What is the minimum Safe Amount of Backspacing?

[jjwood]

In an effort to get maximum track for my SCCA SoloII FP autoXer,I need help determining the minimum #of inches that I can safely incorporate into the backspace distance on a 16 x10" wheel. Fine tuning of track width will eventually be done using wheel spacers, but if I can start with say a 3" backspace instead of the typical 5" then all other things being equal, I could reduce the amount of wheel spacers needed.

Thanks,
Jeremy

[Joe Bob]

Sounds like trial and error to me....I assume that you have the proper longer studs? Use a 3 inch spacer and then add spacers at 1/4 inch increments until you have proper inside clearance and appropriate outside width to fill the flare.

[jjwood]

Mike --> let me rephrase then. I've got a wheel with a 10" width. I want to move the hub face as far inward as possible. A typical backspace (the measurement from the inner bead to the hub face)on a 911 wheel is 5". Now how far can I move that hub face (ie shorten the backspace) and still have a "safe" (from an engineering standpoint) wheel. Somewhere between "0" and 5". Wheel stud length and flare size is not is not the issue here. Now think about this...does a wheel with a 3" or 2" or 1" backspace create structural issues that would preclude such a radical backspace.

Tks,
Jeremy

[Joe Bob]

It's hard(er) on wheel bearings....structurally....10 inches is not going to break MOST rear ends. But in a race environment is is best to periodically inspect for fractures.

[Bill Verburg]

152.40mm(6") gives this much clearance w/ an 11" wide tire

[Az911]

Bill will 275s work with sway a way spring plates?

[IROC]

Originally posted by mikez
It's hard(er) on wheel bearings....structurally....10 inches is not going to break MOST rear ends. But in a race environment is is best to periodically inspect for fractures.

Actually the amount of backspacing has no effect on the loads that the wheel bearings see unless the location of the center line of the wheel is actually altered.

Mike

[IROC]

Originally posted by Az911
Bill will 275s work with sway a way spring plates?

FWIW, I have 275s (on 9x17s) with Sway-A-Way spring plates and I have no clearance problems. A 10 is a different story, though...

Mike