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Cranks Length
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Looking for guidance here. Finally got a proper bike fit done with all the bells and whistles and I trust it. I am going to be swapping aerobars and cranks.

I am current running 170mm cranks

I tested out 165mm and 155mm cranks. Both of them felt good. 155 did feel weird...but boy could I breathe easily.

As a cyclist I am more of a spinner than a pusher.

Any thoughts? I have been reading that crank length doesn't impact power.
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Re: Cranks Length [LifeTri] [ In reply to ]
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What guidance are you looking for?

My advice would probably be to listen to your fitter since we know nothing about you and he/she does.
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Re: Cranks Length [LifeTri] [ In reply to ]
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I can only attest to my fit. I'm 5' 11" with a 32" inseam. I switched from 175mm to 150mm cranks. Once the seat height was reset for the shorter cranks (5cm up)... I could barely tell a difference. After one 3 hour ride... It felt like I'd always ridden them.

There was no change in my sustainable power (30+ minutes) in aero or upright following my fit with the shorter cranks.

So, I agree with dfw_tri... Trust your fitter.
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Re: Cranks Length [LifeTri] [ In reply to ]
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I started racing tri's and IM on 170 and trialled down in 5mm steps to 150 which I found too short but 155 seemed to be the limit before my ability to generate sustainable power dropped away. Over that time my cadence dropped from about 99 average over an IM to 83 now on 155. I used to have a high cadence from a cycling background.

P.S. I'm 5' 11 1/2" with long legs for my height...
Last edited by: Shambolic: Nov 13, 18 21:04
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Re: Cranks Length [LifeTri] [ In reply to ]
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I’m 5’8” and recently switched from 165 to 145 cranks. Much more comfy and can’t tell any power differences.
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Re: Cranks Length [LifeTri] [ In reply to ]
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I switched from 172.5mm to 160mm cranks a few months ago. The first hard ride did feel noticeably different and I was a bit worried I'd gone too short, but by just the second ride (with no tweaks) I felt perfectly normal again and the only obvious difference following the change was a smoother top of stroke and happier knees.
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Re: Cranks Length [LifeTri] [ In reply to ]
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Shorter crank :
less angle in the knee and at the hips
BUT
for same power and same RPM, more force need to be produced to the pedal (power = force at pedal x pedal speed), as reducing crank length, for a given RPM, reduce pedal speed

So it is a balance between knee/hips angle (confort and aero) and force/RPM (what is the force where pink muscle fiber get involved, what RPM you can sustain).

RPM not being easy either, the slower being the most efficient energetically, but again involving pink muscle fiber with will lead to some potentials issues, and higher RPM losing efficiency and possibly generating too much friction with saddle.

Sustainable knee angle, hip angle, aero and breathing implications, RPM capabilities, force capabilities, impact on the Run capabilities... all this being highly individual from your skeleton, muscles, training, preferences, history, ...

... nobody can choose for you. If you try something different, take time to adapt, and be aware there is multiple possibles impact, most cannot be predictable.

Change is an opportunity and also a risk... like... ahem... did you get married several times ?
Last edited by: Pyrenean Wolf: Nov 14, 18 4:41
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Re: Cranks Length [LifeTri] [ In reply to ]
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So, who makes shorter cranks? I’m having a hard time finding anything less than 170.
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Re: Cranks Length [dhoose] [ In reply to ]
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Rotor and Cobb
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Re: Cranks Length [dhoose] [ In reply to ]
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Shimano, Cobb just to name a few.
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Re: Cranks Length [Pyrenean Wolf] [ In reply to ]
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Okay, I think I may just split the difference and look for a 160mm crankset to throw on my rig. I know that 10mm will make a significant difference for me from a breathing and knee comfort standpoint.

Everyones comments here have made my decision that much easier.

Thanks!


EDIT: Am i going to have any compatibility issues going to 160mm when I use shimano? I dont see a 160mm option with shimano.
Last edited by: LifeTri: Nov 14, 18 6:21
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Re: Cranks Length [LifeTri] [ In reply to ]
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I started on 172.5 switched to 165 for almost 2 years and I am now 155 on my TT and 165 on my roadie!

You will definitely spin more on the 155 so if that's what you like then go for it, honestly after several TR workouts I can't exactly tell the difference between either crank other than the increased cadence.

