Innovative Energy Engineering



Drive Train

The chain drivetrain is the most common bicycle transmission. There always is a rear derailleur (RD) that moves the chain over the cassette cogs (typically 7-12 cogs). Many bicycles have a front derailleur (FD) that moves the chain over 2 or 3 chainrings. Such drivetrains are referred to as 1x (no FD), 2x or 3x depending on the number of chainrings. The shifters typically are located on the handlebar with the right hand shifting the RD and the left hand shifting the FD. Using modern wide range cassette and no FD allows less complex drive trains, less weight and better tire clearance a the chainstay. 1x12 (12 cogs in cassette) allow a single chainring with a range of 500%. However, those 1x12 drivetrains are (still) expensive and only SRAM offers them. Many MTB or fatbikes use the much cheaper 1x11 that also is offered by Shimano. On road bikes and many cheaper bikes a 3x8 cheapest up to 2x10 are most common nowadays. Chain drivetrains with chain-shifting are relatively cheap and very efficient. A disadvantage is that they are exposed to water and dirt and can be damaged by accidents, laying a bicycle on the drive side etc.

Internal Gear Hubs (IGH) consist of a planetary gear in the rear hub. they often are driven by a chain with a single chainring and a single rear cog. They typically are heavier and power transfer is less efficient. cost also is higher and range is limited. Most also are not rated for abuse off-road. the advantage is all parts are not exposed and can last much longer. Also the chain can be replaced by a belt that is less susceptible to dirt and does not require lubrication, but is more expensive. Rohloff makes a wide range 14-gear hub that allegedly is capable of off-road use. However, the $1,400 pricetag may discourage prospective buyers. Most IGH used are cheaper 3, 8 or 11 speed hubs in commuter, winter, rental and similar durability application bikes. Those cheaper options have fewer gears and range and are not designed for off-road riding.

Cassettes are mounted to a freehub (older freewheel designs may be found on 7-speed Walmart bikes). There is the more common older HG (Shimano Hype Glide from 1980's) with a small cog limit of 11 teeth. Cassettes are available from SRAM, Shimano, Sunrace and many other manufacturers. In recent years SRAM's xD driver hub that allows 10-tooth cogs became available. The big advantage is it allows a wide range without increasing the largest rear cog too much. For example SRAM's 12-speed cassette with 10-50T offers a range of 500%. On an HG hub it would require a 11-55T cassette with heavier cogs to obtain the same range. Some 3rd party manufacturers also offer cassettes with 9 teeth for xD drivers. However, those are very expensive. xD driver body also offers better casette contact and weigh less.

Select a Drivetrain and Gear Ratios

Humans can pedal efficiently at a cadence (pedal strokes per minute) of typically 80-90. Pedaling too slow with lot of force is not only inefficient, but also hurts knees. To ride at a variety of speeds and at different inclines and loads gears are changed to optimize the gear ratio. We generally speak about low (easy, but slow) and high (harder, but faster) gears. The largest front chainring combined with the smallest rear cog presents the highest gear while the smallest chainring combined with the largest rear cog represents the lowest gear. The overall difference is the range. A wide range allows a bicycle to ride fast, but also slow up hill. A narrower range only allows slower speeds or faster speeds. Mountainbikes often have slower gear ratios, while road bikes have higher ratios.

A gear calculator shows the development (meters per revolution, or gear-inches) and speed depending on which gear is used. Overall wheel size (rim + tire) is also taken into account. bicycle manufacturers typically select the gear ratios based on expected riding for the type of bike and those ratios are a good starting point if you design your own drivetrain. Many people over-estimate their speed or assume too low cadence. Steps sizes between gears are important as well. With a given number of usable gears a wider range requires larger steps between gears. At high speed, as for road bikes, this would mean a large change in cadence when shifting, which is difficult. For mountain bikes on the other hand the speeds are slower and terrain changes quickly, requiring faster changes in speed and larger step sizes are not bad or even desired (often double or triple gear shift). This explains why 1x drivetrains are very common among MTB, but 2x drive trains are more common among road bikes.

Note that for 1x drivetrains every possible gear ratio is possible and usable. When you plot a 2x or 3x drivetrain in the gear calculator, you see many redundant or near-redundant gears. Some gear ratios (cross-chained) also are not possible due to added wear. A 3x8 drivetrain may only have 15 usable gears and not 24 as marketing wants you to believe. 1x drivetrains also tend to be lighter (no front derailleur, shifter, cable and chainring) and cause fewer mechanical problems and allow easier shifting throughout all gears (front derailleurs cannot shift under load and are sensitive). For 1x drivetrains it is best to use a narrow-wide chainring (matched size for inner and outer link) to prevent chain-drop.

What drivetrain for what bike? Below are some suggestions or starting points. YMMV.

  1. Fatbikes: 1x11 (Range of ~420%)
  2. MTB: like fatbikes, or 1x12 (Range 450-500%)
  3. Roadbike: 2x11 (Range of ~ 380%)
  4. City or commuter bike: 1x11 or IGH with 8 or 11 speeds

Chains

All chains consist of inner and outer links, rollers and pins. All bicycle chains measure 1" per 1 inner and one outer link. Once the chain elongates more than 0.5% it needs to be replaced or it will wear cogs and chainrings faster. Many expensive chain-checkers are sold to tell chainwear. Most are inaccurate. the best, and cheapest, way to measure chain elongation is to use a steel ruler and measure over 12 links (nominal 12"). Exceeding the length by 1/16" equals about 0.5% elongation. Worn cogs can be recognized by skipping chains. Worn chainrings are recognized by either skipping or chain-suck. Note that not all teeth look the same and some teeth are shorter from the factory to facilitate shifting.

The actual wear causing elongation happens between the pins and plates. Therefore those surfaces need to be clean and lubricated. Some people suggest cleaning chains with solvents and washing them in water-based degreasers. This is a dangerous procedure since it removes lubricant from the wear surfaces and water will prevent lubricant from adhering to the wear surface.

Chains are sold for specific speeds (number or rear cogs) and larger cog count requires thinner chains. Don't use the wrong speed chain.

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