Login required to started new threads

Login required to post replies

Switching from 170mm to 165mm Cranks on TT Bike
Quote | Reply
I'm looking at spending a little money (about $200 - for a Force 22 crankset to interchange the arms with the Quarq) to switch my Quarq crank from 170mm crank arms to 165mm crank arms. For those of you who have made this change did you notice a difference? And was it a positive difference? I ask because it's an experiment I want to test out in the "off season" - albeit a bit of an expensive "test". It may or may not work for me. My goal is for faster TT speeds (TT races, not tri's).

I don't feel "tight" in the hip flexors, but I did raise my bars this season about 5mm and increased power output so I think my hip angle may be affecting my power output.

And will a 5mm crank arm difference be notable? Should I consider 162.5mm arms instead? I'm 6' tall.

If I make the switch I'll likely just raise the saddle 5mm and leave it at that for starters - lowering my position a bit and opening my hip angle. If needed I'll raise the bars and maybe move saddle/bars back 5mm too.

Michael
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [wacomme] [ In reply to ]
Quote | Reply
I made the switch from 172.5 to 165mm 3 years ago and will never go back. Power should go up, lower back should be less fatigued if that is ever an issue, and it gives you a chance to be in a bit more aggressive position.

Are you using round rings?

I am a bad runner.
I met Javier Gomez once.
I don't speak in miles.
I have opinions.
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [MBTRIATHLETE] [ In reply to ]
Quote | Reply
Yes. Round rings.

My biggest flexibility problem is tight hamstrings. So my limitation with going lower and reducing power may be more related to my tight hamstrings than hip flexors. It's why this "experiment" may be for naught, but unless I try shorter cranks I just won't know - so goes my thinking.

Michael
MBTRIATHLETE wrote:
I made the switch from 172.5 to 165mm 3 years ago and will never go back. Power should go up, lower back should be less fatigued if that is ever an issue, and it gives you a chance to be in a bit more aggressive position.

Are you using round rings?
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [wacomme] [ In reply to ]
Quote | Reply
I swapped 170-165 this season. I thought at first the difference in comfort was noticeable. I have a pretty low position and I'm still miserable when riding at FTP. Miserable as in much more miserable than road bike. But maybe less miserable than riding 170's?

My TT FTP is still roughly 30 watts less than my road bike. And I've ridden my TT bike a LOT this year. So I guess for me the jury is out. I think shorter might be more comfortable. I think it might help my knees stay away from my chest a bit better. I do like to ride very open so hoped 165's would put out more power for me. Nope. I ride 172.5 on my road bike.

I'm doing an Ironman here in under 3 weeks and I'm actually considering swapping back to 170 after that just to see how it feels again. We'll see.

24 Hour World TT Champs-American record holder
Fat Bike Worlds - Race Director
Insta: chris.s.apex
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [cmscat50] [ In reply to ]
Quote | Reply
Very interesting. Thanks for sharing. BTW - also ride 172.5mm arms on my road bike. My power is about 20 watts less on my road bike at FTP than on my TT bike. Like you, the difference may merely be an interesting experiment with no significant improvement.
cmscat50 wrote:
I swapped 170-165 this season. I thought at first the difference in comfort was noticeable. I have a pretty low position and I'm still miserable when riding at FTP. Miserable as in much more miserable than road bike. But maybe less miserable than riding 170's?

My TT FTP is still roughly 30 watts less than my road bike. And I've ridden my TT bike a LOT this year. So I guess for me the jury is out. I think shorter might be more comfortable. I think it might help my knees stay away from my chest a bit better. I do like to ride very open so hoped 165's would put out more power for me. Nope. I ride 172.5 on my road bike.

I'm doing an Ironman here in under 3 weeks and I'm actually considering swapping back to 170 after that just to see how it feels again. We'll see.
Last edited by: wacomme: Aug 25, 16 11:33
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [wacomme] [ In reply to ]
Quote | Reply
I thought about doing it for a couple of years and just made the jump 3 weeks ago. Wish I had those couple of years back because it has helped me out a ton. Like you I have extremely tight hamstrings and my pedal stroke is now a lot smoother, maybe 5-7% more powerful, and a lot more comfortable in an aero position.

