Trek Seat Mast Cap: Bike Fit Problems

I am going through the process of getting a bike fit on my Trek Checkpoint 58cm, but am running into an issue with the saddle position. The stock seat mast cap has 10mm setback and does not allow me to put the seat low enough or far enough back for my needs. Trek makes a shorter (135mm) seat mast cap with 25mm setback, but the problem is that they are expensive and out of stock in the US currently. Does anyone have alternatives that have worked for them to overcome the limitations of the Trek seat mast used on their Carbon road and Gravel bikes to get the set lower and/or further back?

I don’t know of any options other than the actual Trek/Bontrager ones.

I checked our access to the Trek site, and see that there are some available for dealers to order via Trek.
9 black, SKU 559538
5 red, SKU W559098

Beyond that, have you done a broad search at any other web retailers? There can be stock on hand at some of them to order from too.

See if you can trade with someone. I traded my old 135 for a 175 back in the day and some LBS may have a spare cap laying around from a fit.

This is really helpful. Funny that my local Trek dealer said they were all out of stock in the US until July 5th. I may have to call back and discuss options. Appreciate the help!

There are a few options at online retailers, but am really trying to avoid paying $150 for the carbon version, if possible.

That would absolutely be ideal to just make a trade. I am sure there are others out there that need the longer version which I am trying to swap. Good to hear that worked for you and might be worth a shot. thanks!

I looked, but couldn’t find the aluminum one on the site. Might be more OEM only for the lower end, but odd I couldn’t find it for replacement at the very least.

Good luck. Let me know if you need more info. :smiley:

I’d offer half, the seller is clearly huffing epoxy


Thank you Chad! Makes sense that they would only supply the aluminum version on the lower end bikes to save some $. Looks like I will have to go with the carbon option.

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Various offsets. Reputable seller. Spray paint is cheap :person_shrugging:

They also have a 135mm with 5mm offset but link doesn’t paste properly


Seems like a good option. unclear if the collar components will fit, but I think they do.

Those are universal for the masts.

Great! Thank you!

I just ordered one from the shop this weekend, there was 34 left when I ordered, now 5. It’s crazy how fast parts are going! I ordered it just in case I need it on an upcoming bike fit on emonda, was worried they would be out of stock by the time fit is done in two weeks. If I don’t need it and still looking in a few weeks, let me know.


Great to know. Thank you for the offer as a just in case. I will direct message you.

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Hi Alex, I wonder if you solved the problem. I am also having issues but need to change my seatpost bontrager ride tunned for the longer version on 175mm. I have the 135. if you still have the problem maybe we can swap posts because I also think its excesive to pay 160 US for it.