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Discussion Starter · #1 ·
Hello,

I've been lurking on these forums for a long time now, but this is my first time posting. I've been contemplating a sumo project for a dual sport, and I've sourced a set of ZX6R wheels from the local craigslist. The front wheel bearing size in the ZX6R is 25mm x 47mm x 12mm. The stock fork on mine accepts a 20mm axle, and I can get a pair of 6204s that fit in very nicely. So, here goes my questions:

1) What about the cylindrical thingy in between both the bearings? I've always called it a axle spacer, but I realize now that the word means something else :) I am talking about the tube with a ID slightly more than 25mm. Does that have to be 25mm? From what I understand, the only load in the setup should be on the ball bearings which should allow the wheel to rotate without any friction from the axle. Why is this spacer thing even present? Since my axle is 20mm, do I have to get a matching spacer in 20mm or can I reuse the 25mm ZX6R one?

2) In general, once I get the bearings and the innards swapped, I then need to get spacers on the end near the fork so that the disks are aligned correctly, right? In general, are there any other steps I might have to look for? I've eyeballed the width and while the ZX6R rim is thicker, there is plenty of space to fit it in there.

This is probably a very basic question and asked countless times before. I tried the search before posting, I promise!
 

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I've done a few bearing swaps on wheels. The answer to why you need the crush tube can be found HERE.

You should be able to use the 25mm ID tube but it may flop around the smaller axle. Lately, I've been going from 20mm axles to 25mm axles which requires sourcing a bigger tube. I do have a couple 20mm ID tubes that I can get you a length from and model if you want to source a smaller ID tube.

Later, Doug
 

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Discussion Starter · #3 ·
I've done a few bearing swaps on wheels. The answer to why you need the crush tube can be found HERE.

You should be able to use the 25mm ID tube but it may flop around the smaller axle. Lately, I've been going from 20mm axles to 25mm axles which requires sourcing a bigger tube. I do have a couple 20mm ID tubes that I can get you a length from and model if you want to source a smaller ID tube.

Later, Doug
Thanks Doug! That forum post was very useful - the lateral stress part looks apparent in hindsight, I should have thought about it before. I'll likely go to a 20mm ID tube, I first need to get those bearings off. They've been too darn tight and is my weekend project.
 
G

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You need the bearing spacer in the centre of the wheel so stop the bearing centres being forced inwards & collapsing when you tighten the axle, its secondary function is to support the axle

If you go with the 20mm axle you can sleeve down the 25mm bearing spacer, just make sure it wont interfere with the smaller dia bearings

Next you need to get your wheel central with spacers as you said, be aware that the forks will beind in a little as you tighten the axle so allow for this when working out what you need for spacers

Discs can be spaced out a couple of mm with washers & calipers spaced the same way, anything more than 2mm on each though & i would make up some caliper brackets to take the calipers to where you need them
Make sure the brake pads sit fully on the disc & at the right angle when sorting all this out, i find good free moving calipers with new pads will help centralise the caliper on the disk during all this

Hope it helps :)
 

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moron with a hammer
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4cups nailed it.

Two things I can think to add to the above:

1.) The easiest way to check the overall width of the wheel with spacers is to stack up the stock stuff, run the axle through it, and mark the axle. Then, once you get the new stuff in, stack it up and see whether it matches. As above, you want to cut spacers so that the wheel is centered and worry about the brake alignment later.

2.) For a sumo, you're going to want to run a bigger rotor up front anyway, so you'll run a caliper bracket regardless. Easiest to take care of brake alignment issues there.
 

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Discussion Starter · #6 ·
Thanks guys. This is exactly the reason why this forum rocks! I've been trying to get the stock bearings off, and man they are hard. I've tried all the tricks except the blowtorch - I'd rather have a shop take them off than do it myself.

While thinking this through again, I am dropping the rake by roughly 2 degrees (26 to 24), which isn't much. But the trail is dropping from 116mm to 85mm, which is like 25%. Is the bike going to be very twichy in real life? Right now, it's just a slow turning pig, so I wouldn't mind some amount of nimbleness. Googling for a road bike with a <90mm trail doesn't show much. I guess I could take it out for a spin after this is done to see how significant it is in real life.
 

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moron with a hammer
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The bike will be happy there. Don't sweat it. I have a bike with under 30mm of trail, and it gets SKETCHY under very heavy braking, but behaves well otherwise. With your much longer fork, 85mm should be a good match.
 
G

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I agree the rake & trail should be ok at that if the numbers are correct, rake & trail changes constantly while you are riding due to suspension movement which explains things getting a little interesting under heavy breaking ;)

The only other thing i can add is if you are changing the rear wheel which may change the ride height & therfore the rake & trail your numbers may be a little off unless you have taken that into account, just mentioning it in case you hadn't thought of that :)
 
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