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Bearings: 3/16 and 1/4 inch sizes
#1
So I was overhauling the hubs on an a rescue bike I was fixing up and discovered that the rear hub had 1/4" bearings and the front hub had 3/16". I know the provenance of the bike so I'm sure they had not been replaced since it shipped new. As far as I can tell from eyeballing, the cones and races are the same size--you can fit either 9 x 1/4" bearings or 11 x 3/16" bearings in the races.

I went ahead and repacked them with 3/16 in front and 1/4 in the rear but it left me with a few questions. The bike was sold as a mountain bike but would be more of a hybrid by today's standards. It's a TIG'd CroMo mixte with a longish head-tube and curved forks.

Anyway:

- Is this standard or common?
- Does the rear benefit from 1/4" bearings (i.e. withstands the additional stress better)?
- Sheldon implies in one of his articles that going from 9 to 11 bearings is a cheap "upgrade", but he was talking about bottom brackets and keeping the same bearing size and reducing the gap between them. However, would a hub not benefit from a greater number of (albeit smaller) bearings, or is the advantage only in reducing the gaps?

- In other words, is there a reason not to just pack both with 3/16"?

Thanks for any wisdom or insights :-)
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#2
Yes, this is common, as far as I experienced. I also wondered, but replaced the bearing balls with the size I found installed. I think the rear has smaller bearing balls to keep the bearing narrower, at least this was the case for the Maillard Helicomatic hub (one of the first cassette hubs). So when you repack the rear hub with 1/4, it might be too wide to fit in the dropouts.
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#3
3/16" for front and 1/4" for rear and bottom bracket are standard for vast majority of bikes.
You probably could pack both with 3/16 or 1/4 and it will function. But I doubt there is any big benefit and there is possible problems. It is not neccessarily the "size" of the cones/races that are different, but they probably have a different curvature made to fit the intended ball bearing (BB) size. When you put a different diameter BB in there, it won't match with the curvature of the groove in the race.

So you can usually get away with it in a pinch, but I wouldn't recommend it.

Joe_W is right that it would change the width of the hub, but only by 1/8", so that's not a big issue.

The 9 bearing to 11 bearing change Sheldon Brown is talking about is probably putting in "loose" balls instead of using ones in a cage. This allows more room so you can get more bearings as the cage is only there to make installation easier. Hubs are more likely to already have loose balls so less likely you can do this.

Use decent quality bearings, good grease, and get the bearing adjustment very accurate and you'll get good life on the bearings. Grit and bad adjustments are what kill bearings fast. I wouldn't worry about getting tricky with odd sizes.
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#4
Thanks for the good insights Joe and Dave. It's great to have other people to bounce these things off of.
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#5
For completeness sake: I looked it up, the Maillard helicomatic used 13 5/32" balls. There, it actually was an issue. (also 1/8" > 3mm, this will make wheel installation more difficult + hanger will no longer be aligned correctly)
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