embankmentlb

I am considering the possibilities of using this GT frame made for 700d wheels to build a 650b drop bar adventure bike. I would need to keep the rear U-brake and front cantilever brakes. While replacing the drive components with some combination of modern Shimano 10 speed. possibly Tiagra shifters SL-4700, RX-400 rear mech, Tiagra crank and so forth.I would like to hear what do you folks think. It’s kind of a tank of a frame but very well made. No disc brakes. What drawbacks do you see? Any suggestions are welcome.

Thanks much!

PugRider

Awesome, make sure you post updates as you get farther along. This bike's sibling, the drop-bar-equipped Tachyon, is on my grail-ish list. Sounds like you already know that people have had good luck with the 650b conversion; I've even read threads where people have been able to fit certain 650b tires on those 700d rims. The Tachyon came with some crazy Suntour drop-bar thumb shifters, but sounds like you're starting fresh with some modern Tiagra stuff (which will work great I'm sure). The only thing I'd pay attention to is the stem situation once you do the drop conversion; not sure what exactly the geometry is but as the people in the MTB drop-bar conversion thread will tell you, you might be a little stretched out, in which case you would just get a shorter stem. Good luck!

top506

+1.
When I set a Miyata Triplecross up with drops and Brifters I went with a VERY short stem, 60mm or thereabouts.

Top

embankmentlb

My first step, parts on order, is to set up the drop bars & dirt drop stem with the existing drive setup. I want to get the fit right before spending too much $$$. Thanks for the encouragement!
I will post updates.

PugRider

I'm sure you're aware that if your new stem doesn't have a brake cable housing hole you'll have to get a hanger for the headset or the fork. Not sure if that headset is 1-inch or 1 1/8.

embankmentlb

New stem and bars with brake levers from the bin. I am still unsure about the position. Will I like the bars that high? They are just below the saddle. The next step is to get brakes hooked up so l can do some test rides.

jfsail

I just put a Specialized Crossroads 650b tire onto my daughter's GT continuum with the 700D rims. The fit seemed perfect - not too tight and not loose. It looks awesome to me as the tire has much higher volume than the original. Even though it is a much wider tire and larger diameter, it fits perfectly in the frame with lots of room left over. This tire has the advantage that the pressure can be dropped a lot if desired due to the high volume to permit riding on rough surfaces. It has a very sticky tread.
I paid only $30 per tire, I suspect it is clearance of a sort. I will post a picture of the bike with one original tire and one replaced if I can.
So, don't worry about having to change wheels or rims and no problem getting tires! And it makes the bike look like a real mountain bike!

jfsail

System rules won't let me upload photo, but was -- Perfect fit of Specialized crossroads 650b

Perfect fit mechanically, different look, very functional, modern sticky rubber, wheel NOT too wide to be stable on rim.
That is on the stock wheel, no rim change.
Sorry, I became member to post my info that the 650b works okay. I will likely not post 10 posts, so this will NOT let me put the photo up. I can also not post links, so I will just describe it after I went to the trouble of trying to upload the photo.
It is a much larger black-wall tire, looks more like a mountain bike tire and NOT retro, but looks agressive. I would strongly recommend new tires as very old rubber loses its wet "stickiness" and could be a safety issue. This is a new high quality tire, I think many 650bs will fit.
This was the cheapest that looked like it might be good and still not have knobs on the part of the surface of the tire that hits the ground when going straight and the bike is straight up (for efficiency) but has agressive looking studs of to the side.s
The tire looks capable off-road and the larger volume and width would be good for running at lower pressure for comfort. I have experience with many tire sizes, from my 1990 bianchi varsity with 700c 38mm tires to 26" mtb, to my current MTBs with are 29r x 2.6" for summer and 26" fat bike studded 4.2" and 4.6" wide for snow and ice riding.

ThermionicScott 

Welcome to the forums, jfsail ! Please do stick around and chat. 10 posts will go by quickly.

I wouldn't be surprised if Panaracer Col de la Via 650B tires also fit on those "700D" rims -- in 650A they were something of a loose fit for me.


P.S. I hope embankmentlb is doing well. Would be interested to hear news on his project.

jfsail

I wouldn't be surprised if any 650Bs would fit, but I only wanted to post about the tire I tested. I have found large variability between tires, so there may have been an element of luck. I didn't feel the need to keep the tire narrow as I don't think air-resistance is really critical to drag on this bike, and a wider tire can help in many situations.
Even on my "road bike" my 1990 bianchi varsity hybrid (cyclocross? don't know had it since new, before internet) with 700c wheels, I mounted 38mm wide tires for safety and comfort on the road. That used to be my off-road bike until I got a real mountain bike. I didn't know what a mountain bike was for in the old days, I thought "I don't go up mountains!". I also didn't talk to many off-road cyclists.
I don't have vintage bikes because I am into it, I just don't replace what works. I go to the country with my mountain bike, and if the weather is good, I drive my 1987 mustang convertible. Vintage car, vintage bike, but not because I buy vintage, but because I am vintage and I bought those things new when I was in my prime. And I am too cheap to replace things just because they are "newer and better".

jfsail

I bought my daughter's GT continuum not because it was vintage, but I found it for $100 CDN at a swap with no working rear shifter etc.. I was warned by a mechanic that there were no replacement tires available because of the size, but I thought the tires looked OK so would last long enough to justify the $100.
The derailleur seemed to move, so I chanced it. It turned out the only part I needed to make it work was a new cable! and the bike worked perfectly, but I found out a few years later when I was prepping the bike for my daughter's move away to University was that the rear hub was toast (maybe my fault for not adjusting, but by that point it was a glitter factory).
I paid to have the wheel rebuilt, but should have specified a new rim at the time. I didn't think about it. I just hoped the tires would last.
My daughter loved the sizing of the bike.
This summer, the carcass failed, so now was a safety issue. I saw someone mention 650b, so I bought it, and it fit perfectly, so I spent the time to inform the public.

jfsail

I came to post about the possibility of new tires without a wheel change, but looking in detail at your bike, I strongly suggest the higher volume tires I used if you want to go off-road. Larger tire volume at lower pressure is a complete game changer when the going gets rough. And sticky rubber won't hurt.

madpogue 

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