During the last 8 years I have never been able to stay aero longer than 7 mins and I was able to stay aero for 30 straight mins on the trainer during my second ride. I do realize than I am outlier with hamstring flexibility so most people will not see this dramatic of a difference but it was night and day for me after the second pedal stroke on the 165's. I came from 172.5s. Hope you have a similar result if you give it a go. Cheers!
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [mdgreene] [ In reply to ]
Quote | Reply
I'm not quite sure how shorter cranks have helped you mitigate tight hamstring issues. If you kept your position the same (assumption), how do shorter cranks help hamstring flexibility? I can see it affecting hip flexion, but not hamstring issues.

mdgreene wrote:
I thought about doing it for a couple of years and just made the jump 3 weeks ago. Wish I had those couple of years back because it has helped me out a ton. Like you I have extremely tight hamstrings and my pedal stroke is now a lot smoother, maybe 5-7% more powerful, and a lot more comfortable in an aero position.

During the last 8 years I have never been able to stay aero longer than 7 mins and I was able to stay aero for 30 straight mins on the trainer during my second ride. I do realize than I am outlier with hamstring flexibility so most people will not see this dramatic of a difference but it was night and day for me after the second pedal stroke on the 165's. I came from 172.5s. Hope you have a similar result if you give it a go. Cheers!
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [wacomme] [ In reply to ]
Quote | Reply
Just made the switch. Feels amazing. Never going back. Thinking that maybe I could even make use of 160mm. Had 172,5, and still do on road bike. Last years IM I had rash on my quads from bumping into my chest (spilled some sports drink on the legs so got slightly glued to my chest every revolution).This year I was much more comfy and also a little more powerful (but also fitter so yeah apples to apples).

Endurance coach | Physiotherapist (primary care) | Bikefitter | Swede
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [wacomme] [ In reply to ]
Quote | Reply
Great questions. I always struggled to get over the top of my pedal stroke without my hips bouncing and had read several articles suggesting tight hamstrings cause this issue on the top of the stroke. Maybe its caused by tight hip flexors and not tight hamstrings. I took biomechanics in college 8 years ago but never got the opportunity to take a deep dive into the muscle activation from 10 o'clock to 2 o'clock of the pedal stroke so I don't know for certain what causes the limitation.

Whatever it was the 165's solved the problem.
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [mdgreene] [ In reply to ]
Quote | Reply
HI guys,
with the transition from 170 to 165mm cranks did this allow you to raise seatpost by same margin?
thanks
John
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [seanin] [ In reply to ]
Quote | Reply
Basically, yes.
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [jimatbeyond] [ In reply to ]
Quote | Reply
You can raise your seatpost because of the 5mm you save on the bottom end of the stroke -- the benefit I found was at the top end, where the hip angle really feels more open. A side benefit is less likelihood of a pedal strike, but that's only for certain types of situations . . .
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [wacomme] [ In reply to ]
Quote | Reply
I went from 175mm to 165mm. The cadence change is noticeable. I have most of my base miles on 175mm so my legs get tired in a weird way on 165mm, but I’m still getting used to it.

I actually have 175mm on my trainer and 165mm on my tri bike.

https://www.strava.com/...tes/zachary_mckinney
Last edited by: plant_based: Sep 17, 21 13:28
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [plant_based] [ In reply to ]
Quote | Reply
Why would your cadence change?
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [jimatbeyond] [ In reply to ]
Quote | Reply
jimatbeyond wrote:
Why would your cadence change?

My cadence is faster with the 165mm - I think this is somewhat common, right?

https://www.strava.com/...tes/zachary_mckinney
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [plant_based] [ In reply to ]
Quote | Reply
I use 155mm cranks on my TT bike and 170mm cranks on my road bike.

My cadence is always around 90.
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [jimatbeyond] [ In reply to ]
Quote | Reply
jimatbeyond wrote:
Why would your cadence change?

Power = torque * angular velocity

Assuming power remains constant, then shorter crank arm means either same force at the pedal but higher angular velocity (to compensate for reduced distance to center of rotation), greater force applied at the pedal but same angular velocity, or combination of the two.

So shorter crank arm often results in higher angular velocity (which is just cadence multiplied by a constant).
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [echappist] [ In reply to ]
Quote | Reply
I just change which gear I'm using to keep my cadence around 90.
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [plant_based] [ In reply to ]
Quote | Reply
My cadence also went up. I was averaging 75 rpm with 170 cranks and now I’m at 85 for easy spins and just over 90 for intense efforts with 165 cranks.
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [Kay9Cop] [ In reply to ]
Quote | Reply
Change gears.
Quote Reply
Re: Switching from 170mm to 165mm Cranks on TT Bike [jimatbeyond] [ In reply to ]
Quote | Reply
Why would he change gears? It's pretty normal for your muscles to want to stay at some specific force at a specific intensity/power. That will result in a different cadence with a change in crank arm length.

Cadence is a pretty bad measure when you start changing crank length, speed and power. Dividing into force and foot speed would be more useful.
Quote Reply