on the Profile hub/crankset page, it asks for the bearing size, with two options:
6203-3/4-2RS
99R12
I have no idea what this means, all I know is I want to put it on my 2004 KH20 frame. which one should I choose?
In my opinion, it doesn’t matter. Zack Baldwin and Ryan Atkins both ride 2004/03 KH 24 frames on profile hubs. I think they both use 40 mm diameter bearings, but 1 5/8" will work too. I would go with 40mm, but in the end the only difference is a few turns of the allen key.
hmm, okay, I didn’t know if one would fit a certain frame and not others, or what… so as long as either one will fit, I’ll just choose either one. 
thanks!
The difference is the outer diameter of the bearing.
The 6203 bearing has a 40 mm OD
The 99R12 bearing has a 1-5/8" OD
The made in Taiwan KH frames of old fit 42 mm OD bearings. Neither of the Profile bearings are going to be an exact fit. To get an exact fit you’re going to need some sort of shim around the bearing to make it 42 mm OD.
1-5/8 inches is 41.275 mm. You can probably use a home made shim cut from a soda can to make up the difference between the 41.275 mm OD of the bearing and 42 mm. You might even be able to get away without even using a shim at all.
There were some custom shims available back then to fit a 40 mm bearing in the 42 mm KH frame. I don’t recall where the shims were available from. I’d call Unicycle.com and Darren Bedford and ask if they have such a shim. The custom shim with the 40 mm bearing would probably be the preferred solution.
My current bearings actually do have shims around them already. I can just use these ones for the new profile hub, right?
What size are your current bearings?
If you can read off the numbers on the bearing you can determine its size by looking it up in a bearing catalog. Otherwise you need to measure the size with something accurate like a caliper.
You could also use a caliper to measure of OD of the bearing and shim combination.
for the last time, you dont need a stupid shim while running a Profile sized bearing in a 03/04 kh frame!
john, Profile only makes one size of bearing, the 41mm…anything esle that fits on a 19mm Profile axle is not made by Profile…
They’re standard size bearings available from many different manufacturers. Whether the bearing happens to say Profile on the seal or not doesn’t make a difference. If you order the 99R12 (1-5/8") bearings from Unicycle.com you’re probably going to get bearings that have “Profile” branded on the seal. I have no idea what you’ll get if you order the 6203 (40 mm) bearings. Doesn’t really matter what they are.
You can probably get away with using the 1-5/8" bearings in the old KH Taiwan frames. I just don’t consider it ideal because there is going to be a little bit of slop which could allow the bearing to distort into an oval shape or could allow the bearing to rock or move in the bearing holder when pedaling hard. Probably not a big deal, but I’m a perfectionist at some things. Unicycle.com has the necessary bearing adapters in their catalog: UDC Bearing Adapters. That’s the way I’d go if I was fitting a Profile hub in a 42 mm frame. You could go with the adapter for the 1-5/8" bearing. If the adapter turns out to be a pain you could always go back to using the bearing without the adapter.
thats why i quoted you??? you said " Neither of the Profile bearings are going to be an exact fit." and there is only one…im just calling you on that since you didnt seem to know, thats what happens when you ride the same muni for 4 years.
duh?
well i do…ive ordered 5 profile hubs, built them all and sold them all… ive seen more bearings than i ever want to again.
what do you mean “probobly” i rode with you several times in Oregon, California and Nevada…“probobly” give me a brake!
another oversight, there is no slop, the bearing doesnt distort…do you really think that i would build a muni,ride it, and ride it hard if that was going to happen? (see next comment)
i am a perfectionist too and that would be a huge deal…thats why im posting my expierance that its NOT a problem and using Profile sized bearings in a 03/04 kh frame is fine without a shim. I WOULD KNOW, you would not…you’ve never had one…you have rode the same KH pro for years and never tinkered with the Taiwanise bearing holders.
Bingo!!! thats what i did. i tryed the shims and the bearings fit better without them…if the choice is 40mm however the shims are needed and work better since they are a little thicker and more robust. (yes i have done that set up too)
you have excellent advice john, but experiance is the best teacher.
Since you have the new, very strong profile axle, you don’t even really need bearings. Just clamp down on the axle. Make sure it can still spin. Then ride!