Saddle positions on road bike and TT bike?

on-yer-bike

When setting up the saddle position on a road bike the general rule is that the knee should be above the pedal spindle when the pedal is in its most forward position. This apparently generates the most power. Why then on a TT bike is the saddle far more forward so that the knee is in front of the spindle? Is it because when in an aero position more power can be generated with the saddle much further forward? If so, when attaching aero bars to a road bike should you also move the saddle as far forward as you can?

joeyhalloran

I think its because if you have you foot over the axle, then when you are down on the tt bars you would have a very small hip angle which would restrict your power over the dead spot. I dunno what formula there is to fix this, I just played around for a while until I was comfy (my Adamo saddle helped).

SteveR_100Milers

I have pondered this too. If you look at a good TT position sideways on, then you can see that he rier is rotated further forward over the handlebars than on a road bike. Consequently the hip angle is reduced, so to compensate for this and "open" the leg out more I have raised my saddle and moved the saddle forwards. It certainly makes a difference when riding just by using the speedo as a measuring device. When you think about it, when you get out of the saddle on a road bike to climb, you are shifting your body position much further forward, and your knees will be much further forward than when seated.


To quote figures, all of my road and track bikes are at an 85mm saddle offset, my TT bile is probably around 20mm. I have seen plenty where the nose of the saddle is vertically above the bottom bracket centreline.

andy_wrx

See the article on Tri bike fitting at SlowTwitch.com if you want the full blurb http://www.slowtwitch.com/mainheadings/ ... kefit.html

But basically they describe it with this diagram


Tourquoise is a road position, upright and on the hoods.
Black is a full-on Tri/TT bike position, down on the aerobars on a bike with a very low front end and a steeper seat tube with the rear wheel tucked-in tight.
Pink they call a 'multisport position', a position somewhere between that you'd get on a roadbike with clip-on aerobars.

The rider in all three positions is actually in the same position - same 90-degree angle between torso and thigh, same 90-degree angle between arms and body.
But what's happened is that the rider has been rotated forward and down, as though there's a pin through the bottom bracket and the rider has been rotated around it
- down at the front onto aerobars means that the bum is up and forward.

SteveR_100Milers

Great explanation Andy, the picture explains it far more succinctly than I could!

Avoneer

Something also to do with having legs left for the run afterwards - that's if you're doing a tri.

Pat...