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Crank length - advice please!

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 jonathan watt 06 Sep 2020

I need to replace the chainset on my road bike fairly soon. Currently I am running an ultegra (50/34) with 170mm cranks. I am looking at changing to a semi-compact. At the same time I am considering shorter cranks. The reason being I am not the tallest in the world! I am just over 5'6" with inside leg of less than 30". Having read a few articles there are a good few that seem to suggest that a shorter crank, perhaps 165mm would be beneficial for someone of my height/leg length.

I was wondering if anyone has been in the same position or are indeed running 165mm cranks? Does anyone have any experience of this or any advice?

Many thanks in advance.

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 Joez 06 Sep 2020
In reply to jonathan watt:

170 will be fine, I doubt you'd even notice much of a difference. Going shorter just makes life hard for spares or upgrades as its less common.

I'm 5'7 with 29" inside leg (measured the cycling way) I use 170.

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 Arthur Parkin 06 Sep 2020
In reply to jonathan watt:

There is evidence that the cycling-world's custom and practice of longer - 170+ - cranks is wrong for most people. Yet, 20-years ago, 175 was standard - as were 53/39 chain-sets. 

As Joez says, you probably won't notice much difference. As he also points out, because most stock cranks are 170 - 175, shorter versions could be (much) more expensive. I'm 5'11" and use 172.5 cranks.

PS - edited to note whilst a shorter crank probably won't increase your top speed it might make climbing easier/more efficient, as there's less of a dead spot at TDC.

Post edited at 18:08
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 gezebo 06 Sep 2020
In reply to jonathan watt:

Nairo Quintana uses 172.5mm cranks. I wouldn’t get to hung up over the length. 

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In reply to jonathan watt:

In all honesty, with an increasing move towards shorter cranks in both time trialling and mountain biking, you'll probably find that 165s are easier to get than ever.

There are plenty of places that you can get a 165mm 52/36 Ultegra chainset. The only downside is if you don't like them you may find them trickier to sell secondhand.

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 JLS 06 Sep 2020
In reply to jonathan watt:

I wouldn’t worry about it either way. I regularly swap between bikes with 165 and 170; I barely notice. I dare say any given gear ratio is going to feel a little stiffer on the shorter cranks and high cadence will be easier too but it’s fairly subtle.
I probably knew this at the time but recently I was surprised to find my old track chainset from the 1980s had 170 left and 165 right (ie shorter on the banking side)...

Post edited at 18:51
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 Toby_W 06 Sep 2020
In reply to jonathan watt:

Really interesting question, I’ve swapped to 180s, I had gone to 177.5s and they were so much comfier/better and I won’t ever go back from the 180’s now.  I am 189cm with an 89 inseam.  It took a while to get used to them cadence dropped on the flat increased on the hills, I seem to be less tired and faster on hills though I am pretty unfit at the moment.  Armstrong rode long cranks for his size at 175 and still span.

The thing that swung me was the engineer who had worked out all the proportional lengths, mine should  be 192!!!!  On his web page it said at this point you think i’m absolutely mad.   A few of the well known bike fitters are sometimes quoted as not agreeing with this but from 20-30 years ago and have changed their minds.  Steve Hogg who I think really understands bike fit gives a good overview of longer cranks purely from a power and cadence view, he’s so, so on it.

i will never go back, my sprints are faster, my climbing is faster and it seems to be more efficient on the flat.  Again, just me.

My wife who is shorter has 165s on the bikes where possible.

Good luck, hope you find your sweet spot.

Toby

just trying to find links for you and 20% leg length seems to be the published paper conclusion, for me 178mm, who new.  Also if in doubt go shorter.

The below I think provide a balanced view on proportional crank lengths.

http://www.nettally.com/palmk/crankset.html

http://www.myra-simon.com/bike/cranks.html

https://www.velonews.com/gear/technical-qa-with-lennard-zinn-a-question-of-crank-length/

https://ridefar.info/2017/02/crank-length-and-comfort-for-long-distance-cyclists/

https://www.stevehoggbikefitting.com/bikefit/2011/06/crank-length-which-one/

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In reply to jonathan watt:

FWIW I changed from 175 to 170 cranks about 20 years ago (gulp!) and have never regretted it. I never felt comfortable with 175s. I learned that, for my height, 172.5 cranks were recommended; I didn't want to spend large amounts of cash, so sourced some inexpensive 170s.

