I agonized over these numbers for months before converting my older Rivendell custom to 650b. Why speculate? It's 23 mm lower to go from 630 (27") to 584 (650B) whereas it's 19mm to go from 622 (700c) to 584 (650b).
So, there's not much difference between a 27" to 650b conversion and a 700c to 650b conversion. Less than half a centimeter. Some of the distance will be made up by the larger tires, so there's that as well. Someone else said BB drop was in the lower 70s on your Trek so you're in better shape than I was with 80mm drop. Many old Treks have been converted to 650b and AFAIK most owners have been happy with them. There's pictures all over the Internet. If you are absolutely sure that a 700c x 38mm tire will fit, then 700c could be ok, but if there's any question, go 650b. I did and I have been very happy running 650b x 38mm Compass LoupLoup Pass. I'm also a really big guy and i recommend staying away from Velocity Synergy rims. Had to send one back with cracks along the spoke holes. I've had good luck with their Atlas rim so far though that they rebuilt the wheel with. On Aug 28, 2014 7:14 PM, "Chris Chen" <cc...@nougat.org> wrote: > Remember that you'll be dropping the bottom bracket quite a bit if you go > to 650b. 700 sounds like a good place to go. > > Granted, if you put FATTYS with 650b then you don't drop all that much but > you get my point. > > > On Thu, Aug 28, 2014 at 5:03 PM, cbone97 <cbon...@gmail.com> wrote: > >> So after selling my Sam (sniff sniff), I scored a 1985 Trek 420 with 27" >> wheels. It's a beautiful lugged frame that looks like it was barely ridden >> and I can't wait to get my collection of Rivy parts on it: SunRace >> thumbshifter (singular, no front der), Dirt Drop stem, fancy drilled Tektro >> levers, etc. >> >> Here's the hard part. I'm a hefty lad and need/want a fatter tire than >> the fattest 27"ers made. The Trek has a rear hub spacing of 126mm and I >> don't really want to cold set it to 130mm. At 126mm, options seem limited >> to freewheel hubs. I'm ok with that, but all the prebuilt 700c 126mm >> wheelsets have skinny rims for skinny tires. So it seems I need a custom >> rear wheel - 126mm hub with a rim that will accommodate 38-50mm tires. >> >> If I'm going to have a rear wheel built on a 126mm hub, would it be >> preferable to go 650b or 700c? Can I really get that much more air volume >> with 650b tires? My rough measurements suggest that with 700c the rear >> will fit 38mm tires. With 700c, I might? even fit a 50mm Big Ben on the >> front a and a little Ben on the rear. While 650b theoretically will allow >> a bigger tire, I'm not sure a 650b Big Ben will fit the rear, which might >> put me >> >> Assuming that the Silvers will work for either size (reach the 650b >> rims), which size might be best? I think either would be fine/ok, am I >> forgetting anything? Should I REALLY not rule out cold setting to 130mm >> and going with a freehub wheel? >> >> Thanks! >> >> -- >> You received this message because you are subscribed to the Google Groups >> "RBW Owners Bunch" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to rbw-owners-bunch+unsubscr...@googlegroups.com. >> To post to this group, send email to rbw-owners-bunch@googlegroups.com. >> Visit this group at http://groups.google.com/group/rbw-owners-bunch. >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > "I want the kind of six pack you can't drink." -- Micah > > -- > You received this message because you are subscribed to the Google Groups > "RBW Owners Bunch" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to rbw-owners-bunch+unsubscr...@googlegroups.com. > To post to this group, send email to rbw-owners-bunch@googlegroups.com. > Visit this group at http://groups.google.com/group/rbw-owners-bunch. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
