Gearing for Beginners
Learning to use your gears well is an important part of feeling comfortable and confident when riding. Gearing for Beginners is a simple introduction to gear ratios, to help you ride efficiently and with minimum wear on your bike.
To calculate the gear ratio for the gear you are riding in, divide the number of teeth on the front cog by the number on the rear cog. Mechanically, the gear ratio determines how many times the rear wheel is pushed around by one turn of the pedals. High gear ratios let you go faster at the same pedaling rate, but require more power. Low gear ratios mean there is less resistance when you turn the pedals, which helps on hills.
Depending on the set-up of your bike, you will have a different range of gear ratios available. Road bikes often have a compact crank at the front, with 50 teeth on the big chain ring and 34 teeth on the small ring. The rear cassette will also have a range of teeth sizes. For example an 11-speed cassette might have 11, 12, 13, 14, 15, 17, 19, 21, 23, 25 and 28 teeth. Calculating gear ratios for this set-up gives:
|Cog||Small ring (34)||Big ring (50)|
The gear ratios change by nearly four from the highest to the lowest gear, but some of the values overlap. For this reason, 2 chain rings plus an 11-speed cassette doesn’t give you 22 distinct gear ratios. Similarly, for a triple chain ring, the number of gear ratios is not three times the cassette size.
Crossing the Chain
A couple of entries in the table are marked in red as combinations it is best to avoid. These are gear choices that stress the chain and put lateral wear on the rear cassette. Using the big front ring with a big rear cog pulls the chain sideways, increasing the risk of a break. Similarly, using the small chain ring with a small rear cog stretches the chain.
This is sometimes referred to as “crossing the chain”, and more experienced riders will advise you to avoid it. There is no need to use these combinations anyway, as similar gear ratios are available on the other ring. If you are on low gears on the big chain ring and feel the need to go lower, it’s best to switch to the small ring. Similarly, if you are in low gears and moving up, such as when cresting a hill, you should plan to make a shift to the big chain ring.
Left: crossed chains in the big ring. Right: the same gear ratio in the small ring.
Knowing Your Set-Up
It’s well worth knowing what crank and rear cassette you have on your bike. This involves nothing more complicated than reading off the values on the cogs. (Equivalently, you can count the teeth). Road bikes are sometimes fitted with standard cranks that give higher gear ratios. Standard cranks have 53 teeth on the big chain ring and 39 on the small chain ring. This gives you 6% higher gearing on the big ring and 13% higher on the small ring, compared to a compact crank. You can use more power on the flat, but it makes it harder to climb hills.
Conversely, if your largest rear cog has 28 rather than 25 teeth you’ll need 12% less power to climb in first gear. You could even switch to a rear cassette with 32 teeth on the largest cog, for a gear ratio of almost 1.0. At the same time, road bike gearing is generally higher than mountain bike gearing. Mountain bikes often have a gear ratio of 0.7 at the bottom end of the range.
Bike Knack is happy to assist with gearing for beginners by advising on and fitting suitable parts. You can find prices for labour in our Pricing Table. You can reach Dave can by phone on 0437 017022, email at email@example.com, or via the Contact page. All enquiries are welcome.