Friday, December 26, 2014

Trek 620 650B conversion

One of my projects over winter break has been to convert to my old Trek 620 to 650B wheels. For mountain bikes, I don't see any special value for 650B wheels over 26", but for road bikes, they really do open up some new possibilities. In my case, my Trek didn't have much clearance for fat tires and fenders with either 27" or 700c wheels. The smaller diameter should fix that.

The key to a good 650B conversion is... math. The 27" wheels I had lately on the Trek have a bead seat diameter of 630mm. A 650B wheel has a BSD of 584mm. Subtract those two numbers (630-584=46) and divide by two to look at the radius (46/2=23) means I need to look for a brake with 23mm more reach than the current calipers I have on there. My current brake reach is about 47mm (front) and 53mm (rear), meaning I need a brake caliper capable of 70~75mm.

I ordered up the parts earlier this month, just about doubling the initial $300 I spent on the Trek:

Did it work? I'll save you the heartache of anticipation right now, and tell you it transformed the Trek into my new favorite bike. Read on.

The wheels are the blowout ebay Pacenti PL23 rims with low level Shimano hubs, the tires are premium Compass Loup Loup pass 38mm, and the brakes are Tektro R559, 55-73mm reach. Hmm, not quite enough to reach what I calculated above. That will come into play later.

The wheels were cheap because these rims have a reputation for cracking at the spokes if overtensioned. Since I got the 36h versions, and I'm pretty easy on wheels, I'm not losing sleep over this. Aside from that, they are really lovely rims: polished, with a nicely machined surface.

The hubs are low level Shimano 2200 series. Cheap, but they do have cool machined marks on them, like a Thomson seat post, and they spin well. The rims were also pretty true on my quick check:

The tires almost cost more than the wheels:

But they were worth it for the ride they gave. Overall, I'm very satisfied with my wheels and tires, with one caveat: it was a real struggle to get the tires mounted. Using only thin strapping tape on the spoke bed, I still have to use tire levers to force the last bit of tire bead over. In the process, I pinched both my front and rear tubes, so I had to undo everything, patch the tubes, and do it all again. I hope this will get a bit easier as the tire stretches. Also, I'm using 26" tubes, which I think makes the tube a bit more likely to pinch (it's smaller, so tends to pull over to the bead when mounting the tire)

Mounting up the rear wheel, I saw I was indeed going to have a brake reach issue:

The pad is just a bit too high on the rim to clear the tire. That's easy enough to fix, if you don't mind voiding a warranty:

I had to dremel a millimeter or so off each brake arm to allow the pad to sit low enough. There's enough material left on the brake arm that I don't have any worries about my modification.

It was worth it to get this kind of clearance with a fat tire:

I put on some 700c fenders I had lying around, played with my shifting for a bit, and ended up with this:

The larger radius fenders don't quite follow the tire line perfectly, so I probably won't be winning any internet bike beauty contests. I think my shifting system would probably disqualify me anyway:

I started with the stock down tube shifters, but down tube shifters suck, especially for tall guys like me. I didn't have a spare bar end shifter, so I used this $5 thumbshifter mounted as a stem shifter. The shifter itself has all the surface quality of a cereal prize, but its internal mechanism is a copy of the wonderful-to-use Suntour power ratchet. I haven't used stem shifters since I was riding my dad's 1972 Schwinn Continental back in high school, but I'm finding I actually really like this location: easy to use, and super clean cable routing... if you don't consider the zip ties.

No front shifter, since I don't like 'em. I have 42/36 rings on my chainrings, and I'll just move the chain over manually if I ever need to downshift or use the bike for bike camping.

My handlebar is a flipped over Soma Oxford, with a rubber shim to allow the road brake levers to fit, mounted on a threadless adapter. Another kludge that works super well.

Somehow, between these non-aero (drilled out for lightness!) brake levers and Tektro brakes, I've achieved pretty good stopping power. Not V brake good, but much, much better than the brakes on my Rawland Nordavinden.

The seatpost is one of the few original parts I still have on the Trek.

(Note also more zip ties holding on my fenders. Grant Petersen, I think, would be proud (Jan Heine, not so much)).

Actually, the only original parts I still have on the Trek are the post, crank arms, bottom bracket, headset, and brake levers. It's gone from this when I bought it in January:

to this:

It's a joy to ride. The tires make it fast and comfortable. With the big sweep of the bars, I can sit anywhere from almost bolt upright to low and forward. With fenders, I can ride it in the rain. The bottom bracket is just 10.25" off the ground, but I haven't had any issues yet with pedal strikes in corners. Perhaps my narrower Grip King pedals help with that.

I've had the Trek for sale at a few points during its tenure, but this conversion has vaulted it to the top of my pecking order (which right now would be Trek, CC, Razzo, VO, ERB). If for some reason I had to radically downsize my bike fleet today, I could happily get by with the Trek and a mountain bike of some sort, though I really need to try out the Trek as a kid hauler before I make such a bold prediction.


  1. Nice conversion and informative write-up! Thanks for sharing. I'm slowly getting towards having all the needed parts for trying a conversion of my Gunnar Roadie. We'll see how that goes.

  2. Like the before and after photos. I love bikes highly customized by their riders for their own preferences. Too much cookie-cutter, herd mentality in bicycling. Put me in the Grant Petersen camp -- do what ever you need to in order to be out riding. If it's zip tied down parts and a stem shifter, that's cool factor for doing it "your way". Last week on our weekly road race training ride I saw a guy with MTB thumb shifters on the tops of his drop bars. He love them -- especially exclaiming the $15 replacement price if they get broken in a crash.

    1. Dave, thanks for the comments. I think most of bikes would be looked at askance on a group ride. Then again, I don't do group rides, so who knows?

      By the way, my Trek build has changed about three times since this post. Back to a 700c fixed gear, I just can't stay away from that:)


Clem Again

Regular reader(s) may recall that I journeyed up to Ann Arbor to buy a Rivendell Clem Smith Jr last summer. That particular bike ride didn&#...