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Old 09-11-10, 09:40 PM   #1
CCrew
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172.5 to 175: Noticeable?

Offered a deal on a 175 crank armed Ultegra to replace my crappy 172.5 FSA. Is the crank arm length really noticeable? I'll admit going in that I'm old and have cranky knees, and all my bikes are 172.5. Its a deal from a friend that gave him fits trying from 170, so although he's about giving it to me ($50) Id feel bad trying and flipping it if it didn't work. I'd ask to borrow it and buy it if it works, but it's about new and if I did that and it didn't work really wouldn't be "right" to hand them back.

Thoughts? (not on the deal, just whether it's a huge/noticeable change)
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Old 09-11-10, 09:44 PM   #2
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You will not notice . . .
Once worked on a tandem whereby someone had mixed up the crossover cranks between stoker and pilot (pilot was 175, stoker was 170) neither rider had noticed!
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Old 09-11-10, 10:02 PM   #3
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It is a subtle difference. I have 170s on my old road bike and 180s on my mountain bike and I can percieve a difference when I think about it, but if I had just hopped on to a bike with without knowing the crank length it wouldn't be the first thing I would notice. 172.5 to 175 will be noticeable but not distracting.
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Old 09-11-10, 10:09 PM   #4
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you probably wont notice.

i have 172.5 on my fixed gear, 175 on my aluminum bike, and 180 on my steel bike.

my "ideal" length according to one measurement is 177mm or something like that. some days i think i can feel the difference between the 175 and 180s but i cant tell a thing between the 172.5s and 175s
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Old 09-11-10, 10:14 PM   #5
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it depends on your leg length and flexibility.
If you legs are long and you're flexible, then you're very unlikely to notice the difference. The only difference you might notice is that your cadence has dropped by single digits.

If your legs are short, even for 172.5mm cranks, then you will most likely notice it.
If your legs are short and you're not very flexible, then you will notice it.

and even then, there are variations in how the legs are proportioned, so you might feel it, or not.

For me, I notice I have a much easier time using 165mm cranks due to my limited flexibility.
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Old 09-11-10, 10:17 PM   #6
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CCrew, My road bike's cranksets range from one 165 mm, two 172.5 mm and one 175 mm. If I jump from one straight to another I can tell the difference for the first few revolutions and then I adapt and it becomes a non issue. Your knees will have more range of motion, but work output will diminish a tad because of the added mechanical leverage.

If they don't work, flip them and split any profit with your friend.

Brad
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Old 09-12-10, 06:05 PM   #7
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Ccrew,

You mention that you have creaky knees. For this this reason I highly recommend that you not incrase the length of the crankarms. Longer crankarms cause your knee to bend more at the top of your pedal stroke. This "hyperflexion" (I believe that is the correct word) puts more strain on the knee joint. You may not feel the difference after a test ride or ever after a few medium distance riders but you will start to feel the pain in your knees the more your ride with the longer crank arms. Stick with shorter crankarms and higher rpms for the sake of your knees. I speak from experience.
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Old 09-12-10, 06:49 PM   #8
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If they don't work give your friend the opportunity to flip them. If they don't want to and you don't feel right about making a profit, then pay it forward and sell them for the same price. I like to flip bikes, when I have a friend that wants one I pay it forward and sell it to them for what I paid, with the free tune-up.
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Old 09-12-10, 06:53 PM   #9
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My knees do not like 175's and are happy with 172.5. My leg length in bare feet is 33.75".
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Old 09-12-10, 07:02 PM   #10
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Yeah, when I went to 165's from 170's, my cranky old knees really liked it. You're going in the wrong direction. bk
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Old 09-12-10, 07:09 PM   #11
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Can only say the difference might be noticeable. I've used 170/172.5/175 on a variety of bikes. Used a 177.5 for a while on one bike and my knees said no. YMMV.
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