This is my first time posting, so apologies if I did something incorrectly.

I recently bought a used Marin Bobcat Trail 3 mountain bike and noticed the front hub was really tight. After removing the hub, I counted ten 1/4" bearings on both sides (only nine would comfortably fit when I tried reassembling). Most bikes use ten 3/16" bearings on the front hub and I suspect a prior owner installed the wrong bearings. There is no damage or excess wear to the cup, cone, or bearings though. Does anyone know what size the front bearings should be?

Here's what I've found so far:

  • I tried to find the model number for the hubs, but unfortunately they only have the Marin logo and nothing else.
  • This post says the hubs are most likely DC20, but I couldn't find any information about the bearing size. Even if I did, there are no markings on the hubs so I don't know if they are actually DC20.
  • The Marin website did not have any information about bearing size. All it says for the hubs is "Forged Alloy, 32H". Owner's manual did not have any information either. Marin support never responded to my email request.

My best guess is that 3/16" is the correct size, but was hoping someone else knows the correct bearing size.

1 Answer 1


Welcome to Bicycle Stack Exchange.

I have never seen a loose ball front hub that had 1/4" bearing balls. It seems you're able to disassemble the hub if you can report the measurement of the balls currently residing in the front, I suggest you continue the maintenance and remove the 1/4" balls and replace with a 10 count of 3/16" balls. Reassemble the axle, cone nuts and lock nuts into the hub, paying special attention to the amount of play as you reach the appropriate preload. A slight amount of play in the axle assembly is necessary in a QR axle to allow for the distortion of the axle--and resulting increase in bearing preload--when the QR skewer is closed/tightened.

Any abnormal findings like inability to get rid of all play (in the refreshed hub with 3/16" ball bearings) unless the system preload is so much that it affects smooth rotation of the wheel, and you might be dealing with cone nuts or hub cups that have been damaged by the too large balls.

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