rim sizes ???

[jackal]

ive got a spare Rial split rim in the garage
hwvaing a clearout so its going on ebay
anyoen know how i measure it ?
its obviosly a 13" rim and from one edge to another it measures about 8.5 inches si am I right in thinking that its a 13 x8.5 ? Also, how do I work out what the offset is ?


thanks
R

[Fat Arnie]

Measure the width of the rim between its outer edges, lets call that "A" and also the distance between the bead seats. Lets call that "B".

Lay a straight edge across the rim on the 'inside' side of the wheel. Measure the distance between the backface of the wheel centre and the point where this intersects the straight edge (i.e the shortest distance) Lets call that "C"

Now work through these:

(A-B)/2 = D
C-D = E

E is the backface dimension.
B/2 - E = Offset

If the Offset is a +ve value you have that amount of Negative Offset - i.e the offfset figure is preceeded by a "-". Typically for a Caterham you will have offsets of around -20m to -30mm.