Track and Wheelbase definition?

[mr0077]

Jim, I think to get at the flange-to-flange dimension, the wheel offset is what you want; you add twice the wheel offset to the track to get this dimension.

Backspacing is the distance from the inside lip of the wheel to the mounting flange, and offset is the numerical distance (plus or minus) from the wheel centerline to the mounting flange, with a positive offset placing the flange closer to the outside of the wheel. If you had a -2" offset on the rear wheels and the rear track was 52.5", the flange dimension would be 52.5" + [2 x (-2")] = 52.5" - 4" = 48.5".

[Jim Holden]

So, if the 6" 70 spoke wire wheel (according to Dayton) has a back spacing of 3.25" you would add 1/4" x 2= 1/2" to the track number (52.5" for the rear for example) to get the flange to flange measurement of 53"... Right?

Jim

I feel like I need (as in the old Arlo Gutherie song) 8x12 glossy photos with circles and arrows and a description on the back.

[speed220mph]

Originally Posted by Jim Holden

So, if the 6" 70 spoke wire wheel (according to Dayton) has a back spacing of 3.25" you would add 1/4" x 2= 1/5" to the track number (52.5" for the rear for example) to get the flange to flange measurement of 53"... Right?

Jim

I feel like I need (as in the old Arlo Gutherie song) 8x12 glossy photos with circles and arrows and a description on the back.

Start with your math: 1/4" X 2 = 1/2". Because the backspacing is more that 1/2 rim width--hope you accounted for the bead--subtract 1/2" from 52.5" to arrive at a flange-to-flange distance of 52.00"! Your spoke wheel in this case is what was called "laced in" in the old days, so the center of the tires moves in on both sides from the hub flange by 1/4" per side. Simple . . . right?

[strictlypersonl]

Unfortunately backspacing is not measured from the bead, it's measured from the outer edge of the casting. Typically a wheel is 3/4"-1" wider overall than its "nominal" width. Your 6" wheel might be 7" total width so that 3.25" backspacing puts the wheel mounting surface 1/4" in from the centerline of the wheel. Which is why I much prefer to specify mounting-surface-to-centerline rather than backspacing.

[speed220mph]

Bob: That includes you and me. Problem is when you're starting with a wheel and don't have the specs like in your drawing, you've got to measure the bead from the edge of the rim.

[Jim Holden]

I hit the wrong key, obviously 1/4 x2= 1/2".

...and Bob comes through with the 8x12.

For the sake of the discussion I was omitting consideration of wheel flanges, etc. and essentially viewing this as Bob has suggested i.e.; that the centerline of the 6" wheel is 3" in and (inasmuch as I don't have any other dimensions than the backspacing) the backspace is 3.25", I would have to add the negative offset number, less the centerline number to the track to get the flange to flange number.

Maybe I can coerce Bob into going into his data base and coming up with the magic number for the 6" Dayton 70 spoke wire wheel... and even a diagram.

Jim