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Old 11-17-11, 07:03 PM   #1
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Vintage Treks and 650b

Ok, there really was something interesting in the now-closed Banjomole thread. That is, will vintage Treks work for 650b? If not, why not? If so, what are the compromises?

I have a 610 and a desire to try 650. What brakes are necessary with the stock forks? Do you need the older forks with 55 mm offset, or will the higher-trail 52 mm or even 45 mm forks work?

What about cornering clearance? 650bs are are about 5 mm closer to the ground than 700cs. Vintage Treks have 7.2 cm BB drop virtually across the board. Does a user of 172.5 cranks have to go to 165s?

Clearance for 58 mm fenders?

inquiring minds want to know more, but a 650b Trek does not look like a slam-dunk to me. Nonetheless it's what I have as an experimental platform.
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Old 11-17-11, 07:07 PM   #2
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I wouldn't go so far as to say that all vintage Treks make great 650B conversion candidates, but probably some of their touring models would. Use Justin's Trek 6xx as an example-- that one proved to be quite a successful conversion, and I'm sure Justin can answer some of your questions regarding specifics. If yours is the same as Justin's 6xx series, then you're in luck. FWIW, many 80s Japanese touring bikes make great platforms for conversion to 650B.
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Old 11-17-11, 07:10 PM   #3
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there's a site that gives you all the formulas you will need to see if you will have a successful conversion. you can google it or someone will probably chime in.

brakes are really the easiest thing, imo. you get the tektro long reach brakes. done.

the interesting parts you need to figure out are the bottom bracket height/crank length (as you stated) and tire clearance. you should be thinking about 38+mm tires or it is not worth the conversion.

if your 610 originally had 27" wheels, it might be difficult.
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Old 11-17-11, 07:46 PM   #4
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Hey Ken
Check out the 650B page on flickr,there are several Trek conversions found there. Several that I can think of have had there chainstays pinched a bit to take bigger tires.

Cheers,
Chris
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Old 11-17-11, 10:37 PM   #5
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I ran an '86 310 (Bridgestone built) with 650B for a while. Worked fine.
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Old 11-17-11, 10:40 PM   #6
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Originally Posted by southpawboston View Post
I wouldn't go so far as to say that all vintage Treks make great 650B conversion candidates, but probably some of their touring models would. Use Justin's Trek 6xx as an example-- that one proved to be quite a successful conversion, and I'm sure Justin can answer some of your questions regarding specifics. If yours is the same as Justin's 6xx series, then you're in luck. FWIW, many 80s Japanese touring bikes make great platforms for conversion to 650B.
The 620 I built up for my dad was a 27" to 700c conversion. However, some Trek models are very good 650B conversion candidates. A fellow Louisvillian has a Flickr page detailing a 520 conversion. Of course, cantilever post relocation and rack modification were required.
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Old 11-17-11, 11:17 PM   #7
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I converted a Trek 600 Series to 650A, using CR18 rims, Schwalbe Marathon tires, Mafac Racers. In fact we changed over 3 vintage frames this exact same way, then toured on them for 2 months. As you all probably know 650A is 590mm, as opposed to the B's 584mm.







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Old 11-17-11, 11:40 PM   #8
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I just bought an '84 Trek 760 that has been converted to 650B. As you probably know, the 760 has full-on racing geometry with 74/73.5 seat and head angles, 38mm fork offset, and 41cm chainstays. It seems to work just fine, although I admit I haven't gotten in much ride-time just yet. For the record, my bike uses Rivendell Silver brake calipers (basically Tektro long reach), 170mm cranks, and the 33mm Nifty Swifty tires. The rear tire clears the chainstays with about 3mm on each side. When the bike is upright the cranks clear the ground by about 65mm, 13mm less than my other bike (which has slightly longer 172.5 cranks) so I'm definitely not pedaling through any corners!
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Old 11-18-11, 08:18 AM   #9
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I am converting a Trek 630 to 650B. Weinmann or Dia-comp 750s will reach the rim with the pads at the bottom of the slots. 38mm wide Soma B-Lines will fit inside the chainstays and forks. Hetres might clear the chainstays, but not by much if they do.

