This January, I switched from 165mm to 150mm cranks on my tri bike. I did this in an attempt to reduce hamstring strain (I have very tight hamstrings), flatten out my back with lower effective position, and also reduce knee tracking out to the side. Previously, I had to keep the front end fairly high to avoid hamstring strain during races, and I was hoping to be able to lower it by going to shorter cranks.
With the 165mm cranks, I had been riding with an effective seat angle of about 80 degrees and it was comfortable (except for hamstring strain during races if I had the front end too low). After switching to 150 mm cranks (and raising my seat 15 mm), this winter, I found that I wasn't able to tolerate the 80 degree seat tube angle with the same amount of seat to armrest drop as I previously had, it felt like I had way too much weight on my arms and shoulders. I had to move the seat back to about 78 degrees effective seat tube angle to be able to tolerate the same amount of seat to armrest drop as I had before with the 165 mm cranks.
As a result of the change to shorter cranks, I don't seem to be able to sustain a flatter position as a result of the shorter cranks, however, they did stop my knees from going out to the side at the top of stroke and so far I haven't had strained hamstrings. My 20 min FTP (on the trainer) seems to be about the same with the 150mm cranks as it was with 165mm. I probably won't definitively know about the hamstring strain until a race, since I've only rode on the trainer so far since January.
Has anyone else switched to very short cranks and found they needed to move their seat back a fair bit to be comfortable?
As a sidenote: After the switch to 155 mm cranks and with the the original 80 degree seat angle, I did try moving my cleats fairly far back (with speedplay cleat extender plate) to see if this would take some of the weight off my arms and shoulders (attempt to mimic the position in space at 90 deg crank angle (downstroke) that my feet would have been with the 165 mm cranks), but it didn't seem to make a noticeable difference. That being said, I did keep the near midfoot cleat position because it seemed okay otherwise and I think it keeps my calves a bit fresher.
With the 165mm cranks, I had been riding with an effective seat angle of about 80 degrees and it was comfortable (except for hamstring strain during races if I had the front end too low). After switching to 150 mm cranks (and raising my seat 15 mm), this winter, I found that I wasn't able to tolerate the 80 degree seat tube angle with the same amount of seat to armrest drop as I previously had, it felt like I had way too much weight on my arms and shoulders. I had to move the seat back to about 78 degrees effective seat tube angle to be able to tolerate the same amount of seat to armrest drop as I had before with the 165 mm cranks.
As a result of the change to shorter cranks, I don't seem to be able to sustain a flatter position as a result of the shorter cranks, however, they did stop my knees from going out to the side at the top of stroke and so far I haven't had strained hamstrings. My 20 min FTP (on the trainer) seems to be about the same with the 150mm cranks as it was with 165mm. I probably won't definitively know about the hamstring strain until a race, since I've only rode on the trainer so far since January.
Has anyone else switched to very short cranks and found they needed to move their seat back a fair bit to be comfortable?
As a sidenote: After the switch to 155 mm cranks and with the the original 80 degree seat angle, I did try moving my cleats fairly far back (with speedplay cleat extender plate) to see if this would take some of the weight off my arms and shoulders (attempt to mimic the position in space at 90 deg crank angle (downstroke) that my feet would have been with the 165 mm cranks), but it didn't seem to make a noticeable difference. That being said, I did keep the near midfoot cleat position because it seemed okay otherwise and I think it keeps my calves a bit fresher.