The Wheels on the Bike Go Round and Round

Last week, a coworker and I were discussing bicycle lubrication. He, like a lot of cyclists, has a nearly-obsessive love of the Park Tools company and their multitude of products, including their “Polylube” grease, a fairly thin polyurea-based lube that Park markets as not just suitable, but pretty much perfect, for every bicycle application. My take is that the stuff is too thin, and creeps too much, to be a universal lubricant the way it’s marketed.

Everything on a bike moves at about the same speed, my coworker argued. Surely that suggests a single lubricant is suitable for all the various bits?

The same speed? Really? Eh, no.

The slowest-moving part on a bike is probably the headset, and this is probably an area that a thin lube like Polylube is well-suited to. (On old English three-speeds, the headsets were often just oiled, not greased.) The hub bearings on the rear wheel are probably the most loaded, seeing as they take most of the weight of the rider, and (IMO) a thicker grease is more suitable here.

But what’s the fastest-moving part on a bicycle?

My coworker thought it was the crankset, which revolves around the bottom bracket. A bottom bracket that either has really old-school cup-and-cone bearings, or – on more modern, or at least more expensive, bicycles – sealed cartridge bearings, in it.

People get really obsessive about their bottom bracket bearings, and you can spend over $100 on a new headset with sealed low-drag ceramic bearings, or close to that much on ceramic replacement bearings for your front or rear hub. Most bike nerds recommend regular servicing of these bearings, if possible. (There’s not much you can do to most sealed bearings, except replace them.)

The fastest-moving part on many if not most bicycles, though, are extremely un-glamorous, and mostly overlooked by bike nerds. They’re the jockey wheels on the rear derailleur, which – on a lot of deraileurs – rotate around a ridiculously crude, and cheap, sleeve bearing.

Don’t believe me? The math is really simple. On an old ten-speed road bike, say, the larger chainring might be 53-tooth, and the freewheel runs from 14-24 or -28 teeth. In a median, cruising-around-town gear, the chain might be on an 18-tooth rear sprocket, meaning that every time the pedals go around once, the rear wheel goes around nearly three times. (53 teeth / 18 teeth = 2.94 revolutions.)

Most older, and many newer, derailleurs (including, by the way, some seriously expensive ones from the likes of Campagnolo) have pulleys / jockey wheels with eleven teeth. This means that the derailleur wheels revolve once for every eleven links of chain that pass through – so that while (in this gear) one revolution of the cranks turns the rear wheel 2.94 revolutions, it rotates the derailleur wheels 4.8 revolutions. You’re climbing up a hill in this gear at a reasonably healthy cadence of 100bpm (i.e. 50 RPM), your rear wheel is turning at 147RPM, and your deraileur wheels are spinning at 240RPM.

Yet almost nobody cares about the hideously crude bearings on derailleur pulleys, or whether thin grease is the best way to lubricate them. (General consensus seems to be that light oil is the lube of choice for sleeve bearings.) Derailleurs aren’t sexy and exciting (though headsets are, for some reason… huh?) so the incredible crudeness of their bearings generally get overlooked. Go figure.

As to lubes, my take is that you probably want a somewhat thicker lube than Park’s mystery goop on your hub, pedal, and bottom-bracket bearings, and a light oil on the derailleur gears. What is Polylube good for? Headsets. Saddle springs. Brake and derailleur pivots, possibly. The springs on your rack, if any. Stems and seat tubes. The threads of any bolts you don’t want to rust or seize in place.

What can I say? One size rarely fits all… and the fastest-moving part on most bicycles is among the crudest and cheapest.

Published in: General | on September 8th, 2010| Comments Off on The Wheels on the Bike Go Round and Round

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