Will an incorrect crank length really ruin my knees or is it hype?

Discussion in 'Cycling Equipment' started by kaian, Sep 21, 2004.

  1. kaian

    kaian New Member

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    I've read several of the threads here concerning crank length, but I guess I want to know how important it is to everyone here or how serious of an issue it really is. I bought a Specialized Allez triple a couple of months ago and the Specialized Comp crankset that came with it is 172.5 mm. The bike is 50cm (XS) and fits me well, however I am 5 feet tall and from what I read, 172.5 is way too big for me. I have my seat adjusted correctly (I believe), but sometimes I feel like my knees are coming up more than they should. I have had problems with patellar tendonitis in my right knee in the past and I'm worried that maybe the longer crank length will be harmful in the long run.

    Any thoughts?

    My LBS said he could install a Shimano Sora crank for $70-75 or a Tiagra for $90-95 without having to change the bottom bracket.

    Also, will I lose power if I switch?

    Again, I'd like to hear opinions. Does anyone think this is important or should I save my hard earned cash?? :) Thanks!
     
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  2. gclark8

    gclark8 New Member

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    If you are going to ride for any length of time the "correct" crank length is of great benefit. I just changed the cranks on a friend's (lady) bike. She is 4'11" and her ideal length is 160mm, no Shimano at that length, but there are plenty of quality ones available. Yes it made a big diffence to her comfort, legs, knees, bottom, etc...

    Do a web search on "160 cranks", for lots of articles...
     
  3. gruppo

    gruppo New Member

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    Here is a quote from "Bicycling Medicine by Arnie Baker, MD":

    "Caution: Once you have use one crankarm length for awhile, modyfying the length by more than 2.5mm at a time is not recommended. Although another length may be advantageous in the long run, your body, having adapted to the current length, will take time to readapt and become economical at a new length."

    Others who have changed their crankarm length claim that it can be a very difficult transition because it affects every aspect of the pedaling technique. Experienced riders who changed have been know to have completely relearn proper pedaling mechanics. A long slow process.

    This doesn't mean you shouldn't consider the change. Just have your eyes wide open going in.
     
  4. boudreaux

    boudreaux New Member

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    I've randomly switched between 170,72.5 and 175 for years with no ill effect.Started with 170 and have gradually migrated to 72.5, 175 for most, but still have a few 170s.
     
  5. boudreaux

    boudreaux New Member

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    172.5 was wrong for that size bike and wrong for your height. Shame on Specialized.
     
  6. kaian

    kaian New Member

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    Yeah, I think a 165mm crankset might be best. I don't want to mess up my knees. I hope I won't lose to much leverage and power. I don't think I've fully adapted to the size of the cranks on there yet - I've only been riding for 2 months. Yeah it seemed kind of odd to me that they didn't put the smaller cranks on a smaller bike. ???? Maybe because it's considered a beginner level bike. ???? Thanks for the comments thus far. Please keep them coming!!!

    Does anyone think it's worth the extra $20 to get the Tiagra cranks (instead of Sora) or should I go even better and get 105s (I'd have to get a different BB to do that I think). The rest of the bike is Tiagra/Sora.
     
  7. gclark8

    gclark8 New Member

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  8. e_guevara

    e_guevara New Member

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    Some things to ponder on before dropping your money into the bowl...
    - Do you plan to race?
    - Is weight a big issue for you?
    - Is stiffness an issue too?

    Both Sora and Tiagra are square-tapered - works on the same bottom bracket. Not so much difference IMO. A 105 crank uses an Octalink interface - yes, you have to change your BB which means an additional expense.

    General rule on groupsets: "Higher groupsets mean lighter weight, stiffer components, and more expensive."

    I don't think there's a Shimano crank shorter then 165mm. If you're planning to use a shorter crank length, look elsewhere.
     
  9. gclark8

    gclark8 New Member

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  10. 531Aussie

    531Aussie Well-Known Member

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    In my opnion, it's potentially more damaging to your knees if you increase the crank length because knee flexion is increased. So, reducing crank length shouldn't be a problem, but it would be wise to ease into the knew length.

