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Thread: crank size

  1. #1
    Senior Member glassman's Avatar
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    crank size

    I bought a new bike and it came with 172.5 crank, my old bike has a 170 crank. After a 15 mile ride, I noticed my calves and knees were a little sore. Is the 172.5 crank more work on my legs or is it just something I need to get used to or change out the crank to a 170? I ride the 15 mile ride every day and have never experienced soreness with the 170 crank on my old bike. Any ideas?

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    Dolce far niente bigbossman's Avatar
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    Quote Originally Posted by glassman
    I bought a new bike and it came with 172.5 crank, my old bike has a 170 crank. After a 15 mile ride, I noticed my calves and knees were a little sore. Is the 172.5 crank more work on my legs or is it just something I need to get used to or change out the crank to a 170? I ride the 15 mile ride every day and have never experienced soreness with the 170 crank on my old bike. Any ideas?
    Pay attention to your knees - something isn't right. Just a thought - were you fitted to the new bike, so that your saddle and knee/foot position were set up right? I just bought a new bike, and went from 170 crank arms to 175's. I was fitted to the bike after the purchase, and it has been a positive difference. Instead of pushing and grinding up hills on the old "not fitted to me" bike, I'm spinning and (relatively) flying up hills like the Wicked Witch of the West on the new "fitted to me" bike.

    I'd say either you're not fitted right to the bike, or the cranks are too long for you.
    "Love is not the dying moan of a distant violin, itís the triumphant twang of a bedspring."

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    Senior Member late's Avatar
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    Hi,
    what's your inseam?

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    I went from 170 to 172.5 because the new bike was speced that way. I ride with my saddle 2.5cm higher, but then that chages body position in regards to handlebar height and stem length. Everything is connected to everything else. I tweaked a lot before getting things the way I wnated them. I'm not sure that there is any real advantage in longer cranks. In theroy, of course, but I often cannot feel theoretical differences.
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    The old sadlewas 17 cm the new one is 17.25 cm.

    Why adjust the saddle 2.5 cm?

  6. #6
    Senior Member glassman's Avatar
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    Quote Originally Posted by late
    Hi,
    what's your inseam?
    My inseam is 30.75

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    I raised my saddle because the longer crank causes my knee to come up higher on the top of the stroke. I found this a little unconfortable so I raised the saddle. Of course, leg extension is increased at the bottom of the stroke, but it didn't bother me.
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    Time for a change. stapfam's Avatar
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    There is a formula somewhere that tells you what crank length you should be using. According to it I should be using 167.5 cranks. I don't-- I use 175's. and I am only 29" inseam. I would not blame the cranks if only 2.5cm is in question. There must be something different on the set up of this new bike, and I would not mind betting that the saddle is a bit further back from the old one. Mind you, if the new bike also feels comfortable, you may just be stretching a muscle just a different way that in a few rides will sort itself out. If not, get the old bike out again.

    Crank length will affect riding cadence, style and power input. Longer cranks takes more effort to turn, this will slow down cadence but you will be putting in more power. I still cannot see how 2.5 cms will affect this that much though, unless you a finely tuned athlete, and you are getting critical, but not many of us like that on this forum. Thank goodness- most of us just get out and ride.

    Incidentally my calves and knees ache this morning. This was due to a slightly trickier ride yesterday that took a bit more effort than usual.

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    Senior Member glassman's Avatar
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    It's probably fit then as I have to lean over further on the new bike, I might need a longer stem to be more like my Lemond. But 2.5cm is one inch difference so I am not sure but I will ride it and see if it gets better. However, I can reach 34.mph down the slight hill near my house on old bike and can only get the new bike up to 30.9 so it could be my pedal stroke.

