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. 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. Additionally, 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 can’t say for certain, but 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;

Everything about Shimano’s two-piece crank design is best on the market. . .in my view. The 30mm spindle standard of their competitors is cool, but lacks the simplicity of Shimano’s tried and true crank/bb connection. What to me seems like a short spindle, sours my usually high praise.

Final thoughts

If given the chance to purchase Deore 6100 series again, I would, save for the cranks. If the 6100’s Q-factor was a bit wider I would most certainly use them. I’ve moved on to a set of Race Face Turbines that allow for a 52mm chainline, Q-factor that clears my frame, and that accommodate third-party, direct mount chainrings for use with Shimano’s HG+ system.

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. It’s mostly right and I’m in.

Welcome back from your long years slumber Shimano.

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