Why do Shimano have so many Q factor variations?

I mis brought a crankset, I wanted M7100 and accidentally brought / was mis sold M7120 and I don’tike the 6mm added Q factor (3mm extra per side).

I know I can move my cleats but then that messes with other bike pedal set ups.

It’s pretty much accepted that a 52mm chainline works on Boost frames.
Has anyone encountered a 52mm chainline not working on a boost frame?

Why do Shimano faff so much with “boosting” their axles, when boosting a chainring makes tweaks so much easier?

Current Shimano Q factors range from 162/168/171/172/174/178/181mm in Deore/SLX/XT/XTR.

Shimano chainlines are available in: 52/55/56.5mm

That’s almost 1cm of Q factor variation!

Gutted cos I miss my narrower cranks.

You must be very sensitive to this!

FWIW, I’ve been riding for over 30 years and can’t say I’ve ever detected variations in Q factor in any of the bikes I’ve ridden…

Precisely because some people are sensitive to it I’d imagine.

I think some new frames are forcing you onto a 55mm chainline or stopping you running anything over 30t chainring, superboost frames and fat tyre lovers are causing wider Q factors otherwise their heels would be clipping the stays, frame makers are creating these stupid issues and Shimano make a solution working together to make more standards nobody really asked for.

the chain line on Shimano cranks are set using different length axles. all the arms and rings are the same, so the q factor increases with the chain line. spacers between the bb and the axle take up the slack.

i think the 52mm xt crank has a 172 (or similar, pretty standard dimension) q factor.

i’m not sure how they ended up with the notion that 55mm is a boost chain line v

52 is for 135/142 or 148 55 is for Boost frames and ring combos noeffsgiven describes.

reread the op. you know why they are different q factors, but wondering why shimano do it like this. it does seem strange when an offset ring seems like a more straightforward solution.

i bought the boost version for the wider q factor, but as i mentioned, the chain line is terrible in the low gears.

The55mm chainline with wider q factor is the new boost std so manufacturers can have wider chainstays whilst still having clearance.
Sram also now he this.

Is that aimed at me LAT?

I’d already responded to the Q-Factor question, and was replying to your question.

Shimano chainlines are available in: 52/55/56.5mm

That’s almost 1cm of Q factor variation!

Its because the cranks are designed to do something other than just be a PITA chainline smorgasbord.

52 is old boost, so normal 52mm front end, 148 rear.
55 is ‘new’ boost, wider 55mm front end, with presumably wider chainstays near the crank to take advantage of the width.
56.5 is super boost, with the 56.5mm front end paired with the 157 rear. Now your stays are even wider so need even more clearance.

Changing the chainring only gets you half way there. You’ll notice the same on SRAM cranks too, they just dropped the idea of a 142 & 148 crank a while before Shimano adopted the same policy. SRAM superboost cranks are wider for example, need more DUB spacers, but still only run a 3mm ring like normal boost.