Is a Trek 760 Too Racy for a 650b Conversion?
#26
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These machines were some of the 1st production versions of the then new American tight clearance, short wheelbase designs that derived from the radical excess of the custom "Crit Bikes" of the late '70's.
We found that the older Euro designs intended for racing on cobble stones and un-paved mountain roads were (big surprise) not ideal for the steady diet of city park criterium races on good(ish) pavement, in tight quarters at high speed with multiple max accelerations every lap. The Euros followed suit in design, another story.
Choosing a frame-set designed for 23-25mm tubulars with just enough clearance to install an inflated tire and lacking any provision for mounting mudguards to convert to 650b x 38 with fenders ?
Right church, wrong pew.
-Bandera
We found that the older Euro designs intended for racing on cobble stones and un-paved mountain roads were (big surprise) not ideal for the steady diet of city park criterium races on good(ish) pavement, in tight quarters at high speed with multiple max accelerations every lap. The Euros followed suit in design, another story.
Choosing a frame-set designed for 23-25mm tubulars with just enough clearance to install an inflated tire and lacking any provision for mounting mudguards to convert to 650b x 38 with fenders ?
Right church, wrong pew.
-Bandera
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I have an '84 770 and an '85 760 bare frame hanging up in the spare bedroom. At aproximately 320 mm from the midpoint of the dropout slot, there is about 38 to 40 mm between the chainstays. So thats probably the pinch point. Plenty width on the front fork and seatstays. As someone else mentioned, this bike has a good bit of toe overlap. Not a problem at speed with skinny tires but requires caution during slow speed manuveurs, and I think with fenders on there it would be kind of tricky, and they would be really close to the down tube and right up against the seat tube. I have an '84 760 as well that I used to run with a spare set of wheels that had 27x 1-1/8 tires and it worked, but there was only about 1/8" clearence at the fork crown, and I definetly noticed the increased toe overlap from the 700x23's that I usually ran.
Here it is with 700x23's.
Here it is with 700x23's.
Last edited by Hobbiano; 04-30-19 at 05:16 PM.
#29
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Installed 650b 38mm pari motos on a track frame that barely took 25mm tires, about 3mm of space on all sides of tire (38mm one), rides awesome
No space for fenders, it was fun and a bit ugly...
You could make a conversion no doubt but fenders would be an issue, even the geometry would be similar as the difference in radius of 622/23 and 584/38 is only 4mm
No space for fenders, it was fun and a bit ugly...
You could make a conversion no doubt but fenders would be an issue, even the geometry would be similar as the difference in radius of 622/23 and 584/38 is only 4mm
Last edited by Nikola88; 05-01-19 at 03:34 AM.
#30
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This all has my chuckling because that is in fact MY bike. Well, my old bike, I sold it a year or so back. Those are 25mm Continental Grand Prix Classics and man they barely fit. This bike also had ridiculous toe overlap. I don't know much about 650 conversion but I'm guessing no.
Happy to see this picture though. I remember it was the same day as Eroica in Gaiole so I went out looking for some gravel
Happy to see this picture though. I remember it was the same day as Eroica in Gaiole so I went out looking for some gravel
Since you mention toe overlap - you can really see it in the photo.
#31
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FWIW- putting 700c x 35 Compass tires was the best thing I ever did for my 85 Trek 720.
FWIW- the geometry of the 85 620 was identical to the 85 660 race bike- with the exception of the chain stay length and fork rake. I don't know about the 84 model.
If you're that on the idea of cushy tires- I'd do 700C and Compass Bon Jon Pass tires on the 620.
FWIW- my 86 400 Elance has the most aggressive geometry of all of my bikes- with the exception of the chain stay length at 42.5.
I've toyed with the idea of doing 650B on my 400 Elance. While I don't have the tires I really want on it- I do have the brakes I really want on it.
FWIW- the geometry of the 85 620 was identical to the 85 660 race bike- with the exception of the chain stay length and fork rake. I don't know about the 84 model.
If you're that on the idea of cushy tires- I'd do 700C and Compass Bon Jon Pass tires on the 620.
