Help with wheel terminology

[Roland]

I'm looking at these for a '68 on a '72 chassis. It will be a short step with '72 cab, '68 front clip. With 5X5"BC discs front 5X5"BC drums rear. Stock suspension. The description says (offset is -11 and the Hub Bore is 78.3.) There is no information on backspacing. I assume the "hub bore" dimension is in millimeters???? I have no clue what "offset" means. The description specifically states that they fit '71 thru '98 Chevy pick up 2WD. What questions should I get answered before I buy?

These are 17" X 8"Wide. Comments please.

[special-K]

I know`88-ups have more backspace/ofest than`87-back.They don`t take the same wheel.

[Palf70Step]

Normally the -11 would mean that the wheels are not equal with the amount of rim inside the mounting hub and outside the mounting hub. In this case you have 11 more mm towards the inside. Means you have more back spacing.

I am roughing this, but with an 8" wide rim, I think that means about a 5.5" backspace or about 1.5" more inward than outward.

Like you I get a little confused with the metric ratings, but I think that is close to it.

You are correct about the bore measurement, and I believe that may be a bit small for our trucks.

Before you by. measure your hub diameter and conert it to metric to see if it will clear. Then check on backspacing. I think 5.5 may be a little too much, but if not it is real close to causing clearance issues.

[Roland]

Thanks for the info! I will shoot off some questions to the seller before commiting.

[Sinisterspeed]

actually the -11 is also in mm. It is the mesurment from center. negitave would mean more of the wheel is outside of center. and a + would mean a positive offset wheel. Front wheel drive cars take positive offset such as +20 to +40. Due to the wheel needing to me mostly all behind the mounting flange. Where a rear wheel drive wheel which is what your going to find will go from 0 to -18 usually. I have -12 on the front and -18 on the rear of my 4x4 with a 20x9 wheel. This in turn makes it about 3.5in of backspacing on the front ones. Would be less on the rears. Hope this helps.


Here is something I found that might help.

Offset

The offset of a wheel is the distance from the mounting surface of the wheel to the true centerline of the rim. A positive offset means the mounting surface of the wheel is positioned in front of the true centerline of the rim / tire assembly. This in effect brings the tire in to the fender well more. Conversely, a negative offset means the mounting surface of the wheel is behind the true centerline of the rim / tire assembly. This will cause the tire to stick out away from the vehicle.

To compare the effects of changing the offset and width of your wheels use the

[Roland]

So it appears now that these wheels have an effective backspacing of 3.56 inches if -11 mm equals .433 inches off the centerline of 4 inches?? The vendor also offers them with zero offset which would give a backspacing of 4 inches on an eight inch wheel. I think I'll go with that one. Good information!

Thanks
Roland

[Boog]

Did you determine that the center bore was large enough to fit the truck's hub?

[Roland]

I did not determine that the 78.3 mm is large enough to fit the '72 wheel hub. I did calculate that 78.3 mm is slightly over 3 inches. Anybody know what the hub diameter is?

[es67chevy]

Did you ever figure this out? Did you order the wheels?

Originally Posted by Roland

I did not determine that the 78.3 mm is large enough to fit the '72 wheel hub. I did calculate that 78.3 mm is slightly over 3 inches. Anybody know what the hub diameter is?