Road Bike, Cycling Forums banner

Changing crank length

5K views 88 replies 16 participants last post by  smokersteve 
#1 · (Edited)
Gidday guys.

I have been riding 175mm cranks all my life. The first bike I bought had them, and not knowing any better, any other bike I bought had them, and bike shops just said "you are 6'1", it's what you need". Any groupset I bought had them, because it's what I though I needed.
Now that I am getting older, I am finding my knees are getting sore after a ride, so started researching via the good old internet and questioning if they were the right length.
With a 860mm inseam, all the research I did indicated 172.5 was the optimum length for me, so I took the plunge and got a set of Ultegra R8000, 52-36 in 172.5.
I really wasn't expecting to feel any difference with a change of only 2.5mm, and really thought I had just wasted my money, but wanted to give it a try.
Well, I was pleasantly surprised. As well as my knees feeling a lot better, it just felt smoother. My 175's didn't feel bad to turn in any way, but the 172.5's just feel smoother turning them.
Anyway, I know it's very subjective, and there are multiple formulas and opinions, and what worked for me, may not work for others, but just sharing my experience.

I wasn't expecting any noticeable difference, but I am glad I was willing to spend a relatively small amount of money to be a lot more comfortable on my bike. I didn't make any other setup changes.

Regards to all.
 
See less See more
#4 ·
Yeah, I did think about 170, but as I said, pretty much all the "formulas" and opinions I could find steered me towards the 172.5. I may try them later, but I have only done 2 short rides (25 miles) with the 172.5's so far so I will run them for a while to get used to them before trying shorter again.
 
#7 ·
For a few years, I'd develop iliotibial band syndrome (ITBS) in my left knee around mid season (fair weather rider here). My legs are slightly different lengths. After countless adjustments to seat and cleat positioning -- the final result of which helped a bit -- it was when I replaced my 172.5 with 170 that the left knee problem disappeared and has not returned. I highly recommend at least trying 170.
 
#12 ·
Wettek , What type of cadence do you typically ride at ? I researched this a few years ago and never took the plunge to buy shorter cranks .I have always rode 172.5 and my research indicated I should be on 165 cranks , I am a spinner and find anything under 95 for a cadence feels like I am lugging . I too as I age find my knees aching more .
I would be interested in any other people to chime in on this topic . Thanks
 
#13 ·
There are all kinds of formulas published / discussed out there. Some are based on femur length, some are on shoes size, overall leg length, overall height, ...etc. I plugged in my numbers and the crank length results ranged from 175mm to 170mm which is basically everywhere, which means nowhere. :rolleyes:

What did I do? I bought 3 different lengths and tried it myself over a period of about a year and settled with one that I felt the most comfortable with. It is an expensive process.
 
#17 ·
My inseam is 32" and have little longer than average femur length. Some formula suggested 175mm crank length. It wasn't comfortable for me. There is a slight difference in feel between 172.5mm and 170mm for me and I settled with 170mm. Just because it worked for me isn't a guarantee that it will work for someone with the same inseam measurement. I've seen a crank set with adjustable length but it wasn't for the bottom bracket of my bike so I had to buy 3 crank sets. If you buy used ones and sell the ones you don't want, it will be a smaller loss than trying this process with 3 new sets.
 
#18 ·
My inseam is 30.5" and the calculation I have done put me at 167.5 crank which with the supply issues would be almost impossible to find . Research also shows I could go with a 165 .
My oldest bike which I still enjoy riding and put around 3k miles a year on could honestly use some new chainrings , so now may be the time to try this
 
#19 ·
If I were you, I would try a 170mm crank for awhile and see how that works for you. Small changes are best.
 
#20 ·
I rode 170's for over 20 yrs and decided to try 172.5's and found I preferred them and have gone with the 172.5's anytime I got a new crank. But I still have bikes with 170's and ride either length with no issues. So while I prefer 172.5, I can't feel the difference when riding 170. My cadence may be a bit higher on the 170's but I haven't really takin the time to compare.

It seems to me, in my case, that my preference is all in my head.

Kinda on the same note a friend picked up a bike and rode it for a number of months before giving it a good once over and when he got to the bottom bracket that one crankarm was 170 and the other was either a 172.5 or 175. He didn't realize till then that they were different.
 
#23 ·
Went out and did 30 miles this morning, I can say the shorter cranks have definitely made a difference, I feel heaps better after a ride, and my average pace has picked up by about .8 mph. Just goes to show that just because we've done something for the last 35 years, doesn't mean it's still "right". We all get older. (and fatter). 😀
 
#24 ·
As more data and understanding of bike fit is generated, the industry is definitely trending towards shorter crank lengths. Long-held beliefs about optimal lengths are being rethought and products are evolving to reflect this. Note Shimano now offers multple versions of the latest 12-speed Ultegra and Dura-Ace cranksets in 160mm. In the previous 11-speed road gruppos, you could only get 160mm cranks as a 105 50/34T compact.