FWIW- my 86 400 Elance has the most aggressive geometry of all of my bikes- with the exception of the chain stay length at 42.5.
I've toyed with the idea of doing 650B on my 400 Elance. While I don't have the tires I really want on it- I do have the brakes I really want on it.
I haven't given up on the 620 - just need to figure out the best way to modify it to find the sweet spot. This winter I took it down to the frame and rebuilt it mostly (for me) with the original parts. Currently it's a 3x7 half-step w/granny and ratcheting bar ends. I am still using the 27" wheels which are in VGC. You're right that a switch to good 700c wheels and slightly bigger quality tires would be an improvement.
And, maybe I'll take the Gevenalle 10 speed plunge on my 620.
You've probably seen what this guy did with his '85 620 - an interesting read and money is no object.
Fuji Otaku: The Phoenix Project - The 1985 Trek 620 Alights
#32
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I have an '84 770 and an '85 760 bare frame hanging up in the spare bedroom. At aproximately 320 mm from the midpoint of the dropout slot, there is about 38 to 40 mm between the chainstays. So thats probably the pinch point. Plenty width on the front fork and seatstays. As someone else mentioned, this bike has a good bit of toe overlap. Not a problem at speed with skinny tires but requires caution during slow speed manuveurs, and I think with fenders on there it would be kind of tricky, and they would be really close to the down tube and right up against the seat tube. I have an '84 760 as well that I used to run with a spare set of wheels that had 27x 1-1/8 tires and it worked, but there was only about 1/8" clearence at the fork crown, and I definetly noticed the increased toe overlap from the 700x23's that I usually ran.
Here it is with 700x23's.
Here it is with 700x23's.
Beautiful bike - love the color.
Seeing photos of several Trek full-on race bikes show that toe overlap and tight chain stay clearance is a problem - verifying the many knowledgeable comments about this type of bike being marginal for 650b conversion.
A 'sport/tour' geometry - like my Trek 410 - is much better for 650b.
Thanks.
#33
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Thread Starter
As you're seeing, tire size and geometry are two different "knobs" to affect your ride. Tubing brand and make are essentially inconsequential - as long as the wall diameter and thicknesses are the same. The vintage bikes you're looking at all use "standard" diameter tubing sets (not oversized). A True Temper tubeset will ride about the same as a 531 for the same wall thicknesses. The only difference might be the butted lengths, but now we're talking "princess and the pea" difference in ride.
What you're looking for are "long legs" - long chainstays will give you more width where the tire's widest point is, longer fork blades (crown to axle dimension) gives you more vertical room - fork ID is rarely an issue. BITD, these were sold as sport touring or touring bikes.
A 400 Elance would be an excelent bike for a 650b conversion.
What you're looking for are "long legs" - long chainstays will give you more width where the tire's widest point is, longer fork blades (crown to axle dimension) gives you more vertical room - fork ID is rarely an issue. BITD, these were sold as sport touring or touring bikes.
A 400 Elance would be an excelent bike for a 650b conversion.
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Sure, but the 720 is a far different frame than the 760. The chain stays on the 720 are several centimeters longer than those of the 760, and the 720 has longer fork blades and a Haden crown, rather than the Cinelli or Tange crowns used on the 760. The Tange (flat) crown might have enough clearance (I don't have one to check), but the blade length was not designed to accommodate fenders. I'd measure carefully before inventing too much in this change.
#36
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Sure, but the 720 is a far different frame than the 760. The chain stays on the 720 are several centimeters longer than those of the 760, and the 720 has longer fork blades and a Haden crown, rather than the Cinelli or Tange crowns used on the 760. The Tange (flat) crown might have enough clearance (I don't have one to check), but the blade length was not designed to accommodate fenders. I'd measure carefully before inventing too much in this change.
In other words- you can cush out with Compass 35s and have a racing main triangle geometry with just a wheel and tire switch on the 620.