    I injured my knee by going from 170 to 175, then "hammering" for a month. It was almost a year before my knee was back to normal.

    As far as power goes, I don't think you'll notice much difference. The leverage can't be that crucial if one of the world's best time-trialers (Armstrong) puts shorter cranks on for a time-trial.
     
  11. rtol299

    rtol299 New Member

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    Yeah dont do it man youll regret it in the long run I mean for NZ$ 300 (170US) dolalrs youll get cranks of decent quality . He in the US what would it cost to have Knee recosntrution suregry
     
  12. kaian

    kaian New Member

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    George,

    Thanks for the link. I already checked into that crankset and it's sold already! I appreciate your help.
     
  13. retrogeek

    retrogeek New Member

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    Crank length is just as important to get right in terms of fitting a bike as is frame size, stem length, handle bar width, pedals, shoes, saddle...they're all important if you want to ride in comfort, with efficiency, and with control.

    Make sure you have read the thread "Poll:Cranks" 141 posts and about 18,000 hits, great reading.

    If you are still unsure type "crank length" in google and you will get more info if you like.

    Ultimately, however, you should really consult someone who knows how to fit riders to a bike. They can measure you (your inseam is the important measurement here) and look at you while you ride to determine what is needed, its money well spent.

    If you need cranks shorter than 165mm they are available, High Sierra Cycle Center has them (expensive but nice) as does Revolution Bike (much cheaper). Your situation is similar to what I am facing now with putting together a decent bike for my 10 year old son. He has a Terry bicycle (a great bike for youth racers, they're not just for the ladies!!!) but the cranks that came with it were 165mm and he is visibly not comfortable with that length, he should be riding 145-150mm cranks, which I have just ordered recently.

    As a general rule going down in size is a much easier adjustment than going up in length. But still take it easy the first 2-3 months. Ride on the flats only if possible, and no hammering. 172.5 is way to long for that size of bicycle, I second the "shame" sentiments posted above!

    After further research you might find that you need even shorter than 165mm, most of the approximately 5 foot tall riders I have helped to fit needed in the range of 150-160mm cranks.
     
  14. kaian

    kaian New Member

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    Thanks for the info, Retrogeek. I appreciate it!

    Sorry to sound like a silly newbie, but I have a question...is it possible to only change the crank arms and not the whole crankset? My LBS basically came to the solution of changing the whole thing, but I noticed on a lot of these sites, you can but just the arms.

    I have the Specialized Comp crankset on the bike - it wouldn't hurt to change it out to Shimano, but my options are limited (due to my budget and what will work). I just found out that I will have to change the BB, too. :( Specialized put a Shimano BB on there that doesn't work with Sora or Tiagra or 105.

    And I am also learning that maybe I should've gotten a bike with 9 speed components (instead of 8 speed) so it would be upgradeable, too. But I guess it's all a learning process, right?

    Thanks for all the info everyone!
     
  15. retrogeek

    retrogeek New Member

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    The bicycling industry has many standards of compatibility between parts and it can be really confusing to anyone new coming into the sport. When I started riding in the early 70's you either rode Campagnolo or you rode garbage, things were very simple in those days. Its a learning curve that everyone goes through. Don't feel bad when cycling geeks try to impress you with their knowledge of cycling jargon, just smile and keep asking questions until you understand what they are telling you.

    But, first things first. As gclark8 said measure, don't guess! You need to first decide on the crank length you want to try and then put together a setup that will suit you. The www.gstrikes.com/measurements is a good one to look at, and Leonard Zinn uses the formula of 21% of the inseam. My inseam is 85cm x .21 = 178.5mm, I ride 180's.

    After you have the crank length that is best for your inseam let us know, then I am sure many can give advice on a setup that would be apropriate.

    In answer to your question, yes you can buy just the arms and use the sprockets you already have. Find out the "BCD" size your current crank has and if you buy another set of crank arms you just have to make sure that your sprockets and the new crank arm are the same size before you buy. Concerning bottom brackets, however, most of the sub-165mm cranks I have seen use the older square tapered type Shimano bottom bracket, but these are cheap, approx. $22, easily available, and are very easy to change.

