Shimano Deore 12-Speed

Because buying bike parts is almost as fun as riding with them, I nearly immediately replaced the OEM SRAM drivetrain on a 2020 Santa Cruz Chameleon with Shimano’s budget friendly 12-speed option.

After 250 miles and a few part pull-offs/put-ons for the heck of it, I’m left with a few questions. In particular, the definition and application of two of Shimano’s crank models. Let’s talk about aesthetics real quick though.

Nice touches

It’s usually true that lower-tier components don’t look as good as their flagship counterparts’ and never quite match the streamlined look of high-end industrial design. One can’t argue with the absolute beauty of Shimano’s 12-speed XTR, but Deore isn’t too far off. I’d even say it has some touches that are a bit nicer than that of its high end siblings. It’s true.

Shimano Deore 12-Speed crank
The abalone shell/pearl effect of the Deore logo is a thing of beauty.

The shimmer of pearl on the cranks and derailleur logo can’t be ignored. It’s subtle against a backdrop of matte and glossy black and adds interest to a part that naturally draws a lot of visual attention. A+ for the Shimano team on this one.

Design matters. Looks matter. If you’re spending your hard earned cash for bike parts, it’s never function only. Form has an equal place; at least, for me it does. Minus a little heft here and there, for the most part, I am pleasantly surprised by the presentation of Deore. However, the praise stops at the chainring.

Its bulky plastic carrier and cheap looking rivets that look like screws but are still rivets, is confusing and unnecessary. . .even for the cheap stuff. There’s just no reason for it. I replaced it with a direct mount option from Wolftooth.

Q-factor and Chainline. Does it matter? FC-M6100 and FC-M6120.

Yes. It matters. I’m riding a 148 Boost spaced Chameleon. Shimano designed the 6100 for use with 142/148mm O.L.D. frames and 6120 for 148mm O.L.D. frames. So, which is the correct option for boost spaced frames? Right. The difference between the two is Q-factor and chainline. The 6100’s have a 172mm Q-factor and a chainline of 52mm. The 6120’s, a 178mm Q-factor and 55mm chainline. Help yourself understand the conversation by reading Wolftooth’s or OneUp’s thoughts on the matter and geek out on chainline theory.

I initially purchased the 6100’s for the ideal 52mm chainline. However, the massive drive-side chainstay weld only left 1mm between it and the crank. The Q-factor was too narrow. On to the 6120’s. These installed with the ease and simplicity Shimano is known for and the 6mm additional distance between the cranks eliminated clearance problems. But I was locked in to a 55mm chainline. Hmm.

3-4mm clearance after swapping to the 6120’s.

Does a 55mm chainline work?

Briefly, if you read forums on the topic (with all of their very scientific and data driven talking points, and equally professional avatars, might I add) regarding optimal chainline, you’d be forgiven your skepticism on the logic of 55mm. However, this is Shimano we are talking about. Par excellence goes the belief of many. Doubt must be measured against decades of reliability and podiums. And podiums. And Podiums, again. Surely they must know what they are doing.

I think so? That’s about as good as I can come up with. When installed, the angle between largest cog and chainring is noticeable. In fact, it’s huge. Shifts are mostly crisp and smooth, and that’s all that matters. I’m left wondering why Shimano didn’t offset the chainline 3mm to bring it back to 52mm. I can’t say for certain shifting would be better, though, common sense says it would, but I am curious about durability of the system. It seems like something has to give. . .a busted chain or a more quickly worn cassette. Also, maybe I’m totally wrong. Time will tell.

Spindle spacers used to fill the extra 6mm on the 6120 cranks with 178mm Q-factor

Another interesting observation is the spacers used to fill the gaps between bottom bracket and crank arm. The 6120 comes with 2, 3mm spacers. They are unsightly. Maybe I shouldn’t care. I care. They seem out of place and an afterthought. In the name of industrial design and engineering. . .because I’m an expert. . .this was a miss. Why couldn’t they have been made the same diameter as the bottom bracket cups? Perhaps they match Shimano’s larger bottom brackets. If so, great! But, it would have been nice to offer a smaller diameter option to match the smaller bottom bracket’s cup size.

Spindle Length

Most curious is the the amount of spindle that remains to clamp the non-drive side crank to. My bottom bracket shell is 73mm and as is standard, the drive side cup uses 1 x 2.5mm spacer between the shell and cup. As a result, the non-drive side crank’s outer pinch bolt only partially clamps on the spindle. There is no slop or play in the connection and it feels as secure as every other Shimano crank/bb interface previously used and the preload bolt has plenty of thread to grab onto and secure the crank arm to the spindle. Still, during installation, I kept thinking I was doing something incorrectly that caused loss of spindle real estate. What’s going on here?

I suspect that both the 6100 and 6120 models are the exact same cranks and that the 55mm chainline of the 6120’s is the result of the 3mm drive-side spindle spacer; a clever way for Shimano to keep part numbers down and manage inventory. As much of a pain as it would be for them to bond a longer spindle on the 6120’s, which would add greater complexity to purchasing, manufacturing and inventory tracking processes, I would prefer the visual comfort of the non-drive side crank’s pinch bolt securely overlapping the spindle end. This is all speculation of course. I don’t actually know.

Everything about Shimano’s two-piece crank design is best on the market. . .in my view. The 30mm spindles of some competitors are unnecessary and Shimano’s crank/spindle connection is tops. However, the short spindle issue sours my usually high praise.

Micro Spline Durability

My Deore XT freehub broke after 1 month of riding. I can’t explain why. The internal mechanism’s teeth wouldn’t engage. Freewheel in both directions! Again, a look on the forums from our trusted bike advisors tell of a frightening trend with Shimano’s quality control and design flaws. Maybe. But I’m unwilling to throw in the towel on Shimano’s 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 good ‘ole days of Shimano’s 1/2/3/4/5/6/7/8/9/10/11 HG freehub bodies. Did I get that right? Anyway, little information and fewer tutorials exist on how to remove it. YouTube was mostly unhelpful, save for the one Portuguese bike mechanic who posted a couple of videos. Good tutorial, I had mine off in minutes. I also learned how to speak Portuguese for the exact scenario when a Brazilian may need to remove their Micro Spline freehub.

I must pause to give a shout out to both Shimano and Universal Cycles. The UC team built the wheel for me and handled the replacement part with great speed and humility. They were on my side the whole time and worked with Shimano to get me back on the trail soonest. Nice work both.

Final thoughts

Perhaps I’m griping too much, but I can’t ignore what seems like cost savings driving bad decisions from the cross functional team of product managers, engineers, and finance folks. However, and most importantly, if given the chance to purchase again, I would.

I believe Shimano knows what they are doing and given their undeniable market share loss on the mountain side of things for the last couple of product generations, much needed to be right for this group’s price point. While flawed with bizarre design rationale (if I’m right), it works. An until it doesn’t, I’m in.

Welcome back from your long years slumber Shimano.