Re: [CR]Table for Seat Tube Angle Calculation


Example: Component Manufacturers:Avocet

To: LouDeeter@aol.com
Cc: classicrendezvous@bikelist.org
Date: Sun, 13 Jan 2002 20:40:18 -0500
Subject: Re: [CR]Table for Seat Tube Angle Calculation
From: Richard M Sachs <richardsachs@juno.com>


i'm missing something here... how can you ride two bikes that differ in size by four centimeters and have the two differing angles that you describe? compared to one another, these frames would yield setbacks that are in seperate zipcodes. while changing out seatposts with less or more setback, and raising/lowering the saddle could let you 'mimic' your static position between the two mounts, all the resultant measurements AND your center of gravity, as well, will be skewed. while that newfangled 'fitstick' is a decent tool that can help a rider replicate a desired position between one to who-knows-how- many frames, that postion also has to be optimized between and above the wheels. how can frames which vary 4 cm.s allow that possibility?

angles are a means to an end. linear measurements are the end. to determine lower body position, setback of seat and top tube centerlines as well as setback of saddle nose should act as the control. not all horizontal top tubes are 'level'. (figure that one out!). differing tires, wheels and/or air pressure will skew the seat tube angle to the ground. think of a frame as having no seat tube; the concern for the angle would cease to exist. but you would/could still measure the saddle's placement with plumb lines, verticals, and a tape measure.

using angles as a guide to types of frames is based in pre-bike boom bicycling magazine gobbledygook. you can't generalize. and as far as the three listed types of frames go, your position will/should not differ. (an exception being a kilo or sprint frame, but not a pusuit frame). altering the angles will only necessitate moving the saddle up/down and front/back and also cause odd size stems to be chosen to make up for the design deficiencies.

wow. that's alotta typing. e-RICHIE in Chester without a protractor

On Sun, 13 Jan 2002 19:42:42 EST LouDeeter@aol.com writes:
> Mark, great tips, but I think where the seatube and the plumb drop to
> the bb
> aren't a 90 degree angle that my trigonometric table doesn't work.
> The angle
> at the ground is the correct seattube measurement, but if the
> toptube is
> parallel to the ground then the inside seattube/toptube angle is
> identical.
> You are correct about the saddle positioning. I recently have been
> riding
> longer seattube bikes with toptubes that are relatively short. I've
> found
> that while the seattube and seatpost could be viewed as just an
> extension of
> the measurement, in fact, most builders built the longer seattube
> frames with
> a shallower angle. So, my previous 53cm bikes, which mostly have
> 74.5-75
> seattube angles, had the right setback; but, the 57cm Chris Kvale
> has a 73
> degree angle. The changed measurements have forced me to buy posts
> with
> little or no setback, although in the Kvale case, I just shoved the
> saddle as
> far forward as I could on a 27.4 Amercan Classic post that Karen
> Rawls sent
> me (thanks Karen). Thanks for the tips. Lou Deeter, Orlando FL