I've found it more comfortable for my knees and more efficient. Because I'm spinning a smaller circle, I'm not having to heft my body weight from side to side. On smoother surfaces (or on road) I can keep my upper body virtually still, and just spin from the hips downwards. I find it's more ecnomical, hence I can sustain out-of-the-saddle work for longer.

Hope that's of some help. Happy riding

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In reply to jonathan watt:

Didn't you have  bike fit a while ago? Did that say anything about crank length?

I would think for you especially it would be worth trying, but it's quite an expensive "try"

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 Dave the Rave 06 Sep 2020
In reply to jonathan watt:

Surely the longer leaver length the easier it is to pedal? 

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 kevin stephens 07 Sep 2020
In reply to jonathan watt:

I have 30 inch legs and ride 165mm cranks on my Ultegra setup which are far better. With my saddle height adjusted correctly my knee is 10mm lower at top of stroke can compared to 170mm cranks. I find this puts less strain on my knee joints and also impingement on my chest when I’m down on the drops.

Post edited at 07:45
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 neuromancer 07 Sep 2020
In reply to Dave the Rave:

For a specific gear a shorter crank marginally increases the torque required to turn the pedals, but watts are watts.

That said, if by swapping to a shorter crank you can get yourself into a more aerodynamic position, then actually you will reduce the effort required.

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 Basemetal 07 Sep 2020
In reply to Dave the Rave:

> Surely the longer leaver length the easier it is to pedal? 

I'm 6' (I83cm) with long femurs- 35" inseam (probably 1.5-2" longer in the leg for my height than average), and long cranks have me kneeing myself in the chest when on the drops. I use 175s. The critical limit seems to be the geometry you find yourself in with the cranks at 12 o'c.

Another factor might be foot length and pedalling style- whether you "ankle" or not...how big a circle your ankle moves in relative to your pedal axle.

And, of course, your choice of gears.

Post edited at 09:01
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 jonathan watt 08 Sep 2020
In reply to Basemetal:

Thank you to all for your comments. It's interesting as all the articles I have read, there doesn't seem to be a definitive answer. Some seem to suggest that there may be quite a noticeable difference, others not so sure. The bit that gets me interested is the ability to raise the saddle by another 10mm, meaning my knee at the top of the pedal stroke is further from my chest and also less strain on the knee. It would hopefully mean I can use the drops more comfortably, something I struggle with at present. May give it a go and see what happens!

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 jonathan watt 08 Sep 2020
In reply to balmybaldwin:

It wasn't something that was mentioned in the fit. 

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In reply to jonathan watt:

I have a track bike with 165mm cranks, a road bike with 170 and a mtb with 175, so prob can use any in a fairly wide range, although bike set up is obviously different in all 3 bikes. I prefer pedalling the track bike, just feels nicer, may be the crank length plays a part in this.

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 mattbell 08 Sep 2020
In reply to jonathan watt:

If you decide you want a 170mm 52/36 let me know, I've got a VGC Ultegra one

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 LastBoyScout 08 Sep 2020
In reply to jonathan watt:

Interesting question. A bike fit for my road bike put me on 172.5mm cranks, which I was already using on my old road bike, but I think my really old one might have been 170mm. For my height, I do have long legs, though.

Pretty sure my mountain bike is 175mm and I've never noticed that much difference, but it's a different style of riding and different gears.

Might have to go and check them all, now!

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In reply to jonathan watt:

> Thank you to all for your comments. It's interesting as all the articles I have read, there doesn't seem to be a definitive answer. Some seem to suggest that there may be quite a noticeable difference, others not so sure. The bit that gets me interested is the ability to raise the saddle by another 10mm, meaning my knee at the top of the pedal stroke is further from my chest and also less strain on the knee. It would hopefully mean I can use the drops more comfortably, something I struggle with at present. May give it a go and see what happens!

I wouldn't put to much store in being able in raising your saddle by 10mm. What works for Kevin might not work for you. Variation in so many factors could make a world of difference or none at all in your circumstances. You're dealing with hinges, bone length, ability for muscle to apply a given force etc etc. And all of it can get mitigated as soon as soon as you start doing something as simple as shifting on the saddle. 

