I thought I'd write up the process of measuring up the front end to
determine spacer sizes for the new triple clamps and front axle. I
hope this will be useful for those of you thinking about fork or wheel
The Harris triple clamps are wider than the stock CBR parts my forks
came from, so new spacers for the axle and brake calipers need to
be made. I have stock Honda parts available for comparison, but I
wanted to go through the math to make sure everything comes out
right and the wheel is centered in the forks. I knew that the nominal
difference was 11 mm, so Harris supplied a new axle 11 mm longer
than stock. I'll start by taking measurements to determine what
the real difference is. (All measurements are rounded off to whole
First the fork tubes were fitted to the CBR triple clamps and some
measurements taken between the bottom of the sliders and between
the brake caliper mounting lugs. The same measurements were
then taken with the forks mounted in the Harris triple clamps. The
difference was 10mm. So my axle spacers should be 5 mm longer
on each side of the wheel. I'll also need to fabricate spacers to locate each caliper 5 mm inwards.
The distance between the sliders came in at 162 mm. Measuring
through the wheel across the bearings gave me a dimension of 114
mm, leaving a difference of 48mm. This is the "space" that needs
to be taken up by spacers and at first glance it might seem that a
couple of 24 mm spacers would do the job. But they won't.
In the pic below it can be seen that the axle has a "step" in it. The
nominal (smaller) diameter is 20 mm and that's the size of the inner
bearing races. The larger diameter is 25 mm. The bottoms of the
sliders are bored to accept the two different diameters. When the
wheel and spacers are fitted to the forks and the bolt at the end is
tightened, the axle is drawn to the left (left in the photo) until the
shoulder on the axle tube pulls the parts up against the left slider.
So the spacer on that side (left in the photo) is what locates the
wheel in the forks: the other spacer just takes up the "slack". Pinch
bolts secure both ends. Notice that this design avoids "pinching"
of the fork tubes when tightened and reduces binding in the
Also, the larger diameter has to protrude a little from the right
slider in order to bear against the adjacent spacer, so we'll allocate
1 mm to that. That suggests that the difference between the two
spacers should be 1 mm and that a 24 mm spacer and a 23 mm
spacer will work. They won't either.
The reason is that Honda threw a curve ball: The difference in length
between the stock Honda spacers was 7 mm. Why the difference?
The reason is the wheel itself. The bearings are offset to one side
and aren't centered in the wheel. I measured off the brake discs
(since I know they are centered) and found a 6 mm difference.
While I don't know for certain why Honda designed the wheel this
way, I suspect that it goes back to F2 which had a speedo drive on
one side. Honda may have carried the design over and adjusted the
spacers to suit. Cheaper than a new wheel.
So in the end I wind up with a 27 mm spacer on one side and a 20
mm spacer on the other. Added to my 1 mm shoulder allowance
that gives me the 48 mm I need and accounts for the bearing offset
in the wheel. And it just happens to be 5 mm wider than the stock
spacers which measure 15 and 22 mm.
Now all that's needed is to make them!