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Old 01-31-11, 11:05 PM   #1
John Ummel
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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?
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Old 02-01-11, 12:23 AM   #2
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Is it an 830 or 850?? (not sure they had an 830 in '83)
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Old 02-01-11, 04:26 AM   #3
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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.
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Old 02-01-11, 05:58 AM   #4
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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

Last edited by a77impala; 02-01-11 at 11:37 AM. Reason: more info Trek mtn bikes
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Old 02-01-11, 11:39 AM   #5
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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.

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Old 02-01-11, 11:43 AM   #6
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doesn't the current seatpost have the size stamped on it somewhere?
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Old 02-01-11, 12:12 PM   #7
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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.

Last edited by 531phile; 02-01-11 at 12:18 PM.
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Old 02-01-11, 12:16 PM   #8
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Here's the Mombat page on it. No seatpost diameter listed, however.

They claim it's Tange Champion MTB tubing.

Pic from Mombat:
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Old 02-01-11, 12:22 PM   #9
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Brochure at Vintage Trek says Tange also.

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.
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Old 02-01-11, 12:27 PM   #10
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Oops, velobase claims the post came in 26.6 - 27.2mm sizes.
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Old 02-01-11, 12:59 PM   #11
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They claim it's Tange Champion MTB tubing.
The first run used Reynolds 531AT. Later runs used Tange MTB and eventually Tange Prestige tubing.
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Old 02-01-11, 01:05 PM   #12
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Wouldn't any bike shop be able to measure. Hell, I had a Performance shop do it once.
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Old 02-01-11, 01:17 PM   #13
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Quote:
Originally Posted by 531phile View Post
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

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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.



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.
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Old 02-01-11, 01:29 PM   #14
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wonder what the price was on that 850 in 83
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Old 02-01-11, 02:27 PM   #15
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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!
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Old 02-01-11, 05:00 PM   #16
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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.
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Old 02-01-11, 09:11 PM   #17
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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.

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'?? TST Mtn Bike frame--project, '07 Tsunami Tandem--home-built

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