Shinkers

So in the spirit of making my bike a bit more dirt friendly, I'm looking into building some 650b wheels for it.

I still need to check clearance for larger tires and all that, but so far the biggest obstacle to overcome appears to be brakes with enough reach.

My current brakes have about 45mm reach. Sheldon brown says to add 19mm to that which gives me 64mm. Tektro R559's look like they have enough reach.

As long as tires fit and brakes reach, is that all there is to it?

Thanks.

JT1973

hi,

That is about it. Bottom bracket drop is another consideration. But if you're running 170 cranks and the bike was designed with 23-28mm tires, it's probably not an issue. Things will become much clearer with a 650b wheelset built up. I'd say you might want to crimp chain stays while frame is naked, but you know more about your clearances than me. Finding clearance for 38mm is easier than 40-42, btw.

If you're looking for brakes, I've got some near mint dura-ace center-pulls (1973) that have 68 mm reach according to velobase. They worked well for me with some modern tektro levers. Let me know if you're interested in a trade of brake set plus cash for wheel-set you're selling. I can't PM. leifeckstrom at Google dot com.

Good luck!

gugie 

Correct.

700c diameter = 622mm
650b diameter = 584mm
diameter difference = 38mm
brake reach difference is diameter/2 (the radius) = 19mm

If you're maxed out on reach with 700c with 45mm, then 64mm reach is what you'd need

Tektro reach is stated between 55-73mm, so you'd be right in the middle. They're a very good brake to boot. That's why they're "value" brake for 650b conversions, you can get a set for about $50 online.

The one drawback would be using fenders. If you're using a really wide tire, say a 42mm, and you have proper width fenders on them, sidepulls generally will hit an unmodified fender when you squeeze them. Centerpulls and cantilevers won't - centerpulls pivot right near the edge of the fenders, cantilevers below.

I stated in an earlier post that one would do well to decide on the tire first, and build the bike around it. I'd say tires first, fenders yes or no as your second choice, then build.

What bike are you thinking about converting? Pics? My litmus test for 650b conversion is chainstay length. Having done several, this seems to be the key. Longer (chainstays) = fatter (tires) on vintage steel frames.

Shinkers

Thanks both of you for the very helpful info.

Gugie, embarrassingly, the bike is an aluminum 88 Trek 1200. Probably not the best candidate for something like this, but I love the bike. It's a bit racier frame and will only fit 25c tires as 700c, which is why I'm considering 650b after seeing a few bikes like that on here.

Chainstays are 41.5cm long. I went out and checked to see what I think will fit, and at the chainstays (where it's tightest) it looks like the biggest that would go in there is about 35mm. Everywhere else there's plenty of clearance. So I'm figuring that if 650bx42c tires would be the rough equivalent to 700cx25c, I'd get at least 7mm of BB drop. To help with that I could go to 170mm cranks vs. the 175's I'm running now.

However I'm not sure if that would mess with geometry enough to be problematic. I'm also not sure if I'd be gaining enough to justify the cost I'll be looking at.

At least I have no plans to run fenders ever.

JT, if I do decide to go this route I'll let you know on the brakes, thanks for the offer.

Edit: I now see that 38c is about as small as these come. Well, that was fun while it lasted...

tcs

I went EA3 instead of 650B, but Tektro R559s did the trick. In polished finish they're quite nice looking modern brakes, too. (I had a choice of some long legged, rather more C&V 'Schwinn Approved' center pulls out of my big ol' box of parts, and knew from experience that with Kool Stop Salmons and quality cable and housing, they would have done the job.) My bike sits down some mm's, but since I don't use it to race criteriums or cyclocross, I've actually come to prefer the lower stance. YMMV

ThermionicScott 

There are several 650B tires available in 32-35mm widths. I wouldn't give up on the idea yet.

Shinkers

Scott, I see two at compass and that's all I've managed to find.

I went out and double checked and in reality could probably fit the 38 but man would it be tight.

It's so damn hard to say without the actual wheels though, everything I'm measuring is half speculation using a 38mm template I cut out of some paper.

rando_couche

If you can find a set, MAFAC Raids are outstanding brakes. In addition to having the necessary reach for a 650b conversion, they're designed for wide tires so you can remove and install your wheels with much less drama that with more generic long-reach centerpulls.

