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Just bought a Falcon Interceptor bike with Shimano gears - whatever that means. I've had bikes in the past but only those with one set of gears for the rear wheel.

What's the need for front and rear gears? What should I be doing with them?

What are the front gears for? What should I be considering when selecting front gears and rear gears? Are they (front and rear gears) interdependent or independent?

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See also (but not a duplicate): bicycles.stackexchange.com/questions/10594/… –  amcnabb Aug 1 '13 at 21:45
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actually its not a stupid question at all, but I can straightaway say that a good answer to this would be quite lengthy. I'd definitely suggest a Google search. If you're in any way mathematically minded you can look up terms like "gear ratio" or "gear inches" which can illustrate how varying the number of teeth (either at the front or the back) affects the mechanical gain of the gearing system. –  PeteH Aug 1 '13 at 22:04
    
Not to forget that there's nothing so rewarding as finding things out empirically - go climb a hill and you'll soon realise why that smaller ring is there! –  PeteH Aug 1 '13 at 22:20

2 Answers 2

Having more than one chainring (one of the front gears) expands the total gearing range available to you. Having multiple chainrings gives you a higher high gear for cruising at high speed as well as a lower low gear for spinning up hills.

The difference in the number of teeth between chainrings is much larger than the difference between sprockets in the rear. You can think of chainrings as being for major adjustments and sprockets for minor adjustments. You don't need to change gears in front nearly as often as in back.

The simplest gear changing strategy is to adjust the rear gears as needed and then change the front gears whenever you start to cross-chain. Cross-chaining is using the big chainring with a big sprocket or the small chainring with a small sprocket.

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All excellent responses for which I thank you. Much obliged for the "basics" as well as the technical stuff. Having read Rob P's original post as well, a thought occurred to me about making a "sticky" thread on this subject for newbies such as us ? So you pro's dont have to keep answering our newbie questions over and over again ? :) –  Andy Aug 2 '13 at 9:26
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@Andy Stack Exchange doesn't have the concept of a sticky thread, but questions and answers are easily searchable. And if someone asks the same question again, it can get closed as a duplicate. In short, don't feel bad at all about asking "newbie questions." Also, feel free to upvote any and all answers that you find helpful. –  amcnabb Aug 2 '13 at 15:05
    
It is also adviseable if you have 3 chainrings not to 'cross gears' too much (that is small ring to small sprocket and vice versa) This causes the chain to run at a less than straight angle and will cause problems –  Mark W Mar 6 at 14:56

My standard approach, and the approach I'd recommend for starting, is to use the front derailer to select a "range" -- big ring for flat road with no headwind, middle ring for slightly more challenging conditions (or riding in traffic), and small ring for serious uphill climbs. Then adjust the rear to select a comfortable gear within that range.

Or, if you're really unsure, just select the middle ring in front and only shift the front up/down if you notice that you need to.

As you gain more skill you'll notice that you can often, say, shift up in the front and down in the rear (or vice-versa) to achieve an "in-between" gear between two rear-only choices. But with modern bikes with 20+ speeds total this is not as important a "feature" as it was on old 15-speed bikes.

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