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sizing- why so many different opinions?(6 posts)

sizing- why so many different opinions?tml
Sep 14, 2002 7:45 AM
looking for a road bike, and it seems every bike shop tells me something different. I am 5'11-6'00,( 183cm) and I've heard I need a frame size from 57 to 60 cm. Who do I listen to? Any suggestions from people who are not trying to sell me a bike based on their stock would be greatly appreciated.
opinions are like [you know] everyone has one and they allbill
Sep 14, 2002 8:52 AM
[you know, smell].
There are so many different opinions for several different reasons. The most superficial is that different manu's size differently. Why they do that is no business of mine, but they do.
Then there are different theories of bike fit. Some people say that you should have x amount of seatpost showing, some x plus (with the corresponding changes in geometry around the bike). Just different theories on how to make the bike ride well.
The most subjective is somewhat related to this last, which is how you are going to use the bike. If you are a young, fit racer, or want to be (and have a realistic chance at it), then you may want a little smaller frame, which will allow you to run your seatpost long and get lots of drop to your bars. If you're not so, or you are buying a touring bike, then you don't need as much seatpost, because you don't want as much drop, and, rather than run your steerer too high, you'll want your saddle relatively lower to begin with. Other stuff, too, about bike weight, stiffness (generally, the smaller the bike frame, the stiffer and lighter).
There's lots on this on the Internet. I think Sheldon Brown's site has a bunch of links -- http://www.sheldonbrown.com/harris/index.html
You are a wise personfiltersweep
Sep 14, 2002 8:55 AM
Some bike shops push sizes they stock.

Some bike shops cater to the S-M-L-XLg Mtn bike crowd and know very little about road bike sizing (or you might be talking to their snowboard expert).

Some frames are measured differently c-c vs. t-t.

People HERE will all give you differenct advise as well... and there is no shortage of self-proclaimed experts.

Who do you trust?
they may be the same size...C-40
Sep 14, 2002 9:00 AM
All frames are not measured the the same way. All measurement methods start from the center of the bottom bracket and measure parallel to the seat tube, but the opposite end may be the center of top tube (c-c), the top of top tube (c-t) or the top of the seat tube (nonstandard and least meaningful).

The other issue to consider is that many brands only come if 2cm increments. Some brands have all even sizes and some have all odd sizes. If a 57 is the best size and the brand that you like only comes in 56 or 58, a compromise will be necessary.

For a given "size", a frame measured c-c will be the largest. The c-t frame will be about 1.5cm smaller. A frame measure to the top of the seat tube could an additional 1-3cm smaller, depending on how much the seat tube extends above the top tube.

To avoid confusion, take a tape measure to the store to make an accurate comparison. Don't believe anything about size unless you've measured it yourself.

For the "size" that's best for you, your height and inseam must be considered. Check out www.coloradocyclist.com for an explanation of the proper technique for measuring inseam. Post an accurate inseaam measurement and I can provide a suggested size range.


For a proper vertical fit you need to have between 2cm and 5cm of clearance to weight-bearing crotch contact with the top tube in bare feet. Smaller riders and those with short legs will generally have the smaller amount and big or long-legged riders the larger amount. Measuring the stanover height from the floor to the top of the top tube will tell you quickly how a frame measures up to your needs.

Horizontal fit is determined by the top tube (TT) length, the seat tube angle (STA) and the stem length. A proper fitting will start by determining the optimum STA that will allow some adjustment of the knee position both fore and aft of the pedal centerline, with the crank at the 3'o'clock position. From there, a combination of TT length and stem length can be figured that will combine to produce the proper total reach.

The total reach to the bars varies widely, even among riders of the same size. I like enough stem length to keep my knees and elbows from hitting when I ride with my hands in the drops and the the upper part of my back horizontal. Beginners may find this position too stretched out for comfort. I lengthed the total reach on my bike by about 2cm as I became more experienced and increased my level of fitness.
C-40's got a pointGeekRoadie
Sep 14, 2002 3:17 PM
Some LBS's may just try to push what they have in stock.
Something to think about, though->

As far as your 3cm swing in frame sizes, consider this.. I'm 5'-6" and ride anywhere from a 50cm-53cm. Manufacturers certainly do a pretty good job of complicating things by measuring frame sizes differently. Add to this how different geometries yield shorter/longer toptubes (some suggest that this just as important as "size"). The standard formulas for fitting also assume that you are of "regular" proportions. For example, you might have a longer torso for your given height and would probably benefit from getting a frame larger than what the formula might indicate.

I would suggest checking all the resources on the net for bike fitting. You might also want to consider reviewing literature of frame manufacturers that you are interested in for geometry info. Comparing "apples to apples" might lead you to your optimum frame size.

hth
Mike
Stand over and lift...jose_Tex_mex
Sep 14, 2002 6:00 PM
if you have an inch or two then you should be fine. I like to be able to lift my road bike one inch without shoes on.

If you want to be technical you can do a Serotta Size or better yet get the Fit Kit system. Serotta Size IHMO tends to have to many variables based upon individual taste.

If you don't mind spending the $60 go to Serotta's web site and see where there is someone close by who will fit you.