Speed kills unless you have speed skills!!!
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Re: Cranks Length [playero] [ In reply to ]
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I know this is an oft mentioned effect that's attributed to shortened cranks, however I haven't seen it.
My cadence tends to be rather low. I haven't noticed any real tendency to increase it since significantly reducing crank length from 172.5 to 160.
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Re: Cranks Length [Tom_hampton] [ In reply to ]
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Tom_hampton wrote:
I can only attest to my fit. I'm 5' 11" with a 32" inseam. I switched from 175mm to 150mm cranks. Once the seat height was reset for the shorter cranks (5cm up)... I could barely tell a difference. After one 3 hour ride... It felt like I'd always ridden them.

There was no change in my sustainable power (30+ minutes) in aero or upright following my fit with the shorter cranks.

So, I agree with dfw_tri... Trust your fitter.

I agree, both with shorter cranks (for most) and trusting one's fitter. I'm a little surprised at your saddle change. It looks like you shortened your cranks by 2.5cm, but raised your saddle by 5cm. What am I missing?
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Re: Cranks Length [Pyrenean Wolf] [ In reply to ]
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The difference in force is minimal. For example, at 300w, 80rpm, you have to exert 20N more force for 155mm cranks than you do 170mm. As studies have shown, there are few, if any, advantages to having longer cranks for time trialing.

Basically all I'm trying to say is you're making this out to be a big change with potential negative side effects, whereas it's more likely the OP will switch cranks and notice an immediate positive one in aero.
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Re: Cranks Length [FatandSlow] [ In reply to ]
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FatandSlow wrote:

I agree, both with shorter cranks (for most) and trusting one's fitter. I'm a little surprised at your saddle change. It looks like you shortened your cranks by 2.5cm, but raised your saddle by 5cm. What am I missing?

That my seat might have been too low to start with. :-)

When I built my tri-bike this summer, I built it up with 150mm cranks (my road bike is 175mm). I chose the 150mm cranks based on FindingFreestyle's thread "maybe your seat is too high because your cranks are too long":

FindinFreestyle wrote:

Finally, this is a rough range of crank lengths that riders have been selecting as a loose function of seat height.

<60cm seat height :: Crank 145mm or less. Really as short as you can find, maybe go custom. I’ve fit down to 135mm with custom cut BMX cranks.
60-65cm :: Crank length 140-145mm
65-70cm :: 145-150mm
70-75cm :: 150-155mm
75-80cm :: 155-160mm
80-85cm :: 160-165mm
>85cm :: 165-170mm, maybe 172.5 Keep in mind that of the tallest, strongest professional athletes I have fit literally ZERO of them have preferred anything over 165mm. These are 6’3” and taller athletes pushing wattage over 375 watts at threshold and upper 200s to 300 for IM races.


I set my initial seat height on the TT bike at my road bike seat height (730mm). I might have raised it a little bit, I don't recall. I road the TT bike that way for a week until I could get an appointment with a fitter. During that first week, my comfortable cadence was elevated by about 12rpm. I also felt like I was pedaling in little tiny circles like I was on a kid's bike. I did my usual 2x20s, power was ok...but, cadence was up (upper-90s vice mid-80s).

The following Saturday I had my fit appointment, where my seat was raised the 5cm (to 779mm), amongst the other usual fit changes. As soon as my saddle was raised my pedaling sensations immediately returned to normal. It was one of those Ah-Ha! moments. The following week, I did the 2x20s and power was again normal, and cadence was back into my typical range (mid-80s). The week after that I did the 2x20s again, 1st on the horns 2nd in full-aero. And again power and cadence were normal between the two positions. The week after that I did the full 2x20 in aero with the same results as previous.
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Re: Cranks Length [Pyrenean Wolf] [ In reply to ]
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That's true....on a fixie, and the corollary to a fixie the minimum gear on a muti-speed bike. Otherwise, cadence is self-selected to a comfortable combination of foot-speed and pedal-force. So, any effective gear-inch change resulting from shorter cranks is offset by a slight change in shifting points by the rider.
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Re: Cranks Length [imswimmer328] [ In reply to ]
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imswimmer328 wrote:
The difference in force is minimal. For example, at 300w, 80rpm, you have to exert 20N more force for 155mm cranks than you do 170mm. As studies have shown, there are few, if any, advantages to having longer cranks for time trialing.

