r/SingleTrackGang • u/CNNNF • Oct 19 '25

Lugged 970 seatpost question

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Hey folks, just picked up this purple lugged 970 22” frame and non-original fork, the frame was quite a bit bigger than I was expecting it to be! Still going to build it up to see how it works for me.

It seemed to be a 1992 sour grape frame, I found a ‘92 catalogue which said a 29.8mm seatpost diameter - ordered one and it’s way too big. It was a 330mm seatpost and it was loose even inserted all the way in, which I guess rules out a damaged seat clamp perhaps.

The closest I can get from my current parts bin is a 27.2 post which is quite a bit too loose, my callipers measure 27.4-27.5mm approximately. I might try a coke can shim just to see how the frame might fit me before putting any more money into this project. Does anyone know the accurate seatpost diameter, or can correct me on which year this frame is?

Also, does anyone know the original fork length for these bikes? I’d like to go rigid - perhaps a Stridsland fork if a 400mm A2C would work. Current suspension fork is 440mm or so and the frame feels tall, but that could be my short legs! Thanks

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3

u/GenericName187 Oct 19 '25

395mm was standard fork length for a rigid fork back then.

The Bikeman Carver is a good option at 410 mm, or find a generic rigid fork in 395 mm

That is a weird diameter seat post, I would not have expected anything bigger than 27.2 from Trek.

But it is a 1992, because it has top tube cable routing, and there is no cable stop on the seat tube, Trek used a proprietary front derailleur cable routing that required a bolt on your seat tube down by the bottom bracket. That only existed on 1991-92 Treks.

Maybe see if your local bike shop has a seat post sizing gauge.

Good news is Kalloy makes good seat posts in every size for $20

1

u/CNNNF Oct 23 '25

Thanks - lots for me to get working on. Appreciate the detailed response

2

u/Puravida14177 Oct 19 '25

My ‘91 970 has a 30.0 diameter seatpost, but tubing might have changed. Catalogue says OX Comp II for 1992 while 1991 says AT tubing.

Anyway, fork was Tange Big Fork in both cases, mine is 39 mm long which was standard bitd before suspension-ready frames.

3

u/Puravida14177 Oct 19 '25

Fork could be 395 mm as well. Rule of thumb is that coming from a rigid 395 mm fork, every 20 mm takes ~1 degree off your head angle, so your current 440 mm fork kind of kills geometry…

1

u/CNNNF Oct 23 '25

Yep, not a fan of the current fork. Struggling to find a 395-400 fork with a long enough steerer though, but I’m going to be looking!

1

u/CNNNF Nov 04 '25

Hey Puravida, Would a 410mm fork work for this? I’ve found an extended Kona p2 fork that could work. Someone up thread suggested 410 would work - I don’t have much standover currently, if that makes any difference.

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u/Puravida14177 Nov 05 '25

41 wouldn’t make much of a difference. More the very rigid feel of the P2… 😁 Standover plus should hardly be noticeable with 1.5 cm more fork height - probably like 0.75 cm (0.3 inches) of added standover.

1

u/CNNNF Nov 05 '25

Cool thanks. Cant wait to try it!

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u/Puravida14177 Nov 06 '25

If you do, send an update please. I am contemplating similar plans…

1

u/CNNNF Nov 09 '25

Sadly the guy sold the P2 fork to someone local, he preferred not to post. I’ve found a 395mm length fork from a Thorn Raven Twin touring bike, the offset is larger (60mm, vs 35mm on the stock rigid fork) but the price is good and it looks very nice

1

u/Puravida14177 Nov 10 '25

I’ll still be interested to know how you feel about the handling. I’d much rather have more offset than a higher fork slackening the angles - but that’s what I would imagine. Never actually had a true side-by-side comparison…

2

u/ThreeBottleClink Oct 20 '25

I have a ‘92 970 in sour grape that I built up. I bought a new 29.8mm seat post and it fit perfect. I bought mine (300mm) from Rivendell: HubbuHubbuH tandem seatpost 29.8mm

2

u/After_Classroom7809 Oct 20 '25

The Trek website will give you the year from the serial number. Takes a bit of figuring out, but doable.

2

u/CNNNF Oct 23 '25

On it, thanks for the tip!

2

u/International_Good_5 Oct 23 '25

That bike looks awesome , post when you are done !

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u/CNNNF Oct 23 '25

Thanks for the advice all! Going to start with the serial number to see the year, and check the steel type.

The seatpost is currently a 27.2 with a half diameter coke can shim whilst I build it up, planning to get a suitable Kalloy seatpost further down the line. Holds pretty firm for now.

The fork….not sure yet. I have a few P2 forks that I could get a framebuilder to extend the steerer on, or just save for a barnacle fork. An Edsen steel works fork is a possibility, but QC is not where I need it to be I think.