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Does crank length matter?

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Does crank length matter?

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Old 01-16-18, 06:05 PM
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phtomita
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Does crank length matter?

I was trying to get more educated about the crank length and got to a video from GNC guys on Youtube.
From their formula, inseam x 1.25 + 65.
For short person like me, I get less than minimum 165 (Shimano crankset).

Does keeping as close as to this formula help to make biking more comfortable?
(= no knee, back, hip pain after long rides)

Anyone has experience getting improvement of riding experience when changing the crank length?

Thank you,
Paulo
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Old 01-16-18, 09:53 PM
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I went from 170 to 165mm and found it helped a lot with knee discomfort. I am 5'4 1/2" tall.
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Old 01-16-18, 10:34 PM
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I'm a shorty too, and I have two modern cranksets that were cut short and redrilled by Mark Stonich of BikeSmith Design and Fabrication. Both are less than 150mm.

Takeaway: Much easier to spin, but also less leverage against hills and wind. So I've gone back to 165 and 170 on all my bikes.
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Old 01-17-18, 12:37 PM
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Originally Posted by phtomita View Post
I was trying to get more educated about the crank length and got to a video from GNC guys on Youtube.
From their formula, inseam x 1.25 + 65.
For short person like me, I get less than minimum 165 (Shimano crankset).

Does keeping as close as to this formula help to make biking more comfortable?
(= no knee, back, hip pain after long rides)

Anyone has experience getting improvement of riding experience when changing the crank length?

Thank you,
Paulo
Sugino makes a lot of their models (even the "modern" cranks) in shorter lengths like 160mm and the "Mighty Mignon" in lengths from 140-155mm.

If you go too short, you can get that "shoes tied together" feeling, but I think my knees do like 165mm more than 170mm. I'm 5'7"ish.

Whatever crank length you use, it's important to set the saddle height carefully. Going from a long crank to a shorter crank, you'll need to raise the saddle a little. And vice versa.
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Old 01-17-18, 10:56 PM
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wow, just calculated my crank length to be 160 cm.

I have been getting front knee discomfort after a quick bike fit from the LBS.

I got it initially from running and wondering now if crank length adjustment will reduce discomfort.
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Old 01-17-18, 11:41 PM
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I have not seen any strong science behind any crank length formula. They are generally based on the assumption that since average size pros are good on 170s that everyone else should be on cranks in some proportion to leg length based on that starting point. But there is no reason to think that traditional 170s are ideally ergonomic for any particular height or that cranks scale geometrically.
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Old 01-18-18, 11:35 AM
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I'm coming up with 98.75,,, have to be doing something wrong I have a 27" inseam?
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Old 01-18-18, 11:44 AM
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Originally Posted by airforce1 View Post
wow, just calculated my crank length to be 160 cm.

I have been getting front knee discomfort after a quick bike fit from the LBS.

I got it initially from running and wondering now if crank length adjustment will reduce discomfort.
Pain in the front of the knee often means your saddle is too low.
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Old 01-18-18, 12:06 PM
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Originally Posted by Tajue17 View Post
I'm coming up with 98.75,,, have to be doing something wrong I have a 27" inseam?
Use centimeters.

Originally Posted by ThermionicScott View Post
Pain in the front of the knee often means your saddle is too low.
Or too high, or the cleat is at a bad angle, or you're sitting too far forward, or your crank is too big.
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Old 01-18-18, 12:23 PM
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I would expect pain from a too-high saddle to manifest itself at the back of the knee rather than front, but agree that there are many possible causes. Note my use of the word "often".
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Old 01-18-18, 12:27 PM
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Originally Posted by ThermionicScott View Post
I would expect pain from a too-high saddle to manifest itself at the back of the knee rather than front, but agree that there are many possible causes. Note my use of the word "often".
It seemed unlikely that the quick fit he got at a bike shop would leave the saddle too low, of all things.
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Old 01-18-18, 12:42 PM
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Originally Posted by Kontact View Post
It seemed unlikely that the quick fit he got at a bike shop would leave the saddle too low, of all things.
Who knows? It's not uncommon for a quickie bike shop fit to prove itself inadequate in real riding.
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Old 01-18-18, 02:29 PM
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Originally Posted by ThermionicScott View Post
Pain in the front of the knee often means your saddle is too low.

