offset to backspace conversion ?

[Bob Lacey]

Hi all.

This is a confusing subject for many builders /owners ,we have recently added this conversion chart to our tech info section - click on the link below -hope it helps!
Offset to Backspace Conversion : Vintage Wheels, Hot Rod and Muscle car

Bob Vintage Wheels

[ERA2076]

That is very useful for me - Thanks You.

[strictlypersonl]

Simple calculation:

Offset=backspacing - (wheel width/2)

(That's bead to bead width, not rim edge to rim edge).

Be careful when comparing offset numbers. Some (like me...) define positive offset as moving the wheel toward the outside. Others (like the chart) define it to the other direction. The change probably comes from the transition from rear drive to front drive and/or a reduction of the king pin offset in most cars.

[ERA2076]

Originally Posted by strictlypersonl

Be careful when comparing offset numbers. Some (like me...) define positive offset as moving the wheel toward the outside. Others (like the chart) define it to the other direction.

That's a tastie bit of information

Why is backspace and width expressed in English units and the offset expressed in metric units?

It's always seemed like a funny way to run a railroad.

x-chr

[strictlypersonl]

Welcome to a world where 99% of the aftermarket wheels are made in Metric Countries (and 95% of the world's population lives). We in the US are the anomaly.

I changed from a Physics major (even in the late 60s, most of the process was done in Metric) to Mechanical Engineering (Back then, mostly "English" units), and I can tell you the the first system is much easier to use.

Intellectual inertia is not a scientific thing...

[ERA2076]

Originally Posted by strictlypersonl

Intellectual inertia is not a scientific thing...

Well said -