Monday, January 20, 2014

(Really) Low Gears

A half-step plus granny triple crank. 
My first two touring/commuter bikes were set up like this 
(48-44-24) back in the days of five and six speed freewheels.
Someone left a note mentioning that I succumbed to low gears on the Long Haul Trucker, given that I replaced the 26 tooth granny with a 24, which is as low as you can go on that Sugino 110/74 mm triple crank. My reply was that I've long been a disciple of Frank Berto's School of Learning to Turn Really Low Gears.

Back when I started riding in the late seventies (nineteen seventies, that is), five speed freewheels were standard and sixes/ultra-sixes were just coming out. So wide range gearing on a touring or all-around work bike might involve a cogset such as 13-32 or 13-34, something along the lines of 13-17-22-27-34. Race bikes might have a 13-14-15-17-19 cogset in the flatlands of Long Island. My first "adult bike", a 1979 Motobecane Mirage, arrived with a 14-32 five speed and 52-40 chainrings; a gearchart was provided in the catalog.

On a work or tour bike, one could pair a wide range cogset with a triple crank having two main chainrings with only a 4 or 5 tooth difference between the big rings, and the granny, i.e., a "half step plus granny". Chainrings would be something like 48-43 (or 48-44) and a small ring, say a 24. The small percentage difference between the big and middle chainring, or "half step", in front let you split the gear ratio difference between those huge 4,5, and 7 tooth jumps in back. Dropping (carefully) into the granny ring got you up over the mountain. One would make a big shift in back and then fine tune with the 48 and 44 to settle into an acceptable cadence. Frank Berto presaged Lance Armstrong and the more recent trend that recognizes its better to spin up a grade than to crush your knees with overgeared bicycles. At sixty, that is even more important. Gear charts were used to calculate drivetrains (see chart below) to avoid duplicating ratios since there were fewer of them in those days of 5 speed freewheels. Gearheads would calculate optimum cogset and chainring combinations in those days and assemble them by hand from loose cogs (in pre-indexed days) with chain whips. Yes, I still have some chainwhips...

Gear ratios, in gear inches, from the gearing example above (48-44-24 chainrings from left to right, 13-17-22-27-34 cogset from top to bottom) on a nominally 26 inch wheel bicycle. Calculations from Sheldon Brown's Bicycle Gear Calculator.

"Tell me all about those really low gears, Dave..."
With the advent of nine and ten speed cassettes (and now eleven!), the jumps between gears on even wide range cassettes is much smaller, making the half step setup a historical footnote (although John Allen thinks this setup might be viable). Still, many off the shelf bikes arrive with a silly-large granny ring, which barely drops you to a 1:1 gear inch ratio, if that. That's fine for fit credit card touring or century rides, but woe be to the guy or gal trying to do a self-supported tour through the mountains. For that, a 24x34 low gear on a 26" wheel Long Haul Trucker provides a low gear of 18.4 gear inches, right in there with Frank's recommendations.

Anyway, have a great week.


Anonymous said...

The Volpe came with a 28 granny and a 32 cog. I suppose that's Bianchi's idea of cyclo-cross set up. For touring it's not so great. It has been modified to a 24x36 which is 21 gear inches and a bit better on the uphill when loaded. A 24x36 returns 18 gear inches so swapping the granny is this winter's project.


Steve A said...

I frequently ride a Nishiki with a half-step gear setup.

JerryM said...

Those Sugino triple cranks are great. They are versatile, relatively inexpensive, and allow for a small inner ring, unlike a lot of other modern triples. I have Sugino triples on both my road bikes. One has a 26T and the other 24T inner. Pairing these Suginos with a Phil Wood square taper bottom bracket is a killer combo.