Tuesday, May 5, 2009

Fit Check

Many of us have more than one bike and ideally our saddle positions would be the same on all of them. This is especially true if you have two mtn bikes that you plan to race over the course of the season. I try to keep my bikes dialed in on my own but yesterday I sought the help of a pro. Fitzy helped me with a quick fit check on my mtn bikes and I learned something: The sag of a full suspension bike while sitting on it slackens the seat angle and therefore changes your fore-aft saddle position. It seems so obvious now but I was not taking this into account when measuring my bikes.

Here is my Turner Sultan. The lime green line is an over-exagerration of the seatpost angle once I am sitting on the bike and the shock is compressed 20%.

Here is my Alma 29er hardtail. In order to duplicate the position of my Turner, I needed a seatpost with more setback so that my knee alignment was not too far forward.

This FSA seatpost has 32mm of setback and allowed me to get my knees slightly behind the pedal spindle where I like them.

My favorite Thomson seatpost, with 16mm of setback, doesn't have enough setback for the Alma but works on the Sultan.

Yesterday confirmed that my positon on the Alma was off just a bit and that my position on the Sultan was great so no changes were made there. It is interesting that I require so much setback on bikes with a seat tube steeper than 73 degrees given that I am average height. However, everone's femur lengths are a different percentage of their leg length and this has a huge effect on saddle position.

3 comments:

Dave Harris said...

Doh!

Awesome. Now I know exactly why my fore/aft preference is 1.5 cm farther back on hardtails. duh. Having just set up the Lev recently and moving the saddle forward I was wondering why...

epicrides said...

very interesting. i have been having some knee issues since i got my new indy fab. this makes me want to get a fit done so i can get all of that dialed it.

Kelly said...

Huh! I am glad I am not the only one who hadn't figured this out!