Gears & Gadgets: One, Two, Three
by David Cohen, Maryland National Capital Park Police Reserve Unit
Aside from e-Bikes vs conventional bikes, no single topic in bicycle world seems to elicit more debate than the one over the proper number of front chain rings a bicycle should have: single, double or triple. There are certainly advantages and disadvantages to each one, but the question remains: which makes the most sense for the public safety cyclist?
There’s no doubt that when it comes to bicycles, particularly in the public safety role, I’m old school. I prefer my bikes and componentry to be simple and rugged. I’ve learned from years of tinkering on everything from bikes to airplanes that the quickest way to get myself in trouble is to try to fix something that isn’t broken. On the flip side, I don’t want to be so resistant to change that I’m missing the boat on technology that could be beneficial to the public safety cyclist. I don’t want to be the proverbial old guy telling the kids to “get off my lawn!”
While there is no substitute for an actual trial under genuine riding conditions, I thought that mathematically analyzing the various gear combinations afforded by the various systems would be a good place to start. Digging out my old high school geometry lessons, I’ve come up with a hypothetical 29-inch wheel patrol bicycle (I may be old school, but I’m not that old school!) to at least do a paper exercise on what the bicycle is theoretically capable of with each type of front chainring system.
For you math geeks, the mathematical formula works like this: take the circumference of the 29-inch wheel, which is two times the radius (from the tire to the hub) times Pi (3.14, etc.). That gives us a measurement in inches, which for a 29er is 91.1 inches. You then take this measurement and multiply it by the gear ratio (i.e., a 33 front / 11 rear yields a 3 to 1 gear ratio) and you find out how much ground you can cover in one full revolution of the pedals. Divide the result by 12 and you have the measurement in feet. I then used these formulae to measure and compare the lowest and highest gear ratios afforded by each system.
Single Chain Ring
The single chain ring with an 11 or 12 speed rear cassette combination seems to be the latest fad in high- end mountain bikes. The main advantage is that you do away with the front derailleur altogether, which is one less thing to go wrong. There is a slight weight advantage, which is somewhat negated by the larger cassette on the rear. Rear derailleur technology has advanced to the point where smoother shifts are available across the entire range. Most single chain ring bikes have a 32-tooth front chain ring with a 10–50 cassette. We’ll examine the low end and the high end:
Low End: 32 front / 50 rear = 0.64:1 gear ratio. For every one crank of the pedals, the wheel only turns a bit less than 2/3rds of its distance. The bike will only move forward about 4.85 feet with each crank. This is a very low gear and capable of scaling extremely steep grades.
High End: 32 front / 10 rear = 3.2:1 gear ratio. For every one crank of the pedals, the wheel turns 3.2 times. That translates to roughly 24.3 feet.
Those are not bad gear ratios, particular on the low end. Let’s see how they compare to the double and triples.
Double Chain Ring
The double chain ring is really the oldest of the technologies. Growing up, my Schwinn World Sport had a non-indexed double with a 39 low gear and a 54 high gear. Quite a few first generation mountain bikes from the 1980’s were equipped with the double. They became obsolete almost overnight with the advent of the triple chain ring. While always a staple for road bikes, the double chain ring is making a comeback in the mountain bike world. It has the advantages of being less complicated mechanically than a triple ring, while giving a greater gear range than the single ring. There is a slight weight penalty, as you have the same 11 or 12 speed rear cassette and the front derailleur. However, we’re only talking about ounces, which is almost negligible on a public safety bike when you consider how much gear both the bike and the rider carry.
Most double chain rings are 26 low / 36 high gearing, combined with an 11 –42 rear cassette. Once again, let’s do the math on the low end and high end:
Low End: 26 front / 42 rear = 0.62 gear ratio. Even lower than the single chain ring, which translates to 4.7 feet for every turn of the crank, roughly two fewer inches than on a single chain ring, which I would consider a negligible difference
High End: 36 high / 11 rear = 3.27 gear ration. This gives you a slightly higher gear ratio, yielding about 24.8 feet for every turn of the crank, This is a slight advantage; about six inches for each crank turn. While six inches per crank turn might not seem like a big deal, if you are in pursuit in top gear, and running a crank rate of 90 rpms, that translates into a difference of 45 feet each minute, which could make a critical difference.
The other very slight advantage on the double crankset is having a slightly wider chain (5.5 mm to 5.3 mm). Generally, a wider chain is going to be stronger. Single speed chains are very wide for a reason. They have to stand up to the enormous amounts of torque placed on them.
Triple Chain Ring
While the double chain ring may be the oldest of the technologies, it was the triple chain ring that made mountain biking, particularly cross-country style mountain biking, a reality for most of the cycling public. It provides a very wide spread gear range, from super-low for climbing roads off-road, to fairly high gears for pavement riding. The common chain ring for mountain bikes is 22 / 33 / 44. Some 700c commuter bikes use a 28 / 38 / 48 front combination; both mountain and commuter bikes typically use an 11 – 34 rear cassette, although I’ve seen 11 – 32 and 11 -28 combinations. The advantage of the triple chain ring is that it is supposed to have a wider gear range than a single or double. The disadvantage is that it is mechanically more complex. It would have a slight weight advantage over the double chain ring due to the smaller cassette needed in the rear. For our exercise, we’ll stick with the mountain gearing.
