Jimbopclyons

I am trying to replace a missing seat post on a 1980’s Trek Navigator 200. The label on the bike says 36.8 cm. I searched on Trek and google, but the largest seat post is 31.8 cm. I then looked for adapters to use a smaller diameter seat post. None were listed for 36.8 cm.

I actually am just trying to sell the bike, but without a seat post and seat, that may be impossible. Any help or suggestions would be appreciated.

icemilkcoffee 

Do you have a ruler? Measure the width of the hole there. It's almost impossible that it was 36.8mm. Most likely 31.6mm

Jimbopclyons

The quick release is labeled 31.6 mm. Thanks for your reply. I can get a seat and post for $31.00 on Amazon. 😎✅

maddog34

36.8mm is most likely the Seatpost Clamp's Bore Dimension. Trek DOES have a rather large seat post used for certain models.. it's 34.9mm OD...

the Navigator you're dealing with probably has a 31.6mm post size.

MEASURE the inside of the Seat tube of the frame..if you can't do this accurately, then find someone that can.. any Auto Parts store, a Welding/Fabrication shop, or Machine shop will be glad to help you.

You can also Measure it yourself if you have a metric ruler and a keen eye...

https://bike.bikegremlin.com/3114/se...zes-standards/

soyabean

Unless you can find out without a shadow of a doubt, the only reliable way is to try every seatpost on hand (with the help of an LBS or hoarder) until one size has the right give and feel.

Measuring is not and never reliable. For example, math from verniers and micrometers may say it is 26.4mm, but in reality it is a 26.2 .

And yes, 0.2mm makes a world of difference. A seatpost 0.2mm too large actually doesn't fit, a seatpost 0.2mm to small and the clamping area often squishes so much the bolt bosses are touching one another.

Many of my seatposts have come from smart folks that couldn't return a scratched up purchase.

Being a 1980's makes it even worse as there exists all sorts of weird seatpost diamaters, but still may be any one of these based on my experience with my collection of seatposts:

22.2 (baby bikes)
25.0 (80's BMX)
25.4 (kids bikes, also 80's BMX)
25.8 (vintage big box store bikes)
26.0 (never seen a bike with this, but I have the seatpost)
26.2 (Tange Taiwan frames)
26.4 (Kuwahara, also a lot of stuff from France)
26.6 (I saw once on a Trek VW Jetta)
26.8 (vintage big box store bikes)
27.0 (never seen a bike with this, but I have the seatpost)
27.2 (most popular seatpost size ever since the dawn of time)
28.6 (some recent bikes, like Jetson, and also a lot of Schwinn from the 00's)
29.2 (I saw once on a Trek Marlin)
30.0 (never seen a bike with this, but I have the seatpost)
30.4 (never seen a bike with this, but I have the seatpost)
30.9 (many recent bikes)
31.6 (many recent bikes)

I am grateful that all my seatposts are hoarded in a box the size of a breifcase.

So do yourself a favor, bring the bike to a LBS, they will do the above, and sell you what you need for a few dollars more than mail order.

KerryIrons

36.8 cm is 14.5 inches. Just saying

Jimbopclyons

Great info! TY!😎🚴‍♂️

Jimbopclyons

Well! i looked at the quick release on the seat post and it was labeled 31.6 - so I ordered a 31.6 seat post and it does not fit. I do not have an accurate metric measuring ruler or calipers, so it’s off to the bike store I go. I apologize for the lateness of my reply. I might ask the bike store to assemble the bike (I have the wheels/tires) and tune it up, but I will try to do this myself first. I had a Colnago back in the day!

soyabean

The 31.6 stamped on the seatclamp is the correct ID diameter of the seatclamp for the correct OD diameter of the frame's seattube, which is not and NEVER the OD diameter of the seatpost.

My experience tells me that seatpost should be a 27.2 with a 90% probability, that still means there is a chance for 27.0, 26.8, 26.6, 26.4, as ALL these sizes were used in vintage Trek mtb bikes.

It's been nearly a year and the OP still hasn't solved something so trivial that any LBS can service in seconds by selling the correct seatpost required.

veganbikes

In situations like this always go to. your local shop and have them measure or confirm measurements, they probably also have a seatpost in stock or can get one pretty easily and help install.

We had a seatpost we measured twice and ordered and it was just a hair off for some reason so we made the guy a nice shim and it worked like a charm and he was happy and his seatpost wasn't slipping or anything and his kid won't be riding that bike anymore.

Bill Kapaun

36.8 cm is maybe a frame size? It would be a pretty small frame.