Go to the tech center tab on the main Slowtwitch page. There are many articles pertaining to your questions.

all other things equal, the rearward config of the seat post clamp = 75 degrees, the forward = 78 degrees. you also ought to raise the seatpost just a little, only so that your seat height from the bottom bracket is the same as it was when it was shallower.

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Dan Empfield
aka Slowman

[reply]all other things equal, the rearward config of the seat post clamp = 75 degrees, the forward = 78 degrees. you also ought to raise the seatpost just a little, only so that your seat height from the bottom bracket is the same as it was when it was shallower.[/reply]

You normally do not need to raise the saddle to accomplish this, but it depends a bit on the angle between your saddle rails and saddle deck. When you flip the head, you don't flip it around a vertical axis but under an angle, meaning that the clamp stays just as far away from the bb as it was before.

That said, it can be off a bit depending on the saddle an where you clamp it, so it is wise to check.

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Gerard Vroomen
3T.bike
OPEN cycle

Dan, just noticed that you're re-doing your articles on tri bike fit. Previously you had a chart diagram demonstrating the relationship of seat to BB relating to effective seat tube angle. That chart would answer the question perfectly. Are you going to repost it?

Tom is referring to a specific detailed drawing/chart that allows you to find your virtual seat post angle...all you need to know is the distance from the center of your bottom bracket spindle to the top of the middle of your seat, and the distance (positive, negative, or directly upon) from a plumb line dropped from the nose of your saddle to the center of the bottom bracket spindle. Then look it up on the chart.

This chart clearly demonstrates something so many people seem to be confused about; the larger your bike, the further back this plumb line is for a given seat tube angle. So, someone with a large bike (62 cm) will be set up steeply when this plumb line passes directly through their BB spindle, and someone on a 47 cm won't be nearly as steep when the plumb line drops through the middle of their BB spindle.

This relationship is also one of the reasons smaller wheels can be specified for smaller frames...the actual physical seatpost can be steeper to produce a final given virtual seatpost angle relative to the BB, so the gap between the seatpost and the rear wheel gets larger...giving an opportunity to shorten the chainstays and using a smaller wheel to snug it up closer to the actual seatpost. Of course, the "cut-out" seatpost designs can allow larger wheels to be used on smaller frames.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

Here are a few related questions: My P2K is set up in the 78 degree position yet I have a 40K duathlon leg coming up that involves a rather substantial climb, at altitude, right from the transition to the turnaround. I'm considering flipping the seatpost or can I just slide the seat back to create a more climb-friendly position? If the post is flipped, do I need to fiddle with my aero bar setup? I upgraded to C-2's, Stratos base bars in the front and added a Sigma Sport computer and ran the wire down the leading edge of the fork as aerodynamically as possible...is this how CSC's Soloists are wired?

You should raise your seat just a tad as you move it forward, but as you are now effectively shortenning your cockpit, you would also want to lower your bars a bit to compensate. Dan is re-writing his tri bike fit info on the slowtwitch site including a revamped formula to determine your bar/seat height relationship.

There is no reason to guess or generalize about this. Tell us the position of the nose of the saddle relative to the bottom bracket and the height of the top center of the saddle relative to the center of the bottom bracket. The Slowtwitch Official Mathematician will then turn the mystical trigonometric crank and give you your seat angle.

First off, good for you: You are thinking and learning. That is how it works. My compliments. To measure your seat tube angle effectively try to make an imaginary (about) vertical line bisecting the bottom bracket and extending upward through the center of the saddle, 13.5 cm. back from the tip on most saddles. If you measure that angle from the ground that is the angle you are sitting at. Most people are steeper than they think. 82 degrees is not entirely uncommon. Keep up the good work.

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Tom Demerly
The Tri Shop.com

[reply]Here are a few related questions: My P2K is set up in the 78 degree position yet I have a 40K duathlon leg coming up that involves a rather substantial climb, at altitude, right from the transition to the turnaround. I'm considering flipping the seatpost or can I just slide the seat back to create a more climb-friendly position?[/reply]

I don't necessarily agree with the assumption that a slacker position is more climb-friendly. Stay aero, spin and win. I would suggest you find the best position for you, and stick with that position for (almost) any race course.

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Gerard Vroomen
3T.bike
OPEN cycle

I am with Gerard (and probably Slowman) I have taken my P2 up two climbs to test it out, its set up steep. I have no problems climbing at all, but the technique is a little different from what I would do with a road bike. I dont stand much if at all and just sit in and spin. I dont lose much time on the climbs and may set you up better for the run.

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Simple Simon
Where's the Fried Chicken??