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  1. #1
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    Bike fitting and frame size indicator

    I understand a full pro bike fit must prove what frame size, stem and crank arm lenght is appropriate for the body size.
    But i'd really like to know on what basis reach, stack and crank arm lenght is determined. Is it anyone who knows how to calculate that on my own?

    Please share here or send a private mail are you nice

  2. #2
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    no. there is no substitute for an experienced fitter that takes all the variables into account. you really can not fit yourself properly, especially if you have very little knowledge.
    there is a very good reason that a 'pro' or thorough fitting by an experienced, trained fitter costs as much as it does. at the shop i work at the 4 people that do fittings have combined 75yrs experience. one is a specialized bg master, the rest have at the very least completed trek fit training seminars . 2 of us have been to brain bike. it's not the first rodeo for any of us. we have a balanced, well-rounded methodology that allows us to properly fit virtually any type of rider.
    you can't do that for yourself by reading articles on the interwebs.
    i work for some bike racers...
    2013 Trek Madone 5.9 w/ '12 SRAM Red
    2010 Cervelo T1 sprint bike
    Ruger 10-22TD
    Smith&Wesson M&P 15-22
    Smith&Wesson M&P 9
    oh, those belong in another forum

  3. #3
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    Thanks for the Reply! I still hope this doesn't put anybody else off giving other points of view. In my world there ought to be some measurements pointing at ideal frames etc. Might be that all brands doesn't suit all. I think this subject is very interesting and should perhaps(?) be of importance to most prone to buy a bike on the net?
    I ain't saying i dislike my bike or how i am fitted, but i would like pure facts or as close as it comes to facts. Some makers and brands has quite large leaps in frame sizes and some has very tight and many options of frames which according to me makes it more difficult to pinpoint which is the better choice. For instance when buying online it is quite good having a better clue why and what size of frame and stem i (or anyone) should go for. So, again, i am mostly curious of stack, reach and even crank arms lenght.

  4. #4
    Burnum Upus Quadricepus
    Reputation: brucew's Avatar
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    You mean something like Competitive Cycling's Fit Calculator?

    Be sure to read all the extra articles at the bottom of the page.

    As for crank size, stick with what your were born with. Forget about those spam offers.

    Seriously, the rest comes from experience. There's no shortcut for that. The reason is that we're more than just the sum of our measurements. No formula can anticipate, then account for, all the little quirks and problems we each bring to the table.

    Take flexibility as an example. For most of us, that's a moving target, not only within the season (I'm less flexible in the spring) but as we move through life. And then consider that beginners are usually less flexible than seasoned riders. Me? I have a selection of stems and make certain my steerers are cut a little long. As the season progresses, I swap stems and move spacers from below the stem to above it. In winter, I reverse the process.

    After reading the several hundred threads here on crank length alone, you'll probably come to the same conclusion that I did--personal preference. In the end, we go with what feels best. How do you calculate that? It's like trying to calculate someone's favorite color.

    Cranks and stairs work the legs in a similar manner. Architects have been calculating staircases for millennia. Yet with thousands of years of experience, and with all the high-tech wizardry available today, the best we have is a range of measurements for rise and run that work for most people. There's no ideal.

    In my own case, I've always climbed stairs two at a time. It just feels better to me. So it's no surprise I prefer longer cranks. My first bike had 170s, which are deemed appropriate for my measurements. They felt like I was taking baby steps, or the pedaling equivalent of pulling my punches. It comes back to personal preference.

    But if you want to go back to the source data, do a search here and at the other cycling forums. You'll find hundreds of threads with thousands of posts, each making different arguments. The only conclusion any of them have reached is that there is no conclusion.
    Last edited by brucew; 02-23-2013 at 01:20 PM.

  5. #5
    RoadBikeReview Member
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    Purchase a copy of Bike Fit from roadbikerider.com.

    It doesn't provide just ONE method for bike fit, but explores several different theories for all the aspects of each criteria.

