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Thread: Sizing question

  1. #1
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    Sizing question

    In response to frame sizing questions I've often seen the advice "slightly too small is better than slightly too large". (I've seen the opposite as well, but much less frequently). This advice rarely comes with any evidence or anecdotes as to why a slightly-too-large frame is worse.

    It seems like, in either case, adjustments to saddle position and stem angle/reach could produce a pretty much identical fit. Right? Assuming the exact same triangle between handlebars/bottom bracket/saddle can be achieved by two frames, is there really any reason to prefer the smaller one?

    I guess the smaller frame would be slightly lighter, easier to mount/dismount, less chance of smashing one's testicles on the top tube... I guess steering would also be different (better?) with a longer stem on a smaller frame... but I don't know if these issues are what people have in mind when giving advice to err on the small side.

    So, for anyone who has given said advice, I'm curious: what is the reasoning? what are your experiences? How does frame size contribute to ride quality/comfort?

    Thanks. (I know this question isn't fixie/single-speed specific, but I've been lurking in this forum for a while so it seemed an appropriate place for my first post.)

  2. #2
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    There's no short answer. Well, there's no good short answer.

    Trends come and go in cycling. Those trends include ideas on fit. Sometimes we want little tiny bikes, sometimes we want great big ones. Right now, little tiny bikes are the hot ticket and you have to bear that in mind: a lot of folks believe that small bikes are absolutely critical, because they've been told so. That's all.

    Having said that, there are advantages to smaller bikes, along with disadvantages. The same is true with big bikes.

    Small bikes are lighter and stiffer, on average. Light is always nice, of course. Prospective buyers should take note of any weight differences between sizes, however. They're often the equivalent of skipping the extra bagel. "Stiffer" is a mixed bag. A stiffer bottom bracket may or may not allow better power transfer. There's some intelligent argument from both sides of that coin. A stiffer front end handles better, almost without question. A stiffer frame overall usually results in a harsher ride, but IMO tire width and pressure is far more important when discussing ride quality.

    Smaller bikes also tend to force a rider into a lower and more compact position. This may or may not be what you want. And yes, a small bike can usually be made to fit like a larger one with appropriate parts and adjustments. I'm not quite sure why someone looking for an upright position would want to start out with a small frame, but I see it quite a bit.

    Larger frames tend to be a bit more flexible. Riders looking for comfort appreciate this. Riders looking for speed at all costs don't. Neither group is wrong. Larger frames allow you a more upright position, which is good for long distance riders and those looking for greater comfort. There's no easy way to make a big frame fit like a small one, so racer wannabes avoid them.

    Steering is affected strongly by several factors, none of which have anything to do with size or stem length.

    Assuming similar seat heights and bottom bracket heights, I don't see how frame size will affect ease of mounting, unless you are a complete idiot.

    If you tend to hop off the bike with both feet on the ground when straddling the top tube, then you certainly want a low top tube. If you don't tend to hop off the bike with both feet on the ground while straddling the top tube (and it's certainly not necessary; I don't think I've done it in 30 years of cycling) then you don't need to worry about it.

    So I guess the closest I can get to a short answer is "Size depends on your needs, and once you've figured out your needs, why would you buy a frame that's either too big or too small?"

  3. #3
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    I think you mentioned the main reasons already.

    I think it's because it's easier to make a slightly smaller frame large, by tinkering with seatpost length, saddle position, stem length, etc. than it is to make a slightly larger frame small.

    My first bike was about two sizes too large for me and my lower back was hurting after 4 mile rides. No matter what I did, it was just uncomfortable. Going to a frame size that fit me made that go away and it hasn't ever been an issue since.

  4. #4
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    Quote Originally Posted by Six jours View Post
    There's no short answer. Well, there's no good short answer.
    Thanks. That's more or less what I expected, but still your answer was thorough and helpful.

    Assuming similar seat heights and bottom bracket heights, I don't see how frame size will affect ease of mounting, unless you are a complete idiot.
    It's very possible that I am a complete idiot I haven't ridden a bike in over 10 years, and never have ridden a road bike until this week. Having just done some research about ways of mounting a bicycle (http://www.wikihow.com/Mount-a-Bicycle), I'll be honest, the side mount method never occurred to me. However, the second method ("throw your leg over the middle bar") seems like it would definitely be more difficult on a larger frame, especially for someone as inflexible as me. (On the other hand, maybe I shouldn't be taking advice from someone that doesn't know the correct term for "top tube").

    So I guess the closest I can get to a short answer is "Size depends on your needs, and once you've figured out your needs, why would you buy a frame that's either too big or too small?"
    Touche. The answer is: I'm too lazy to actually get fitted at an LBS, so I'm going to buy an internet bike, sized approximately based off of internet fit calculators and wildly conflicting suggestions on a handful of bike forums and hope for the best

    (To be honest, I just did that, with the should-have-been-expected poor results. Scared by all the "whatever you do don't get a frame that's too big!", I ended up with something much too small. And now I'm trying to avoid replacing it with something too big.)

    Anyway, thanks again for the help.

  5. #5
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    Well, "throw your leg over the middle bar" certainly would be more difficult with a higher bar. However "throw your leg over the middle bar" falls into the "complete idiot" category. IMO, of course.

    FWIW, I'm personally among those people who ride frames "much too large" for me. Or, put another way, I ride frames that were considered appropriately sized 40 years ago, when big frames were "in". I do it because I prefer riding long distances in relative comfort. If I decided to go criterium racing, I'd be on a smaller bike...

    IMO, the LeMond/Hinault/Guimard/Renault sizing method (one example can be found on the Colorado Cyclist website) is pretty good at getting folks into a reasonable size. It was popularized in the 1980s when we were getting away from the "French fit/fistful of seatpost" method that results in really big frames, but hadn't yet gotten to the "monkey humping a football" method that results in today's really tiny frames.

    HTH!

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