Marshall has a double chain set and wants to know which chain ring he should be using and what his cadence should be when he is riding. We suggest his pedal speed and how to know which gear to use
Question:
Can you address which chain ring I should be riding on? I only have two, and I know that some bikes have three. Also, what should my cadence be at when I ride?
Hi Marshall,
The correct chain ring to use is the one that gives you the pedal revs that you want and that on the flat should be around 80 to 90 revs. On a steep hard climb you will find that your pedaling will slow and the cadence will drop. If you look at the riding style of Lance Armstrong when he is climbing he keeps his revs at around 100, this he has proved gives more power and acceleration. The problem is that not every one can do this; you would have to train to be able to pedal at that rate, so go for around the 90 mark.
Bikes that have three chain rings have more hears, but the question is; do you need more? You find that with a triple chain set many of the gears are the same, you will probably have some smaller gears for climbing very steep hills, but you will not have higher gears and lots of middle gears that are the same. Triple chain sets are great for off-road riding or if you are carrying loads on a touring bike, a triple will give you the small gears needed for very difficult conditions. A compact chain set can give you a wider range of gears than a triple chain set or having a cassette with a small sprocket of 12 teeth and going up to a 28 or 32 tooth sprocket, of course for this you would need a long arm rear derailleur.
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Cadence and RPM's(revolutions per minute)on a bike is just like a car. The 90 rpm mark is a rule of thumb for being the most efficient for a bike similar to the 2300 rpm for a car.
So when riding, keep your cadence at 90, as you find that it starts to decline to 86-88 and you cannot increase your effort to compensate for the drop, shift down. When you find your cadence is at 95-96 shift up.
If you watch your car's tachometer you will see a similar reaction.
To answer the shifting using the front chainring vs of the rear sprocket it helps to understand the gear ratios you have available. Set up a table in a spreadsheet one column the number of teeth in each sprocket, one column divide the 1st column number by the number of teeth on the small chainring (39, 42 are common) and one more column divide the 1st column number by the number of teeth on the large chainring (53 is common). The lower the number the harder it is to pedal but the faster you will go while maintaining 90 rpm cadence. The important thing to identify from this exercise is that you will see that there is a range of ratios that are similar in both columns. In your spreadsheet, try to find the crossover point that minimizes the difference in ratios.
Answered my questions perfectly, and very consistent with some of the answers I have recieved from other cyclists.
Thank you very much.
Marshall
Just a comment about the compact versus triple chain ring question.
I have a trek 7.5 FX with a 48/36/26 triple and a 11-26 cassette. This gives a pretty big top gear and a nice low gear for the many hills around here. It seems to work quite well.
If the Chainring is on the 39T and the 12t sprocket(smallest)the ratio is 12/39 or 0.307. The problem is the chain is under a lot of stress and friction causing drag which requires increased effort from the cyclist to overcome.
It is far better to use the large front chainring 53t and the 16t sprocket with a 0.301 gear ratio. The chain will be straighter which means less friction and less work for you.