[djw]

I bought some vintage 14x6 torq thrust wheels on ebay that say "0 offset" on the inside. Would this equate to a 3" backspacing since it is a 6" wheel? Is that how it relates? If so, would a 7" wheel with "0 offset" equal a 3 1/2" backspacing? Thanks in advance for the help.

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[Clark]

0 Offset on a 6 inch wheel will equal about 3.5 inch back space.

Heres why, When measuring wheel width the manufacture will tell us the distance between the rim beads. On a 6 inch wide wheel the rim beads will be 6 inches apart. However, the total width of the wheel will be somewhat wider. Probably around 7 inches.

So in short, a "6 inch wheel" is actually closer to 7 inches wide. 0 offset will place the mounting pad directly in the middle of the wheel or 3.5 inches from the back edge.

Clark

 

[djw]

Thanks, Clark.

 

[Glenn1018]

Rims are a little wider than advertised, but a 0 offset 6" rim will have 3" bs if the extra lip isn't included, that is if you measure from the most outward vertical part on the inside of the wheel to the surface that bolts to the drum, I think.

[This message has been edited by Glenn1018 (edited 05-07-2002).]

 

[Guest]

Clark's way is easier to measure and very accurate. Wheels are generally 1" wider than their quoted size.

My question is which way is negative offset vs. positive offset? A 6" rim with zero offset has a BS of 3.5". But if the rim BS was 4", is that 0.5" positive or negative offset?

 

[Glenn1018]

Positive offset moves the tire towards the frame, negative offset moves the tire towards the fender. Going from 3 1/2 bs to 4 bs would make it positive offset.

I recently measured some 15x8s and they were 8 7/8 wide overall. Two had tires, two didn't. I believe the engineers measure it from the part of the wheel that contacts the bead of the tire as Clark said. That's hard to do with a tire so I found a straight 1x2 and cut it to length to extend beyond the entire wheel, and cut notches in one side so that it would slide down inside and fit across the inner lip. I doubt if it's perfectly accurate, but by putting it there you can measure backspace, as well as putting it on the outside lip and measure frontspace (if there is such a thing...I'm thinking in terms that too much frontspace, or negative offset, will put the tire in the fender lip). Anyway, when I added the bs and fs it was very close to 8, the advertised rim width.

I have a question too...how much side clearance is enough for a rear tire?

 

[Guest]

Your 15x8 were 8 7/8" wide? BS would only be off a 1/16", wouldn't it, if measured from the rim edge. I could live with that. Whatever, no big deal As far as clearance, I think a quarter inch is plenty. Some guys I know have less. Of course, it will depend on how low or high the rear is, how much side to side movement there is, etc.

 

[Glenn1018]

I'm concerned with side clearance, and think a 275-60 will leave 3/4" at the tightest spot on both sides, which I hope is enough.

I'd like to clarify something I said earlier about "going from 3 1/2 bs to 4 bs would make it positive offset". That's not necessarily true. Doing that would move the offset in the positive direction, but say you were working with a 10" rim instead of a 6" or 7". The 10" wheel with 3.5 bs has a negative offset of 1.5". Going to 4" bs the wheel would have 1" negative offset. Negative means that more than 1/2 of the rim width (however you choose to measure it)is on the fender lip side of the mounting pad; positive offset means that more than 1/2 is on the frame side...O offset is when the mounting pad is centered in the rim. Hope this makes sense.

 

[Guest]

I think 3/4" is plenty...a veritable Grand Canyon.