Basically all I'm trying to say is you're making this out to be a big change with potential negative side effects, whereas it's more likely the OP will switch cranks and notice an immediate positive one in aero.

"minimal" mean nothing. There is an impact, it can be calculated, any comment on its possible consequences on someone is... a comment, an uneducated guess, not a fact, not a proof.

Wich studies ? Didn't noticed that TT serious peoples goes with 150mm crank for TT or Hour Record.
Dumoulin goes 150mm ?
Wiggins or Dowsett went 150mm for Hour Record ?
How stupid they are...

What I say is : there is some impacts, some can be positive, some can be negatives, and it is hard to tell, because this is very personal.

Maybe it works for you, fine. Does not mean it will work for someone else. An exemple is never a proof. A cohort result can be a proof, in a limited context. Many PhD thesis have been made on crank length and RPM. And the results are... well, not so easy to tell.

Not trying to push in one direction (short, short, short....or long, long, long, ...), just trying to give a view of the possible impacts.

Wandering what kind of "minimal" thing pushed Frodeno out of Kona podium the 2 last years.
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Re: Cranks Length [LifeTri] [ In reply to ]
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As a very short (5') rider, shortening my cranks from 170 to 165mm was really helpful. It allowed some space to open up, get more aero and honestly fit my body better.
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Re: Cranks Length [Tom_hampton] [ In reply to ]
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Thanks for your reply. That was my guess, but without evidence, I didn't want to make the accusation. I've known FindinFreestyle for quite a while. Can't go wrong listening to him.
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Re: Cranks Length [LifeTri] [ In reply to ]
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LifeTri wrote:
Okay, I think I may just split the difference and look for a 160mm crankset to throw on my rig. I know that 10mm will make a significant difference for me from a breathing and knee comfort standpoint.

Everyones comments here have made my decision that much easier.

Thanks!


EDIT: Am i going to have any compatibility issues going to 160mm when I use shimano? I dont see a 160mm option with shimano.

The new 105 cranks (FC-R7000) are now available in 160mm...

"I'm thinking of a number between 1 and 10, and I don't know why!"
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Re: Cranks Length [Tom_hampton] [ In reply to ]
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Tom_hampton wrote:
That's true....on a fixie, and the corollary to a fixie the minimum gear on a muti-speed bike. Otherwise, cadence is self-selected to a comfortable combination of foot-speed and pedal-force. So, any effective gear-inch change resulting from shorter cranks is offset by a slight change in shifting points by the rider.

Sorry, dont get it

What is true on a fixie ?
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Re: Cranks Length [Pyrenean Wolf] [ In reply to ]
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The coupling between power, pedal RPM, and torque...or foot-speed and pedal-force, if you prefer. As long as we are riding multi-gear bikes, we can change the speed/force or RPM/torque relationships by shifting gears to whatever our body finds most comfortable.

Going to shorter cranks doesn't REQUIRE me to sit and grind at a higher pedal-force/torque (thus recruiting different muscle fiber types), because I can down shift.
Last edited by: Tom_hampton: Nov 14, 18 9:14
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Re: Cranks Length [dhoose] [ In reply to ]
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dhoose wrote:
So, who makes shorter cranks? I’m having a hard time finding anything less than 170.

If your bike has a BSA or BB30 BB, then there are loads of BMX or other kids cranks that come in short lengths.

There is also a guy who will shorten cranks for a nominal fee. I had him do some Ultegra Octalinks a few years back and he did great work. Think it was about $80 for the pair. http://bikesmithdesign.com/...t_Cranks/hollow.html
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Re: Cranks Length [Warbird] [ In reply to ]
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Warbird wrote:
LifeTri wrote:
Okay, I think I may just split the difference and look for a 160mm crankset to throw on my rig. I know that 10mm will make a significant difference for me from a breathing and knee comfort standpoint.

Everyones comments here have made my decision that much easier.

Thanks!


EDIT: Am i going to have any compatibility issues going to 160mm when I use shimano? I dont see a 160mm option with shimano.


The new 105 cranks (FC-R7000) are now available in 160mm...


I think you just saved me $100.
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