Offset vs backspacing?

[DriverzInc]

Did the math myself to check too, and yes, a +19mm on a 10" wide wheel is a 6.248 (or 6.25") backspace.

The way I do it is I take the overall width of the wheel, which in this case is 11" and divide it by 2, which will give you "0 offset", which in this case, it is a 5.5" BS.
Then, I take 19, and divide it by 25.4001 which is how many mm's are in an inch. This gives you .748. Now, since its a positive offset, you just add your .748 to the 5.5" and you have your backspace.



Hope that breaks it down for everyone. If not, guys like me are always here to help.

[JRouche]

Ok, dummy me, I always wondered why there was, in my vision, two measuring systems for wheel offset or backspacing. I always thought it was a metric VS us type thing. Seems the import car world is bent on using offset numbers and the muscle car, hot rod, pro-touring folks wanted to use back spacing. What the heck. I was lost.

And I read and read, learned and listened, still the same. Till one day on the crapper reading one of my favorite novels. Ok, no, not my wifes People magazine but my "Chassis Engineering" book. I kinda take it all around the house

Anyway, up to this point I was still unaware of the differences. Backspacing? Offset? All just words to describe the same thing right, how far a wheel sets out from the mount. Well not really...

So I sat and learned, and my eyes were opened.. All in one paragraph.

For fear of copywrite issues Im gonna paraphrase slightly. What I read.......

In order to reduce your cars front scrub radius you should use wheels with zero or negative offset. Zero offset means that the mounting surface of the wheel is on the same centerline as the tire. Because a 10 inch wheel is actually 11 inches flange to flange, the backspacing for a zero offset on the 10" wheel is 5.50 inches.

That single paragraph summed it up and made sense. Offset is a term used for suspension purposes (not always) and back spacing in used for fitment issues.

I never knew..... Offset is really important, meaning the offset from centerline, if you are concerned about handling. Backspace is a term for fitment issues. Which is just as important. But on different levels.

Oh, I was kinda lucky to have my front wheels on a zero offset, but my main concern was the backspacing for fitment. Cause if it doesn't fit what the hell, its all out the door... So I learned the diff, its not all about fitment, some handling issues come into play.. Nice to know info.... JR

[68Formula]

And I read and read, learned and listened, still the same. Till one day on the crapper reading one of my favorite novels. Ok, no, not my wifes People magazine but my "Chassis Engineering" book. I kinda take it all around the house


In order to reduce your cars front scrub radius you should use wheels with zero or negative offset. Zero offset means that the mounting surface of the wheel is on the same centerline as the tire. Because a 10 inch wheel is actually 11 inches flange to flange, the backspacing for a zero offset on the 10" wheel is 5.50 inches.

Be careful. For some strange reason, Herb's definition of positive vs. negative offset is different than typically used today. He calls negative "mounting surface outboard of the wheel centerline," and then uses an example of 1" negative offset creating a 11" wheel with a 6.5" backspace. Usually a positive offset by most definitions today, creates more backspacing. (The above links are prime examples).

[JRouche]

Be careful. For some strange reason, Herb's defition of positive vs. negative offset is different than typically used today. He calls negative "mounting surface outboard of the wheel centerline," and then uses an example of 1" negative offset creating a 11" wheel with a 6.5" backspace. Usually a positive offset by most definitions today, creates more backspacing. (The above links are prime examples).

Oh yeah, not just that one, there are other typos. Someone has a thread asking about which books are good. I wrote this below.. Thanks for the heads up.. JR

That one and "how to make your car handle" by Fred Phun.. I use both and they cover everything I need. Even still, you gotta watch the reading, I "think" I have seen some typos in both books. But if yer reading it carefully you can pick it up and realize it was just a typo. JR