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#37
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I haven't given up on the 620 - just need to figure out the best way to modify it to find the sweet spot. This winter I took it down to the frame and rebuilt it mostly (for me) with the original parts. Currently it's a 3x7 half-step w/granny and ratcheting bar ends. I am still using the 27" wheels which are in VGC. You're right that a switch to good 700c wheels and slightly bigger quality tires would be an improvement.
And, maybe I'll take the Gevenalle 10 speed plunge on my 620.
You've probably seen what this guy did with his '85 620 - an interesting read and money is no object.
Fuji Otaku: The Phoenix Project - The 1985 Trek 620 Alights
And, maybe I'll take the Gevenalle 10 speed plunge on my 620.
You've probably seen what this guy did with his '85 620 - an interesting read and money is no object.
Fuji Otaku: The Phoenix Project - The 1985 Trek 620 Alights
I'm not so much of a fan of the Gevenalle setups. I'd rather have bar ends or Command Shifters.
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#39
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Installed 650b 38mm pari motos on a track frame that barely took 25mm tires, about 3mm of space on all sides of tire, rides awesome, looks are questionable lol
No space for fenders, it was fun and a bit ugly...
You could make a conversion no doubt but fenders would be an issue, even the geometry would be similar as the difference in radius of 622/23 and 584/38 is only 4mm
No space for fenders, it was fun and a bit ugly...
You could make a conversion no doubt but fenders would be an issue, even the geometry would be similar as the difference in radius of 622/23 and 584/38 is only 4mm
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It's never a bad time to go frame shopping!
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#42
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Oh man, I cringe reading this. The 760 is never too racy for such a thing but in this case too undervalued. I have a full Campy and near mint 760 that is worth leaving alone to experience the ride 20mm tubulars and full 531c can give.
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#44
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The older the decal the faster the bike. Yours looks pretty fast.
#45
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Now, re: my original post - I wasn't going to take a pristine 760 off the wall of the Smithsonian and melt it down for bird shot.
I was simply considering giving a new and prolonged life to a well-used 760 frame and fork that is for sale on this site and nobody seems to want - been sitting for a while. If nobody buys this thing and re-builds/re-purposes it, then who knows - it could wind-up sitting on the curb some day because it never got a second life. Is that preferable to an evil 650b conversion?
So, calling all BF vintage bike purists - here's your chance!! For $275 you can rescue this classic frame and fork from the likes of ME! Act now, operators are waiting!
p.s. If the guy who is selling this F/F makes a sale because of this discussion he owes me $50!!!
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Now, re: my original post - I wasn't going to take a pristine 760 off the wall of the Smithsonian and melt it down for bird shot.
I was simply considering giving a new and prolonged life to a well-used 760 frame and fork that is for sale on this site and nobody seems to want - been sitting for a while. If nobody buys this thing and re-builds/re-purposes it, then who knows - it could wind-up sitting on the curb some day because it never got a second life. Is that preferable to an evil 650b conversion?
I was simply considering giving a new and prolonged life to a well-used 760 frame and fork that is for sale on this site and nobody seems to want - been sitting for a while. If nobody buys this thing and re-builds/re-purposes it, then who knows - it could wind-up sitting on the curb some day because it never got a second life. Is that preferable to an evil 650b conversion?
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I'm with you on this. I've got a bunch of classic racing bikes in my garage that I've fitted with triple cranksets, wide range cassettes or freewheels, and the fattest tires they'd take. Why? Because I wanted to ride them. Sure they'd look better with a 53-42, a corncob freewheel, and skinny tubulars, but that wouldn't be of much use to me. My DeRosa and Gios are the only two I hesitated in triplizing, and the DeRosa is a repaint so I did it anyway. So far I've kept the Gios pure, but I'm pretty certain it's racing days are long gone, even if I found a fast rider for it.
I have a mercier 300 that is a frankenbike and I'm seriously thinking of going 650b on it and running some wide ranging gearing.
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Hey, if a 760 isnt going to be restored, convert it. But by all means ride it.
#50
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I saw that frame & fork when it was posted (not my size). I don't think it lasts that long at that price if posted on eBay. It is very nice and a great color.