27 gears, correct gear usage?
 

My Trek has 27 gears, does this gear usage look safe as far as "wear & tear" go?

Green being "good gear combinations" and red being "bad gear combinations".

1st Chainring
12345 6789

2nd Chainring
12 34567 89

3rd Chainring
1234 56789

Obviously from reading these forums I've gathered that some of those gear combinations are considered "duplicates". I haven't reached that skill level yet. :p

If your bike is a 27 speed it may a halfshift function which would open up most of the red numbers without the front derailleur rubbing although the cain would still be crossed. Otherwise, looks good

You've got the right idea except that, in my experience, the middle ring is Ok to use across the freewheel and your inner ring (your're third) is only for the 3 largest cogs. :)

I use that exact same "pattern".
Not only do I avoid extreme angles, it also happens to, in my case, provide a smooth and progressive gearing increase. If I mix in any other combo, I move away from the "curve" and they're all duplicates of combos inside the "green" range, more or less.

Next geared bike will be a 9 speed with only one chainring .... I heard that they are crazy expensive.

Think of the front chainring's shifter as Uphill, Flats, Downhill and then it begins to make sense.

The middle chainring will gladly use all of the rear gears.

Using a rear derailer with no front derailer will quickly toss the chain off the single front chainring.
Yet, until that happens, the system provides enjoyable, fast shifting. Of course, you can use a front derailer that does nothing but hold the chain on. For 11-34 combination, 9 speeds and expense is unnecessary when it is available in 7 if you use a $2 spacer and a $23 indexing lever shifter to work a Deore rear derailer.
Whatever rear-only system you choose, make certain that you use a lever shifter (use a bar end shifter if you get that 9 speed), because you must cross over every gear very slowly if you have a packet shifter.

A Nexus 8 provides the same gearing as that hyper-expensive 9, and they are available pre-built into a 700c wheel for just over $250. The road version is called "premium" and is lighter weight. Shifting is extraordinarily fast. Range is like a road double with a road cassette. You get any gear at any time, under every condition. Revo and packet shift are both available. Weight is quite a lot, but not more than an entire Ultegra derailer system plus a rear freehub. Sachs makes a more durable 7 with the same range (as Nexus 8) for MTB application. Rohloff $1000 to $1500 is a similar product with far more range and extremely fast shifting. It is a heavy MTB or tandem product and requires a large size front chainring if it will be used at roadie speeds. Any IG hub has a break-in period of 300 miles before they loosen up and speed up. After that, it is about 22000 miles until maintenance. It will outlast its rim. Despite a possible addition of a bit of weight (in case of the Swiss/German-made products), the IG hub can accelerate so fast that it pays its way. The Nexus 8 is also known for favoring the high gears with less drag than a derailer system. And, it just makes sense.

If you really want to understand your gears, read Frank Berto's book. Can't recommend it enough! I haven't checked out his newest, The Dancing Chain, yet, but he says it picks up where Upgrading Your Bike left off, so he may have some relevant advice for 27 speeds in there.

Go to http://www.panix.com/~jbarrm/cycal/cycal.30f.html and put in your chainrings and gears. You want something between 6-12%. Start with low ring, and when no longer can get the right percentage, select middle, etc.