For sure try it. We've all been there! ☺ 

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 Frank4short 14 Sep 2020
In reply to jonathan watt:

>The bit that gets me interested is the ability to raise the saddle by another 10mm, meaning my knee at the top of the pedal stroke is further from my chest and also less strain on the knee. It would hopefully mean I can use the drops more comfortably, something I struggle with at present. May give it a go and see what happens!

^^^This^^^ I relatively recently built a gravel bike from scratch. I'm similar dimensions to you but possibly slightly shorter legs. Shorter cranks raise the saddle and increase the distance between your thighs and chest/belly. Making it more comfortable to cycle in a tucked position. When i had a bike fit my fitter suggested i go for shorter again cranks for more comfort (i'm an old mtber so really not comfortable on the drops).

Anyway all of that notwithstanding it's relatively easy to get 165mm cranks these days after market (most shimano and sram cranks will come in that length), rotor will even go as low as 155mm. An ultegra crank is the cost of an ultegra crank, it might be slightly easier to get a 170mm on discount but the 165mm ones aren't actually more expensive. re: spare parts there are no spare parts on a crankset that relate to its length so that's absolutely moot. Finally they're actually easier to sell if you decide against them as there are lots of people who want to try shorter cranks but cause its not an option almost any manufacturers offer on new bikes it means the number available on the second hand market is vanishingly rare actually making them worth more money than the equivalent 170/2.5/5 mm crank. 

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 Frank4short 14 Sep 2020
In reply to Stuart (aka brt):

Nonsense. Saddle height is based on the exact length from bottom dead centre of the pedal axle (your shoe and cleat stack on bottom dead centre of the pedal axle to be precise) to the underside of the chammy on your shorts. It's an absolute length for a person for a given saddle position on the same bike, therefore if your cranks are 10mm shorter, the bottom dead centre is 10mm higher and your saddle should go up 10mm. 

The only way this should change is if you change bikes or significantly move your saddle position on the seat rails and even then it won't be that much. 

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In reply to Frank4short:

> Nonsense. Saddle height is based on the exact length from bottom dead centre of the pedal axle (your shoe and cleat stack on bottom dead centre of the pedal axle to be precise) to the underside of the chammy on your shorts. It's an absolute length for a person for a given saddle position on the same bike, therefore if your cranks are 10mm shorter, the bottom dead centre is 10mm higher and your saddle should go up 10mm. 

> The only way this should change is if you change bikes or significantly move your saddle position on the seat rails and even then it won't be that much. 

I didn't say he wouldn't get 10mm. But how it actually feels on the bike might not be the instant fix he wants. It might be, which is why I said try it. Besides he'd be getting 5mm from 170mm to 165mm. 

Just look at the pro's and what their crank lengths are. Such a disparity based on what should be the perceived wisdom (midgets running long cranks - lanks running short). 

I'm 172cm and have 175mm cranks. Tried 172.5mm and 170mm. The feel of the 175mm for climbing is just 'better' for me. So I'll arrange my other measurements around that.

I'll happily chat all day about this and I'm usually pretty resolute on not being absolute. But if you start with 'nonsense' again, I might just not bother... 

Post edited at 14:31
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 Toby_W 14 Sep 2020
In reply to jonathan watt:

I only posted the Steve Hogg link to his post on crank length but I have found his site invaluable to being comfortable and fast on my bike.  The best thing he started was the balance test thing which you now see other YouTube posters and bikefitters using.  This is all set around saddle height and setback along with bar drop.  If you can’t ride on your drops for 20min without feeling uncomfortable you should be looking at your bike fit.

His explanation of muscles used to hold your posture vs the ones pushing the pedals is interesting to.  

https://www.stevehoggbikefitting.com/bikefit/2011/05/seat-set-back-for-road-bikes/

Basically you don’t want to be straining to hold yourself on the bike as this will fatigue you and make you uncomfortable.  Any effort should be make you go faster!

As someone above said absolutes are bad as bike fitting is not rocket science, if it was it would be easier!

Hope it’s useful/interesting.

Toby

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