Mountain Bike Reviews Forum banner

Sorting out chainline and spindle length (square taper)?

1162 Views 1 Reply 2 Participants Last post by  SteveF
I just received my new bike frame...a Tumbleweed Prospector. The frame is designed around a 54mm chainline to run a Rohloff IGH with 4.0" tires, but it does have a derailleur hanger to run a cassette drivetrain with 27.5 or 29+. It takes a 73mm bottom bracket.

I have a nice set of Middleburn RS7 crank arms (square taper, w/ an Uno direct mount chainring, and a spider for up to 3x) and had a 73x113 BB in the parts box, so I threaded the BB in and snugged up the crank arms, just to see. The Uno chainline measured at 49-49.5mm. This would be fine to run a 1x drivetrain with 29+ wheels/tires, but it won't work with a fat setup. The bigger issue is the the drive-side crank arm would not clear the chainstay (see pic - where you see no gap is where the crankarm touches...just barely). The non-drive side has 2mm of clearance. So no drive-side spacer will help; I think I need a longer spindle.

My thought is a 123mm spindle, and will probably need to swap to the spider + standard chainring if/when I run a 1x derailleur setup. With a drive-side 1mm spacer, I should end up with around 5mm of clearance on each side. If my math is right, an Uno chainring should end up at near 54mm...just right for single speed or Rohloff, but too far for derailleur + cassette setup (I think the published max. is 50mm?).

I'm hoping someone can confirm if my thinking is right before I go shopping. I've been hearing that parts are hard to get due to supply chain issues. I will also be reaching out to the manufacturer to see if they have a spindle length recommendation as well.
Bicycle Crankset Bicycle tire Bicycle frame Automotive tire

Bicycle tire Bicycle part Rim Electrical wiring Bumper

See less See more
1 - 2 of 2 Posts
Well, the math checks out more or less-a 120+ spindle would give you about the right clearance on either side. I'd go with a Phil Bottom Bracket. They have a good bit of side to side adjustability so you can fine tune your chainline, and many spindle lengths to choose from. It wouldn't hurt to ask both Phil Wood and Middleburn for spindle length recommendations. Square Taper Bottom Brackets 103-145 mm (JIS Taper)
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.