Shimano Deore XT 8100 Micro Spline Freehub

Shimano Deore XT Freehub

Up the rock I went. A steep 5 ft. face and round edge that transitioned to a gently sloped wheel’s length plateau. I made it. A quick pause and pedal kick to the opposite edge for a controlled, feel-good rear wheel drop and. . .a lost connection from crank to the rear wheel. Thud! Crack!. . .went my chest into the bars and stem after a barely made it landing. My rear hub broke; the freewheel did anyway. Three months of riding. Dunzo. I can’t explain why. The internal mechanism’s teeth wouldn’t engage. Freewheel in both directions!

Prior the break, I listened to some well meaning and well respected reviewers make passing comments with concern and frustration about Shimano’s new 12 speed hubs. Compared to previous Shimano hubs, they pointed out the inconsistent sound of the freehub when the wheel spun in a stand. Loud, silent. Loud, silent. And on and on. I thought it a bit strange, though I reasoned that all hubs have a slight loud-soft variation when the wheel spins. I wasn’t concerned. Then my hub broke.

Why did it break?

My guess? Three months of riding hard with Shimano’s Deore 6120, 55cm chainline cranks AND my unevenly adjusted adjustable dropouts. The wheel sat slightly crooked and favored the non-drive side. Common sense would tell you that forces on the internal mechanisms in the freehub from a crooked wheel, wide chainline, and high torque loads produced by the 51 and 45 tooth cogs may be the culprit. Again, I can’t confirm this, but I’m going with it. Curious what the actual bike engineers think?

Sign of things to come?

I don’t think so. As I wrote previously, a look on the many forums from our trusted bike advisors armchair engineers tell of a frightening trend with Shimano’s degraded quality control and compromised product design. Maybe. But I’m unwilling to throw in the towel on Shimano’s new hubs after years of near perfection and reliability. Micro Spline technology is only a couple of years old and is a big departure from the age and ubiquity (largely because of its age) of Shimano’s 1/2/3/4/5/6/7/8/9/10/11 HG freehub bodies. Did I get that right? I don’t believe Shimano rushed an untested technology to the market. Micro Spline is an epic departure and warrants judgement on its own. HG was good for what it was. Micro Spline is altogether different and a very compelling solution in the evolution of 1x drivetrains. I’m all in.

Back in action

Both Shimano and Universal Cycles (they built the wheel) handled this repair with great speed and humility. UC was on my side the whole time and worked with Shimano to get me back on the trail soonest. Nice work both. It took a week. Since then, and after a new 52mm chainline and evenly adjusted dropouts, there has been no incident. That was 4 months ago.