Gear ratios...educate me please!!!

[hobbitonabike]

Todays subject in my ongoing battle to actually know what I am talking about is gear ratios. I ride a Cannondale synapse which has a triple chainring. On the largest ring it has this

On the cassette the smallest cog has this

And the largest cog has this

So...what does this actually mean...I am presuming that this is a ratio aimed at making it easier to climb? Go...I am ready to learn!!!

 

[Supersuperleeds]

@Nigelnaturist will be along in a while to explain it all

 

[MattMM]

You have an 11-26 rear cassette and a 50 largest ring on your triple. 26 is quite a hard gear comparatively, some rear cassettes would go up to a 32, which is easier to pedal/spin going up hills etc. 50 is the quite common for a large ring on a triple, the other two would probably be 40ish and 30ish respectively. Conversely, the smallest ring on your front triple is the easiest gear, so for a really hard hill you'd be using the 30 front ring and the 26 on your rear cassette.

That's a 6 month newbies explanation, @Nigelnaturist the Keeper of the Cog may go into some more detail...

 

[Peteaud]

It means when you bought your bike you had no idea of what you were actually buying.

 

[hobbitonabike]

You are totally right!! Complete novice without a clue lol. Trying to change that now though!! I aim to be able to take my bike apart and do what ever needs doing with it. I want to be as self sufficient as possible!

 

[helston90]

I think 26 is a perfectly reasonable rear cassette as you have a triple- it's what I run with my 30 at the front- on a compact double you'd struggle.
Without meaning to patronise what is it you're trying to understand?

 

[hobbitonabike]

I am trying to understand anything I need to know. If someone asked my advice on gear ratios I want to be able to know what I am talking about...so I guess I want to know everything lol. Assume I know nothing and go from there

 

[Shut Up Legs]

This might help: http://www.sheldonbrown.com/gears/
Also, this web site has a wealth of information about anything bicycle-related. Its founder, Sheldon Brown, has sadly passed away (a few years ago, I think?), but his legacy lives on...

 

[Rasmus]

The important number is the ratio between the number of teeth on the front and rear. This tells you how many revolutions of the wheel you get for each turn of the cranks.

Some people will also refer to "gear inches", which is how big a diameter your drive wheel would have to be if you were on direct-drive bike like a penny farthing. This is simply the gear ratio multiplied by the wheel circumference.

If you do some arithmetic, you'll realize that there is significant overlap in your gears. So, the hardest gears in the smallest front ring, and the easiest gears in the biggest ring, can be replicated using the middle ring. This is intended, to limit the amount of changing on the front required, and to reduce cross-chaining, which us inefficient and causes wear.

 

[Nigelnaturist]

A gear ratio is how (in bike terms) many times the rear will turn when you rotate the crank (pedals) one rotation i.e. on a 48x12 you rotate the crank once the rear will turn 4 times, to get this you divide the number of teeth on the front ring by the number of teeth on the rear 48/12=4 or 1:4 ratio the lower the ratio the lower the gear so in the above example of 50x26 it is 1:1.92 or just over half, in other words you rotate the front once and the back rotates 2 times, this is why lower gears are easier.

Gear inches refer to how far the wheel will travel, from a fixed point so wheel size also comes into the equation of overall gearing (all be it in a small way), smaller wheels reduce the overall gearing as they dont travel as far.
A 52x13 is the same as 48x12.
Hope this helps

 

[swansonj]

Just in passing, am I the only person to have spent his (or possibly her, but sadly more likely to be his) youth playing with Meccano, and therefore having an unnatural retention of the 19 times table, because that was the standard increment for teeth on Meccano gears - 19, 38, 37, 95, 133? Oh, and of course that helpful but stand-alone 15:60 pair that allowed you to get the 1:12 reduction you needed to drive the hour hand of a clock...

 

[Nigelnaturist]

This is a table of gear inch ratios and the difference in gear inches between each gear, it also shows the percentage change between gears and the teeth count front and rear and what the RD needs to be able to do. I think its 11 the smallest, which I personally think is a little on the long side a 12 would be better. If your struggling on hills you could put a 28th on probably without any issues, but an idea of what RD you have will help.

There is however no Shimano 13-28 8sp cassette but you can make up your own from the sprockets from two or more cassettes say a 12-13-14-15-17-19-21-23 and a 11-13-15-18-21-24-28-32 the firsts is a HG50 the second a HG51, remove the pins holding the gears together then place in order the gears you want, make sure you have the right lock nut sprocket you want to use, so from that you could make up a 12-13-15-17-19-21-24-28 or just keep your 26 as its not likely to be worn and go 12-13-15-17-19-21-23-26

The 30x28 @ 1:1.07 (or 28.18") is lower than a compact 34x30 @ 1:1.13 (or 29.81")