base2 

***All conversation stops, room gets quiet***

Ha! Just kidding.
The gist of it is more tire volume helps with a smoother ride over rougher terrain. Because of various geometry limitations of individual bike frame construction, the maximum tire diameter and width is restricted by some limitation. IOW bigger volume tires just won't fit in the frame. Besides, bigger tires would raise the whole bike up too high off the ground and have all sorts of knock-on effects with regard to the bikes handeling characteristics.

The solution is often smaller rims and taller tires so that the tire circumference the bike was designed around remains preserved, but the tire volume is increased.

Bianchi84

Thank you very much for the clear explanation! I think the main concerns would then be brake reach and tire availability. That's again!

gugie 

And to give you some numbers, a 650b x 42mm tire diameter is just a bit less than a 700c x 25mm tire. If you approximate the tire cross section as a circle, and remembering "pie are squared" from high school math, you get nearly 3X the air volume between you and the road. The road buzz from chip seal goes away, well packed gravel feels like asphalt, and loose gravel becomes rideable. Modern wide, light, supple tires ride very nicely compared to the heavy "balloon" tires of my youth.

ehcoplex 

LOTS of 650b tires (currently...) available, as the size has become fairly popular in the 'gravel' world. For vintage retro-fits you've got Mafac Raids, Weinmann Vainqueur (and their DC copies) and Tektro 559 brakes. Rim-brake rims are probably the real limiting factor, though Velo Orange and others produce them.

Also, as yet unmentioned, 650B conversions allow old fogies with aging/less absorptive joints to continue to ride the racy dream-bikes of their youths on disintegrating roads of our crumbling infrastructure (at least in the US....).

noglider 

@Bianchi84, when your bike has rim brakes, you usually need to change the calipers to accommodate 650b wheels. It's possible, in some conversions, to do it with no changes other than brake calipers.

bulgie 

Almost always the reason is to fit fatter tires. Bikes made for 700c and short-reach brakes are a good choice because with 650b, long-reach brakes can bolt right on to reach the rim at its new lower position.

If you don't mind the bone-jarring ride of the high-pressure tires on your bike currently, if you don't mind denting your rims on pot-holes and not being able to ride off-road much, then you have no reason to upgrade.

But for me, 32 mm tires are just too limiting, I need 38 minimum preferably 48 mm. The comfort safety and reliability improvements are huge and cost you nothing in terms of speed, if you buy high-quality supple tires.

mountaindave 

My first fender installation was on a ‘79 710. It probably took two hours per fender. And I have added a spring thing to make removing the wheel easier.

The link to the fender blog is probably the best one I’ve seen, and I’ve read Jan’s Honjo install with Peter Weigle in BQ as well.

I had to dimple the fender to get it between the fork legs. I had to simple it to snug it up to the fork. I have also used a recessed brake nut mates to the Daruma for extra clearance under the fork - it requires a bigger hole, but since you’re drilling your own anyway, not an issue. Eliminates the female connector to the Daruma and fender bolt. I used a longer brake nut one time for a bigger gap between fork and fender to maintain good lines.

wish I had photos, but I’m taking off in a plane. Check my bike links in my sig for some photos - desktop mode.

Lovely bike and great work so far!!

mountaindave 

You have the dreaded shimmy! Most of my large, flexy frames have it, including my 710. Usually it’s not an issue until descending at speed (also known as speed wobble). Riding no hands and bumping the stem laterally is the classic way to check for it - but you didn’t even need to bump the stem.

I got a roller bearing headset that dampens it so I can usually ride no handed even with a front bag, but it’s still there. I just learned to descend with a knee on the top tube. It’s not the right kind of thrilling to be bombing down a mountain on an inky black night with a rock wall on your right, a cliff on your left and only an Edelux II for light when your bike tries to buck you off. (It’s not just two teenage daughters that caused me to go gray before I’m 50!)

Boy, we thoroughly highjacked this thread like we’re a bunch of iBOB’s…