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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.
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.
 

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Your book is wrong. So tell me, is moving your saddle up or down 2.5mm insignificant? I know I can feel the differnece here.
Statisticians draw it at 5%

An inch is 2.54 cm. 10% of 2.54 cm is .254 cm, or 2.54 mm, Right? So we're talking 1/10 of an inch. I think that's right. Get a tape measure and measure out 1/10 of an inch. Mark that distance on a piece of paper. It's tiny. It would difficult to even raise your seat post that little with any accuracy. Why don't stems come in finer increments than one cm if 2.5 mm is such a significant distance?

I know you consider yourself the god of bike fitting, but look at the paper again and tell me you'd really be able to tell a 1/10" difference in your crank length, or seat post length. I sure couldn't.
 

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Try riding without all of those and you will need to adjust your saddle.
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.
 

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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.
 
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