Trek 720 touring frame for 650b?

[Ken Freeman]

Has anyone converted a Trek 720 (the road touring frame with the 47 cm chainstays) for 650b?

I have a line on such a frame in decent condition.  I wonder if the long graceful chainstays on these frames have any problem taking 650 b wheels?  I'd assume dimpling is necessary for 42 mm, but I might stay with 38 mm and below.

[Josiah Anderson]

Except for the first year, 1982, the 720 had cantilever brakes. What brakes does the one you're looking at have? You could have the posts moved by a framebuilder, but if it were my project I would start with a 61x or similar sport tourer rather than a 720. I fit 42s in my '82 614 with indented chainstays, and IIRC 38s were fine without dimpling. If you want that specific 720, it would probably be a wonderful bike with 700x35 tires- that's what I'd do. 

Josiah Anderson

Tacoma, WA

[Michael Mann]

I have restored 3 lugged Trek 750's and they are wonderful, versatile bikes. But as said, going from 700 to 650b on a cantilever frame is problematic without moving the brake posts. I HAVE done a 650b conversion on a lugged Trek 930. The 900 series bikes work great for this, going from 26" to 650b using the Tektro CR 720 cantilevers is a simple and inexpensive conversion. Just make sure to swap out the stock brake pads for Koolstop salmon pads and you're off to the races.

Mike M

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Michael Mann

[Michael Mann]

Whoops - my bad. I thought OP was talking about the hybrid 700 series, not the 720 touring bike. Should have read closer.

Mike M

[Kevin McCool]

Works beautifully. I have one (1982 model with calipers) I recently converted with a gravel king 38c in the rear and baby shoe pass 42c in the front with Berthoud fenders. The ride is best described as “regal.”

Kevin
Ann Arbor

[Steve Chan]

    I really liked my old Trek 720's ride, especially with a low/mid trail fork. I imagine it would be incredibly stable and plush with the fatter 650B tires. The one thing it didn't seem to have (for me at least) was the planing that was pretty obvious on a bunch of my other bikes. But that level of frame flex is probably not appropriate for a loaded tourer. Maybe the casing flex on the fat 650B tires could compensate for the more rigid frame?

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[William Harrison]

I bought an 83 720 locally whose previous owner had ignored the canti posts and just attached long reach tektro calipers. It was totally fine, and I would totally do this too. You’d even still have the front cantis to use for rack attachments.

Will
Portland

[Paul Clifton]

This is a brilliant idea, and, sooner or later, I will try it on my '84 720. Can't believe it never occurred to me.

The 700 series Deore canitlever brakes on my 720 will not move down far enough to reach a 650b rim, and I don't think any will. But it does just barely fit a 700x38 tire within my margin of comfort at the chainstays, so I'm not missing much. And, Ken, you won't be either if you don't have long reach brakes lying around.

Paul

[Drew Henson]

just curious, what's the process for dimpling the chainstays? is this pretty straightforward for a framebuilder, and is it costly?

[David Parsons]

On Thursday, June 4, 2020 at 10:29:46 AM UTC-7, Drew Henson wrote:

> just curious, what's the process for dimpling the chainstays? is this pretty straightforward for a framebuilder, and is it costly?

You squash them with a dimpling tool.  Mine is a (trimmed down) head from a golf club that I've clipped to the fixed jaw of a C-clamp;  I use an aluminum form (a 1 1/8th tube block to support the other side of the tube while I squash it down.   This won't work on some of the air-hardening steels out there (I've a junker Indyfab frame that I wanted to convert to 650b, but the dimpling shoe just skittered off the chainstay when I attempted to dimple it) but old frames aren't made from that stuff.

 -david parsons

[Jeffery]

David, would you share a photo of your dimpling tool? And how did you "clip" the golf club head on the clamp? I've read about doing something similar with a large diameter allen wrench and c-clamp, but I don't have the guts to try it without being able to keep the allen wrench firmly attached.

[David Parsons]

On Thursday, June 4, 2020 at 8:05:39 PM UTC-7, Jeffery wrote:

David, would you share a photo of your dimpling tool? And how did you "clip" the golf club head on the clamp? I've read about doing something similar with a large diameter allen wrench and c-clamp, but I don't have the guts to try it without being able to keep the allen wrench firmly attached.

Tada:

The club head is attached by a somewhat rube goldbergy method;  I notched the edges of the fixed jaw, then drilled, m5 tapped two holes in the head, and bolted it into place.

A /better/ dimpler would have the 1 1/8th tube clamp attached to the movable jaw, but I occasionally use that to hold a frame by the downtube when I'm cleaning up the HUGE GLOBS OF BRASS left over from gluing everything together.     If I ever start doing framebuilding for a living, I'll bite the bullet and buy a second set of 1 1/8ths tube clamps, but until then what you see is what I've got.

-david parsons