650b/ 700c
 

650b = 584mm
700c = 622mm

Thinking about a frame built for 700c wheels with ample tire clearance, and ignoring for a moment bottom bracket height issues, would it be feasible to use a pair of 650b wheels as a second option? I'm wondering about braking and whether a long reach caliper would be able to reach down to the 650b rim wall.

What size 700c tires are you planning to build it around?

How about using disks? NM
 

Nm

Well, probably 38+.

Certainly feasible, given the right frame. I'm almost done building a Surly Pacer (designed for 700C) with 650B wheels/tires. Got the idea here: http://www.freewebs.com/650b/the650bpacerproject.htm . Picked up a leftover model Pacer from bikeman.com for a very good price, and had the fine fellows at Trinity Bicycles www.trinitybicycles.com build me up a set of wheels using Shimano hubs & Velocity rims. The loooong reach Tektro brakes work fine with this conversion.

I've got too many bike projects going, and too little time these days(especially if I want to get ANY riding in), so I can't yet really comment on the ride. I do plan to eventually do some comparison tests swapping out the 650B & 700C wheels, but no idea when that'll be. I'm just taking my time & having fun with this project.

Brake reach needs to increase by 19mm to go from 622 to 584. Any brake that has enough reach to support a reasonably wide 700c tire is likely not going to have the additional reach to get to 650B... For example, Paul Racer centerpulls (my favorite) go from 59mm to 73mm (according to the Paul website); the Silver sidepulls go from 55 to 73 (according to Riv). Neither of those would support both 650B and 700C.

If you really want to swap wheel sizes without swapping out brakes, I think discs are your only choice...

You could design a bike for short-reach brakes and relatively narrow 700C tires, with the option to change the brakes and use wide 650Bs. I think I'd rather have two bikes!

Dave

Yes, discs look a good way to go. I especially like the design of the Serotta elongated disc dropouts - visually obtrusive, but in an appealing sort of a way. Not to everyones taste though I'm sure.

650b would lower the frame a little to give extra tt clearance for off road rough stuff. I was thinking of having a second/ alternate braking option on the frame though as I doubt the idea of discs for the road. Or, pop in a road fork with calipers for the asphalt (?).

I'll be going 135mm for the Rohloff 'option'.

38mm tires probably are too high volume to allow the switch to 650B if you use modern medium/long reach calipers but older centerpulls should work. Search the files at http://search.bikelist.org or post your question on the Boblist or 650B forums. There a quite a few people on The Boblist who are converting older 700c frames to 650B and someone there should be able to answer you question.

...and Paul's Motolite brakes? They seem to have ample vertical range. In this config I would be using a Rohloff and straight bars.

But isn't this range going in the wrong direction? It MIGHT work if you're starting with a frame made for 650B and wanted to substitute a 700C wheel. This is similar to what some people use Paul's MotoBMX brakes for (using a 700C wheel in place of a 26" MTB wheel). I don't think canti frames are generally a good fit for 650B conversion (if ever?).

dauwhe now has me thinking about my Pacer project. I was most concerned about the brakes being long enough to reach down to the 650B rim, which the Tektro (R556's, IIRC) do. But I hadn't thought about them having enough range to acommodate seamlessly swapping in a 700C wheel. Hmmmm, I'll have to quickly test this out tonight. This frame is already designed for "standard reach" brakes anyway, so with 650B rims the brakes are at the bottom of the slot. So, maybe I'll get lucky.

As an aside, when I took a quick look at Paul's website I noticed the cross pass-through levers are no longer on the menu. Are these just seasonal, or has he discontinued them? The E-lever is kinda cool, but I liked his version of the cross levers better than any others I've seen/felt.

Lots of things might be possible that I don't know about. But the most common scenario has been to convert a 'racy' 700c bike (with shortish brake reach and a high bottom bracket) to 650B (with very long reach brakes).

I'm not aware of people going back and forth... I know the titanium Tournesol reviewed in BQ a while back was designed to be able to switch, but it had disc brakes. If you're willing to swap brakes back and forth, more things are likely to work. Ed Braley has converted recent Trek Pilots from 700c to 650B; just swaps in the wheels and Silver sidepulls, and that's it.

Might be worth asking some questions on the 650B list:

http://www.bikelist.org/mailman/listinfo/650b

Dave

When Steve H posted this:

[QUOTE=Steve Hampsten]...Bob, elsewhere Douglas has postulated that frames over 60 or 61cm tall start looking pretty funky when built around 650B - the head tubes get mighty long. Sure it can be done, but it can probably be done just as well in 700c X 37mm and your rims will be lighter.../QUOTE]


http://forums.thepaceline.net/showpo...0&postcount=20

I always wondered why 650b was necessary in a bigger frame, let alone a smaller frame when an all rounder style bike with 700c wheels seems to be equal to the task.

For me, it's all about the tires. In the 25mm to 30mm range, there are lots of good 700c tires. 650B is great for the 32mm to 37mm range. The Trimline and Grand Bois are great; and I'm hoping there will be an equally-good replacement for the Trimline.

I wouldn't use the same bike for both these size ranges, as I imagine there would be significant compromises in handling. I doubt that a single 700C bike would be well suited for both 25mm and 37mm tires, although it's certainly possible to set it up.

Dave

I tend to agree with 93legendti. While tire selections might be somewhat different, there are enough offerings in a 700 tire that I just don't see the advantage of 650b other than it's a smaller wheel with less rotational inertia (if that means anything on a country type bike).

