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Need help in understand sizing....(6 posts)

Need help in understand sizing....cyclejim
May 26, 2002 9:20 AM
I'm trying to understand how mountain bike sizing compares to road bike sizing.

For example if I typically ride a 21 inch center to top mtn frame, I understand that normally that puts me in the 62cm center to top road bike range depending on manufacturer, geometry, etc.

The part I don't get is this: If I convert 21 inches to centimeters I get 53.34 centimeters. How does this make sense when a 21 inch center to top mtn frame is roughly equivilant to a 62 cm center to top road frame?
MTB = compact frameweiwentg
May 26, 2002 9:24 AM
the TT may be 21", but the EFFECTIVE TT (straight line from bars to seatpost) is longer.
That part I understand ....cyclejim
May 26, 2002 9:34 AM
as far as effective top tube can differ....but what about the frame size measurement?
That part I understand ....gtx
May 26, 2002 9:40 AM
I ride a 18.5 c-t mtb and a 57 c-c road bike. Obviously, you have a lot more post showing on a (compact) mtb frame than you do on a standard (ie non-compact) road frame. In both cases, effective tt length is one of the keys to getting a good fit.

More info here
May 26, 2002 10:26 AM
For a certain rider, seat tube lenght of a MT frame will always be significantly smaller than seat tube lengh of a classic (i.e. non compact) road frame.

This is due to the slooping top tube which is essential for handling a MTB.

Seat tube length of my MTB: 47 cm (c-t)
seat tube length of my road bike: 58,5 cm (c-t)
re: Need help in understand sizing....yeah right
May 26, 2002 11:51 AM
two very necessary words, which are very much more applicable to mtb than road: crotch clearance.