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Trek TT frame question(4 posts)

Trek TT frame questionempacher6seat
Jan 10, 2003 12:08 PM
I've just heard bits and pieces of what I'm about to ask, so I'm not too sure how accurate some statements may be. Anyways, I hear in some TT's, such as those in the Tour, don't allow a seat tube angle over 74 degrees, or the saddle can be no closer then a certain amount of centimeters to the bottom bracket on a horizontal axis.... Something about the seat tube angle having to be shallower then those on "regular" TT bikes. My question is how would the geometry of a bike, such as the Trek which was rode in the Tour TT's, be set up to have a shallow seat tube angle and still get the riders back in a flat and aero position?
re: Trek TT frame questionDougSloan
Jan 10, 2003 12:47 PM
I think the rules keep the nose of the saddle at or behind the bottom bracket, but the rule is more lax for time trial bikes.

You can get a flat back with any seat tube angle, at it's largely related to handlebar height compared to saddle. However, too much drop at a shallow angle and the knees start slamming into the chest and you can't breathe. It's all a trade off of aero drag and power.

re: Trek TT frame questionJon Billheimer
Jan 10, 2003 3:44 PM
UCI rules state that the setback of the saddle from the bottom bracket can be no less than 5 cm, regardless of the frame geometry. So what some riders do is to use a saddle with a shortened nose. Fizik even came out with their Chrono model for just such a purpose. This is also why you see a lot of guys sitting forward right on the nose of the saddle, to give them a more open hip angle.
Jan 10, 2003 3:57 PM
The peak of the saddle shall be a minimum of 5 cm to the rear of a vertical plane passing through
the bottom bracket spindle. This restriction shall not be applied to the bicycle ridden by a rider in a
track sprint event,keirin,500 metres or 1 kilometre time trials;however,in no circumstances shall
the peak of the saddle extend in front of a vertical line passing through the bottom bracket spindle.

The distances mentioned in footnote 1 to the articles 1.3.013 and 1.3.016 above may be
reduced where that is necessary for morphological reasons.By morphological reasons should be
understood everything to do with the size and limb-length of the rider.
Any rider who,for these reasons,considers that he needs to use a bicycle of lesser dimensions than
those given shall inform the Commissaires Panel to that effect when presenting his licence.In that
case,the Panel may conduct the following test.Using a plumb-line,they shall check to see whether,
when pedalling,the point of the rider 's knee when at its foremost position passes beyond a vertical
line passing through the pedal spindle (see diagram "Measurements (2)").