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    small differences in crank length do make a difference.
    it takes some time (at least few rides) to get used to a change.
    make sure you are not extending your leg too far (if your seat is the same height and your crank is longer it is possible that you are overextending).
    ideal crank length is a function of rider's femur length, riding style and terrain preferences, thus if you are always in the hills at relatively low cadences you'll probably want longer cranks, if you are a crit fanatic who spins at 140 rpm and sprints all day, you'll definitely want to go with shorter cranks

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    Get A Life - Get A Bike cheeseflavor's Avatar
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    Quote Originally Posted by glassman
    I bought a new bike and it came with 172.5 crank, my old bike has a 170 crank. After a 15 mile ride, I noticed my calves and knees were a little sore. Is the 172.5 crank more work on my legs or is it just something I need to get used to or change out the crank to a 170? I ride the 15 mile ride every day and have never experienced soreness with the 170 crank on my old bike. Any ideas?
    Could be crank length. A saddle that's not adjusted properly will cause knee problems too. Sheldon Brown has some good info on crank length on his site here.

    Good luck!

    Steve

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    Senior Member glassman's Avatar
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    Thanks for the advice, the Sheldon Brown link was good also. That guy knows something about everything...LOL I will ride it some more and see what the problem is.

  13. #13
    Violin guitar mandolin
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    Makes exact foot position over pedal more important. I like ball of foot a little forward of pedal. Pedaling 175 mm cranks. I'm 5 10.

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    Berry Pie..the Holy Grail GrannyGear's Avatar
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    yet more advice.......crank length could be a culprit, but consider your seat height (bottom bracket center to top of seat along the seat tube), fore and aft position of the saddle--which could position your knee differently, and where the pedal axel lands under your foot.

    Traditional wisdom was to change fit incrementally no more than half a centimeter at a time. Why don't you try setting up your bike's relevant-to-knees fit as close as possible to your Lemond. Then, because the Scattante is, after all, a structurally different bike, experiment to find your best position on this, your new bike.

    Dialing in a new bike is seems both a joy and a pain 8-)
    ..... "I renewed my youth, to outward appearance, by mounting a bicycle for the first time." Mark Twain, Speeches
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    Senior Member glassman's Avatar
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    I rode my old bike today and averaged 18.7 and was not too tired, while I averaged 18.8 a couple of days ago on the Scattante. I would not think the crank length would make such a difference but apparently it is a factor along with the Scattante being 3 inches lower on the handlebars. I now believe that most bikes when you reach a certain point will be fairly close to performance by the same engine. I still favor the Lemond geometry but both bikes are fairly close in performance. I just need to figure out whats out of adjustment and fix it. I appreciate all the comments and help. I wonder how many people are using the wrong size crank for them or something else is out of adjustment. If I was really knowledgable of fitting and measuring, I would run an ad in the paper and get rich helping peoiple like me....

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    Berry Pie..the Holy Grail GrannyGear's Avatar
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    Glassman,
    Keep us posted on your fitting progress and your "feeling" for the bike as you fit yourself to it as well. How do your back and neck do with bars 3" lower? Also, any noticable differences going from steel or steel/carbon to all carbon...given geometries, wheels, etc. are also different.

    Oh yeah, in the meantime......have a ball!!
    ..... "I renewed my youth, to outward appearance, by mounting a bicycle for the first time." Mark Twain, Speeches
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    Senior Member glassman's Avatar
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    Quote Originally Posted by GrannyGear
    Glassman,
    Keep us posted on your fitting progress and your "feeling" for the bike as you fit yourself to it as well. How do your back and neck do with bars 3" lower? Also, any noticable differences going from steel or steel/carbon to all carbon...given geometries, wheels, etc. are also different.

    Oh yeah, in the meantime......have a ball!!
    I will, but the cfr is smoother riding, I know that already. My Lemond is aluminum, the 2005 Tourmalet and it is a very nice bike. I guess at my age I should stick with the more upright riding position but like everyone, I want better, faster, more comfortable, a seat that will enhance my life, well you know what I mean.

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    Berry Pie..the Holy Grail GrannyGear's Avatar
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    Wouldn't it be cool if all cyclists were issued by a paternal gov't agency (Dept. of Velo?) the same bike except for saddle and pedals--fit would be scientifically guaranteed. Equipment would no longer be an issue. Tech/weight/aero/snob wienies would cease to exist. It would just be mano y mano with all equalized and no more eternal searching for the perfect piece of gear.

