speeds27

So i have a set of wheels and i'm trying to calculate the offset. From my understanding, the offset is the wheel backspace minus the wheel centerline multiplied by 25.4 to get it into mm.

So the set of wheels i have are the following.

Wheel Width = 9

Wheel Center Line = 4.50

Wheel Backspace = 5.75

Thus = 5.75 - 4.5 = 1.25 * 25.4 (to convert to mm) = 31.75

But according to this graph from rsracing.com, it says with a wheel width of 9 and a backspace of 5.75, the offset should be 19

Now i know i'm not the brightest crayon in the box, but whats up with my math?



https://www.rsracing.com/tech-wheel.html

Measuring Wheel Offset

To calculate offset you'll need the following measurements:
Wheel backspace
Wheel Width
Wheel Center line (outboard flange to inboard flange measurement / 2)

Subtract:
Wheel center line from Wheel backspace to get offset.
If backspace is less than the wheel centerline the offset is negative
If backspace is greater than the wheel centerline the offset is positive

Tip:
To convert from inches to mm multiply by 25.4
To convert from mm to inches divide by 25.4

rominl

iTrader: (4)

i will give this one a try. it has to do with definition i think, and you can also see it from the following picture



definition of wheel width is not outboard flange to inboard flange, but instead, outboard bead seat to inboard beat seat. so when you do the flange to flange, it's not the wheel width, and they seem to add about 1/2" to each side (1" in total).

so for example, a 10" wheel, the flange to flange is actually 10"+0.5"+0.5" = 11" (center line 5.5"). that's why when you look at the table, if you have a 10" wheel and the back space is 5.5", your offset is zero.

using the same idea on your example, for a 9" wheel, the flange to flange is 10", center line 5". back space 5.75", so offset is +0.75", which is +19mm

speeds27

Thanks for the clarification rominl. I think i got what you're saying. So lets see if i have this correct.

I have a staggered set.

Front wheels are 8.5 (flange to flange 9.5)
5.75 (wheel backspace) - 4.75 (center line) = 1 * 25.4 = 25.4 offset



Rear wheels are 9.5 (flange to flange 10.5)
7 (wheel backspace) - 5.25 (center line) = 1.75 * 25.4 = 44.45 offset

rominl

iTrader: (4)

i think that sounds right

ClearP

This clarified a few things for me!

Rominl, do you mind me using your "Support Authenticity" Avatar and your signature?

rominl

iTrader: (4)

hahhaa of course no problem, please feel free

Brandon@TR

Why not just put on a flat surface, measure the width with a ruler through the center bore, divide by 2, then use another straight edge to calculate the difference between the center line of the wheel and the mounting flange, while you still have the ruler sticking up through the center bore. Use the MM side of the ruler also.

ClearP

Thanks Rominl!