So is there a way to calculate or estimate the effect this has on gearing? Would a 165 crank require an 11-30 to replicate an 11-32 with 172.5s for example?
Was a fit with him worth the money as heâs quite expensive?
Both track disciplines, 165s would be normal? Itâs to avoid catching pedals afaik. Not sure if thatâs a good reason to do the same on the road.
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Indispensable bike calculator from the indomitable Sheldon Brown:
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Iâm 173cm with an 80cm inseam. Switched to 170mm crank and itâs been one of the best changes Iâve ever made. Cadence is up, but comfort is way up.
Youâre spot on, youâre applying more force but over a shorter distance so power is the same.
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Make that 100 %. However, shorter cranks allow some people to increase their cadence at a given power. Since shorter cranks donât magically increase your FTP, though, that means you may need to change gears.
Plus theyâre putting out constant power, plus they have very aggressive aero positions so hip angle
From what I can glean, TT riders and triathletes generally have shorter cranks for these reasons, whereas road riders stick to more traditional lengths. E.g. Geraint Thomas was on 175s for his Tour win (and having previously been part of the GB pursuit team would presumably have been on 165s on the track), Sagan rides 172.5, Bernal as a shorter rider is on 170.
My motivation to look at shorter cranks is primarily a hip angle issue I have: when I go aero I often feel as if I am massaging my breakfast.
Good to know. Fortunately, I am not much of a sprinter.
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Thatâs classic! 
Shorter can help/address hip angle. For me the 165âs didnât feel or show any difference in power or aero in the tt position. All that Iâve experienced with tt positioning is more on the front end getting the head low and trying to determine how wide the elbows should be and getting the torso to elongate (create smaller hole) and being really really still at high power. 7.5mm of crank length was just not where I needed to be spending time/money.
I guess itâs good that I tried them to experience first hand and not try and determine reading a forum. I just went back to 175âs honestly believe I generate more power with those. Who knowsâŚ
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Iâm not sure, it is only a 5% difference hence more like 19->18. Raising rpm from 90 to 95 does the same thing.
The one time I used a 11-30 I found the steps way to wide for the riding I do, felt like I was in the wrong gear all the time. I usually have 12-25.
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Yeah, in my case it is a fit issue. I have ridden bikes with 170 mm cranks, but they were also smaller, so fit wasnât comparable and other issues cropped up (I have long arms, so the stem was too short and I felt âcrammed inâ).
Based on all the research I have done (and I am a complete amateur, this is just what has come up on Google and Youtube), there are few if any bad side effects from running a crank that is by conventional wisdom too short. One of the few I remembered was that it raises your center of gravity slightly.
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Adam Hansen rides 320s or some crazy pavement-scraping length.
Biggest crank in the peloton! 
Apparently was on 185s as an amateur and now rides 180s so nothing too dramatic! From Inside Peloton: Adam Hansen - Peloton Magazine
Does seem like itâs one of those things where thereâs no right or wrong answer and most people can adapt to what theyâve got, so unless youâre having a specific issue with your current cranks (like being unable to get aero enough due to hip angles), it doesnât seem worth the considerable cost of replacing your crankset. Am not even sure that struggling to hit high cadence would be a reason to consider shorter cranks, havenât really seen much evidence to convince me that thereâs much benefit in deliberately trying to ride at a higher cadence. Self-selected cadence seems to work fine for most people most of the time.
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The main reason is aero position. He had team sprinters on 177.5s and they would be banking much harder than TP.
Also, hour record is steady state but TP or TTT is anything but a steady effort
For those of you that went short, can you recommend an aftermarket manufacturer? I have a full Ultegra R8000 setup currently, and my fitter recommended 155-160mm cranks (I have a super short inseam).
Iâve got friends who have used 155mm Cobbâs and are pretty happy. Not as pretty as the R8000 crank, but should be a simple drop in replacement. They also do a 160mm version.
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Praxis works alba comes in 160mm (30 mm spindle so you need to change bottom brackets)
Rotor aldhu 24 (direct replacement for shimano) goes as low as 155mm (also expensive)
Shimano R7000 105 comes in 160mm
Rotor Aldhu with 30mm spindle goes as low as 150mm but are very expensive.
Turns out there are new versions for the praxis works cranks
Alba X - 160 mm (840 grams weight) 30 mm spindle
Zayante Carbon - 160 mm (620 grams weight) 30 mm spindle
Hope it helps!
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The cadence might be the same but the speed of your pedal and foot increases (and hence work done) with crank length and therefore (I think) power output is proportional to crank length for the same force and cadence. I am, however, quite willing to be proved wrong. The last time I worked anything like this out was 40 years ago.
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I didnât mention force 
With shorter cranks, if you keep the same cadence in the same gear, the force goes up and the foot speed goes down. Youâve got a shorter lever, but less distance to move it. But power (=work done) stays the same since itâs a product of both force and velocity, and as the former increases (less leverage) the latter decreases (smaller pedalling circle).
To put it another way, if shorter cranks allowed us to go the same speed with less work, the logical conclusion would be to fit 1mm cranks and learn to pedal in tiny tiny circlesâŚ
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