Thursday, July 19, 2012

Bike Talk: Change from 27" to 700c rims?

Kenneth from Cyberspace writes:

I have a early 80s fuji with steel 27" rims. I'm going to change the steel rims for aluminum and plan on re-lacing the new aluminum rims to the original aluminum hubs. Is it worth changing to 700c? It looks like my brake pads have the 4mm adjustment so mechanically there shouldn't be a problem. The main reason I'd consider 700c is for the better tire size selection, I'm just wondering if there are other benefits? I plan on using the bike for around town and overnight camping. Also I don't mind sticking with 27" rims.

First off, while I do have a fondness for older steel bikes like Kenneth's Fuji, those warm thoughts do not extend to the steel rims found on some bikes of that era. Chromed steel rims were inexpensive and strong but wet weather braking was always poor. Good brakepads, like Kool Stop Salmon pads could make the braking a bit better, but one of the best things you can do to upgrade an old bike is replace the rims with aluminum alloy rims, as Kenneth is planning on doing. He'll wind up with a lighter wheel that actually is capable of stopping well in the rain.

As with most things bike related, the late Sheldon Brown has great pages that address the issues of upgrading older bikes and the mysteries of tire sizing. Sheldon explains and Kenneth clearly understands that 700C rims have a diameter that is 8 millimeters smaller than the 27" rims, so the brake pads must be moved 4 millimeters closer to the center of the wheel.

In theory, he could order a replacement 27" inch aluminum rim and reuse not only his hubs, but his spokes as well, but I think that would be a false economy. The old spokes have been stressed to the old rim and if you're going through the work and expense of rebuilding the wheel, opt for new spokes.

As Sheldon notes, "the 630 mm/27 inch size was used on most sporty bikes in the U.S. up until the early 1980s, when it was gradually replaced by the slightly smaller 622 mm size also known as 700C." While 27 inch rims are still available, as are tires, the selection of 700C tires is far, far greater. The older size exists because the U.S. was a large, non-metric market but it has been several decades since anyone has made and marketed a bicycle with 27 inch wheels (Commenters please correct me if I'm wrong on this). 

While there is a sufficient mass of old bicycles to keep the 27 inch market alive, there is really no effective demand for new tires to be made in that size. While people with a good sense of and respect for the past, folks like Grant Petersen and Jan Heine, may argue and work for the preservation of the useful wheel size of 650B, it's worth noting that neither of these gentlemen wax poetic on the virtues of 27 inch tires. Steve Miller was wrong in his lyrics. Time doesn't go slippin, slippin, slippin into the future, it slips into the past. And that is where 27 inch wheels mostly exist now. The tires and rims may not go extinct in our lifetimes, but the market for that rim size is certainly not a booming one.

And that extra 4 millimeters of clearance at the rim is a good thing. It give you more room for fitting wider tires. Or fenders. Or both. Good things. Jan Heine has all kinds of good things to say about wider tires, as do many of us who ride on less than perfect roads.

Riders who are happy with their 27 inch wheeled bikes probably don't need to rush out and rebuild their wheels. If you love your existing brakes and don't have 4 mm of travel to move the pads down, you can stick with 27 inch wheels and still find tires in the world. But if you are like Kenneth and are planning on rebuilding your wheels with new rims, go for 700C. You'll have a greater tire selection, more clearance and a more certain future.

Keep 'em rolling,

Kent "Mountain Turtle" Peterson
Issaquah WA USA

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