You could find many Scientific Articles about Bike Gear
I leave Physics and Algorithms to cycling scientists
Let us talk in simple language
Let’s keep it simple. General speaking, bike gear is a system to move your chain up-and-down the sprockets to get different gear ratios.
What is a gear ratio?
Mountain bike gear ratio is a value that measures rotations of your legs vs. rotations of your bike wheels.
It means – depending on gear ratio, the same pedals rotation speed (let’s say turns per minute) results in different ride distance and your cycling speed.
So… you may choose appropriate gear according to your fitness, trail, required speed, comfort level and other conditions.
To keep it simple again...
Low gear is (usually) for uphill. It provides more power and less speed with the same pedaling strength.
High gear is (usually) for downhill. Compared with low gear, it gives you more speed with the same pedaling strength.
Universal. You will probably use it most. There are many variables, as you see. The preference is yours.
Guess how many gears does a single speed mountain bike have?.. Correct!
It may be your decision if you like simplicity and minimalism. What you get with a single-speed mountain bike is a typical mountain bike frame without derailers or hub gearing. You just pedal it like it is. Simple.
Where can you use it?
Although single speed mountain bike may look as a crazy concept, you may find it useful in several occasions. It may be perfect for cross-country races on flatlands. Or serve you as your commuting bike.
Buy yourself a single-speed 29er mountain bike (bigger wheels may find easier way over obstacles despite lack of gearing) if you are looking for something unusual.
And what about freewheel?
Most basic single-speeds do not have even this “comfort”. Be ready to rotate your legs constantly, even rolling down the mountain.
Also known as derailer. French or English approach, doesn’t matter.
This is the same bicycle part. The one which moves bicycle chain from sprocket to sprocket (front sprocket is usually called “chainwheel”), so you can cycle using different gears according to your trail conditions.
Now, little bit of math…
Let’s say, you have your mountain bike gear with three chainwheels and nine sprockets. How many gear ratios you have?
Correct – 27. How many of them can you use effectively? Twenty seven again? Wrong.
3x9 combination doesn’t provide you with 27 usable gears. You get less.
It is so, because some combinations of chainwheels and sprockets result in the same gear ratio.
The same efforts, the same speed, different gear combination, though.
It’s just physics.
Since front wheel hub may have dynamo installed to provide electricity (green energy!) for your mountain bike lights or even iPhone chargers, rear hub may be used for other purpose.
Rear hub can contain gears inside it. That’s why we call it internal gears.
Why would you need that?
It is simpler to switch between the gears since you can change gears even when you are not moving.
For those whose bike is on diet, this mountain bike gear provides less weight.
And for those who love clean hands…
With hub gear you have no risk of the chain jumping off the sprockets. You could also like simpler maintenance.
No more scrubbing your sprockets with your toothbrush. Clean looks and more time for mountains.
Don’t be confused.
Such things as mountain bike clothing, helmets, gloves, saddlebags, fenders, lights, bike computer...
and other endless accessories for your bike may be called mountain bike gear as well.
Same name with the different story.
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