by Davide Petucco translated by Gillian Shaw (source text)
Using gears correctly is one of the most important technical aspects of cycling.
We have already talked about how important it is to pedal with ease in other articles and to do this we have to do this based on the type of terrain (flat, ascent, descent), our own physical fitness and not least our own ‘feel’ and ‘habits’ when cycling.
We are not talking here about the pedalling speed, but we are focussing on the correct use of the combination of the front chainring and the cogset.
When you are on the flat and using the largest chainring, you sometimes feel as though you want to lighten the ratio because we are cycling into the wind, or on a slight incline or we just want to get our breath back.
The problem arises when we try to use a very low gear in the sprocket set, because the chain is stretched too far transversally.
Obviously the same goes in the opposite direction, with the smallest chainring and the smallest sprocket.
For me, I use a compact chainset and often find myself having to pedal at 50% and trying to find that ‘extra cog’ at the back to let me pedal comfortably. When I realise that the chain is on the last-but-one sprocket, then I have to use the 34 and find a ratio that offers the same feel.
Let’s look at an example
In the table below are the metric development of the various gearing combinations, namely how many metres my bike will go forward with each full pedal stroke.
I have taken the example of the 34-17 and 50-15 gear combinations, where you can see that the metric development is identical, namely 4.23m.
Yet pedalling with the 50-25 combination feels smoother.
Does this happen to you too?
I don’t want to get into a a complicated discussion on physical mechanics and talk about ‘leverage’ and ‘effort’ – it isn’t my thing (and in any case this theory calculates that pedalling with the smallest chainring effective).
Let’s look at the ratios we have available.
How many combinations are there?
In theory, if we have 2 chainrings and 10 sprockets, we have 2×10=20 different combinations.
Actually, though – for the reasons discussed above – we can’t use all of the combinations as some would put the chain under too much transversal strain that would cause unwanted friction either on the chain or on the sprocket teeth.
In the worst case scenario, you can hear the chain touching the derailleur and this is a sound no cyclist wants to hear!
The old ‘rule of 2’
This unwritten rule of cycling says that the large, front chainset should never be used with the two largest sprockets.
But if you are using the small chainset, then you must not use the 2 smallest sprockets at the back.
Really these images from a video I found online, suggest that the last 4-5 cogs should not be used at all – this seems a bit excessive to me!
I like the old ‘rule of 2’ – it seems to work.