    In regard to 8spd. vs. 9 spd. no worries, you'll never know the difference and replacement parts will be available for quite sometime to come. As a new rider it is more important to get a bike that fits properly first. Once you settle on frame size, crank size, stem, etc..., then you can worry about 8 spd. vs. 9spd. vs. 10spd, Shimano vs. Campy, less filling vs. tastes great, you get the picture!
     
  16. crashnigley

    crashnigley New Member

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    Retro,

    Sounds like you,ve got some eperience with this. I'll heed your advice and go in for a re-fitting. But just for fun, can you tell me what you'd reccomend for a fairly strong 44 year old newbie cat 4 wannabie with a 29.5" inseam riding a size 50cm frame? I have been riding for a year with no problems, but recently I upped my training to include more hammering and I'm getting some knee pain (right knee only). My LBS set me up with 172.5's - I can spin them at 110 RPM on the flats no problem - but they seam maybe just a hair too long. Can 2.5mm really make difference or am I just overdping it? Man, thanks in advance for any advice you might provide.

    Cheers
     
  17. retrogeek

    retrogeek New Member

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    Dear Crash,

    I'm sorry, but I never give direct advice to anybody on an issue involving the measurement of body dimensions and bike fit without being there myself. I must see for myself that the measurements are being taken properly and then after a decision is made regarding fit and riding position I would have to be able to observe the rider to determine if the changes made were appropriate. I have experienced too many times where riders have given me their inseam measurement only to find out that when I measured them that the number was quite different.

    It may sound petty, but I would feel very guilty if I found that I had given incorrect advice. Fitting a bike is not an exact science, although it is pretty close. But the factors of individual body mechanics, bone structure, and flexibility can change any dimension of the bike dramatically.

    That is why most of the posters that I have read when addressing issues such as this shy away from getting too specific and prefer to stick to generalities and advice for the person asking the question to further research for themselves.

    Fitting your bike properly is one of the most important things you can do when you begin to get serious. Prevention of injury and learning proper technique early require a bike that fits well. Not to mention the enjoyment and comfort that can be realized.

    However, I can give you some parameters to look at.

    Is your inseam measurement correct? Cycling shorts on, back against a wall, non-carpeted floor to stand on, feet flat on the floor (without shoes), shoulder-width appart? I think the best thing to use is a clip board, put one edge against the wall and bring the top edge up until it firmly touches your crotch/pelvic bone: have a friend measure you from the top of the clip board to the floor (obviously). This to a certain degree simulates sitting on the seat and gives a good starting point.

    Your meaurements indicate a 155-160mm crank length as a "starting point", that is why I asked if you meaurements are correct.

    I am from the camp that believes that 2.5mm increment changes are not significant enough to warrant the spending of hard-earned cash. Think in 5mm increments.

    Crank length is about matching the correct length crank to your body's proportions to insure good mechanics while pedalling and injury prevention. You shouldn't think about it as leverage, gearing takes care of that.

    Also, if you feel pain, back off!! Pain is your body's way of telling you something is wrong.

    You may get completely different advice from a bike shop tech, the only thing I can say about LBS's is that they want to stay in business and usually they only stock 170-175mm cranks for road bikes. Do the research, especially if you are going to race, it is your body. After getting a fit ask for a second opinion from another experienced rider. Bike clubs and organized group rides are good for this.

    Sorry for the long-winded response.

    Good luck.
     
  18. crashnigley

    crashnigley New Member

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    Thanks for taking the time to respond - very helpful. I'll post again after I visit the local fitting specialist.

    Cheers
     
  19. kaian

    kaian New Member

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    Thanks for all of your suggestions everyone. I went to my LBS and I ended up ordering a 165mm Shimano Tiagra crankset. It should be in within a week or so. I can't wait to feel the difference! I thought about getting something better than Tiagra, but just decided to be conservative about it. It's my first road bike and I am not doing any racing - just semi-serious recreational riding (3-4 times a week at speeds around 15-20 MPH). I figure I can always upgrade later or just get a new bike.
     
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