires
The documentation I have says the the stock wheel has -0.5" offset. That's arround 4" backspace.

Is that info correct?

I ask because I "need" to buy new wheels and don´t know what backspace to order.

If my info is correct I should buy this:

front 18x8" 4"BS
rear 18x9.5" 5.5"BS
 
The documentation I have says the the stock wheel has -0.5" offset. That's arround 4" backspace.

Is that info correct?

I ask because I "need" to buy new wheels and don´t know what backspace to order.

If my info is correct I should buy this:

front 18x8" 4"BS
rear 18x9.5" 5.5"BS

On my '72 the stock 15x8 steel wheels are/were 3.5 inches offset measured from the face of the mounting flange where the wheel weights set...outside the rim....to the mounting face against the rotor....

now IF you look at a engineering diagram, you find they measure from where the tire bead sets, so subtract about 1/4-3/8 inch from that measure....

your offset would be then about 3.25 inches....

I changed to later vette wheels years ago....and used VBP adaptors still on the car, same size...

:amazed:
 
I have 17x9 wheels on Ol' Red- the front are 4.5 and the rears are 4. Everything clears just fine.

I'll have to measure, but I think the origianl rally wheels are 15x8 and 4 something
 
I have 17x9 wheels on Ol' Red- the front are 4.5 and the rears are 4. Everything clears just fine.

I'll have to measure, but I think the origianl rally wheels are 15x8 and 4 something

I'll decide in favour of 4"BS then.

Thanks
 
hope this helps:

rimoffsetbs.jpg

THAT is the way I measure MY wheels, as i'ts just plainly simpler...BUT if you look close there is a dash line from the inside of the mounting flange, and going to a site like Tire Rack maybe another....and looking for measurements, you find that dash line if the ref for offset measures.....

like I tried to say above, I do it my way and subtract 1/4 inch and call it a day....

:beer::banghead:
 
hope this helps:

rimoffsetbs.jpg

THAT is the way I measure MY wheels, as i'ts just plainly simpler...BUT if you look close there is a dash line from the inside of the mounting flange, and going to a site like Tire Rack maybe another....and looking for measurements, you find that dash line if the ref for offset measures.....

like I tried to say above, I do it my way and subtract 1/4 inch and call it a day....

:beer::banghead:


Yes I've seen it too, it seems that there are two ways to measure BS. I'll buy the 4,5"BS and use a spacer if needed

Thanks
 
Hi

Don't mistake Offset with Backspace.

The very low line from is Backspace = 4 " ( if I remember right , but I also have 3 3/4 " in mind ? ) on original 15x8 wheels for C3.

Rgds. Günther

Edit: the 8x15 had 4 " backspacing, the 1968 Vette 7 " probably had the 3 3/4 " I remember )
 
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My stock 15 x 8 rally wheels measured just over 3.9" backspacing which requires about 1/2" of offset. I ended up buying 17 x 8 wheels with 4" backspacing and they fit perfectly.

There is only one correct way to measure backspacing and offset. The diagram is correct. Measure from the outer edge of the rim to the mounting surface to get backspacing. Best way is to lay a straight edge across the rim and the measure from there to the mounting surface. Offset is how far the mounting surface is from the center line of the wheel.

Remember that a 15 x 8 wheel is actually 9" wide from outside rim to outside rim.

DC
 
yesterday I measured the BS on the sparewheel (original) of a friend's vette and It measured 4.00"
I know that BS should be measured from outer edge, but in some places I have seen it measured from the flat part before the outer edge.

Regards,

Pacha
 
Eastwood sells an adjustable plastic tool that you bolt to the hub (wheel having been removed from the car). It's adjustable to simulate 16, 17, 18, etc inch wheels and it has adjustments for wheel rim width and an adjustment for back spacing/offset. When you get it adjusted, you can then spin the tool (simulating a rotating tire) and see if it hits the frame. It costs about $90.00 Seems like a smart buy since a lot of custom wheel vendors won't allow you to return a set of custom made wheels.
 
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