Bradley Wiggins started out his career on 177.5mm cranks and won gold in the Team Pursuit in the Rio Olympics using 165s. I believe I read elsewhere that he did his hour record attempt using 170s. He's 6'3".

Guys that have been riding for years may find this a bit of a paradigm shift, but it's not a fad. However, I don't think you should look into changing your crank arm lengths unless you have a compelling reason.

I think these articles do a good job in explaining the benefits and liablities of shorter and longer cranks and align with my exact experience when I switched to shorter cranks (-5mm):

What's the best crank length for cycling?
What is the best crank length for cycling?

The takeaway: There's no right or wrong length, but most people will benefit from using shorter cranks than what has been considered the industry standard.
 
#29 ·
As more data and understanding of bike fit is generated, the industry is definitely trending towards shorter crank lengths. Long-held beliefs about optimal lengths are being rethought and products are evolving to reflect this. Note Shimano now offers multple versions of the latest 12-speed Ultegra and Dura-Ace cranksets in 160mm. In the previous 11-speed road gruppos, you could only get 160mm cranks as a 105 50/34T compact.

Bradley Wiggins started out his career on 177.5mm cranks and won gold in the Team Pursuit in the Rio Olympics using 165s. I believe I read elsewhere that he did his hour record attempt using 170s. He's 6'3".

Guys that have been riding for years may find this a bit of a paradigm shift, but it's not a fad. However, I don't think you should look into changing your crank arm lengths unless you have a compelling reason.

I think these articles do a good job in explaining the benefits and liablities of shorter and longer cranks and align with my exact experience when I switched to shorter cranks (-5mm):

What's the best crank length for cycling?
What is the best crank length for cycling?

The takeaway: There's no right or wrong length, but most people will benefit from using shorter cranks than what has been considered the industry standard.
This reinforces everything I have read , in my situation it recommends a drop from 5mm to 7.5mm which in my mind is huge. If you have been riding for a long time most people I think would agree small changes at a time .
One fitter that I follow say's most people will not notice a change of 2.5mm , decisions decisions.
 
#25 ·
OP, did you adjust your saddle height? You should have raised your saddle 2.5mm to adjust for the shorter crank length.

My knees have been hurting me (front of the knee). I raised my saddle about 2mm and they feel a lot better. I found that saddles sag after a while, and thus your position becomes lower over time.

Conventional wisdom is if there's front of the knee pain, raise the saddle; behind the knee, lower it.
 
#26 ·
OP, did you adjust your saddle height? You should have raised your saddle 2.5mm to adjust for the shorter crank length.
Is there really a need to? If yoy have shorter crank arms, you will also be extending less, so it's really a wash.

I would say leave well enough alone and if you still have pain in front of the knees, then raise the saddle a bit.
 
#36 ·
Fair enough, but I'm not racing, just doing 25 miles a day for general fitness. If I was serious, I would fine tune my seat position by millimetres, but at the moment I am very comfortable and the crank change has helped. One day I will pay for a professional fit!
 
#47 ·
Yes, this would be trading one problem for another. But I don't think that was being discussed. Some were suggesting raising the saddle AFTER getting shorter crank arms which I think is changing too many variables at a time anyway.
 
#53 ·
I went the other way, from 172.5 to 175. I was changing cranks on an older bike and I wanted to match the crank arm length on my other bikes, which both had 175 cranks.
I, also, did not notice a difference in feel, but I did see a slower cadence.

That was it. No change to saddle height, no difference in speed (of course, when you upgrade a bike you always "feel" faster, but it is rarely borne out by actual results), no difference in recovery. When pedaling the longer cranks I had a lower cadence by a few rpm (3 - 5 rpm, maybe) that I couldn't feel but could see when I checked my cyclecomputer.
 
#56 ·
So my old brain cells finally kicked in and recalled that I had an old FSA Gossamer Crankset in my tickle trunk , turns out it is a compact with 170mm arms . Then I had a look at my oldest daughters bike which she rarely rides and it also has Gossamer cranks with 165mm arms .
So I just ordered some cheap adapters as my older road bike has a 386 bottom bracket , these adapters will reduce it down to the 24mm spindle and the experiment will be underway with minimal cost. May take some time but I will give an update down the road .
 
#66 · (Edited)
Your book is wrong. So tell me, is moving your saddle up or down 2.5mm insignificant? I know I can feel the difference here.
 
#69 ·
If I lower my seat 2.5mm's I can feel it because I lowered it, but if my seatpost slips I probably won't realize till it's 5mm or more. I'm not throwing stones here, but I think a lot of feeling a tiny adjustment is psychological.

How much of a difference is there in the thickness of one chamois to another? All chamois are not created equal, from brand to brand or model to model or just plain acceptable tolerances within the manufacturing process, yet how many of us are taking the time to measure the thickness from one to another? Shux, how dense are they and how much do they compress from one to another?

I think a lot of this is in our heads. That matters and it's not a small thing but I really think it's more psychological than physical.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top