Seat post offset

[Katana]

Hi guys, just wanted to pick your brains. I need to change the seat post insert on my recently acquired Trek Madone SLR9 which I bought second hand. It’s size 54cm(Medium) so it came standard with 160mm seat piston insert with 25mm offset. Whereas large models come with 205mm insert. I need to raise the seat height therefore 205mm will do the trick. Although 205mm insert is available in both 5mm and 25mm offset but I can get a 5mm for under £80 whereas 205mm is for £200. Since the difference in size is of only 0.7 inches therefore inclined to think that it shouldn’t make a huge difference in riding position? Any thoughts

 

[Sharky]

Bit confused by some of your terminology - inserts, piston, mm/inches

The offset will matter, if the position of the saddle clamp is already at the forward end of the saddle rail. If you can adjust the saddle by sliding it back on the saddle rail, then it won't be a problem.

Plus, when you raise a saddle, the angle of the seat tube, will cause the saddle to be set back a little as well.

Presume the new Trek is an N+1 purchase? Careful comparison of measurements between the old and new bikes, should give enough data to confirm if the saddle can be set in the correct position.

Good luck

 

[davidphilips]

Really shocked at price of a seat post for your Madone SLR9, even used posts on Ebay seem expensive?
Perhaps this video may help in setting up n+1 and finding out if you need the larger and more expensive offset. My concern would be if the Madone seat post is to short is the bike big enough? Good luck in any case.

View: https://www.youtube.com/watch?v=wy27DFXN4yI

 

[Katana]

Bit confused by some of your terminology - inserts, piston, mm/inches

The offset will matter, if the position of the saddle clamp is already at the forward end of the saddle rail. If you can adjust the saddle by sliding it back on the saddle rail, then it won't be a problem.

Plus, when you raise a saddle, the angle of the seat tube, will cause the saddle to be set back a little as well.

Presume the new Trek is an N+1 purchase? Careful comparison of measurements between the old and new bikes, should give enough data to confirm if the saddle can be set in the correct position.

Good luck

 

[Katana]

Many thanks that’s really helpful. It took me a while to get myself familiarised with the terminologies used on various websites so don’t blame me😂

 

[Katana]

Really shocked at price of a seat post for your Madone SLR9, even used posts on Ebay seem expensive?
Perhaps this video may help in setting up n+1 and finding out if you need the larger and more expensive offset. My concern would be if the Madone seat post is to short is the bike big enough? Good luck in any case.

View: https://www.youtube.com/watch?v=wy27DFXN4yI

Thanks buddy🙏🏻

 

[MichaelW2]

Mark the BB position with a plumb line, on the top tube.
Measure from this back to you saddle reference point. And also forward to your bar reference point

 

[Katana]

Really shocked at price of a seat post for your Madone SLR9, even used posts on Ebay seem expensive?
Perhaps this video may help in setting up n+1 and finding out if you need the larger and more expensive offset. My concern would be if the Madone seat post is to short is the bike big enough? Good luck in any case.

View: https://www.youtube.com/watch?v=wy27DFXN4yI

TBH I would have personally preferred 56cm size as from past experience for TREK bikes that’s the right size for me. However since it was a second hand bike I bought from Cycle Exchange and it ticked all the other boxes so I went for 54cm size. I think it still is ok for me as I am almost between two sizes. Therefore best option was to go for a longer seat insert which thankfully is available.