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Discussion Starter · #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.
 

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Discussion Starter · #4 ·
you should have gone 170mm, it's even better
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.
 

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Discussion Starter · #5 ·
Holy Cow, my knees just started hurting about a month ago. My inseam is way shorter than yours and running 172.5 I think. I'm ready to try anything before I stop riding, which I have thought about.
I reckon give 165 a try, or at most 170. I was surprised how much better I felt.
 

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Discussion Starter · #22 ·
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
Gidday mate. I like 95-100. I can definitely feel the difference in my knees going to the shorter crank. Previously my knees would have a "dull ache" for a couple of days, that's gone now. I did not think 2.5mm would make as much difference as it has.
 

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Discussion Starter · #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). 😀
 

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Discussion Starter · #28 ·
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.
No, I actually left it where it was. I only changed by 2.5mm, so figured I would leave until I had "settled in" to the new length. Didn't want to change variables too much, then point at the crank length alone as the big change.
 

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Discussion Starter · #30 ·
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.
I had heard the same thing, but I didn't want to make a "big" jump of 5mm, I figured small changes would find the optimum length for me. Might cost me a few extra dollars, but better than the scatter gun approach of jumping straight to a large change. I have definitely noticed the 2.5mm.
 

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Discussion Starter · #36 ·
Only to promote both sides of this conversation - recently changed from 172.5mm to 175mm. So much better.
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!
 

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Discussion Starter · #40 ·
Were you able to find the individual crank arms or did you have to replace the whole crank set?
Searched the internet to see if I could get the drive side spider and non drive side arm separately, but it was by far easier (and cheaper) to get a complete set (chainrings and cranks)
 

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Discussion Starter · #42 · (Edited)
Yeah, I see lots of 5800 non-drive side crank arms on eBay for $50-60. The correct drive side spiders are much harder to find.
I figure that in the big scheme of things, a $240 US ($320 AUS) crankset that you can resell for $150 if it doesn't suit, is bugger all when you consider how much we "happily" drop on a new bike or wheelset.
 

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Discussion Starter · #44 ·
Were you able to find the exact same crankset with shorter arms? If not, did you notice any difference in front shifting?
Yep, I went from 52-36 @ 175 to 52-36 @ 172.5, so I didn't have to adjust anything. Stock was limited here in Aus for a while, but came good.
 

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Discussion Starter · #50 ·
I have 5800 and 6800, but those are impossible to find anymore. I would need to go to 7000 or 8000. As long as they are Hollowtech II, I presume they should work.
I really like the 8000. Probably the best (and last) mechanical Ultegra. Although a crankset will always be mechanical!
 

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Discussion Starter · #58 · (Edited)
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 .
Good find!. Be interested to see how your change goes. Yeah, Shimano had the debonding issue, but I am pretty sure they sorted it. As much it would suck to be one of the few people who had an issue (hopefully no injuries), I guess out of the thousands of cranksets produced it would be a very small percentage that had an issue.
 

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Discussion Starter · #72 ·
2.5 mm is a tiny change in crank length. Its like a 1.5% change. The sole thickness on different shoes probably differs by a lot more than that. I think its all in your head.
Well good for you. Seeing as how you think you know what's in my head you're obviously pyschic, how about passing on next week's lottery numbers. My body is telling me it's made a difference and that's what matters to me. What percentage of your height is a 2.5 mm seat change, but a lot of people regularly adjust their seats by this amount.
 

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Discussion Starter · #78 · (Edited)
Oh thank you. More golden nuggets from the God of Bike Fit. I'll adjust my saddle height 0.1" when I wear different shorts.

And to the OP, I mean no disrespect. If changing your crank length a tiny bit has helped you -- good for you. No reason to be defensive. I've been riding bikes for a lot of years. I have 5 road bikes. I've been down the rabbit hole on supposed improvements and never felt much difference. But maybe you do and that's OK. If it works for you -- real or imagined, that's all that counts.
I'm not defensive, you were offensive. I originally posted to describe my experience and what I felt, because I had also heard numerous stories of "yes you can feel a 2.5mm difference, no you will not feel a 2.5mm difference". My knees aren't getting sore anymore, so it's definitely made a difference for me. I take offence to you playing amateur psychologist and telling me you suspect it's all in my head. For me it's real, not imagined.
 

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Discussion Starter · #82 ·
Hey Wettek --

" If it works for you -- real or imagined, that's all that counts." That's offensive? You're fitting into RBR quite well. Don't hang out under the bridge with Lombard.

Here's 1/10" of an inch __. Actually that's too much. It's less than that.

Hey -- I was getting soreness in my right hip last Fall. I tried those horse pill Glucosamine Chondroitin with MSM pills with no luck. I bought a different pill at Costco that's a knock off of Move Free Ultra and it made it go away. $30 for 110 tabs. I take one day as directed on the bottle. It makes a huge difference. Imagined or not.

I guess all I've been trying to say is I've ridden a bunch of different crank sizes and noticed no difference. I don't race bikes anymore. I'm 59 years old. I still get in 4-5K miles a year. I've been riding bikes for a long time. Wish you the best and I hope the shorter crank solves your woes. For me, its up there with latex tubes. For you -- something different. The older I get, the more I find 'bike knowledge' borders on the ridiculousness.
God I love keyboard warriors whose opinion is always right. I'm out.
 
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