Low End: 22 front / 34 rear. This yields a gear ratio of 0.65, just slightly higher than the single chain ring, and also higher than the double chain ring. This actually came as a bit of a surprise. In terms of distance, though, it translates to about 4.93 feet per crank, about 2.75 inches less than a double chain ring, and about 9/10ths of an inch less than a single chain ring bike. At the low end, there really is no appreciable difference in chain rings.
High End: 44 front / 11 rear. This yields a 4 to 1 gear ratio, which is a very significant difference from the single and double chain ring bikes. In terms of distance, that is more than six feet further than a single chain ring bike per crank and 5½ feet further than the double crank set. Using our hypothetical pursuit at 90 rpm, that means an advantage of 540 feet in just one minute of riding over a single chain ring bike and an advantage of 405 feet over a double chain ring. Several bike versus car pursuits have been documented on the pages of the IPMBA News over the years. The kind of difference between the high end of a triple chain ring and its competitors could literally make the difference between an apprehension and the suspect getting away.
Triple chain rings offer one other important advantage. The drivetrain has a wider and stronger chain because the rear cassette has fewer gears. My personal preference is for the 8-speed chain, which is 7mm wide; that is, 32% wider than a 12-speed chain and 27% wider than an 11-speed chain. As mentioned earlier, the wider chains can handle more torque without snapping. Even the more commonplace 9-speed chain is 22% and 18% wider than the 12- and 11-speed chains, respectively.
Conclusions
Mountain bikes have made breathtaking leaps in technology in a relatively short time. When I first cut my teeth on mountain bikes, I was riding an 18 -speed with thumb shifters, a fork that had 60mm travel, and cantilever brakes. To say that this bike would be obsolete today would be a grand understatement. Many of the improvements in mountain bikes have carried over to the public safety cycling arena and have dramatically improved our experience, most notably, disc brakes. However, some improvements, such as slacker head angles, which make a bike more stable but not as responsive, aren’t so good. As far as the increasing use of single and double chain-rings vs the triple chain-ring in the public safety environment, I find myself very guarded, at best.
I’ve read in other articles that the conventional wisdom is/was that EMS bikes should retain the triple chain ring because of the better low end gearing. As we have seen by the math, the differences in the low end gearing between the three chain ring types is negligible. And, for the kind of riding EMS personnel do, having the low end and the simplicity of not having to deal with a front derailleur may be worth investigating. I don’t think the shallower top end gearing would come into serious play in the EMS bike role. They need speed, but they don’t need the kind of pursuit speed a police officer may need.
My primary concern with the single and double chain ring setups is the loss of the top end for the police bicycle. As demonstrated above, the 4:1 top end ratio of a triple-chain ring bike has a considerable advantage over single / double chain rings. A good analogy for this is the Dodge Charger police cruiser. The Charger has a top speed of 145 miles per hour. Odds are, there will never be a point in your career where you’re going to have to take the car that fast. But, if the need ever arose, it’s nice to know that you have that kind of speed and power at your disposal. That is the same rationale for having the 44/11 combination on a triple chain ring bike. As a rider, you may never need to use the 44 /11 combination, but it’s nice to know it’s there. In fact, if I was patrolling in a relatively flat jurisdiction, I’d even consider running a 28/38/48 triple combination to have an even stronger top end.
There is absolutely no doubt in my mind that the single chain ring mountain bike yields a magnificent bike for natural surface trails, where the top end gears aren’t really necessary. I seldom have used anything deeper than a 44/14 combination off- road, a 3.14 to 1 ratio, which is roughly equivalent to the 3.2 to 1 top end gear ratio offered by a single chain ring mountain bike. The use of the single chain ring on higher end mountain bikes is emblematic of a bigger trend: while the public safety bike and the mountain bike can trace their lineage to a common ancestor – the early mountain bikes – the evolution of both bikes has taken them down two increasingly divergent paths. The continued development of the mountain bike may not necessarily translate into usable improvements to the public safety bicycle.
By trying to relegate the triple chain ring setup to the scrapheap of bicycle history, I believe we’re trying to fix something that was never broken. A properly set up and adjusted front derailleur should last an entire season without giving the rider much trouble. As an avid mountain biker who has led numerous group rides over the years, I’m very hard-pressed to come up with any incidents where riders suffered front derailleur failures. A more common issue is a bent chain ring that interferes with the derailleur’s operation. The rear derailleur is far more vulnerable, as I can think of dozens of times on group rides when riders have lost their rear derailleurs to an errant stick or rock, or tore the derailleur up in a crash.
I continue to wrestle with my conscience about being a stick-in-the-mud for not embracing the “latest and greatest” advancement in mountain bikes. However, I simply cannot escape the mathematical calculations showing that abandoning the triple chain ring would be a mistake for public safety cycling, in general, and police cycling, specifically.
I know this is a hot topic. I do not claim to be the know-all / be-all when it comes to bicycling and I certainly encourage your feedback, good, bad or indifferent. I imagine this debate will continue. Until then, ride safely, everyone!
About the author: David Cohen is a 12 year volunteer with the Maryland-National Capital Park Police. When he isn’t riding or tinkering with bicycles, David can be found tinkering with vintage cars or World War II airplanes. An avid historian, David enjoys researching and writing as well. He can be reached at onyxsax@aol.com.
(c) 2019 IPMBA.