Blog

Originally published January 4, 2007

Last week we introduced the 650B wheeled bicycle, and provided a brief overview on the background for this wheel format. In this week's installment of the 650Blog we're going to discuss the conversion of modern production bicycles to 650B. There's a lot happening in the world of 650B bikes right now, and I'll try to bring you up to speed quickly, so this article will have a lot of information.

A 650B converted bike, or 650B-Enabled(tm) bikes, as I like to call them, will "enable" the rider to explore places where narrow 700C tires are not suitable or comfortable to ride. And there is virtually no penalty for riding these 650B machines to those rough roads, dirt roads, and paths, unlike the experience of riding a mountain bike with big tires over 20 miles of smooth pavement to get to that dirt road adventure.

Even the cyclocross bike is not as well suited or as comfortable in this use. And most riders will find that the 650x38B wheels are just as fast, or perhaps even faster than 700C wheels fitted with cyclocross tires. Again, this is because a big 650B tire and wheel is about the same diameter as a 19mm tire on a 700C wheel. The mass of the rim, tire bead, and spoke nipples is closer to the axle, where it is easier to accelerate, and the tire is filled with a cushion of air inflated to a mere 45-50psi. And so it is just the tread of the 650B tire which is out there at about the same radius as the 700C tire tread.

As you will recall from last week, the 650B rim has a bead seat diameter (BSD) of 584mm. In comparison, the 700C wheel has a BSD of 622mm. This means that a 650B rim is 19mm smaller in radius than a 700C wheel. The idea behind a 650B conversion is to fit a slightly smaller wheel into a 700C bike, which allows the use of a lightweight, high volume tire, and that still leaves enough room for practical fenders. The 650B converted bicycle will sit about 8mm-10mm lower to the ground, and retain the handling characteristics and most of the acceleration and speed of the 700C configuration, while gaining considerable versatility and comfort for use on a variety of paved and unpaved surfaces. This improvement in ride comfort and in versatility is very significant, and it cannot be similarly achieved by fitting the 700C wheels with 38mm tires. Most bikes have no room for such large 700C tires, and those that will fit them will demonstrate a marked reduction in the areas of acceleration and handling quality.

In the past, most of the bikes which we converted to 650B wheels were older, steel-framed racing and sport touring bikes. We changed the brakes in order to span the additional 19mm distance to the 650B rim, and we typically used 75mm reach centerpull caliper brakes because these were the best option available to us at the time. There were some other unique brakes used on occasion, and we may identify some of them in a future 650Blog installment. But for the most part we used centerpull brakes. And we needed to fit cable hangers and straddle wires for these centerpull calipers, which made the installation more complex. But now there are new braking options for 650B converters. And these new brakes have made it possible for us to convert a whole new generation of high performance bicycles to 650B.

The modern disc brakes found on certain cyclocross, touring, and urban bicycles are not affected by the diameter of the rim. So, it is possible to convert some of these bicycles to 650B simply by substituting an appropriate 650B disc brake wheelset. Many of these bikes have high bottom brackets and generous tire and fender clearances to begin with, and so the 650x38B wheel is complimentary for these bicycles. With disc brakes, a 650B/700C bike can be a true convertible, switching from one format to another with a simple wheel swap. This is tremendous flexibility.

And there is a new long-reach caliper brake. Just recently, Tektro introduced the R-556 caliper brake. This brake, also marketed as the Rivendell "Silver" caliper, is a modern 73mm reach dual-pivot caliper brake. It's a high quality, lightweight caliper with strong, progressive stopping power. The brake geometry is designed for use with standard drop-bar levers, including STI and Ergo variants. The quick release lever opens the caliper wide enough to clear an inflated 38mm tire when the wheels are removed from the bike. The width and shape of the brake arch is generous enough to fit a 45mm fender. The brake pads utilize refillable inserts, and there are salmon compound and dual compound inserts available to tailor the braking response further. This is a fantastic new option for 650B conversions!

These new braking products are suitable for use on modern implementations of 650B bikes. And that's what this week's examples are all about. The same qualities that make 650B wheels attractive in vintage steel bicycles are equally desirable, and perhaps even more appropriate in modern bicycles. The ride quality of the big tires will smooth-out the harshest riding aluminum frames, and allow the accurate steering response of threadless steerers and integrated headsets to be used to full advantage in rough conditions riding. The all-roads versatility of the 650x38B wheels is well served by modern drivetrain and pedaling systems. Modern bicycles and 650B wheels are a good match. And even though the manufacturers do not offer complete 650B production bicycles this year, the pieces are now available to create them quite easily.

