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 

[MENTION=455882]Bianchi84[/MENTION], 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…

steine13

>> You have the dreaded shimmy! Most of my large, flexy frames have it, including my 710.

I'm not disputing this, but I do not believe it's the flex in the frame that causes the shimmy, I believe it's the geometry. It's a bit like disturbing a spinning top, and the question is whether the motion gets damped out or doesn't. Nothing obvious about resonances.

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

Well, let's hope nobody asks for their money back..


I do think that a fender installation discussion is very much on point for a 650b conversion thread. I appreciate the suggestions and examples posted, and I've been riding fully fendered for a couple, three weeks now. The P-clamp-and-cork advice was helpful, and maybe it's time for some pictures of the bike as it sits now.

I was able to keep the front rack. I love the front rack. Such a goofy design, and very much of its time. I don't see anyone designing another in this style. For my cantlever-brake bikes, I'm on the lookout for one or two Nitto M12 racks, but those are sold out at all the usual outlets.

The bottom bracket height is 267 mm, and that's before my considerable weight squishes the tires. I scraped a few times early on but have adjusted. I think. I hope. Yesterday I put on thin Black Ops pedals. Every millimeter helps. I considered mounting SPD pedals but I've been fine with these, and the next long ride will be a flat 200k with the Detroit Randonneurs, Audax style, next Saturday. That's almost cheating, especially if the lovely weather forecast holds.






This is from last weekend, where I made sure I had enough capacity to score some farm-fresh eggs.
Like the man said: Thy god is thy belly.






Nobody said anything about rattles. We hates rattles. And the way these Honjos are designed, they couldn't help but rattle, what with the sub-mm gap between the fender stays and the edge of the 45 mm fenders. I found some double-sided automotive molding tape in the basement. Sparingly applied, it's hard to see as well as effective.



This bike is now OK to ride, if not quite finished. I need to order add-on barrel adjusters in order to get the STI dialed in; for now I'm Ok with friction shifting. And the rear fender stays need trimming. The Technomic could be a cm or two longer -- it's a 60 -- and it creaks a little, which I hope to get fixed this week with a little thick oil.After the brevet I'll know more.

cheers -mathias

mountaindave 

Those are some nice fender lines - she's a beaut!

There have been dissertations on shimmy or speed wobble probably since before I was born. I don't think we'll ever definitively settle it, my readings and experience tell me frame material also influences shimmy. It's all about resonance and material choice will influence that.

TedTown

You've summed it up nicely. I just turned 68, still have a thing for lugged steel bikes but lost my taste for skinny tires long ago. Hence my weekend purchase: an early to mid-70s Motobecane Grand Jubile. The previous owner brazed on cantilever posts and set the rear dropouts to 130mm.

It was cantilevers that swayed my decision. I was concerned about flex with long-reach Tektros, and my experience with brakes that would reach - MAFAC Racers - taught me that racers love them because they don't slow you down at all.

ehcoplex 

But..... are the canti posts positioned for 650b rims?

non-fixie 

A while back I bought a cheap set of 650B wheels. It ended up om my resto-modded Halfords Sport, which was originally equipped with 700C. The result wasn't as awkward-looking as I'd feared.

TedTown

The seller assured me they were. He had swapped out the wheels and drive train to an old Raleigh he'd converted to to 650b, said it was not as nimble as the Motobecane, but went through the rough stuff easier.

It will be a while before I can find out for sure, seeing as I have no wheels yet. Worst case scenario, if things don't line up I'll just have to run 700c rims.

52telecaster

Beautiful, what wheels did you get?

noglider 

non-fixie that's gorgeous.

Long reach Tektros work great for me. I guess they use a stiffer alloy than the older calipers because Weinmann 750s definitely are not ideal.

TedTown

You must either be extremely anxious or have super high standards, or both, because nothing about that bike is remotely awkward-looking.

non-fixie 

Thanks! Fun to build and - somewhat surprisingly, given the department store frame and wheels - fun to ride as well.

I got these wheels. Made to keep all those old French bikes on the road without breaking the bank.

non-fixie 

My initial worries were based on having seen large bikes with 650B wheels before, and their proportions just didn't look right. And this is a 25" frame after all. But it has a relatively short head tube, which apparently makes a big difference.

52telecaster

It's really lovely. Those are definitely inexpensive wheels!

ehcoplex 

I’m not sure why exactly, but it also seems like fenders help with the proportions/aesthetics. I ran my 25” Raleigh Comp GS 650b conversion without fenders for a bit, & while the look didn’t bother me, it all seemed more ‘right’ when I finally got around to putting the fenders on.

Wharf Rat

I don’t think I’ve posted my miyata 710 conversion, 82’ maybe. It’s my commuter and I put plenty of miles on it. I had a Miyata 610 that I loved, but I really enjoyed the ride of this more. So I converted it to 650b and sold the 610. I wasn’t disappointed with the conversion in the least.

bulgie 

Well done, smartly set up.

I too am a fan of the Mounttech front derailer, and the Shimano "Fingertip" shifters (if my eyes don't deceive me). Comfy bars & brake levers, saddle, and Pacenti tires that are like fluffy clouds, makes me wanna go for a ride.

The weight-weenie in me wants you to shorten those fender stays, but I know that's a silly thing to fixate on, and maybe the extra length is even a safety feature? I dunno.

Also that bike deserves a nicer-looking saddle bag. Acorn, Swift, Ruthworks, Waxwing or...? But I know I get too "precious" about bags on bikes, and yours gets the job done.

Wharf Rat

Thanks Bulgie. Spot on with the shifters. They’re great, the springs are good and they really do lighten up the action. I think the mountech FD came from a trek 520 doner. It’s been on there for years and has not given me an once of trouble. I run a half step double, I’m on the Jersey shore and it’s flat as a pancake here. We have wind and bridges and wind. That FD handles it perfectly. The rest of the parts were slowly upgraded to what you see. It rides like a dream, I’m a card carrying member of the Miyata cult.

I laugh about the fender stay comment. I cut one stay. I think the front nds and never got around to the others. I recently put a stiffener in the bag and it’s rounder and looks much better. Not like a tea bag. I’ve got a nice pannier backpack that fits perfectly on the rear rack and carries all my stuff to work.

daywood 

I like the whole bike but those polished pedals are next level! Or is it just the way the light is hitting them? Anyway, I like ‘em.