Does a Grand Bois 32 in 650b ride significantly different/better than a Grand Bois 30 in 700?

No, but there's nothing like the Trimline in 700C. I won't claim there's any mysterious advantage to the size, but something about 650B just feels and looks right to me. For an "all-surfaces" bike, 650B x 37mm seems to hit the sweet spot. I like the proportions, I like the history, and I like that I'm familiar with almost every 650B tire on the market. It's a lot easier than choosing from hundreds of 700C tires :)

Dave, happy to have choices...

Now that there are plenty of rims and easy access to tires, 650B is no longer difficult to access even if it remains esoteric and virtually unknown in bike shops whose experience and memories don't extend in these directions. I think Dave's nailed it pretty well here: as tires get wider, 650B becomes an excellent choice. I rarely ride a tire narrower than a Michelin ProRace 25c because I the advantages are obvious and the putative disadvantages just don't obtain to my riding or preferences. I never get dropped because of my tires. I would go so far as to say that the selection of 650B in wider sizes is far, far better than in 700c if only because the vast majority of 700c tires are just overbuilt, too thick, as if the tire makers can't imagine what we are really doing going fast(ish) on fat tires. I like Rivendell RT/RP, Gran Bois Cypres, IRCs (that Mike Barry has available) and Michelin Dyanmics, particularly.

I think that the handling differences that arise from changing tire sizes are easy adjustments. The "pneumatic trail" notion doesn't correspond to my experience (like "planing" I can't say I experience it though I can see the logic, I think it makes little difference).

650B gives us (back---it's been around a long, long time) a different sense of cycling. It's not so much a tire size or an advantage but rather a style that presents another option. Folks think that bikes with fenders and fat tires are slow or heavy. I think of them as just as fast as any other bike I ride (because it's mostly dependent on me) and only a few pounds heavier than my lightest bike (so, so what). Ride what you like! But remember that there's more than one sort of great bike for the road, more than race bikes, more than one kind of fit, design, and cycling experience.

dbrk

Certainly. Another way of looking at it is, a 650B conversion. Ed Braley's converted a bunch, including current production Trek Pilots. To read more about the process, issues and critical dimensions, see the 650B web site:
http://www.freewebs.com/650b/conversions.htm

"I tend to agree with 93legendti. While tire selections might be somewhat different, there are enough offerings in a 700 tire that I just don't see the advantage of 650b other than it's a smaller wheel with less rotational inertia (if that means anything on a country type bike)..."



As far as the need for a 650b bike, between dirt's magnificent Kirk Montana Road Bike:

http://forums.thepaceline.net/showth...0&page=1&pp=15
http://forums.thepaceline.net/showthread.php?t=11148
http://forums.thepaceline.net/showthread.php?t=11167,


and dbrk's comments about fast riding and 23c tires,

http://forums.thepaceline.net/showpo...59&postcount=1

I became convinced it was a solution that wasn't needed for me.

I have 700 x 32c tires on my '00 Serotta Rapid Tour and it is as comfortable and versatile a bike as any I would ever need. Winter riding, trail riding or group riding, this bike is a real workhorse.

Fat 700s
 

I've only ridden a handful of miles on Trimlines, so I won't claim to be an expert on them.

However, I have ridden many thousands on 700x38 Schwalbe Marathon Racers and they have proven themselves to be rather nice. They roll well, are a joy to corner hard on and soak up the roughest of roads with consummate ease. I would consider them to be very close to a 700C Trimline.

-- John

My question is how long are you planning on ignoring the bottom bracket height issue? Using tires of similar girth on both sets of wheels would result in up to a 2 cm difference in bottom bracket height. That's a more significant design consideration in my mind than the ability to use two different wheel sizes.

I guess for my purposes (Surly Pacer conversion), I'm not ignoring it. Or rather, I'm not concerned with it because I do not intend to swap between the two wheel/tire combinations that you cite. My intentions were to swap between a 700C wheel with a typical 23-25 tire to a 650B wheel w/ a 38mm Panaracer tire, both of which would have similar diameters at the outside of the tire. So, no issue, right?

I'm coming late to the party here, but I think I can add something to the chat.

I was the one who originally suggested using the Surly Pacer as a new stock production frameset for 650B conversions almost 3 years ago, and several people have done just that since then. It's inexpensive, and it works just fine. Tim at Acme Bicycle sold several of them before the Bleriot was available.

The Surly Pacer that I own is one of the baby blue models from a couple of years ago. As a reference, with 700C wheels I can run short reach sidepull brakes on this frameset, which means that the brake reach is about 49mm. Putting 650B wheels on the bike will require an additional 19mm reach for a distance of 68mm. I am not aware of a caliper that spans those two end points, so you'll need to swap calipers when you swap between 700C and 650B wheels. You'd have to readjust brake pads anyway, so I don't see this as a greater inconvenience. And with the new Tektro R556 dual pivot brakes the swap would be simple. At worst you'll need to readjust the cable and install a new crimp cap. No biggie, but perhaps not a spur of the moment wheel swap before each ride.

If you use 23mm 700C tires and 650x38B tires, the difference in bottom bracket height will be about 8-10mm, 650B will sit lower. The bike will handle fine either way.

This is a good conversion, and you won't have to modify anything about the bike or the components to make it work. So try it!

BTW, send or post some pics, I'd love to see the finished machine.

And check out the 650Built Soma Speedster I just finished and wrote about on the Bikeman.com 650Blog:

http://www.bikeman.com/content/view/1183/33/

Regards,
Ed.

That's a nice write up Ed and good info. Your Soma looks super nice.