Shaun Abram
Technology and Leadership Blog
Subscribe to RSS FeedBike Gear Ratios
Not the usual software-related post, but I’ve been looking at road bikes recently, and specifically gears and gear ratios. Some notes on how to decipher the terminology and what it actually means when riding.
Crankset/Chainset
This is the part of your bike that has 2 crank arms that your pedals screw into, and 1-3 chainrings that the chain runs over. Basically, it is what turns when you pedal.
In the US, it is typically called a crankset; In the Ireland and UK, the chainset.
The 2 most common types of cranksets are the standard and compact. Less commonly, there is also the semi-compact, and a now much less common triple (which I personally liked!).
As you can see below, cranksets (or more specifically, the chainring) is usually described as
number-of-cogs-on-big-ring / number-of-cogs-on-small-ring
with a “t” at the end which just means teeth
e.g. 53/39t or 53/39t means 53 teeth on the big ring and 39 teeth on the small ring.
By convention, the largest chainring is outboard and the smallest is inboard. (Src: Wikipedia)
source: cyclingweekly.com
In short:
- Standard: 53/39t (for powerful riders)
- Compact: 50/34 (better for climbing)
And the less common:
- Semi-compact 52/36t (in between standard and compact)
- Triple: e.g. 59/39/30t (rare these days)
In more detail:
Standard: 53/39t
According to bikeradar.com, “Although it’s called standard, it’s not a very common configuration to see these days and is mainly the preserve of racers”.
Basically, it is a “bigger” set of gears, ideal for strong riders who can tackle the hills using string muscles rather than relying on smaller gears and higher cadence.
Semi-compact: 52/36t
According to bikeradar.com, a semi-compact “gives you slightly lower top-end gears than a 53/39, but opens up more low-range options for tackling hills.”
compact: 50/34t
Provides a larger range and slightly easier gearing, i.e. better for hill climbing and still OK for downhills.
“The reduction in gearing at the lower end is enough for most to tackle even Alpine climbs, yet there is not a huge reduction of the top gear, still allowing fast descending.” (cyclingweekly.com)
Cassette
A cassette is the gears on the back wheel.
A typical modern road bike cassette may be an 11-32t, which means 11 teeth in the small (harder, faster) cog and 32 in the biggest, easiest one. If you have 11 gears, the number of teeth in each might be something like 11/12/13/14/16/18/20/22/25/28/
Gear Ratios
The front crankset and the rear cassette are (obviously) connected by a chain. Their combination. connected by the chain, is what determines what gear you are in.
“On the same terrain, an easier gear means higher cadence (the speed you pedal) whereas a harder gear means lower cadence. In other words, it takes less power to push an easier gear than it does a hard gear.
A gear ratio is how many times the rear wheel turns in one rotation of the cranks.” (canyon.com)
In other words, the gear ratio shows how many times the wheel will turn for a single (full, 360 degree) turn on the pedal. So, the higher the ratio, the harder it is to turn and the faster you are likely to go.
Examples
How does all that translate into real work experience? Here are some examples that look at the ratios of the biggest and smallest gears.
Scott Speedster 30
See at scott-sports.com
- Chainset: 50/34t (aka a Compact)
- Cassette: 11-32t
So, doing some quick math on ratios:
| (Rear) Cassette | |||
| 11t | 32t | ||
| (Front) Crankset |
50t | 4.55 | 1.56 |
| 34t | 3.09 | 1.06 | |
In other words, turning the pedals once
- On the hardest gear (big front 50t, with the small back 11t) turns the wheel 4.55 times. It will be hard and you will go fast.
- On the easiest gear (small front 34t, with the big back 32t) turns the wheel 1.06 times. This would be considered a very easy gear that allows you to go up steep hills with high cadence.
2009 Specialized Roubaix Elite
With the now very uncommon triple chainset…
- Chainset: 50/39/30t (A triple)
- Cassette: 12-27t
| (Rear) Cassette | |||
| 12t | 27t | ||
| (Front) Crankset |
50t | 4.17 | 1.85 |
| 39t | 3.25 | 1.44 | |
| 30t | 2.50 | 1.11 | |
In other words, turning the pedals once on the easiest gear (small front 30t, with the big back 27t) turns the wheel 1.11 times. Again, a fairly easy gear for hills.
2008 Trek Madone
- Chainset: 50/34t (aka a Compact)
- Cassette: 11-26t
| 2008 Trek Madone | |||
| (Rear) Cassette | |||
| 11t | 26t | ||
| (Front) Crankset |
50t | 4.55 | 1.92 |
| 34t | 3.09 | 1.31 | |
So this one has a harder “easiest” gear.
Endurace CF 7 Di2
- Chainset: 52/36t (aka a sub-compact)
- Cassette: 10-34t
| (Rear) Cassette | |||
| 10t | 34t | ||
| (Front) Crankset |
52t | 5.20 | 1.53 |
| 36t | 3.60 | 1.06 | |
Sources & references
- What is a compact crank? (bikeradar.com)
- Bike gears explained (yellowjersey.co.uk)
- Crankset (wikipedia.org)
- Using bike gears efficiently (cyclingweekly.com)
- Bike gears (road.cc)
- How to find the right gear ratio for your bike (canyon.com)
Tags: biking