i need some input on which powermeter to buy along with which crank arm length as well. i am doing IM maryland my first full so looking to be long course friendly. My current TT bike is a p2 with a sram red crank with 175 crank arms. i am 6’ 33 inseam ish inseam and ride 78.5mm from center of BB to saddle. i am thinking of going to 172.5 for 170 crank arms. What do you wall think of the RIken vs the Elsa and what direction should i go here. i really appreciate the input on this topic and look forward to your responses.
I’d go 170mm if I were your height. I think the Riken and Elsa are so close technologically, I’d opt for whichever one is cheap and/or looks the best. Unless you have the brand new P2, you’ll need a GXP crank, which will pop right in.
You might be able to get lower, depending on your bike. How is your current position? Do your thighs hit your chest? Then a shorter-length crank could help. There’s not a very big difference between 170 and 172.5. I couldn’t tell the difference.
The advantage of a shorter crank arm is that the ‘top’ of the pedal is lower. That is, going from a 175 to a 170 crank means when the pedal is at the top it is 1cm lower relative to the saddle. This means less knee flexion at the top of the pedal stroke. A shorter crank also means, at the same cadence, slightly lower muscle velocity as the circumference of the pedal circle is slightly less.
Talk to your bike fitter before you switch crank arm length. Your not going to gain any more power or magical superpowers. Crank arm length corresponds to fit
This is a generalization but here goes - go with the 170mm because (as eluded to already in the thread) your can perhaps drop a hair lower in the front end (which is nice) and get more or sustain existing power at the top of the pedal stroke (which is GREAT and more important). This happens not because your thighs are so much hitting your chest but because your hip flexor is perhaps being impinged at the top of the pedal stroke and the short crank will (again, generalization) free it up. And that means greater comfort (finally we get to the most important aspect of being on the bike).
I’m 6’1" and went to 170s 2 years ago. It was dreamy for me - cadence sped up, rode a taller gear than normal in my typical route and…what happens when you spin a bigger gear? You generate more power (that also happens when you spin a higher cadence in the same gear or the same cadence in a bigger gear but you gotta love increasing the numbers on both side of the multiplication symbol). Let me add - as a fitter and a teacher of fitters - I really like BryanD’s comment about going to see your fitter to have this done. Nice!
Can you explain this further? How is there a 1 cm difference between the top of the saddle and the pedal at the top of its rotation when we’ve only shortened our crank by 5mm?
How does this allow you to get lower? If we shorten our crank length by 5 mm, in order to keep our ideal saddle height, we would need to raise the saddle 5 mm, right?
Zero advantage unless you look at your position/talk to a fitter etc and feel that you can get a better CDA through position changes with the shorter crank.
When moving to a shorter crank the saddle is raised the same amount as the crank is shortened. i.e. If going from a 175mm to a 170mm crank the saddle height is raised 5mm. This means that the distance from the pedal at the bottom to the saddle remains unchanged therefore the Knee Angle extension (straightening of the leg) remains the same.
Let’s say, for example, the height from the pedal at the bottom of the pedal stroke to the saddle is 1000mm The diameter of the circle when using 175mm cranks is 2 x the radius i.e. 2 x 175 or 350mm. The distance from the pedal at the TOP of the stroke to the saddle is therefore 1000 - 350 = 650mm. The diameter when using 170mm cranks is therefore 340mm meaning the distance at the Top of the pedal stroke to the saddle is 10mm MORE - 1000 - 340 = 660mm.
This decreases knee angle flexion (bending of knee measured at the top of the pedal stroke) as the knee isn’t coming as high. The distance between the knee and the chest is also less meaning the torso can be lower i.e. a smaller back angle.
Hence why you can be lower in terms of Back Angle.
Of course making changes in cranks, saddle etc can manifest in different ways i.e. change of ankle range of motion so it is important, as others have mentioned, that a change in crank length be viewed as part of an overall fit.
Thanks guys I started this conversation with my fitter who said he thought I should go with one or the other. He said they are very similar and we will still be able to get the bike to fit without issues. I am a bigger guy at 200 lbs will be dropping down to 185 or 180 for race day. My current ftp is 250 so working on bringing that up. Thanks for all the input
Talk to your bike fitter before you switch crank arm length. Your not going to gain any more power or magical superpowers. Crank arm length corresponds to fit
Exactly. Crank arm length is one of several interacting dimensions. It’s part of the whole fit, which is unique to you.