Gears and Compact Cranks - Can One Setup Do It All?
Gears and Compact Cranks
Can One Setup do it all?
By Dave Lieberman and Paul Kopit
As a native “flatlander”, the myriad of drive chain combinations have always intimidated me. All I knew was it was always “cooler” to have a 19 as the biggest rear cog, and 21’s were for wimps. Front chain rings were a 53/42, not 53/39, and you were considered a sucker if someone sold the latter to you. Out in California, there are hills, therefore I needed to change my way of thinking. There are now “compact cranks”, up to 27and more rear sprockets, and triple cranks! Is there a perfect combination that can be used for basic riding, climbing, training AND racing? Maybe so! Read on, as your first thoughts may be different by article’s end.
I asked some experienced experts on the matter, and researched more on Sheldon Brown’s website. In common to all, was a constant factor called “gear inches”.
I’ll start with some basic definitions, some history, then some commentary by Triple Crown expert Paul Kopit, and then some illustrations of different crank and gear ratio combinations.
Compact Crank: A double-chain ring crankset with that permits the use of smaller chain rings than those that fit with the common 130 mm B.C.D. (Bolt Circle Diameter). Most “compact double” cranks use the old standard 110 mm B.C.D. which permits the use of chain rings as small as 33 teeth, or more commonly, 34 or 36 teeth. (FYI, standard Shimano is 130, and standard Campy is 135).
Gear Inches: The simplest system in common use is the “gear inch” system. This dates back to before the invention of the chain-drive bicycle. It originally was the diameter of the drive wheel of a high-wheel bicycle. When chain-drive “safety” bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number. The examples listed above are all around 74-75 inches. The lowest gear on most mountain bikes is around 22-26 inches. The highest gear on road racing bikes is usually around 108-130 inches.
History: 110 mm B.C.D. double cranks with full-sized (52-42, 52-40, etc.) were common in the late 60s and ’70s and early ’80s, but they had become nearly extinct for double chain rings. The rebirth of this format, with smaller rings, was pioneered by Tyler Hamilton who used one of these in the 2003 Tour de France. Compact cranks have been available since the ‘80s. Sugino made, “touring doubles” then, and for you “Q” factor junkies, they had narrower Q than the new ones. Switching from a 53/39 x 12/21 for 50/34 and 11/23, is weight weenie heaven and regular rider folly.
VIEWS:
Paul Kopit states “it is likely that no topic generates more controversy than what ‘gears’ or ‘gear range’ your bicycle should have”. I am of the opinion that most riders that have don’t have a wide enough ‘range’ of gears.”
Usually, average riders lack low enough gears and have high gears that are not necessary. For clarity, high gears are the go fast ones that are difficult to push. A 53 x 11 (130 gear inches”) is usually the highest gear that regular bicycles use. This is seen on today’s standard bikes. The smallest gear, the easiest to push uphill, is usually a 34 x 27 (34 gear inches”), is seen on a bike with a compact crankset. Higher gears are available, 55t x 11 (135) ( 34t x 34 (27”). Triple cranksets have even wider ranges but have lost favor because of fashion, weight, and complexity.
For that reason, ten speed cassettes have made using a “compact” more practical.
I believe that it was Greg Lemond that said that in order to go fast, “Spin…high gears”. Most of us can’t do that and even the best in the World are now spinning higher cadence than in Lemond’s time. Let’s be practical, cadence for normal riders is likely between 70 and 90 rpm. The benefit of lower cadence is you take pressure off your butt and transfer it to your legs. Standing in the pedals, however, is less efficient because your legs have to carry your full body weight. Standing is required when you don’t have low enough gears or you need a burst of power in order to raise your cadence or you’ve run out of gears for the grade encountered.
Having wider ranges of gears creates gaps in your pedaling cadence is a mainly overrated myth. The gap is not “2” teeth but the percentage of increase/decrease in gear inches. The move from a 24 to 27 is 9% and 11 to 12 is 9%. A smooth cassette will have a range of cogs that give similar increase in percentages. Most riders cannot tell 2 to 4% differences in cogs. If you have a smooth pedal stroke with equal pressure on each leg and high cadence, you can realize smaller differences in gear inches. Again, few of us are like that. For those racing or gifted, a lower gear in the big ring may save from having to shift down to the smaller ring. Holding that big ring long enough can help you break away from the peleton or hang on instead of being dropped.
Gear ratio chart at http://sheldonbrown.com/gears
Remember that the smallest inner chain ring on standard cranks is 39 or 38, so you will need a crank with the smaller 100mm BCD bolt pattern. However, with advanced technologies, the problems with the strength of large chain rings on such small crank bolt patterns have been eliminated !
Above are 3 of the most common setups. As stated on the previous page, a 8-9% jump between gears is about average. Some will be lower, and some higher. The common compact setup of 50/34 is great for training, on hills and riding alone, but unacceptable for higher speeds, and pack riding, and a 34 is really too low a gear for anything, period. The thought would be to go to a 36 on this setup, but if you have a 50/36, you might as well go to the 52/36. The advantage of having the 52 for the big chain ring is that it can give you “race speed”, while still having great climbing range in the small chain ring. Two additional notes. First, notice that the 52/12 is actually a bigger gear than a 53/13 and actually closer to a 53/12, (by a small amount). Second, the 36/25 is about the same as the 34/25 (though the thought here is you probably won’t be using this gear anyway unless you are climbing an extremely steep grade).
REMEMBER: THE PURPOSE OF THIS ARTICLE IS TO GIVE US SOMETHING YOU CAN TRAIN, PACK RIDE, AND RACE ON! Even better, SRAM makes a 12/26, or even an 11/26. This is an awesome amount of “range”, and you will never have to swap out a chain ring or a cassette again!!
In summary, A great compromise of gearing with the greatest range of gear inches is 10 speed 52/36 with a 12/25 rear cassette. That combination is not regularly available but as 50/36 is coming into vogue, the 52/36 will soon be a requested. Unless you’re a specially gifted rider, get lower gears and develop the skill of spinning faster and smoother.
Happy Riding.
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