The 72mm bottom bracket drop might be a problem if you pedal through turns. I plan to use 170mm cranks. If they hit, I'll go to 165s.
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Old 11-18-11, 09:33 AM   #10
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That is, will vintage Treks work for 650b? If not, why not? If so, what are the compromises?.
Lots of bikes are suitable.

The Treks in question have a low-trail geometry which, depending on who's brand of Kool-Aid you drink, will improve handling with a Front Load.

There's no special relationship between Vintage Treks and 650B conversions though.
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Old 11-18-11, 10:17 AM   #11
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Assuming I drink a certain brand of Kool-Aid (wink wink), is there a list or resource that would show other vintage frames with low-trail geometry? I had seen the Trek list before, but assume there are other vintage frames with low-trail geometry that would work.
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Old 11-18-11, 11:00 AM   #12
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Not sure about a list but if you look for a fork with a lot of offset you'll find bikes with lower trail.

If you take a low trail 27" or 700c frame and switch it to 650B you will have even lower trail. If you're into carrying loads on the front of the bike that might be something you want. You've just gotta muscle is around corners a little more since it wont be as responsive to body lean
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Old 11-18-11, 12:53 PM   #13
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Add to the list: 1992 Trek 400. I believe that this model was one of the last lugged steel frames from Trek. Came with very heavy suntour Blaze group and all the other hardware was no name. Frame is actually pretty nice considering it's place in the product line. 650b Velocity rims with Tiagra hubs (Rivendell) and a pair of Grand Bois Hetre 41mm (measured width) and a set of Tecktro 556 ( ebay deal around $40- white which matches my frame color!) and Sram Rival shifting gear etc. The Hetres are a little tight at the chain stay but that's about it for build up. Rides very smoothly and from what I can measure, the 650B gets me through my usual 30 mile course about .5 to .8 average MPH faster than the Mavic Open Pro/Passela tourguard 28mm set up it replaced. Bear in mind that the roads I ride on are truly crappy chipseal and eroded asphalt so the difference on smoth asphalt might not be there at all.
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Old 11-18-11, 07:14 PM   #14
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Quote:
Originally Posted by Zaphod Beeblebrox View Post
Lots of bikes are suitable.

The Treks in question have a low-trail geometry which, depending on who's brand of Kool-Aid you drink, will improve handling with a Front Load.

There's no special relationship between Vintage Treks and 650B conversions though.
No, the Treks in question do not have the kind of low-trail geometry usually thought of. There were three variants of fork offset if you peruse a bunch of the Trek catalogs: 55 mm, 52 mm, and 42 (all taken from the 1983 catalog on the Vintage Trek site). The 6xxs of that year (note they are different in other years) have 73 degree head angles and 27" or 700c wheels, with respectively, radii of about 345 mm and 340 mm. For this series which includes the 610 and 620 of that year, the trails are 48 mm and 46 mm for 27 and 700c, and will be 45 mm with 650b wheels. This is not low trail, it's medium trail. Now I know it's better than high trail, the 58 mm of the 720 and the 760, but it's not in the 40mm or less thought to represent low-trail, low flop design.

And I know from recent experience that adding a low-trail fork (65 mm offset in my case) long enough to maintain the original head tube angle will nearly max out a Mafac brake with 700c. It needs to be about ((622-584)/2=19) 19 mm longer than the Mafac to reach down to the brake track on a 650b rim. So the only brake solution with loaded low trail is a canti or brazed CP.

So, how low does it need to be? I do want a front load, but less extreme than a porteur. The V-O Rando, Boxdog Pelican, and (Heine-tested) Boulder Randonneur show 51 (!), 43, 41, and 41 mm (the extra one represents two generations of Pelican). I don't know offhand why I have 51 mm for the Rando. But I would think a target of 40 mm is where a front-loading 650 should be headed.

With 700c, my modified 1984 Trek 610 (73 deg, 340 mm tire radius, 65 mm rake) has trail of 39 mm. With Hetres it would come down to 36 mm, which might be too low.

My former Woodrup with 28 mm Gators had trail of 46 mm, and barely handled a moderage front rack load, though it was much better than another Trek config I had that had a 58 mm trail. This is part of why I'm not confident in vintage Treks with stock forks functioning as we expect "low trail" to do. It would come down to 44 mm with Hetres. AND, it had a BB drop of 6.5 cm, meaning it is ready for a normal crank arm.