Saddle height was set at correct height.
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Old 01-18-18, 02:34 PM
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Originally Posted by airforce1 View Post
Saddle height was set at correct height.
Well, I don't have a horse in this race. Shorter cranks are unlikely to hurt anything, so you might as well try them.
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Old 01-18-18, 03:03 PM
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Not to me . I have 180, 175 172.5 & 170 on various bikes

the saddle height relative to the pedals is similar, because my legs stay same length.
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Old 01-18-18, 04:31 PM
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When I moved from 170mm to 165mm cranks I did not require a seat height adjustment. Measuring from the center of the crank bolt to seat did not change...what I did need to adjust slightly was the fore-aft adjustment as the position of the spindle DID change relative to my knee. Just a small adjustment required to maintain the optimum angle.
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Old 01-19-18, 02:06 PM
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Thank you all for the recommendations.
From the formula, I get 158 for myself - then I was thinking to buy a 175 and have it shortened, but from the web (https://highpath.co.uk/crank-shortening/) there was a mention of NO for the hollowtech cranks from Shimano, so decided to go for compat 50/34T 165mm.

Does someone here have the crank shortened by some metal precision shop in US?
I looked the shortener thing, but that is ugly.
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Old 03-22-18, 04:19 PM
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I am going to my LBS this Saturday to be fitted for a bike - either a Specialized Cross Trail or Ariel, both Elite Alloy models. I have looked at the geometries of each of these and the only difference I can see is that Ariel has a shorter crank length; I am comparing same sizes Ariel small to CT small. Seems odd that all (except for standover height (due to sloped stop tube on the Ariel) are equal. Hoping the Cross Trail is a good fit because the Ariel only comes in grey/pink which I don't especially like.


My current bike is a Crossroads Step-through, size medium. I have been riding it for 5 years now and it seems to be a good fit. The Specialized chart lists my bike as having 170 cranks across all sizes. Men's Crossroads lists S/M as 170 and L-XXL, 175.


When I compare the Cross Trail/Ariel sizing I get confused: Ariel XS/S - 165; M/L - 170. Cross Trail S/M - 170 and L/XL - 172. For reference, I am 5'7 with long legs and short torso; my bike inseam measures 32" which, using the above formula, calculates to a 166 crank. I get where the Crossroads longer crank might be due to the more upright sitting position. Ariel and Cross Trail have a flatter bar, which I plan to change to one with a bit of upsweep for a more relaxed riding position.


I suppose the best answer is, I'll have to wait and "try them on". I just wanted to go into my fitting with an idea of whether a Cross Trail will work for me. I really don't want to buy a $1,000 grey and pink bike!


Comments appreciated, knowing I may be even more confused than I am now
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Old 03-22-18, 04:57 PM
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I'm another one for whom it doesn't make much difference. I'm more likely to ride higher cadence on shorter cranks and have more standing power on longer ones. But no discomfort, just a slightly different style.
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Old 03-23-18, 10:20 AM
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EDIT: Sorry, I posted I went to 165s, but I went to 170s on my LHT.

I'm 5' 11" and switched to 170s. I much prefer them. So it is really personal preference.

Last edited by phughes; 04-11-18 at 11:24 AM. Reason: Wrong crank length
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Old 03-23-18, 02:43 PM
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Am about 5'5" and have always ridden 170mm because that's what came on the road bikes I bought. The MTBs had 175mm cranks. Used an old method of adjusting the saddle height so that with your pelvis level and your knee 'locked out', your heel was on the pedal and when you put the ball of your foot over the pedal spindle, you get a bend in the knee. Now in my mid 60's am starting to experience some knee pain. Using a lower gear mitigates the pain.
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Old 04-11-18, 02:45 AM
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Some claim huge comfort improvement when changing crank length, but to most it seems that it doesn't matter that much. The bike has gears and that will compensate for the leverage change. If you want to try a change, going to a shorter length is more likely to lead to an improvement than going to a longer. Long cranks lifts the knee higher at the top which closes the hip more, which can become a comfort issue. If you are a shorter person and have say 170mm cranks I think it's a good idea to test 165mm, and the thing to observe is comfort/preference, as I don't think it will affect performance.

Short cranks also help reducing the toe front wheel overlap issue if there is one.
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Old 04-11-18, 03:37 AM
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After getting a Trek precision bike fit where the machine can and does vary the crank length, I showed better pedaling on the 165 length and switched to them on my bikes and counld not be more pleased. For me much smoother and comfortable and cadence increased. BTY I'm 5'9" and had 172.5 size cranks.
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Old 04-14-18, 07:29 PM
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There is no evidence to support the fact that crank arm length makes any noticable performance difference. On the other hand different crank arm lengths may suit your knees and legs better. This is really one where "ride what fits you" is the best answer.

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Old 10-08-18, 07:21 PM
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I was looking the new 105 R7000 specs and they added a 160 mm crankset.
Currently I have a 5800 165 mm and don't have any issue, but thinking on getting the shorter one since it means I bend a tiny bit less the knees while spinning.
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