Fitting Rear 5" CBR Cast Wheel with Cush

For what it is worth the following is how I plan to install a 5" rear CBR 17" wheel on my 05 Fe550. Any comments / feedback welcome.

My first thought is to mill the CBR hub and cush so that the "rotor to sprocket" spacing and "outer spacer to spacer" spacing is similar to my existing dirt wheel. Below is a rough cross sectional schematic outlining the spacing of my existing dirt wheel.
Overall width ~179.8mm
Rotor to sprocket spacing ~156.3mm
with 10.8mm and 12.7mm spacers and
The rim centerline ~81.5mm from the left side.

EXISTING REAR DIRT WHEEL SPACING (CROSS SECTION)



The CBR rear wheel had a "rotor to sprocket" spacing of ~168.2mm. So I will need to reduce the CBR wheel "rotor to sprocket" spacing by 11.9mm. See next diagram.

My second thought is how much I should mill from each side of the CBR wheel so that the rim is centered between the swing arm on the left and the chain on the right. I mounted the CBR wheel with the rotor and no cush drive in the swing arm. With the rotor positioned in the caliper, I noted the widest part (the bead) of the rim was about 20mm from the swing arm on the left and about 6mm from the chain on the right. See the diagram below. Given these clearances, I will have to shift the rim 7mm to the left so that the rim would be centered with 13mm of clearance on either side of the rim, between the swing arm and the chain.

Shifting the rim to the left by 7mm requires milling/removing 7mm from the rotor mount surface. This then offsets the center of the rim by about 9mm when compared to my existing dirt rim. I was concerned an offset of this amount would noticable effect ridability. My sense from the Super Moto Junkie Site (http://www.supermotojunkie.com/) is that this amount of offset is not noticable and some what common.

My next thought is how/what to remove from the sprocket side (hub and cush) to obtain the appropriate "rotor to sprocket" spacing and "outer spacer to spacer" spacing while retaining the cush drive. Given I will be taking 7mm from the rotor side then I would have to remove about 5mm from the sprocket side to reduce the overall "rotor to sprocket" spacing by 12mm.

My strategy is to remove 5mm from the right side of the wheel (the outer part of the hub and the inner part of hub around the bearing). This will also require removal of 5mm from the cogs of the cush drive as well as 5mm from the inner axle spacer between the cush bearing and wheel bearing, allowing the cush drive to slide 5mm towards the hub.

The next step is to remove the very outer material of the CBR wheel flush with the outer bearings to ensure clearance between the wheel hub/cush and the swing arm.

The final step is to machine two spacers (~1-2mm and 5mm) so that CBR wheel has a similar "outer spacer to spacer width".

The following image outlines the standard spacing of the 5" CBR wheel. The black areas indicates the 8 separate areas that need to be milled/removed.


STANDARD REAR CBR WHEEL SPACING
(Solid black areas indicate areas that need to be removed)




REDUCED REAR CBR WHEEL SPACING
(Solid black areas indicate areas that need to be removed)


Clear as mud? I should add some pics of the CBR wheels to help make sense of these drawings.

I will keep you posted as to how well this plan works out. Stay tuned.

Hey Taffy,
I figured the best case was to keep the rim centered (ie. the tire should be centered as well). The even 13mm (1/2") spacing on each side should be enough for a 160 tire. Most guys seem to be able to get most 160 tires in with no chain rub.

Although, if I had a specific tire in mind, depending on the amount of overhang, I could minimize the offset to allow a minimal clearance between the chain. I figured best case was to keep it centered.

Stay tuned

Re: RE: Fitting Rear 5" CBR Cast Wheel with Cush

Taffy said:

funnily enough it isn't a big deal because you must align the rear wheel to run behind the front. it must TURN. so everything you do is halved! 7mm becomes 3.5mm etc etc....

regards

Taffy

Click to expand...

Not sure I follow, explain?

Are you suggesting I should offset the front the same amount, so that the two tires line up?

I haven't started thinking about the front yet.

Re: RE: Re: RE: Fitting Rear 5" CBR Cast Wheel with Cus

Taffy said:

try and think it through mate!

Click to expand...

I tried but nothing comes out! :scratch: