Converting From 26" to 650b

By Nicholas Carman

Less than a week working at VO and I already wanted to taste the 650b nectar. I have been riding larger tires for quite some time, but while touring the tires I ride weigh more than some modern racing frames and I have come to realize that at some point in tire size, bigger is not necessarily better. Having settled into town, I opted for a lighter, faster tire; something that would race around town a bit, then take me out to the country with greater ease and enjoyment. The list is short for quality, medium volume tires that would fit my 1985 Schwinn High Sierra or my girlfriend‘s Surly LHT; both are 26” bikes with drops and touring equipment. I saddled up on a pair of 38mm Panaracer T-Serv tires, and was immediately underwhelmed by the ride of small wheels and smaller tires.

The workshop at VO is full of treasures, and I found a pair of space-age cantilever brakes (the next version of the Grand Cru) that I wanted to test. Upon mounting them, I realized that they had a lot of vertical adjustment…some quick calculations and a few minutes later there was a 650b wheel mounted in my frame with the brakes adjusted at the top of their range. The thought of finally riding high-quality, larger volume tires seemed heaven-sent. Road bikes have many high quality tires to choose from, although they are mostly too narrow for my needs. My mountain bike frame is happy with many tough, long-wearing road touring/commuting tires, but the ride quality of even the best options is a bit uninspired. The magic of 650b, I realized was the option to ride lightweight, high-quality tires with reasonable air volume like the Pacenti Neo-Moto  without undersized or oversized wheel dimensions. In short, I didn’t have to choose anymore-- I could ride nice, big tires. I mounted a pair of Pacenti Pari-Moto tires and was immediately hooked. The volume of the tire, the supple casing, and lightweight (less than 300g) made for the most lively ride I’ve ever experienced. With the 650b Pari-Moto, my wheel is the same size as my previous touring wheel, thus, the bike handled in a more familiar way than it did with the undersized Panaracer T-serv tires.

In an effort to deshroud the mystery of wheel/tire size, I calculated that the 26 x 1.75 (653mm…650!) wheel I had been riding had nearly the same nominal outside diameter as the most common 650b tire sizes (38/650b results in a 660mm wheel). I had been riding this wheel size all along, only the details of rim and tire size had changed. This approximate dimension is also shared by narrow high pressure road tires, whose outside dimension with 700c/23mm tires is 668mm.. The discussion of ideal wheel sizes is overstated I discovered, as they are all nearly the same. It is by selection of a tire size to suit your riding needs that a specific rim dimension becomes relevant.

If you wish to ride tires under 32mm, 700c works well as there as more than a few tires to choose from.  For tires over 42mm, 26” is a good place to be.  But if you want the dreamy, quick and comfortable ride on high quality, larger volume tires between 32-42mm, 650b is where it’s at.

26“ to 650b conversion details: Most classic mountain bikes and some popular modern offerings such as the Surly LHT (26”) have adequate clearance for all of the smooth tread 650b tires. A 650b/38mm wheel actually suits the dimensions of the LHT better than a narrow 26”/32-38mm wheel, which leaves gaping clearances and unfamiliar handling. Conversion simply relies on a brake with 12.5 mm of vertical adjustability (half the 25mm difference between 559 and 584). We have already identified that Tektro CR720 brakes work at the top of their range, as did a prototype Grand Cru brake hanging out in our shop. Of course there are a few v-brake designs that have been around since the 90’s with loads of vertical adjustment as well.

A little about Nicholas,

Since diving into bike touring three years ago, Lael and I have toured around much of the US, including trips on both coasts (three times on the west coast). Three months in France early last spring allowed us ample time to travel the countryside, from our home in St. Malo, Brittany to Chamonix-Mt. Blanc and back, among many shorter regional trips. This past winter we biked south from Seattle and down the Baja Peninsula, then sailed to the mainland and rode into the Sierra Madre to the Copper Canyon. We have lived and worked seasonally in St. Malo, FR, Denali, AK and finally in Key West, FL where we worked as pedicab drivers for several months to escape the northern winter.