Trek conversion: '79 710 vs. '83 520

[rcnute]

Hi all: would there be any reason to prefer one or the other Treks noted in subject line for a 650B conversion?  Geometry looks very close, slightly more wheelbase on 710.  Thanks!

Ryan

[Chris Cullum]

The very early Vintage Treks had really shallow BB drop like 6.0cm. Not sure if the '79 falls into that category or not. The later ones like the 83 are 7.2cm. That's the biggest geometry difference I can think of.

On Mon., Nov. 28, 2022, 21:00 rcnute, <rcn...@hotmail.com> wrote:

Hi all: would there be any reason to prefer one or the other Treks noted in subject line for a 650B conversion?  Geometry looks very close, slightly more wheelbase on 710.  Thanks!

Ryan

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[Brad]

Right around '83 Trek started using a cast lug.  Before that they were formed lugs. 

[David Cummings]

I have  ‘79 650b conversion and it’s great.  The fork offset made it low-medium trail (45mm). I converted it to low trail (35mm) with a replacement fork. I use it as my light touring bike. 

By the early 80’s Trek was contracting with manufacturers in Japan to make lower end frames, even just rear triangles that were later assembled in the US. (Think about that economy for a second!) I’m not impugning the work of overseas labor, I just prefer the MUSA Trek frames. 

I also have an ‘81 412 and the difference in BB drop is noticeable - I feel more “in the bike.” It is made with Ishiwata tubing - half in Japan, half in the US. It doesn’t have the cachet of a Reynolds 531, but it’s still a fun bike. It was a 27” to 700c conversion. It has different geometry which results in medium trail (50mm). It has been my in-law bike. But I hanker for more than 35mm tires with fenders. 

Which do I prefer? If I had to choose just one, I would keep the ‘79 710. It was built as a racing bike but has been a work horse for me and rides better for me than the 412. And I also really like the full MUSA, Reynolds 531 heritage. That bike will outlast me!  

David in MT

[Ken Freeman]

My 720, 620, and 610 all have the 72 mm BB drop.  The only bike I have with a higher one is my 1981 Woodrup at 6 mm.  It rides well, but its a bit tall - not much straddle clearance, but still very manageable.

In contrast I also have a Terraferma 650b with 8 cm BB drop, and I see zero problem with pedal or BB clearance in my riding.  Overall folks who want to build a 650b should not IMO worry about pedal strike unless they have bad history of striking their pedals.  I don't think the drop of the frame before modifications is likely to cause a problem for the average rider, or one whom is not a crit rider as a night job.

I like the feeling of pedaling a lower bike , but I guess I'm somehow immune from it's disadvantages.

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Ken Freeman
Ann Arbor, MI USA

[William Harrison]

The 520 was marketed as a touring bike, and the 710 more of a sport-touring bike.  I have an ‘81 710 that I converted to 650b and it rocks.  I also converted an 83 620 and loved it.  The 710 will be Reynolds 531 throughout, whereas the 520 will be Reynolds 501, which is maybe slightly less cool, and at least a little heavier and thicker gauge, except for the downtube which I believe was smaller in diameter — I think I remember Alex Wetmore saying he preferred the flexibility of the smaller diameter downtube on the 520, since Trek’s 531c tubeset used a weirdly oversized downtube.  I would choose the 710, because of the tubing, and also because in my imagination the older Trek frames were more carefully constructed completely in Wisconsin.  But I can’t see you making a wrong choice here — both wonderful options.  

Will Harrison 

San Francisco, CA

[Alex Wetmore]

1983 Trek 520 was a sport touring bike and used 9/6/9 tubing (in a 1-1/8" tube).  The 1983 620 and 630 used a little thicker 10/7/10 downtube, but also 1-1/8" outer diameter.  They are all the same basic geometry, with the 520 having slightly shorter chainstays.  The longer chainstays will fit slightly bigger tires, but all of these are a squeeze with anything over 38mm in 650B.

I personally didn't see the 70s bikes as better built than the 80s ones.  My oldest Trek was a TX500 or TX700 (it's been too long for me to remember) and it already had production shortcuts like the headtube, top tube and downtube lugs were all cast as a single unit.

Alex

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From: 65...@googlegroups.com <65...@googlegroups.com> on behalf of William Harrison <wharri...@gmail.com>
Sent: Tuesday, November 29, 2022 5:52 PM
To: 650b <65...@googlegroups.com>
Subject: [650B] Re: Trek conversion: '79 710 vs. '83 520

 

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[Alex Wetmore]

I found my photos of the TX frame and it also reminded me that it has almost zero braze-ons.  The 1980s frames were much better in that respect.

Here are the photos of a 1977 TX (from over 20 years ago, so very low resolution):

https://phred.org/~alex/pictures/bikes/trekroad/

Alex

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From: 65...@googlegroups.com <65...@googlegroups.com> on behalf of Alex Wetmore <al...@phred.org>
Sent: Wednesday, November 30, 2022 9:27 AM
To: William Harrison <wharri...@gmail.com>; 650b <65...@googlegroups.com>
Subject: Re: [650B] Re: Trek conversion: '79 710 vs. '83 520

 

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[David Cummings]

Notice I didn’t say that the 70’s bikes were made better than the 80’s bikes, only that I preferred the all MUSA, Reynolds 531 frame. 

I have actually had my ‘79 frame checked and it is not straight - it’s hard to ride no-handed. Not sure what that says about other Treks, but I’d warrant Trek were pumping them out as fast as they could and they weren’t all perfect. 

David in MT

[Ken Freeman]

Thr only one I’ve owned new is my 1984 610, and it was not straight nor would ride straight until I took it to an expert builder and asked for it to be aligned. All the others have also been off.  The latest acquisition, the 1982 720, has both the fork ends and the frame ends pressed together a few mm.  Not terrible but not right.  I’m building it up to ride, but mainly to see if it is a good fit, before I think about having it aligned or otherwise restored.

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