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I'm servicing the Quando hubs on my single speed/fixie bike. This hub uses a cup and cone type bearing assembly. When I removed the cones I noticed that one of them is chewed up badly at the end. I have good reason to suspect that the last owner may have used the incorrect bearing size when they attempted to service the hub. The cups still seem to be in good shape though. So, I want to replace the cones and bearings, and be sure that this time I'm putting in the correct sized bearings.

Given that I don't trust the size of the bearings that I'm taking out, how can I determine what is the correct size of bearing to use for this hub? Googling "Quando hub bearing size" hasn't turned anything up for me.

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    Can you post a photo? Its not impossible for one ball bearing to disintegrate despite being the right size.
    – Criggie ♦
    Oct 7, 2016 at 10:40
  • It's unlikely that one or two undersized balls would cause a problem. If one or two were oversized, however, that would be an issue.
    – Daniel R Hicks
    Oct 7, 2016 at 12:04
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    Another point: When you replace the balls, replace all of them. The old ones (if they have many miles on them) will be worn and undersized, and if you replace only one or two those will take all the force, possibly leading to spalling.
    – Daniel R Hicks
    Oct 19, 2016 at 21:07

3 Answers 3

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The vast majority of OEM hubs for adult bikes are 3/16" front, 1/4" rear, usually ten per side in front and nine per side in back. Exceptions do exist, but if nine 1/4" bearings comfortably fit in the cup with little to no extra space, that's very probably what it takes.

Quando is a line of Kun Teng, or KT, one of the largest hub manufacturers. By doing enough homework, or maybe just emailing them a picture of your hub and asking what bearings it's supposed to have, or asking them if they've ever made any singlespeed/track rear looseball hubs with anything but 1/4", you may be able to get a definitive answer.

If one had to figure this out without any external information, it becomes a matter of making an educated guess based on looking at:

  • How the different sizes of bearing mate with the profile of the cone and/or cups. The radii won't be exactly the same, but they do complement each other (a bearing engineer would put that better I'm sure), and by knowing what's normal you can pick up on incongruities. Also if a bearing's radius is way too large for the cup/cone, it will be apparent by the fact that it's making contact at more than one point.
  • What installing the different sizes does to the positioning of the cone relative to the rest of the hub, i.e. whether any sealing will be sitting at the right level and able to work properly, or whether any of the race is exposed that one would normally expect to be hidden.
  • Where the ball track (the line the bearings clear away in the grease) sits on the cone race. If it's at an extreme end of the race's curve, that's a sign of the wrong bearing size. Being somewhere near the middle is a sign of the correct size. Likewise, in some cases one would be able to make inferences based on where the ball track is falling in the grease relative to where existing wear lines are on the races.

All the same considerations, especially ball track, apply to determining appropriate replacement cones.

Wheels Manufacturing makes replacement cones for many common KT hubs. I have no idea if they'd be applicable to your track hub, but maybe.

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I have serviced a KT flip-flop hub and a KT 8-speed hub that both had 10 of 7/32" bearings on the right (or freewheel) side and 9 of 1/4" bearings on the left side.

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Do you have access to a vernier caliper?

enter image description here

Measure the existing unchewed ball bearings. There's a very high chance you need the standard sizes, which are:

  • 3/16" BBs for the front hub
  • 1/4" BBs for the rear hub

Replace all of them together

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  • How would one choose correct cones?
    – Davorin Ruševljan
    Oct 7, 2016 at 14:06
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    @DavorinRuševljan Like what Criggie said, you are going to have to measure them, preferably with calipers and look for some accordingly. This place seems to have a lot to choose from wheelsmfg.com
    – npsantini
    Oct 7, 2016 at 14:25
  • The trouble is I believe that the bearings in there at the moment are the wrong size (not original) so I don't want to measure the existing bearings. Same goes for the cones. I think the wheel was repaired at some time with spare parts and neither the bearings nor the cones are original.
    – John
    Oct 7, 2016 at 17:09
  • @DavorinRuševljan The good thing about cones is that their size is relaed to the length and the width and threads etc.. The bearing running surface is not something that is measured. Can you say why you think the bearings in there were the wrong size? Sounds to me like you have spalling on the cone, where the running surface has been eroded. Since your cups are okay, new cones and new ball bearings should be all you need. Cones are $2-$25 depending on rarity, balls are $2-$10 for a bag big enough to do both sides, with spares. Add grease and its a 1 hour job. Add a photo perhaps?
    – Criggie ♦
    Oct 8, 2016 at 0:21
  • @John Sorry that comment is to OP as well.
    – Criggie ♦
    Oct 8, 2016 at 0:22

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