P2 or P3 and bike fit

Triathlon Forum
1

Here it goes… I have a 51 cm P3 and just got a 54cm P2. Based on the geometry, the P2 has a taller headtube. Stack and reach between the two frames are: P3 (stack 482mm, reach 405mm), P2 (stack 512mm, reach 418mm). I have a 110mm stem on the p3 and I put a 100mm stem ont he P2. Therefore, the 13mm difference in reach is now only 3mm different. One the P3, I have a 18 degree stem and 10mm of spacers. On the P2, I was able to use a 6 degree stem since the headtube is taller.

I am using the front hole on the seatpost on both bikes, but I want to play with the fit of both bikes to see which is better for me. I bought the P2 based on comments about stem length, height, spacers, etc.- and I thought the P2 would be a better choice for me.

Here is my question, how shoudl the seat position change relative to lowering the front end of the bike. In other words, if I change the stem on the P3, how should I adjust the seat to still be comfortable. Is there a rule of themb? Or, are the two seat postions on the seatpost as well as the fore/ aft jsut personal preference?

2

Let me preface this by saying I am in no way a fit expert and I’ve never even been professionally fitted so I’m basing this response mainly on what I’ve read on this site, basic geometry and my personal experience.

If you want to lower your handlebars whilst maintaining the same hip angle you will need to bring your saddle forward and move the handlebars forward as well. If you think you can tolerate a smaller hip angle without losing power or comfort, then you won’t need to bring your saddle forward and may need to bring your handlebars back a little bit depending on how much you lower them.