Sprocket 'teeth'

[Dibs]

Evening all,

Hands up, I do not understand (yet) the differences or benefits of having less/more teeth on your front/rear sprockets.

So, for top speed, is it the higher number on the front, and lower on the rear that you want? If so, for road bike/hybrid, what is a high/low amount of teeth? If so, I presume the lower front higher rear is best for up hills?

I'm swithering between a new hybrid/cx bike next year, so try to increase my knowledge in these areas...

Thanks in advance...

 

[smokeysmoo]

So, for top speed, is it the higher number on the front, and lower on the rear that you want?

Yup.

Using my road bike as an example, the chainset is 53/39, this is commonly referred to as a 'standard double', and my cassette is 11/25. The 'fastest' gearing therefore for me is 53/11.

However, most road bikes nowadays ship with a chainset that is 50:34, this is commonly referred to as a 'compact', and the cassette would be similar to above at 11/25, 11/28 or 12/25, (other ratios are available).

Rule of thumb, if you live in a hilly or hillyish area, are new to riding and are relatively unfit, buy a compact, (or even a triple), but if you live in a flatish area, are used to higher gearing and consider yourself fit enough, get a double.

FWIW I use a double nowadays, live in a hilly area, and am not particularly fit, but there's always an exception isn't there?

 

[Rickshaw Phil]

So, for top speed, is it the higher number on the front, and lower on the rear that you want? If so, for road bike/hybrid, what is a high/low amount of teeth? If so, I presume the lower front higher rear is best for up hills?.

Yes, that's pretty much it. You'll find that most "hybrid" bikes go for a 48-38-28 chainset on the front and the rear will probably be something like 14-28 teeth on a cheaper bike and 11-28 on a more expensive one, though there may be variations. Up to 34 teeth are readily available for the rear and a 28 Front,34 Rear will allow you to wind your way up pretty much anything.

 

[Dibs]

Thanks guys.

Will be out tomorrow night counting my existing set, so I know how much better any new bike will be...

Cheers.

 

[Sterba]

When we used to ride penny farthings a few years ago, the front wheel had to be huge because, without any gears, each time we turned the pedals round once, the wheel travelled forward the distance of its circumference. Unless it was a big wheel, you didn't travel very far. Now that we have invented gears, we still hark back to the size of those original penny farthing wheels. So, gears are measured in inches, relating to the equivalent diameter a penny farthing wheel would be. Are you still with me?

To find out what "size" a particular gear is, you count the teeth on the cog that the chain is on at the back, and divide it into the number of teeth on the chainring at the front, and then multiply it by the diameter of the wheel. As an example, if the cog at the back has 20 teeth on it, and the chainring at the front has 40 teeth on it, twenty into forty gives 2, multiplied by 26 (roughly equivalent to today's 650 wheels), giving a gearing of 56 inches. With a multi-speed derailleur, you will have a range of gears that will get you up the hill more easily when you use the larger cog at the back (because the gearing gets lower, try the maths for yourself) and, when you change up to the smaller cogs at the back, the gearing gets higher so that you can pedal downhill in a more measured way, without having to twiddle the pedals to have any effect.

Conversely, the larger the front chainring, the higher the gear, and the slower you have to pedal to cover the same ground. So, if you have a double or triple chainset at the front, as you change down to the smaller rings, you will lower the gearing and make it easier to go uphill. When you have an idle moment, work out the gearing in inches for all of the possible combinations of front and rear cogs on your own bike, and it will help you see why one gear is faster or slower, easier or harder, than another.

I hope this helps.

 

[Cyclopathic]

I just love the word "swithering".

 

[fossyant]

Don't get too hung up on gearing. As for top end speed, those saying it's not enough aren't pedalling efficiently or aren't able to spin. Having low gears is probably where you need to compare, especially if your fitness won't carry you up some hills.

 

[PeteXXX]

By the way... you don't have to physically count the teeth.
The cogs have a l'il number stamped on them

 

[byegad]

By the way... you don't have to physically count the teeth.
The cogs have a l'il number stamped on them

In most cases covered in oil, grunge and dirt.

 

[HLaB]

Evening all,

Hands up, I do not understand (yet) the differences or benefits of having less/more teeth on your front/rear sprockets.

So, for top speed, is it the higher number on the front, and lower on the rear that you want? If so, for road bike/hybrid, what is a high/low amount of teeth? If so, I presume the lower front higher rear is best for up hills?

I'm swithering between a new hybrid/cx bike next year, so try to increase my knowledge in these areas...

Thanks in advance...

To a degree but if you cant turn the larger gear you are slower. FWIW the fastest I've been this year (45.6mph IIRC) was on a cyclocross bike with only a 48t up front.

I'm in favour of a wide range cassette an 11t or something for downhills, turning when you are upt to speed but a lower/ bigger cassette cog at the other end 25 or 26t, some people don't get on with the bigger transition between cogs but I don't really find it a problem and I'd allways prefer the more extreme gears are there when I need them. PS I fitted an 11-28 for the Alps and then wrote the bike off so never used it

 

[deptfordmarmoset]

Thanks guys.

Will be out tomorrow night counting my existing set, so I know how much better any new bike will be...

Cheers.

As long as that ''better'' is better for you, there's no absolute better. I've rarely seen a CX bike set up with a triple at the front or a big toothed cassette at the back, because they're not generally set up for climbing long, steep hills - here a reasonable amount of gear range is thought of as better. But if you live at the bottom of a deep valley, a wider range of gears might be better for you.

 

[Dibs]

By the way... you don't have to physically count the teeth.
The cogs have a l'il number stamped on them

I knew that...