As a prototype effort, this Fall I acquired a New-Old-Stock 2005 Trek 1200c frameset which had been stripped and parted out. The frame and fork has the necessary clearance for 650x38B tires, and there are fender eyelets front and rear. This machine was rebuilt with a 650B wheelset and the componentry shown for a quick and easy evaluation of 650B wheels in a modern, compact geometry aluminum frame with carbon fiber fork. The resulting bicycle is a successful example of a modern implementation of a 650B wheeled bike. But it's a discontinued model, and essentially a one of a kind conversion.

The goal was to identify current production models suitable for 650B conversion with standard components, and to prove them, assembling production-quality 650B machines which could be duplicated by anyone on a nationwide basis. Enter the 2007 Trek Pilot 2.1.

The 2007 Trek Pilot 2.1 is a modern, high-performance sport bike with Trek's "Tour Winning" geometry. The heart of the machine is an aluminum, compact geometry frame with carbon fiber seatstays and a carbon fork. The frame employs an integrated headset and a 1-1/8 inch threadless steerer tube for direct and accurate steering response. It was designed with a comfortable rider position and the provision to fit larger tires and fenders. The frame and fork have the clearance necessary for 38mm 650B tires, and the brake reach is within the 73mm range of the new Tektro R-556 caliper. The bottom bracket height is within the acceptable range for 650B conversion using the 38mm tires. It's an ideal candidate for 650B conversion!

The 2007 Trek Pilot 2.1 that you see on these pages was converted to 650B in a matter of minutes. There were no modifications whatsoever required to the bicycle to fit the 650x38B wheelset. We swapped the wheels and brake calipers, installed the SKS P-45 fenders, and the bike was ready to ride. We can easily restore the stock wheels and calipers for use on smooth roads and fast rides with the Saturday morning "A" group. But this bike is so much fun, and so versatile that we're leaving it in the 650B configuration.

This converted Trek Pilot behaves like a new-era 650B bicycle. The rigid aluminum frame with the carbon stays and fork efficiently transfer the rider's pedaling energy into the rear wheel. The comfort, handling, and stability of this bike on 650B wheels is extraordinary. The bike tracks straight and true over some of the worst road conditions imaginable, and it can be ridden hands-free on loose or hard-packed surfaces at almost any speed. This machine has been tested on cobblestones, broken pavement, loose gravel shoulders, and paths, and the bike is comfortable, highly maneuverable and very stable on all of these surfaces, while it retains the sharp handling and most of the speed that it exhibits on smooth surfaces with 700C wheels. Yes, the bike is still very fast! The 30 speed STI drivetrain is well matched to the expanded capabilities of the machine on 650x38B wheels. And the plush ride of those big tires totally eliminates any road buzz or vibrations that may have been noticeable on the 700C setup. It's a complimentary setup, and it looks, rides, and performs like a production level 650B sport bike. It's a modern, high-performance 650B machine, and it can be easily duplicated by anyone, anywhere, using the same components.

This is a quantum leap for 650B wheeled bicycles, and it is causing a great deal of excitement within the community of 650B enthusiasts. We are thinking about 650B bicycles differently now. Yes, they are still the "Country Bikes" that we've come to know and love. They are still the smooth, comfortable, and capable machines that we enjoy on long relaxed rides on quiet backroads and dirt roads. But this 650B Trek and other modern 650B-Enabled(tm) machines are high-tech, too. They are versatile, they are comfortable, they are fast, and they utilize the advances in design, materials, drivetrain and braking technologies of the last two decades. These are production bikes which have been enhanced with a simple wheel and brake upgrade. We don't need to wait for the bicycle companies to offer 650B wheeled bikes with these qualities, we can convert modern bikes which already have them. And furthermore, since there are no permanent modifications required to fit the 650B wheels there is no risk in doing these conversions. The bikes can be restored to their 700C configurations just as easily.

This 2007 Trek Pilot 650B conversion is one of a series of modern production bikes that we're working to identify and prove for 650B conversion. There are other models from other manufacturers which we will be highlighting in future installments of the 650Blog. Amongst them will be at least one disc brake machine.

The market is offering us new, high quality 650B-specific production framesets, too. Next time, we'll review the Kogswell P/R, a modern, steel, limited-production 650B frameset package with an intelligent design that allows the finished bicycle to be configured with various drivetrain systems, carrying capabilities, and rider controls for a wide variety of applications.

Watch this space for the next installment of The 650Blog.

Thanks for reading along,

Ed 650Braley