DON’T want to start any arguments or cause POd feelings. When I bought new wheels and tires for my new (then) 94 Silverado. The salesman pointed out this same thing then. The wheel hub was bigger than the axle hub. I went with the rings then and the truck always rode real nice with a 60 series tire.
who is right
- Thread starter scarborough
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I just checked my receipt, they are Mr Lugnut # HR83-7030-4 at Summit and they are only $9.99 for all 4 not $20.00
When I measured my rear hub on my 86' Regal it was 70.50" those list a 70.30" which might be correct for your older El Camino but the OP has a 87' Cutlass so he needs to verify size but these might be what he needs https://www.summitracing.com/parts/mln-hr83-7050-4/overview/
Now as far as lug or hub centric I will say every Gbody I have ever owned over the years I put aftermarket wheels on and they have always been lug centric and I have never had an issue or vibration.
Also your new QTP 9" will probably have a different size hub.
Got my micromiter ready if thats the case. Gotta wonder why GM would have made such a small difference in the size of the axle hub. Did they change the wheel hubs to match?
No PO and no hard feelings. A salesman I am not. I’d personally just bolt on the wheels and run the rings only if needed. Should the tires be balanced with the rings installed in the wheels? Food for thought...............
I could MAYBE see the rings if the wheel was a unilug and the lugs had been run in and off a few times. If it's a direct-drilled lug wheel, I can't see how the ring will help center anything.
That said, have run unilug wheels on many cars, never had an issue with tire vibration. Have also run OE wheels on many, with no appreciable difference in ride.. Now cheap tires, that;s a whole 'nother story.
That said, have run unilug wheels on many cars, never had an issue with tire vibration. Have also run OE wheels on many, with no appreciable difference in ride.. Now cheap tires, that;s a whole 'nother story.
For those that care, wheel diameter size, whether it's 15" or 17" or 22" doesn't matter when it comes to backspacing and offset. Sometimes it's hard to wrap your head around backspace and offset when they both look at the mounting surface of the wheel. It's just where you take things into account when you start.
Stock Super Stock wheels are listed as 15 x 7 on a mid-80s 442 for example. Which means "7" between the rails" of the rim from bead to bead, as it were. You can add approx. 1/2", or 12mm on each side to the edge of the rim so the wheel from outside edge to outside edge is right about 8". Basically, you can add 1" to the advertised rim width size. Backspace takes that 12mm on each side into account on the backside to the mounting surface since you're measuring from outer edge of rim to mounting surface. Offset doesn't care. It's only looking at the equator of the rim first and any difference that the mounting surface is from that.
So if it's a 4" backspace, like factory G-body 442/Hurst Super Stock wheels are, and the rim total width is 8", you end up with a 0 offset. 8 (total rim width) divided by 2 = 4" center point. The 4" backspace shows us a difference between the two of, ZERO.
When you use the 15 x 8 example here, add 1" to the advertised rim width to get a general idea. The point is, you really should measure total rim width because if the outside edges of the rim are anything other than 1/2", you need to account for it. So you really are starting with about a 9" wide rim edge to edge. Divide by 2 and you get 4.5" centerline. Subtract the 4.5" from the 4" back space the wheels say they have, and you get -1/2", or -12 mm offset.
Here's where it can get tricky. The -12 mm offset basically puts the wheel to the outside of the wheel well from a stock 15 x 7 for example about a FULL INCH! The backside of the rim is still in the same place as the 7" rim. Why? Because the 4" backspace is the same, so the rear of the rim didn't go anywhere. But with 4" backspace means you have 5" up front now. With the 15 x 7, you had a 4" backspace as well, leaving 4" in front because the wheel was 8" edge to edge. But 4" backspace with a 9" edge to edge rim leaves 1" left over and it has to go somewhere. If it had a 4.5" backspace, you would basically have 1/2" more toward the inner fender, and 1/2" more toward the outer fender compared to the 7" rim. Confusing? It can get that way fast. And then fitment has a lot to do with tire width from widest point to widest point on the sidewalls as well. Don't just accept advertised tread width as the total tire width because it's likely not. MEASURE widest point of the tire for tire width.
Just remember you have to take into account the edge to edge rim width divided by 2 to get your rim centerline which is your centerline starting point. Then you measure from the outside rear of the rim to the mounting surface for your backspace. Then subtract centerline from backspace to get your offset.
But as stated, .03" of backspace differences is nothing.
Here's a site that has a lot of good info on measuring for aftermarket wheels and stuff. Maybe it can help. It's probably more scientific in explaining backspacing and offset than I can ever be.
Stock Super Stock wheels are listed as 15 x 7 on a mid-80s 442 for example. Which means "7" between the rails" of the rim from bead to bead, as it were. You can add approx. 1/2", or 12mm on each side to the edge of the rim so the wheel from outside edge to outside edge is right about 8". Basically, you can add 1" to the advertised rim width size. Backspace takes that 12mm on each side into account on the backside to the mounting surface since you're measuring from outer edge of rim to mounting surface. Offset doesn't care. It's only looking at the equator of the rim first and any difference that the mounting surface is from that.
So if it's a 4" backspace, like factory G-body 442/Hurst Super Stock wheels are, and the rim total width is 8", you end up with a 0 offset. 8 (total rim width) divided by 2 = 4" center point. The 4" backspace shows us a difference between the two of, ZERO.
When you use the 15 x 8 example here, add 1" to the advertised rim width to get a general idea. The point is, you really should measure total rim width because if the outside edges of the rim are anything other than 1/2", you need to account for it. So you really are starting with about a 9" wide rim edge to edge. Divide by 2 and you get 4.5" centerline. Subtract the 4.5" from the 4" back space the wheels say they have, and you get -1/2", or -12 mm offset.
Here's where it can get tricky. The -12 mm offset basically puts the wheel to the outside of the wheel well from a stock 15 x 7 for example about a FULL INCH! The backside of the rim is still in the same place as the 7" rim. Why? Because the 4" backspace is the same, so the rear of the rim didn't go anywhere. But with 4" backspace means you have 5" up front now. With the 15 x 7, you had a 4" backspace as well, leaving 4" in front because the wheel was 8" edge to edge. But 4" backspace with a 9" edge to edge rim leaves 1" left over and it has to go somewhere. If it had a 4.5" backspace, you would basically have 1/2" more toward the inner fender, and 1/2" more toward the outer fender compared to the 7" rim. Confusing? It can get that way fast. And then fitment has a lot to do with tire width from widest point to widest point on the sidewalls as well. Don't just accept advertised tread width as the total tire width because it's likely not. MEASURE widest point of the tire for tire width.
Just remember you have to take into account the edge to edge rim width divided by 2 to get your rim centerline which is your centerline starting point. Then you measure from the outside rear of the rim to the mounting surface for your backspace. Then subtract centerline from backspace to get your offset.
But as stated, .03" of backspace differences is nothing.
Here's a site that has a lot of good info on measuring for aftermarket wheels and stuff. Maybe it can help. It's probably more scientific in explaining backspacing and offset than I can ever be.
Would you build a house and rely on nails and screws to support the weight? or the foundation and footings because that’s the difference between lug centric and hub centric
Olds did it for YEARS with the sporty versions of their wheels. Wish they didn't, but they did.
I guess you see the point just because You can do it that way doesn’t mean it’s the best way to do it which is why hubcentric is a stronger way to go
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