Explain Cassette Gearing

[OnTerryOh]

I keep reading all these numbers about triple cassettes and compact doubles, and I don't really understand what they mean. Could someone explain this to me? My bike has a 12-25 cassette, and a 48x38x28 chain ring (triple).

To answer your first question
The numbers are the number of teeth on each of your chainrings.

48 x 38 x 28 means that the largest chainring attached to your pedals has 48 teeth, the midsize ring has 38 teeth and the smallest has 28 teeth. A 12-25 cassette means you have a number of chainrings in your rear cassette, ranging from a smallest ring with 12 teeth to a largest with 25 teeth.

Gear ratios and uphill riding
When you pedal, the chainring attached to your pedals drives the chainring in your rear cassette, making your back wheel turn. The number of times you pedal in relation to how many times your back wheel turns is a gear ratio.

The lower the gear ratio, the easier it will be to pedal up the hill.
To calculate a gear ratio, divide the number of teeth on a front chainring by those on a rear. A good gear ratio for uphill riding uses the smallest chainring on the front and the largest on the rear. Think "small front, large back".

For example, the smallest chainring on your pedals has 28 teeth. The largest chainring in your rear cassette has 25 teeth. 28/25 = 1.12, which means that for one revolution of your pedal, your rear wheel will revolve 1.12 times.

This is the lowest gear ratio your bike has to offer, the easiest for riding uphill. You'd be pedaling a lot, but getting up the hill without much pressure on your knees and quadriceps in this gear.

A new cassette or new bike?
The more teeth the back gear has, the easier it is to ride uphill.

Let's suppose that you bought a new cassette with a largest chainwheel having 34 teeth. Using your bike's smallest front chainwheel of 28 teeth with this, the gear ratio would be 28/34, or .82.

For one revolution of your pedals, your back wheel would turn .82 of one revolution. You would be moving slowly but the climb would be much easier than on your present bike.

Is that adequate for serious hill climbing? Someone suggested that I needed a bigger rear cassette. I'd like to know if that is necessary. Thanks.

Yes, I think your present bike is adequate. In my opinion a bigger rear cassette isn't necessary.

Uphill riding and what bike you choose depends on your fitness, cycling experience, the grade of the hills and how much money you want to spend.

[Pedal Wench]

An easy way to remember when you're on the bike - the closer the chain is to your bike, the easier it is to pedal. Move the chain, on either the front or back, closer to the bike is easier - further away is harder to pedal.

[tctrek]

All of these posts are very helpful! I had resorted to a letter game to help me remember about what gearing would make it easier to climb hills: "B"igger in "B"ack - that's why I'm changing out the back from a 12/27 to a 13/30 this week.

[Thorn]

An easy way to remember when you're on the bike - the closer the chain is to your bike, the easier it is to pedal. Move the chain, on either the front or back, closer to the bike is easier - further away is harder to pedal.

What a wonderfully, simple way to look at it...the further away from the bike, the harder the more work. Simple. Elegant. Thank you.

When I read these posts, the engineer in me knows that I can never explain it to someone. Words like gear-inch, gear ratios, etc, want to roll of the finger tips. But, PW, you have the perfect layperson's explanation.

[Pedal Wench]

What a wonderfully, simple way to look at it...the further away from the bike, the harder the more work. Simple. Elegant. Thank you.

When I read these posts, the engineer in me knows that I can never explain it to someone. Words like gear-inch, gear ratios, etc, want to roll of the finger tips. But, PW, you have the perfect layperson's explanation.

Nope - but I'm an engineer too - so I'm just speaking your language!