    Boring.
    ..... "I renewed my youth, to outward appearance, by mounting a bicycle for the first time." Mark Twain, Speeches
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  19. #19
    Senior Member glassman's Avatar
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    Quote Originally Posted by GrannyGear
    Wouldn't it be cool if all cyclists were issued by a paternal gov't agency (Dept. of Velo?) the same bike except for saddle and pedals--fit would be scientifically guaranteed. Equipment would no longer be an issue. Tech/weight/aero/snob wienies would cease to exist. It would just be mano y mano with all equalized and no more eternal searching for the perfect piece of gear.

    Boring.
    That would be boring, I vote we keep it like it is....

  20. #20
    Time for a change. stapfam's Avatar
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    One thing I hate is a new bike. It is going to be different to the old one. As you have found out- a different set up will take some getting used to. Then there are the final adjustments to get right, and the silly things you do not think about like is the gearing the same? Are these tyres giving as much grip/more drag than the old ones? are the bearings on the wheels/ cranks/pedals dragging a bit?

    Mind you, get 500 miles on the new bike to run it in, get the adjustments right, get the body attuned to the new bike, and you will still be riding the old bike in a couple of years time to get a real ride on a real bike.

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    As stepfam pointed out, newer is always different. Because your knees could tell your position was different doesn't mean that it had anything to do with the crank length. I have 165's 170's, 172.5's and 175's. I prefer the 172.5 for flat ground but I prefer the 175's for climbing and I can get used to it. NONE of these cranks made my legs hurt. Though I got tired a great deal faster with the short cranks. Legs: 35" Height 6'4"

    My guess is that 170's are good for anyone under 6' and 172'5 or 175's are fine for taller. There isn't a great difference in any case.

  22. #22
    Senior Member onbike 1939's Avatar
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    Quote Originally Posted by stapfam[B
    ]One thing I hate is a new bike.[/B] It is going to be different to the old one. As you have found out- a different set up will take some getting used to. Then there are the final adjustments to get right, and the silly things you do not think about like is the gearing the same? Are these tyres giving as much grip/more drag than the old ones? are the bearings on the wheels/ cranks/pedals dragging a bit?

    Mind you, get 500 miles on the new bike to run it in, get the adjustments right, get the body attuned to the new bike, and you will still be riding the old bike in a couple of years time to get a real ride on a real bike.
    You are so right. A new bike is absolute hell. Look....just as a favour and for one time only I'll accept a new bike on your behalf. No...don't mention it ...it's the least I can do.

  23. #23
    Old Guy benttrike18's Avatar
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    I agree. Going to a longer crank arm increases leverage and should feel better. Sounds like saddle height is not right. Your knee should be just about ready to lock at the lowest position of the crank arm.
    I always marked my saddle height with a piece of tape, just incase it slips.

    Also keep in mind a change in saddle height changes handlebar height. You didnt mention what you are riding, road and drop bars or something else. Try and keep the bars and saddle as level as possible.
    If you are using drop bars and really want a change to the good, go to a wider handlebar.

    Also, have you changed your pedals? What type do you use? With clipless if there isn't enough float this will really kill your knees.

    Regards
    Jim Smith

  24. #24
    Senior Member glassman's Avatar
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    I think a lot of my problem is the stem is 3 inches shorter. I saw a bike on ebay with a different stem on his bike, same brand, so I might try to find an adjustable stem or one with higher rise. You can see the rise is significant from mine.


  25. #25
    Ancient Clydesdale 2 wheeler's Avatar
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    The difference in crank length is not that big of a change. We're talking an increase of 2.5 MM, not CM as some have stated. Look at a ruler and look at what 2.5MM really is. It's less than 1/10 of an inch! Also stated incorrectly in one of the responses is that longer cranks make you work harder: not true. They give your legs more leverage; more leverage means more power. The trade off is that your feet go in a bigger circle.

    Look elsewhere than the crank.

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