tbo

I picked up a new Trek FX3 to replace a 10 year old 7.2 FX. I use it as my daily driver for errands and wanted a bike that had the same feel, but has a carbon fork so my forearms didn't "buzz" and the hydraulic brakes are nice, too.

Knowing that I have problems with standard OEM seats (Bike Saddle Neuropathy), I had the LBS put on my perfect (for me) seat from the 7.2 on the new bike's seat post, even before I rode it to test it. In the first week, I developed outside knee pain in the right side. No big deal, I thought. Just fit the seat height and angle. No luck at all. The new seat post is a 2-bolt micro adjust design and the old one is an older version of the same seat post with a splined clamp with a single bolt.

I couldn't get the new one into the correct position and have it tight.

I put my seat back on the old post and put it on the new bike. One adjustment later, perfect again.

What did I do wrong and is it worth going after to fix? I am just fine living with the old seat and seat post combination.

HillRider

That's very odd. Splined clamp (Laprade-type) seatposts only allow incremental angle adjustments while two-bolt clamps allow infinitely fine adjustments so you should have been able to set the angle precisely to match the old one. It's possible the "set-back" of the new post was different enough that you couldn't match the position of your knee relative to the pedal spindle on the old one.

If the old seatpost and saddle work on the new bike, count your blessings.

tbo

That's what I thought, too. Thanks.

fietsbob

so they must have been the same , unstated, diameter...

Crankycrank

Make/Model/Photos of seatposts would be helpful. Not a generic problem between types of posts. I've had good luck and problems as well with all different types of clamps. Show us what you have and maybe someone can give you specific help.

tbo

Here are the two post in question - from google image search.



Old Style (currently on the bike)








New style - 2018 Trek OEM, off bike at the moment.

trailangel

Operator error

Crankycrank

Put a little grease on the contact points of the Trek post (Top plate, Screw inserts, Screws, Saddle rail grooves). The top plate can tend to bind when tightening fooling you into thinking everything is tight until you put some weight on it and it will loosen or shift. Can also be a little bit of a PITA to get just the right adjustment but once you get it right it should be fine.

tbo

Certainly could be!

But that new clamp seems to be a lot more complicated than it needs to be. The old clamp only has discrete angle adjustments, but you can't mess it up. Loosen, move one notch, re-tighten, done.

Also, there is a difference in the angles of the clamps to the posts. Not sure if it makes a difference, though.

I will play with the new seat and post on the old bike as a learning experience. If I get it right, I have the option of using either post or seat on either bike. The frames are so similar that the height and angle adjustments should be pretty much the same AFIAK.

trailangel

Old seat post looks to have more set back. Maybe that is your knee pain problem?

79pmooney

I am a huge fan of two bolt posts. "Grew up" as it were with the old Campys that required the special "Z" wrench. When the early '80s came, good 2-bolt posts were barely more common than dodo birds. My Mooney went 8 years with a Laprade post set to halfway between clicks. I knew if I ever loosened the bolts, I'd never get the setting again, My reprieve came when I got a SunTour 2-bolt post, much like your new Trek post. If I were you, I'd consider greasing the barrel of the threaded cylinders the adjust bolts thread into. Also the seats of the bolt heads. (Use "grease" that is compatible with the post material if it is not metal.) I would not grease any of the contacts with the saddle rail until I found this didn't solve my issues. (Maybe stop tightening periodically and rock the seat to get all to settle in properly.)

I know you have your position back with your old seatpost. But there are two reasons for going back to your new 2-bolt post. 1) we change and learn. Tiny adjusts in tilt are very easy on a working two bolt post. 2) injuries and saddle sores happen. 2-bolt posts make it very easy to say crank the tilt forward 1/2 a turn to get off that mid-tour saddle sore. 7 days later all is now good? That 1/2 half turn will get you exactly back to your favorite setting.

Ben

tbo

Could be. I'll research the best way to compensate for that. Thinking that would be pulling the seat to the rear on the new post.

DrIsotope

My current favorite seatpost: the FSA SL-K ITC. It's light, can be found for under $50, and it's a three bolt. One bolt for each rail, and one bolt to set the angle. Being able to change angle without messing with setback, and vice-versa, is simply wonderful.

tbo

Oh my! Very nice.