Classic & Vintage - Seatpost diameter 1983 Trek MTB?

I need to replace the seatpost on my original Trek but the place on the post the states the diameter is worn away. Does anyone know the diameter?

Is it an 830 or 850?? (not sure they had an 830 in '83)

Is it an 830 or 850?? (not sure they had an 830 in '83)

Not sure anybody except Specialized was making a factory bike in 1983. Trek sure wasn't.

I think '83 was Treks first year for Mtn bikes. I have an '85 870 and the seat tube is 27.2 mm. I have six Treks and all have the same size post.


I just checked vintage-trek.com and the 850 was the first Mtn bike by Trek, in 1983. The only one in '83

Not sure anybody except Specialized was making a factory bike in 1983. Trek sure wasn't.
Yes, we were. The Trek model 850 was introduced in 1983, built with Reynolds 531AT tubing.

OP's bike probably uses a 26.8mm post.

http://www.os2.dhs.org/~john/531AT.jpg

doesn't the current seatpost have the size stamped on it somewhere?

Call around and find a shop that has sizing poles(not sure what to call them) that they can insert into the seat tube to find out the exact seatpost size. You won't be able to eyeball the difference between 0.1 or 0.2mm when you line up seatpost. I tried lining up two seatpost because I had your same problem, turns out it was off by 0.4mm. It looked like they had the exact same diameter. It was only after I inserted the sizing poles that I learned I need a 26.8 vs. the 27.2 that I thought it needed.

Don't take the chance by inserting one that is too small because it will mess up your seat tube, maybe even cause it to crack!!!

See if you can find it on the vintage Trek website. Just google it. They have catalogs and a bunch of other info.

Here's the Mombat page on it. No seatpost diameter listed, however. (http://mombat.org/1983_Trek_850.htm) :(

They claim it's Tange Champion MTB tubing.

Pic from Mombat:
http://mombat.org/Trek8502.JPG

Brochure at Vintage Trek says Tange also. (http://www.vintage-trek.com/images/trek/1983/83Trek18.jpg)

Brochure says it's an SR MTE 100 post, but still no diameter listed.

Crazy adjustability on that post!

I'm starting to think John's 26.8 is a good guess, as that's the only size I've seen that post in so far.

Oops, velobase claims the post came in 26.6 - 27.2mm sizes.

They claim it's Tange Champion MTB tubing.
The first run used Reynolds 531AT. Later runs used Tange MTB and eventually Tange Prestige tubing.
http://www.os2.dhs.org/~john/tange-atb.jpg

Wouldn't any bike shop be able to measure. Hell, I had a Performance shop do it once.

Call around and find a shop that has sizing poles(not sure what to call them) that they can insert into the seat tube to find out the exact seatpost size. You won't be able to eyeball the difference between 0.1 or 0.2mm when you line up seatpost. I tried lining up two seatpost because I had your same problem, turns out it was off by 0.4mm. It looked like they had the exact same diameter. It was only after I inserted the sizing poles that I learned I need a 26.8 vs. the 27.2 that I thought it needed.

Don't take the chance by inserting one that is too small because it will mess up your seat tube, maybe even cause it to crack!!!

See if you can find it on the vintage Trek website. Just google it. They have catalogs and a bunch of other info.

Stien calles them "seatpost sizing rods" they are at the bottom of the page. http://www.jastein.com/Html/Tools_for_Frames_Forks.htm


Wouldn't any bike shop be able to measure. Hell, I had a Performance shop do it once.

they should be able to it just depends on the person he runs into. I would not trust too many 'mechanics' these days to do.

http://www.jastein.com/Images/Sizer%20Crossed.jpg

I ha thought these were made of a good polished stainless steel. the set I bought last year were alloy and I was a bit disappointed.

wonder what the price was on that 850 in 83

Yes, it's the 850. 26.8 sounds good but thanks for the many suggestions to take it to the LBS and have it measured. Doy!

I bought a cheap plastic vernier caliper to measure seat posts from Harbor Freight in Austin for just couple bucks, sure saves a lot of time
trying to find the right post.

This is an '84/'85 850 and the seatpost size is 27.0. I have an '87 Stumpjumper Comp w/the same seatpost size. Awesome riding bike BTW:D.

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