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Frame geometry 101?(7 posts)

Frame geometry 101?config
Sep 24, 2003 9:44 AM
I don't understand the differences between different frame geometies. Is there a link that describes all of this? I have a compact (sloping) frame but that was just what I decided to get. What advantage will a traditional frame give me that a compact won't? I'm considering getting another frame so I was wondering. Another thing, are time-trial bikes faster with 650mm wheels? Sorry if this has been brought up before.
my opinion...funknuggets
Sep 24, 2003 9:56 AM
Compact frames do a couple of things, they allow for lower frame weight due to less materials being used for the traditional comparable, and also "allow" for a bit stiffer frame for comparable sided traditional framesets. However, I think it does more for the manufacturer than for the rider. It allows them to basically only make three sizes, S, M, and L, and also save on materials (where they can charge you more for the "lighter" frame). I do not believe there are any distinct aerodynamic or mechanical advantages from comparable compact vs traditional frames.

Lastly, the 650 wheels will likely be stiffer, a tad lighter and supposedly "spin up" quicker. Harder to find overall, and not as common if you need to pick up a tube or tire on the fly at the LBS.

These are just my opinions...
So sayeth the Funk? (nm)PEDDLEFOOT
Sep 24, 2003 10:02 AM
shucks, forgot my standard Tagline...good call(nm)funknuggets
Sep 24, 2003 10:07 AM
re: Frame geometry 101?Steve_0
Sep 24, 2003 9:59 AM
traditional frames advantages - more precise (appropriate) fit. Classic looks

650c wheels - a smaller person can more easily acheive a proper fit with a frame built around 650. Proper fit could affect speed.

Also, ever slightly more aero, slightly increased acceleration (really moot in TT format) but increased rolling resistance.
re: Frame geometry 101?laffeaux
Sep 24, 2003 10:12 AM
A more precise fit has little or nothing to do with sloping or non-sloping tubes. Some manufacturers opt to make fewer sizes with a sloping tube. Other (for instance Klein) opt to make many sizes with a sloping tube. It really depends on each manufacturer's decision. While a sloping top tube can allow a reduction in the number of sizes of frames needed (due to increased stand over), it does not require it.

The advantage of a sloping top tube is that if you have short legs and a long torso, you can actually buy a frame where you can have adequate stand-over.

The other difference is aesthetics. Some people prefer a top tube parallel to the ground, and others could care less.
re: Frame geometry 101?Steve_0
Sep 24, 2003 10:28 AM
"A more precise fit has little or nothing to do with sloping or non-sloping tubes"

Agree, however the majority of manufacturs (perhaps klein excepted) do limit their sizing. It's the very basis of 'compact' geometry.