Normal Reach Brake 700c Frame to 650b Conversion
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Mike Godwin
Jun 21, 2021, 3:43:11 AM6/21/21
to 650b
Hi 650b folks
Mike Godwin (SLO CA), new to this list, but long time on the ibob list (20+ yrs). A question I know you guys and gals can answer.
What brakes do you use when converting a normal reach brake bike to 650b? My calcs indicate there will be 3 mm difference in brake reach between bottom of pad slot for short reach brakes (39-49) and normal reach (57 mm). Have you had good results with the Tektro 559 / Riv silver brakes? Some filing needed?
Thanks in advance
Mike "new owner of SR Semi Pro frame/fork" SLO CA
satanas
Jun 21, 2021, 10:04:01 AM6/21/21
to 650b
I'm not sure where you're getting 3mm from...
Typically short reach brakes come on bikes with 700c wheels, and the pads sit at around 45+/- on most frames. If converting to 650b, the difference in radius is (622-584)/2 = 19mm, so the required brake reach will thus be ~45+19 = 64mm.
Older bikes with 57mm brakes usually had 27" (630mm BSD) rims, which means an extra 4mm reach over 700c; (630-622)/2 = 4. Plus these brakes are most often set at around 54mm (minimum) so for 650b one might end up with say 54+4+19 = 77mm reach required; the R556 & R559 go to 73mm.
Longer than 73mm means old centerpulls, cheaper Tektro dual-pivots, filing, and/or offset brake shoes - or else braze-ons.
Measure carefully...
Later,
Stephen
David Cummings
Jun 21, 2021, 10:20:52 AM6/21/21
to 650b
Mike,
could you share a bit more info about the bike you are interested in converting?
If you have a bike built for 27", you may be able to convert to 700c and fit 38mm tires without issue. I have done this to a handful of bikes from the 70's. The trick is getting fenders in there too. Then you're likely to need centerpulls (Dia Compe 750s are still made) to fit around the tire and fender.
David in MT
David Hays
Jun 21, 2021, 10:54:40 AM6/21/21
to Mike Godwin, 650b
Mike,
I’ve successful converted two older Mercians with Dia Comp 750s and Tektro/Silver 559s without filing.
David
Buffalo, New York
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Cary Weitzman
Jun 21, 2021, 11:19:14 AM6/21/21
to 650b
Mike Godwin wrote:
> What brakes do you use when converting a normal reach brake bike to
> 650b? My calcs indicate there will be 3 mm difference in brake reach
> between bottom of pad slot for short reach brakes (39-49) and normal
> reach (57 mm). Have you had good results with the Tektro 559 / Riv
> silver brakes? Some filing needed?
Tektro 229s with pad extenders worked for me (SOMA Stanyan) although
> What brakes do you use when converting a normal reach brake bike to
> 650b? My calcs indicate there will be 3 mm difference in brake reach
> between bottom of pad slot for short reach brakes (39-49) and normal
> reach (57 mm). Have you had good results with the Tektro 559 / Riv
> silver brakes? Some filing needed?
braking was very mushy and probably wouldn't be acceptable for a lot of
people. Other people report having better experiences with the extenders.
Eventually I got the idea to try KoolStop Eagle Claw II pads tilted down
at an extreme angle, and that was far less mushy, but only worked with
new pads, once they wore a bit the brake arms got very close to the tires.
Had I not gotten a bike designed around 650b I probably would have found
a pair of the DiaCompe 750 centrepulls.
Cary
PTBO.ON.CA
Andy G
Jun 21, 2021, 11:40:06 AM6/21/21
to Mike Godwin, 650b
I used something like this (but in black) on my conversion where I needed slightly more than 73mm: https://www.ebay.com/itm/124684186813
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Mike Godwin
Jun 21, 2021, 12:19:37 PM6/21/21
to 650b
Hi folks,
Thank you all for the information and the brake reach math confirmation. I knew 3 mm did not seem correct. I thought it is 4 mm or more.
The bike is a SR Semi Pro, the only brazeons are one bottle cage set and the tab on the downtube for clamp on shifter band. Oh, and top of bb cable guides. Probably puts in the late 70s era, earliest 80s. It has 600 Arabesque shifters and FD/RD, 600 caliper normal (57mm) brakes. Looks like it originally used 630 wheels.