Maybe the lister who I sold it to still doesn't have time for it and would sell it back to me?

But it seems that for a really good conversion you need low trail and a small BB drop, in addition to wheel side clearances. Here all of the Treks will be deficient, since a 72 mm drop is nearly universal, throughout the steel era.
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Old 11-24-11, 11:49 AM   #15
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I have a few questions about your analysis of fork offset and bottom bracket drop in relation to the suitability of old Treks for a 650B conversion.

As regards to fork offset, there are some riders who use a front rack and bag on their Rivendells and they seem to find the handling satisfactory. Rivendells have a longer trail than the 1983 Treks.

As far as bottom bracket drop goes, I figure that with a 72mm drop and 38mm SOMA B-Lines, the BB height is about 261mm. That is low, but is it too low with 170mm cranks? It would certainly be OK with 165mm cranks. In your last post, you use the term "normal crank arm", for someone 5'6" tall 165 is normal. I'm slightly taller than that and normally use 170mm cranks, but I don't know if I could tell the difference if I rode 165s. A lot of Miyata and Univega bikes in the eighties came with 165mm cranks on models 21" and smaller.

Were I to order a custom 650B bike I think the geometry would be very similar to a Trek 630, except for a smaller bb drop, 65mm perhaps, 5mm more fork offset, and about 5mm more chainstay clearance so I could fit Hetres.
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Old 11-24-11, 01:30 PM   #16
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From Road Fan "My former Woodrup with 28 mm Gators had trail of 46 mm, and barely handled a moderage front rack load, though it was much better than another Trek config I had that had a 58 mm trail. This is part of why I'm not confident in vintage Treks with stock forks functioning as we expect "low trail" to do. It would come down to 44 mm with Hetres. AND, it had a BB drop of 6.5 cm, meaning it is ready for a normal crank arm.

Maybe the lister who I sold it to still doesn't have time for it and would sell it back to me?

But it seems that for a really good conversion you need low trail and a small BB drop, in addition to wheel side clearances. Here all of the Treks will be deficient, since a 72 mm drop is nearly universal, throughout the steel era"

Sorry Ken, I have become quite fond of your old/my new Woodrup!
I have seriously considered converting it to 650b, but not for a while as I have just got it dialed in for 700c.

Cheers,
Chris
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Old 11-24-11, 03:28 PM   #17
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I ran an '86 310 (Bridgestone built) with 650B for a while. Worked fine.
Funny, I am using the same frame to build a Bridgestone XO clone with 700C wheels. Just started the project yesterday.
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Old 06-29-15, 04:32 PM   #18
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Originally Posted by jar351 View Post
I just bought an '84 Trek 760 that has been converted to 650B. As you probably know, the 760 has full-on racing geometry with 74/73.5 seat and head angles, 38mm fork offset, and 41cm chainstays. It seems to work just fine, although I admit I haven't gotten in much ride-time just yet. For the record, my bike uses Rivendell Silver brake calipers (basically Tektro long reach), 170mm cranks, and the 33mm Nifty Swifty tires. The rear tire clears the chainstays with about 3mm on each side. When the bike is upright the cranks clear the ground by about 65mm, 13mm less than my other bike (which has slightly longer 172.5 cranks) so I'm definitely not pedaling through any corners!
Hi there jar351. I wanted to PM you to get your perspective on your 650b converted 760, but was unable to do so (my post count is still too low). Hopefully no one will mine my resurrecting this thread. I'm planning to convert a 760 frame I recently acquired and would really appreciate any insights/feedback/comments you have regarding your experience. Thanks.
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Old 06-29-15, 09:34 PM   #19
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I pmd him for you, but his last post was end of 13 so he might not respond
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Old 06-29-15, 10:30 PM   #20
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Got the PM. To respond to cosmonhat, I rode that bike (650b-converted Trek 760, for those not following) for a very short time, so take what I have to say with a big grain of salt. Basically, my thoughts were that the conversion would only be worthwhile if one could fit decently plush tires into the frame, and I didn't feel that the 33mm Maxy Fasties I had were plush enough. (If I recall correctly that was about as big as you could get away with.) Maybe now there are better options available. I don't know.

The pedal strike was an issue for me too but it's quite possible I would have gotten used to it in the long run. Again, not sure. Sorry I can't be of more help. Anyway, good luck with the project
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