    For instance, under section Crankarm Length, there are the following subsections:

    Rule of Thumb

    Discussion

    Background and Theory: Force and Optimal Crankarm Length

    Cadence

    Acceleration

    This book is 123 pages that provide you with more than one way to determine the various fit aspects, and it's written so the layman can understand it.

    There is no ONE PERFECT WAY to fit a bike. You digest the material and come to your own conclusions. Worth every penny.

  6. #6
    Fred the Clydesdale
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    Once you get the frame right, the rest is something you have to decide. I bought a road bike according to a sizing chart. After getting the bike, I had back trouble and decided I need to raise the handlebar a bit. I bought a stem with a steeper angle and it worked fine for me.

    Seat location - Knee over pedal system is a good starting point, but it is not definitive. There is no perfect position based upon standard measurements etc. It is done through experience.

    YMMV - Good luck.

    BTW - $150 is what it costs at my LBS for a standard fitting. It would have been well worth the time in my opinion if I had gone that way instead of doing it myself. I am fine with what I did, but I could have saved myself some pain and trouble by having a professional fitting done.
    Member of Team Collin, a group of ordinary moreons going to extraordinary levels of awesome in the fight against cancer.

    Love conquers all. God is love. Jesus is love personified. Figure it out.

  7. #7
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    I can see two opposite directions using a longer crank arm. I should really be 175-177.5 but i use 172.5 as bike was fitted with. I asked since i am figuring what to order on a new crank set/ groupset. I have heard suggestions of both stem and frame size according to my lenght (frame) and stem (pro fitter). I feel better on a frame slightly smaller, smallest for my lenght, and a frame with close reach and aggressive positioning (perhaps not Mcipollini, but soon). I am thankful for your inputs, very interesting for me. I would like to have the opportunity to learn bike fitting myself.

  8. #8
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    I try to decide between Dura ace 9000 or new Sram Red. Anyone having tried both?

  9. #9
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    I think i'll stick to the TA option. Also interesting notes, on why not to go for too long crank arms.
    BikeDynamics - Bike Fitting Specialists - Crank Arm Lengths

  10. #10
    nb6
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    So I admit to being confused. Shopping for my first new bike in 19 years. That one was a hybrid ordered on by mail - the only choice in 1994 in Nome Alaska.

    I have visited two bike shops. Both places, the staff have spend a lot of time with me, answering questions, showing bikes. At one shop they had a fit station, measured my height, leg length, should width, arm length, etc, and then when I was testing bikes, the owner spend a long time adjusting each my to my "numbers."

    The second shop, the guy looked at me, suggested a frame size, and set me up on a trainer, adjusting the seat, but nothing else. After mpre questions, he told me that he could do a lot of adjusting, but he felt that I would need to ride for 10+ hours before being ready to fine tune it.

    Both said that the "feel of the bike" was the most important, and at both places I found bikes that "felt" right, a far as I could tell. Both said that I would need to "get used to a road bike after so many years on a hybrid.

    Who's right? Or are these just different philosophies?

  11. #11
    Burnum Upus Quadricepus
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    Quote Originally Posted by nb6 View Post
    Both said that the "feel of the bike" was the most important, and at both places I found bikes that "felt" right, a far as I could tell. Both said that I would need to "get used to a road bike after so many years on a hybrid.

    Who's right? Or are these just different philosophies?
    In my experience, they're both right and they both have different philosophies.

    They're probably both trying to do right by you, the first setting things up for the cyclist they think that you're likely to become, and the second is waiting to see what sort of cyclist you become before starting to charge you money. It could be said one is forward-thinking and the other is results-based.

    When I moved from a hybrid to a road bike I had no idea what it was supposed to feel like. I just knew it felt weird--and wonderful. I also bought second-hand, so I was starting from scratch with no foundation on a bike fitted for someone else. I couldn't tell the difference between something that felt "wrong" and something that was okay but I hadn't gotten used to yet.

    I got something out of sessions with two shops of differing philosophies and approaches.

    Ultimately, it was time in the saddle that made the difference.

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