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Changing to shorter cranks
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Just about to start building a Cervelo P3C for next season and debating whether to go to shorter cranks.

Principal use will be for long distance triathlon: currently running 175mm cranks but was thinking of changing to 165mm.

FTP around 270, weight 76kg, height 1.86 and looking to complete my 4th IM next year so not a complete novice to this. I'm more of a spinner than grinder, typical cadence around 87-90.

For those who have changed what are the pros/cons and anything to consider?
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Re: Changing to shorter cranks [moonmonkey02] [ In reply to ]
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I switched last season and couldn't be happier. I went from 172.5mm to 165mm. Had to raise my saddle a bit to compensate. The new position seems more natural to me.

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Re: Changing to shorter cranks [Timtek] [ In reply to ]
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Timtek wrote:
I switched last season and couldn't be happier. I went from 172.5mm to 165mm. Had to raise my saddle a bit to compensate. The new position seems more natural to me.

I just made the same change a few weeks ago. I wasn't sure if I'd like it or not so I bought a $70 165mm Tiagra crank off ebay and have probably put about 20 - 25 hours of riding on it so far on Trainer Road. All I can say so far is that it doesn't seem to have hurt anything. Whether or not it makes me run better off the bike remains to be seen, but figure it at least can't hurt their either.
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Re: Changing to shorter cranks [SBRcoffee] [ In reply to ]
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My situation was nearly ideal... I picked up a Powertap C1 semi-compact chainring on sale along with a former-generation 105 crank which was heavily discounted. I am extremely happy with how nice the 105 product line is, even after "downgrading" from Ultegra. I probably never would have done that except for reading Jack Mott's positive comments of the 105 stuff on here.

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Last edited by: Timtek: Nov 27, 16 12:53
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Re: Changing to shorter cranks [moonmonkey02] [ In reply to ]
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I am 5'11"@170lbs. Switched from 172.5 to 165s on my TT and track bikes. It's not enough of a change to need an adaptation, but it is nice to have the extra room at the top of the pedal stroke.
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Re: Changing to shorter cranks [Timtek] [ In reply to ]
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Timtek wrote:
My situation was nearly ideal... I picked up a Powertap C1 semi-compact chainring on sale along with a former-generation 105 crank which was heavily discounted. I am extremely happy with how nice the 105 product line is, even after "downgrading" from Ultegra. I probably never would have done that except for reading Jack Mott's positive comments of the 105 stuff on here.

Funny, I've got DA 9000 on my road bike, and had a rotor P2M on my TT bike.....and I was surprised at how nice the 'bottom of the line' Tiagra crank was! Its shiny, it installs deadly easy, and it works. Makes you wonder...
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Re: Changing to shorter cranks [moonmonkey02] [ In reply to ]
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Don't "decide" to go to shorter cranks.

Have a proper bike fit on a proper fit bike with adjustable cranks and explore your options. And yes, there are options. There is not a perfect crank length, more like a range of lengths that allow you to ride an optimized position on a given style of bike.

Most likely though, a simple decision to go shorter would not be detrimental. The only drawback to this method in my experience is not going short enough.
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Re: Changing to shorter cranks [Timtek] [ In reply to ]
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Why raise your saddle? Wouldn't you need to leave it the same . Very new so please don't kill me if this is stupid Q.
Last edited by: Fishbum: Nov 27, 16 17:36
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Re: Changing to shorter cranks [Fishbum] [ In reply to ]
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Fishbum wrote:
Why raise your saddle? Wouldn't you need to leave it the same . Very new so please don't kill me if this is stupid Q.


The crank is shorter, therefore - at the bottom of the pedal stroke - the pedal is higher off the ground. You can raise your seat by a few mm to compensate (175 to 165 cranks will leave your 1cm pedal 1cm higher off the ground for example).

This can mean people are able to have a more aero position, due to their saddle being raised but the front end staying the same. Whether simply having a flatter back means more aero is up to the wind tunnel to decide I guess.

For those with hip angle issues, a 10mm shorter crank, and a 10mm raised saddle can be the same hip angle diff as a 20mm raised saddle in their previous fit. Because .... a saddle raised by 10mm added to the 'top of pedal stroke' pedal being lower by 10mm equals 20mm. Their pedal at the top of the stroke is about 20mm further away from their hip than before.

Using my 175 to 165mm crank example:
  • Leaving the saddle the same will not effect your 'drop' to the bars. Will mean you have less reach to the bottom of the pedal stroke - which might be fine. Will mean that you have 10mm more 'room' at the top of the pedal stroke opening your hip angle a bit.
  • Moving the saddle up by 10mm will increase your drop to the bars. Will mean you have the same reach to the bottom of the pedal stroke. Will mean that you have 20mm more 'room'at the top of the pedal stroke opening your hip angle even further.

Hope that helps. Also hope it's right!

There are basically three contact points - pedal, saddle, bars. Changing one point in that triangle often creates a desire for change in one or both of the others.