Shod with high flange campy hubs, 622 mm Super Champion rims, NR crankset, Super Record headset, Cinelli stem and Mod 66 bars. I figured I would sell some of the parts and recoup bucks. But, when I removed the NDS pedal, it actually pulled some threads out of the crank pedal eye. I was able to clean up the threads with a tap, but once a new pedal goes in, may be the last time it is done. The OMAS/Ofmega cartridge bb is toast. FD/RD/shifters are salvageable. Wheels are actually nice and true and round.
At this point, I think I will attempt to find some used long reach brakes before making up a new wheelset. If no brakes, no 650b wheelset. Perhaps just run the existing wheels. Need to remove the corncob Suntour Perfect freewheel and hope that it does not pull off threads from the hub shell like what happened to the NDS pedal eye.
Mike SLO CA
Mike Godwin
Jun 22, 2021, 1:43:33 PM6/22/21
to 650b
Thanks for all the comments. A Maxxis Refuse 700x40 (39.5 actual) fits on the front, need to confirm the rear triangle. No need to go to 650b unless I want to put =/- 45 mm tires on the machine.
Mike SLO CA
Michael Wong
Jun 22, 2021, 2:04:56 PM6/22/21
to Mike Godwin, 650b
Hey Mike. I highly recommend trying to find a brake from bolt adapter.
It will enable you to the maintain the mechanical advantage in your calipers. Otherwise the longer the reach the more braking power you’ll lose in your conversion.
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Michael Wong
Jun 22, 2021, 2:06:42 PM6/22/21
to Mike Godwin, 650b
PS my brother rides an SR Semi Pro (Mexican?). That bike rides really nicely,
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Mike Godwin
Jun 24, 2021, 12:57:24 AM6/24/21
to 650b
Found some DC 750s at the bike kitchen. Installed the rear brake on the SR Semi Pro, and it measured to about 11 inches from the center of the dropout to the bottom of the brake pad slot. The 750s will work for a 650b conversion, but the crimping on the chainstays is short in length with the maximum width optimized for a 27 inch wheel. There may be no tire width advantage running 650b wheels over 700c wheels without some more chainstay crimping. I'll run what I brung and see how it rides. The goal is a nice riding beater with a front rack and baskets, an easy-peasy errand bike for locking anywhere in town.
Mike SLO CA
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David Cummings
Jun 24, 2021, 4:38:58 AM6/24/21
to Mike Godwin, 650b
Pics or it didn’t happen.
David “setting is believing” in MT
David “setting is believing” in MT
David Cummings
Jun 24, 2021, 3:15:09 PM6/24/21
to Mike Godwin, 650b
Nice. Now for the finished product photos! ;)
David in MT
David in MT
Michael Wong
Jun 24, 2021, 11:14:05 PM6/24/21
to David Cummings, Mike Godwin, 650b
They these:
On Thursday, June 24, 2021, David Cummings <flath...@gmail.com> wrote:
Nice. Now for the finished product photos! ;)
David in MT
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Mike Godwin
Sep 21, 2021, 11:34:20 PM9/21/21
to 650b
Pics to show it happened, but not a 650b conversion. Don't kick me off the list!! I used the 622 Campy/Rigida wheels to try out the machine before converting it to 650b. I made a oval form from fir 2x4 and a section of plastic from a 5-gallon bucket to line the wood form. A 1/4 inch thick flat steel piece and the form were put into the bench vice at the bike co-op, with the chainstays between them. I managed to gain several mm on each side of an already indented chain stay. Rear fits 38 mm actual tires, front has room for 42-45. A demountable Wald basket up front (shipping free when ordered direct). The bike rides great and manages basket loads easily. However, my bike riding buddy checked it out and asked if he could by it for his son. Surely. So its gone and so is the 650b conversion experiment. I'm sure it would have been great!
Mike SLO CA
On Thursday, June 24, 2021 at 8:14:05 PM UTC-7 michael...@gmail.com wrote:
They these:On Thursday, June 24, 2021, David Cummings <flath...@gmail.com> wrote:Nice. Now for the finished product photos! ;)
David in MT
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