Compact vs Double - explain please!

[Yazzoo]

Hi all,

Gears confuse me in general, I know how to work mine when I'm riding obviously but the workings behind it elude me! I know it's something to do with ratios. . . humour me, please!

I ride a compact 50-34
My partner rides a double 52-36

What is the difference? Or what is the advantage or disadvantage of one over the other (given that we live in the same house and ride the same geography!) Neither of us chose to have what we have, they were standard to the models we ride and neither of us has felt the need to change anything. Both of our previous bikes were triples although living where we do I don't think I ever used the smallest chainring - it's pretty flat here!

So, in as laymans terms as possible can someone please explain the point of the difference to me?

 

[Citius]

A compact is also a double - they both have two chainrings.

The difference is between what some describe as 'compact' gearing and 'standard' gearing. There issue there is purely down to personal preference.

 

[w00hoo_kent]

The numbers are the number of teeth on the ring.

The more teeth at the front the harder it is to pull the gear, but the faster it can go.

So flat out, presuming you have the same gearing on the back your partners bike will go faster than yours. A couple of teeth makes a surprising difference.

Before compacts all real men (TM) rode doubles often with more teeth than 52. I think the pro riders are regularly using something like 56-42 (I could be very wrong about this).

I believe 'compact' may also refer to the size of the spider in the middle that holds the front rings in place. Again, I could be very wrong about this.

Compacts exist around the idea that it is 'better' to spin at a higher cadence than grind out a harder gear. I've heard a lot of people talk about it being better for your knees to spin.

 

[SatNavSaysStraightOn]

My understanding was it was the size of the chainrings and the difference between them. A compact has a smaller difference than a double, making it easier to spin but also giving you less of an overall range of gears.

 

[Citius]

I think the pro riders are regularly using something like 56-42 (I could be very wrong about this).

Most are on 52 or 53 outers for flat stages, unless time trialling.

Compacts exist around the idea that it is 'better' to spin at a higher cadence than grind out a harder gear. I've heard a lot of people talk about it being better for your knees to spin.

A compact simply offers a lower range of gearing - that's all. Nothing to do with spinning or grinding. It is perfectly possible to grind on a compact and it is perfectly possible to spin on a double. The choice of gear combination is yours.

 

[Citius]

A compact has a smaller difference than a double,

Please can we all stop saying this. If a chainset has two chainrings, it is a double. The difference is between a compact double, or a standard double.

 

[Origamist]

You both have "doubles". Yours is commonly referred to as a compact and your partner's, a semi-compact. You have a slightly lower gear (34 as opposed to 36) which means it's a bit easier for climbing hills, your partner has a slightly higher top gear (52 as opposed to 50) this means they could conceivably go a tad faster down-hill. However, depending on the ratios of the cassettes you have fitted (11-28, 12-27 12-30 etc) this will also affect the bottom and top end of your gear range.

 

[Yazzoo]

Sorry chaps, I'm aware they're both doubles. Everyone I've spoken to in 'real life' refers to them as a double or a compact though (making the assumption that people really know its a compact double and a standard double)

Much clearer now though thanks! My cassette is 11-28 and his is 11-25, so does this close the gap, or widen it?

 

[w00hoo_kent]

It's exactly the same principles, but the numbers work in the opposite direction on the back so when you are in 50 - 11 and he is in 52 - 11 you can both go as fast as possible, but his fast will ultimately be faster than yours because of the gearing. When you come to a hill your 34 - 28 will make the climb easier than his 36 - 25 by quite a bit more I'd imagine. His ratios might be closer together, depends on how big the cassettes are, so if they were both 10's then his 11-25 would have smaller jumps across it than your 11-28.

If you want you can work it out as gear inches, Sheldon Browns site being as good as any for that, which would tell you how far either bike would move for a single rotation of the crank in the given gear combination.

 

[Yellow Saddle]

My understanding was it was the size of the chainrings and the difference between them. A compact has a smaller difference than a double, making it easier to spin but also giving you less of an overall range of gears.

The range doesn't have to change, but will have different starting and end points. Lets say all bicycles fall within a range of 1 through 10.
A standard crank will have a range form 4 to 8 say and a compact a range from 2 to 6. The range in both cases is 4.

 

[Yellow Saddle]

It's exactly the same principles, but the numbers work in the opposite direction on the back so when you are in 50 - 11 and he is in 52 - 11 you can both go as fast as possible, but his fast will ultimately be faster than yours because of the gearing. When you come to a hill your 34 - 28 will make the climb easier than his 36 - 25 by quite a bit more I'd imagine. His ratios might be closer together, depends on how big the cassettes are, so if they were both 10's then his 11-25 would have smaller jumps across it than your 11-28.

If you want you can work it out as gear inches, Sheldon Browns site being as good as any for that, which would tell you how far either bike would move for a single rotation of the crank in the given gear combination.

Gear inches complicates the matter somewhat and simply adds a quantity to the ratio. But as it is, the quantity means nothing to most of us.

I find it better to explain this in simple ratios than in gear inches. Divide the chainring teeth by the cassette teeth. 52/26=2 This means that in the 52/26 gear the wheel turns twice for every crank revolution. On a compact that would be 50/26=1.92. This can again be expressed as "easiness" or speed, as you explained, by comparing the ratio of 2 and 1.92. A typical question would be: "How much easier is it to pedal on the compact?" The answer is 1.042 times easier.
"How much faster will I go on the standard crank? 1.042 times faster. Etc etc.

 

[Citius]

Everyone I've spoken to in 'real life' refers to them as a double or a compact though (making the assumption that people really know its a compact double and a standard double)

If you know they are both doubles, then referring to one of them as a double (as a means of differentiation) is a logical fallacy.

 

[Dogtrousers]

Some further reading:
Thread on here: Who rides a standard crank?
Article on BikeRadar What is a Compact Crank

 

[Dogtrousers]

If you want you can work it out as gear inches, Sheldon Browns site being as good as any for that, which would tell you how far either bike would move for a single rotation of the crank in the given gear combination.

Actually no. Gear inches don't tell you how far the bike would move for a single rotation. That's "development" (or développement as it's mostly used on the continong, and not expressed in inches). Gear inches is the diameter of the wheel of a penny farthing with equivalent gearing. Reference. So development is gear inches x pi (I think).

 

[DaveReading]

If you know they are both doubles, then referring to one of them as a double (as a means of differentiation) is a logical fallacy.

The English language is full of expressions that are logically fallacious, but nevertheless understood by practically everyone.