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Last edited by: JayPeeWhy: Nov 27, 16 18:20
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Re: Changing to shorter cranks [JayPeeWhy] [ In reply to ]
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Ty. Building a P3 and this post was great timing... Soooo much to learn!
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Re: Changing to shorter cranks [JayPeeWhy] [ In reply to ]
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Crank length affects far more than just the knee to chest angle.
A shorter crank whilst opening your hip angle at the top of the stroke, closes your knee angle unless you move your seat back.
This is approximately the same as simply moving your seat forward to open the angle, but different.
I run two crank lengths on my two road bikes, 5mm different, yet my seat height is not 5mm higher to compensate.
The setback is slightly different as is the stem reach and height.
You need to consider the whole system when changing lengths, not just the simplistic shorter crank/lift the seat.
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Re: Changing to shorter cranks [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
Don't "decide" to go to shorter cranks.

Have a proper bike fit on a proper fit bike with adjustable cranks and explore your options. And yes, there are options. There is not a perfect crank length, more like a range of lengths that allow you to ride an optimized position on a given style of bike.

Most likely though, a simple decision to go shorter would not be detrimental. The only drawback to this method in my experience is not going short enough.

this is what i'm intending to do - had a retul bike fit last year and was very impressed with the whole thing.

i'll probably build the bike with a 165 crank and take my 175 (off the other bike) with me to the fitting.

seems to be lots of reasons to go shorter so might as well try it and see if it works for me, if it doesn't i'll have a few months to revert back to my current cranks before my main race next year.
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Re: Changing to shorter cranks [lyrrad] [ In reply to ]
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lyrrad wrote:
Crank length affects far more than just the knee to chest angle.
A shorter crank whilst opening your hip angle at the top of the stroke, closes your knee angle unless you move your seat back.
This is approximately the same as simply moving your seat forward to open the angle, but different.
I run two crank lengths on my two road bikes, 5mm different, yet my seat height is not 5mm higher to compensate.
The setback is slightly different as is the stem reach and height.
You need to consider the whole system when changing lengths, not just the simplistic shorter crank/lift the seat.

I am not saying you are wrong, just trying to work it through in my head. And on paper. Maybe I am saying you are wrong but just not sure I am right. One of the two. :)

I understand moving the seat forward to open the hip angle, you increase height accordingly, otherwise the 'circle' around the BB, which comprises the bike fit, becomes squashed for want of a better word. So I get the example you mentioned.

But in the case of a shorter crank, and a raised seat, at the top of the pedal stroke you would be 2 x the difference in crank length away from the pedal (if crank diff was 10mm this would mean 20mm away), with both your bum and your foot in the same vertical plane as before. With the vertical plane of your saddle being the same horizontal distance away from the vertical plane of your pedal but now with a greater reach to the top of the pedal stroke if anything your knee angle would be more open.

To decrease the knee angle I thought you have to either decrease the seat vertical distance in comparison to the top of the pedal stroke - which we are not doing - or you need to decrease the horizontal distance from the seat to the top of the pedal stroke, which we are not doing.

Where am I going wrong?

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Re: Changing to shorter cranks [JayPeeWhy] [ In reply to ]
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At the foot in front 90 deg angle where you are applying power, a shorter crank moves your foot closer to the BB without moving your upper leg back, thereby closing your knee angle.
The raised seat height will very slightly compensate for this.
You also, due to the more open hip angle, apply bum power earlier in the stroke when your knee is at a tighter angle, at the same time as you have closed the knee angle down a little more, so knee stress goes up quite markedly, very similar to moving your seat forward.

A longer crank opens the knee angle and by closing down the hip angle delays power delivery from the bum until the knee is open even further, thereby taking all the stress off the knee.

The shorter the crank and the more forward you go, the more you increase knee stress.
Seat height also becomes very critical as a small drop closes the knee even more.

If I ride forward TT geometry (5cm in front) with 175mm cranks, I ride 86.5cm seat height. Drop my seat 3mm and my knees will send me home before I hit 10km.
On standard road geometry with 180mm cranks, (10-12cm behind) I ride at a much lower (and comfier) 82 cm and if I move my seat up or down a couple of cm, I get no knee stress, just start to lose power down low and get uncomfy up high.

Seat height measured 10cm back from the front edge of the seat for all configurations.
Seat height centre of BB to top of seat.

All is not simple in leg geometry land.
Then start playing with handlebar height for hip angle and all of a sudden things get complicated as to the total configuration.
Oh, then there is the fore/aft of the cleats.......

Does it make any sense now?
Last edited by: lyrrad: Nov 29, 16 4:56
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Re: Changing to shorter cranks [moonmonkey02] [ In reply to ]
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I went from 172.5mm to 170mm. This season I went from 170mm to 165mm.

It feels more comfortable on the bike with 165's.

