I have seen people talk about the spread of gear inches they have available such as from 17-110 or something. My question is this. I have heard that you should not ever put your bike into say the highest or lowest gear because of chain angle. So, when the chain is on a given ring in the front, how many sprockets can you safely go to on the cassette. I have a triple in front and a 7 sp. cassette, if I am on the smallest chainring, can I safely use the largest five sprokets for instance? Or the largest four? If this is the case, the biggest and smallest gear inches available for use would be different than the maximum and minimum indicated by the cassette and chainrings right? And the number of gears is reduced as well.

I generally advise largest four. This means that out of a 21-speed bike, you might end up with 12 or 13 useful gears, based on excluding the six on the big/small chainrings, and other combinations that end up being the same or only marginally (a couple of percent) different.

In the long run, though, it is very easy to get absent-minded about gears on a tour. If your chain has been cut to a length that is based on wrapping around the big chainring, then the biggest cog, without running through the rear derailleur, THEN adding an entire link.

You then shouldn't have too major a problem with chain lockup. Rather, you will just wear the sides of the gear teeth, and wear the chain so it has more lateral flex than normal. Even then, that wear should be minimal because the noise usually will alert you to the crosschaining and you will make the required shift.

Thanks for confirming that Rowan. I do pay close attention to the sound of my bike and also try to go with a spread of about four 3-4 cogs per chainring. I just wondered why people strive to have the exreme long and short gear inches when it is not recommended to use them. It seems like it really takes some figuring out to know which are the best gears to use and in which order.

There's nothing wrong with the lowest or highest gear combinations--they aren't cross-geared. It's having big/big or small/small that causes problems.

Yes, the gear spread is somewhat different from cross-chaining and useful number of gears.