SP
OC, OR

ThermionicScott 

The Soma Xpress and Panaracer Col de la Vie measure a little under their labelled 38mm -- something like 35mm in the case of the former, and 36-37mm in my experience for the latter. And man, a good 32mm tire beats riding a high-pressure 25mm any day for me.

I don't have a lot of clearance around the Pacenti Pari-Motos on my bike, but the ride is pretty nice. I just spin the rear wheel every so often to ensure that it's straight in the horizontal dropouts and nothing is rubbing.

Shinkers

Okay thanks Scott.

I just went out and measured my bb height to and got 285ish to the center of the spindle which at least seems pretty high.

Found a link that said the widest portion of a 650b tire should occur at 320mm from the axle center. At that point I'm definitely 38 or 40 at the chain stays.

Sir_Name 

Panaracer Nifty Swiftys measure 650b X ~34mm on 23mm wide rims and you should be able to find Michelin Wild Run'r in 27.5" X 1.4" (equivalent to 650b X 35.6mm).

Shinkers

Do any of you guys think bb drop would really be a concern even going with a smaller 650b size like 32 or 34?

Thanks a ton for the help.

I'm almost convinced to just try it.

Edit: what the hell, I'm gonna do it. With some down time coming up due to some surgery this is a good time.

I'm gonna build the wheels and look at how they sit in the frame before I get tires.

nlerner

I'm also in the midst of converting a road bike to 650B. I have good clearance for 38mm tires plus fenders, BB drop isn't an issue, and for brakes I'll be running old Weinmann/Dia Compe 750 center pulls. They're much more readily available and a small fraction of the price than MAFAC Raids. And they have up to 75mm of reach.

Shinkers

Cool. I'm excited to get some tire than 25c. It will hopefully make my favorite bike that much more versatile.

I think for the time being I'm going to have to think on the brakes. I've never used centerpulls...

TenGrainBread 

Worst comes to worst you the stuff you get doesn't fit and you can get another frame that works with it 😃

Shinkers

I figured I could sell the wheels but I like your idea better...

Sir_Name 

Not sure if you've seen this link yet, but it gives good general guidelines.

650B Conversion Guidlines

There's a shot of a much more recent Trek 1200 conversion toward the end of the page. That one doesn't look like it has much in common with your '88 other than the name, but you might still find it interesting.

Shinkers

I did read that article but totally missed the 1200 at the end because it looks much newer than mine. Thanks for pointing that out!

Shinkers

Got my soma weymouths today. Should have wheels built tomorrow and can finally see what size of tire I can actually fit.

gugie 

Show us some pics!

catgita

285mm is a typical modern high bottom bracket. My bike designed from the ground up for 650b has a BB at 265mm, which was pretty standard 30 years ago. Unless you plan on racing criteriums, that is plenty of ground clearance.

Shinkers

Sadly no pics today. Got the wheels built only to fine my spokes are all a single mm too short.

Sooo... while I wait for spokes to arrive (no bike shop in town carries enough for an entire wheel build, weird right?) this project is back on hold. Sure I could get my brakes set up or something but right now I'm too pissed to even look at the bike.

I was able to check clearance and I have an honest 40-42mm everywhere. So I'll be going with something in the 35mm range (probably the Soma's or Michelin's).

ThermionicScott 

As in, you can still see a little thread when they're tensioned up? Bummer.

Shinkers

Just bought the Soma Xpress's because they seem to be one of the few with puncture protection. Let's hope they actually do measure out closer to 35mm...

Shinkers

Finally got spokes. It's amazing how much better wheels build up with the proper spoke length.

Also mounted the Soma's and they do just barely fit.

Only hiccup so far was a loose freehub I didn't realize until I was dialing in my hub bearings. Ended up having to take my hub apart after mounting the tire already and got black grease spots all over the tan walls.

I cleaned a side off with rubbing alcohol but stopped after I thought I remembered reading somewhere that it will dry tires out. Is that really true?