I see no drawback. I went with the SRAM force crank due to its versatility and its removable spider. I moved my quarq to it.
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Re: Changing to shorter cranks [Orbilius] [ In reply to ]
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Orbilius wrote:
I am 5'11"@170lbs. Switched from 172.5 to 165s on my TT and track bikes. It's not enough of a change to need an adaptation, but it is nice to have the extra room at the top of the pedal stroke.

interesting that you didn't feel "a big change" when you went to 165!!! personally, i've gone from 172.5 to 165 and it was a much need space for my gut, although pedaling was a bit more challenging at the begining than when i had the 172.5 it was a very noticeable change.

for a TT bike, IMHO 165mm or shorter (depending on your height) is almost a necessity! in order to get a straighter back and better hip angle with it being pinched less; a smaller arm is t he easiest way to go about it, at least it has worked for me. once i feel like i can easily pedal my QXL in 165, i might even consider going to 160s!!! next year maybe

Speed kills unless you have speed skills!!!
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Re: Changing to shorter cranks [lyrrad] [ In reply to ]
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lyrrad wrote:
....
You also, due to the more open hip angle, apply bum power earlier in the stroke when your knee is at a tighter angle, at the same time as you have closed the knee angle down a little more, so knee stress goes up quite markedly, very similar to moving your seat forward.
....

Interesting. While I didn't notice a huge overall different feeling moving from 172.5 to 165, I -did- note that after the first several rides my knees were a bit sore!!
All I've done to compensate the change in cranks was to raise my saddle a bit. I see I have a bit more work to do...
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Re: Changing to shorter cranks [lyrrad] [ In reply to ]
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lyrrad wrote:
Does it make any sense now?

Makes sense. I guess the knee angle will be smallest at the top of the pedal stroke but that's a point with less power. It will also be smaller at the 3 o'clock position but I'd be interested in the knee angle change considering the seat is raised and also, usually, not at 90 degrees upwards due to seat post angle.

I am sure it's a simple trig equation. if we could get Rapp to stop fiddling with his coffee machine maybe he;d work it out for us.

https://www.pbandjcoaching.com
https://www.thisbigroadtrip.com
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Re: Changing to shorter cranks [jharris] [ In reply to ]
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jharris wrote:
I went from 172.5mm to 170mm. This season I went from 170mm to 165mm.

It feels more comfortable on the bike with 165's.

I see no drawback. I went with the SRAM force crank due to its versatility and its removable spider. I moved my quarq to it.

I went from 200's to 175s. I saw a huge drawback with lose of leverage in the hills. Went back to 200's

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Re: Changing to shorter cranks [moonmonkey02] [ In reply to ]
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I made the switch to 165 from 175 after I had a proper fit. It was kinda weird at first, but now since I'm used to it I can't even ride my other tri bike which is still at the 175 crank length. On the 165 cranks, my extension is better and my hips are a lot calmer. I am upgrading the chainrings to a 55 since now it seems "easy" to push the 53 as opposed to before. Haven't tried running after riding yet so we will have to see how that goes this spring.

Owner of a few Speed Concepts since 2011.
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Re: Changing to shorter cranks [ttx_tri] [ In reply to ]
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ttx_tri wrote:
I made the switch to 165 from 175 after I had a proper fit. It was kinda weird at first, but now since I'm used to it I can't even ride my other tri bike which is still at the 175 crank length. On the 165 cranks, my extension is better and my hips are a lot calmer. I am upgrading the chainrings to a 55 since now it seems "easy" to push the 53 as opposed to before. Haven't tried running after riding yet so we will have to see how that goes this spring.

i didnt have a single problem running (speed wise) after switching to 165s and i also have the "dreadful" rotor QXL chain rings which people seem to demonize but what do i know! i ran my 5k in 29.31 after an overall top 20 bike leg in my last triathlon (yes i know i am a slow runner) normally run my 2 miles in 16:30~17:00 min so not to far off from my normally slow pace lol

Speed kills unless you have speed skills!!!
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Re: Changing to shorter cranks [ttx_tri] [ In reply to ]
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How did the switch to 55 chain ring feel ? Do you feel like you can use the 55/42 for any course or would you switch back to standard 53 for hillier profile. thanks.
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Re: Changing to shorter cranks [rmg] [ In reply to ]
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I haven't put the larger ring on yet. Hopefully in a couple of weeks, once I get around to it. As soon as I make the switch I will post about it.

Owner of a few Speed Concepts since 2011.
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Re: Changing to shorter cranks [h2ofun] [ In reply to ]
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h2ofun wrote:
jharris wrote:
I went from 172.5mm to 170mm. This season I went from 170mm to 165mm.

It feels more comfortable on the bike with 165's.

I see no drawback. I went with the SRAM force crank due to its versatility and its removable spider. I moved my quarq to it.


I went from 200's to 175s. I saw a huge drawback with lose of leverage in the hills. Went back to 200's

No you didn't. You just thought you would, so you think you did.
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Re: Changing to shorter cranks [moonmonkey02] [ In reply to ]
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Chicks dig longer cranks....don't make the switch!
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