[Nick09]

I understand not using the biggest chainring with the biggest cog ring, and vice-versa, but can someone help me understand the non-extremes, and middle gear ratios where I would be cross-chaining?


Thanks

EDIT: I have a double crankset not a triple...

 

[Kerry Irons]

You've got it

I understand not using the biggest chainring with the biggest cog ring, and vice-versa, but can someone help me understand the non-extremes, and middle gear ratios where I would be cross-chaining? I have a double crankset not a triple...

You essentially have it. On some setups, the chain rubs on the inside of the large chainring when you are on the small ring and the 2nd smallest cog on the cassette and so you should avoid that combination as well. Otherwise, big-big and small-small are not good gears. Note that lots of people occasionally use the big-big (just to crest a hill and avoid shifting the front) without any problems. It's just not a gear to ride in a lot. Small-small is almost always to be avoided because of the chain rubbing on the chain ring, and often the rear derailleur not supplying enough tension on the chain.

For reference, see: Andy Schleck, 2010 TdF, stage 15.

 

[Nick09]

So... Bigger chainring and 2nd largest cog ring and down are okay? And Smaller chainring and 3rd smallest cog ring and up are okay? Sounds like this kinda limits what gears you ride...

 

[PJ352]

So... Bigger chainring and 2nd largest cog ring and down are okay? And Smaller chainring and 3rd smallest cog ring and up are okay? Sounds like this kinda limits what gears you ride...

What you're describing here is ok, but as one example of how you can get the same results two ways:
Let's say you have a 53/39 front and 12-25 rear. When you're in the 53-23 combo you're not really cross chaining, but a similar ratio can be attained by shifting to the 39-17 combo and will straighten your chainline some. As Kerry mentioned, there's nothing wrong with occasional big/ big cross chaining, but if you're cruising for a length of time, it's better to choose a gear combo that allows for a straighter chainline.

Here's a gear calculator that may help you see what combos are available for your drivetrain.
http://sheldonbrown.com/gears/

 

[spade2you]

Try to make your front gear changes while you're in the middle of the rear cluster. There's no reason to be in the big ring up front and 2nd biggest gear in back.

Aside from dropping the chain, jumping to the big gear will usually take more force and will seem to grind. When you run the chain crossed, it really speeds up wear on the chain.

When I know I'm going to climb, I'll switch to the small ring up front and move it cross chained in back, but I'll only be cross chained for a little while.

 

[SidNitzerglobin]

So... Bigger chainring and 2nd largest cog ring and down are okay? And Smaller chainring and 3rd smallest cog ring and up are okay? Sounds like this kinda limits what gears you ride...

These are exactly the limits I use for what I'll run for more than a minute or two.