Blog

Originally Published January 1, 2009

Here's our little 650B Monster Crosser. With 650B 2.0 knobby tires on disc brake wheels, I'd say that this is pushing the envelope for 700C to 650B conversions. And all we did was swap the wheels! Really, it was just that simple - we pulled out the 700C disc brake wheelset with the 700x31 cross tires, and put in a pair of 650B wheels with the new Pacenti Quasi-Moto 2.0 tire. Yes, disc brakes are good like that!

This Salsa La Cruz has a great steel frameset, there is generous tire clearance front and rear, and the bike is designed for disk brakes. Disc brakes have several advantages; they generate tremendous stopping power, they work extremely well in wet conditions, they preserve the rim sidewall which prolongs rim life, and - for our considerations - they are not effected by variations in rim diameter. So changing from a 622mm rim to a 584mm rim does not require that we do anything at all to the brakes.

A 650B conversion utilizing disc brakes is something that we've known about for a couple of years. There have been cross bikes produced for disc brakes, and although there are fewer of them now since the UCI cyclocross rules don't allow discs in sanctioned races, many 700C urban bikes and a few cyclocross rigs are equipped with discs. When I first considered doing a 650B conversion on a disc brake 700C bike we were all using the randonneuring type tires available at the beginning of the 650B renaissance. When the Salsa La Cruz was announced I had identified it as a 650B conversion prospect. Recently I was discussing this with Wally here at Bikeman when he suggested that we try the wheels from one of the 650B Carver bikes in a shop employee's 49cm La Cruz. What you see here is the result.

Creating an aggressive 650B off-road bike wasn't in the realm of possibilities two years ago when this 650Blog began. However, things have really taken off in the 650B mountain bike space with the advent of Kirk Pacenti's new tires. And there are other 650B MTB tires being announced and developed as I write this. So now we have some other interesting tire options. And new 650B rims like this Velocity Blunt disc specific rim just make it all the more interesting.

The new Pacenti Quasi-Moto 2.0 is a 650B cross country tire that happens to have the same diameter as the stock Panaracer Cross Blaster 700x31C. This is significant, because the Salsa La Cruz has the same 280mm bottom bracket height with either wheelset installed in the bike. The wide 2.0 tires are the upper limit for what will fit in this frameset. The clearances are tight, especially between the chainstays where there is only a couple of millimeters to spare. The wheel needs to be dished correctly and spin true, and the tire must be centered on the rim, but it fits, and it's quite workable. In aggressive riding I'm sure you'd get an occasional tire rub, and it would probably be wise to apply some clear protective tape over the chainstay adjacent to the tire. But the bike has a steel frame, and although the tire might rub a little paint, the chainstays will be undamaged. 

Salsa wisely chose to build the La Cruz with 135mm rear wheel spacing. This allows the use of commonly available MTB disc brake hubs. So we built a set of 650B disc brake wheels with Deore XT six bolt disc hubs - the same hubs as the stock wheelset.

With these disc brake wheels it takes literally less than a minute to switch between 650x51B and 700x31C. You can chose the right tire for the conditions, for example, run the 700C setup for fast hardpack, or switch to the big 650B rubber for loose surfaces. The brakes are the same, the ride height is the same, and the weight is about the same.

It's an amazingly cool little 650B Quasi-Moto Monster Crosser!

Ed 650Braley