Road Bike Racing - Using Smallest/Biggest Cog With Smallest/Biggest Chainring

TRIPLE CHAINRING:
I forget the term, which describes how it can be a problem with triple chainrings ... if you have the chain on the smallest chainring and the smallest cog at the same time ... or if you have the chain on the biggest chainring and the biggest cog at the same time. What is that term, which refers to the extreme angle of the chain when using the smallest/biggest cog with the smallest/biggest triple-chainring?

At any rate, is the rule of thumb to never have your chain at such an angle ... or is it okay to have the chain at such an angle for a few minutes at a time?

COMPACT DOUBLE CHAINRING:
With compact double chainrings, is it even an issue if you have the chain on the small chainring and the smallest cog at the same time ... or if you have the chain on the big chainring and the biggest cog at the same time ... since there should be less of angle being put on the chain?

If chain-angle is still an issue with compact double chainrings, can you at least ride on these chainring/cog combinations longer than you could with triple chainrings?

The reason why I ask is to know how useful the biggest cog would be with a compact crank ... to compensate for not having a granny gear.

It's called cross chaining. It exists in both the triple and double configuration. You can ride cross chained for hours. However, you run the risk of stretching/snapping the chain. If you stretch the chain it wears down cassettes and chainrings faster. If you snap the chain, you don't finish your ride. Get a chain wear measurement tool and don't worry about it quite so much. Just use common sense.

I never cross chain in training.. but when racing, depending on the course (crits.) where dropping a chain is a lot worse then cross chaining for a couple seconds up a little riser then cross chaining is ok.


As for you gear question: try an online gear calculator and see for yourself the effects of a compact.

http://www.xsystems.co.uk/machinehead/gearpro.html
http://www.sheldonbrown.com/gears/
http://home.earthlink.net/~mike.sherman/shift.html

Cross chaining will make the drivetrain noisier. On a compact, going small/small can cause the chain to rub on the inside of the big chainring too...

On a triple, going small/small really drops the chain tension, and the rear derailleur spring/cage might not be able to hold enough tension, depending on the length of your chain.

Twice, I've broken chains when I had my bike in the big ring/big cog moving off from a stop. In fact, both breaks happened at the exact same spot. There's a spot in one of my training routes at home where there's a stop sign at the top of a small rise, and I'm forced to come to a stop in order to make a left turn. This spot, in combination with my shifting style (or lack thereof) and the nature of my bike's gearing has caused me to snap two SRAM chains.

Since I've been riding a CX bike with a 48 tooth chainring for a while now, I'm in my big ring about 95 percent of the time. Due to the extreme angles that the chain is under, in addition to the gradient, AND my standing on the pedals to get the bike moving, the chain simply can't handle the strain.

If you don't have to move off from a complete stop, you have a little bit less to worry about from cross-chaining.

I never cross chain in training.. but when racing, depending on the course (crits.) where dropping a chain is a lot worse then cross chaining for a couple seconds up a little riser then cross chaining is ok.
+1 additional wear is acceptable for racing -- the competition takes priority

Note that with a bad chainline, you're less efficient, so cross-chaining should be a temporary condition.

Cross chaining a double is not as big a deal as cross chaining a triple because the acuteness of the angle is not as great.

Given the wide range of gears on a triple, there would rarely be an occassion that you'd need to ride completely cross chained on a triple.

The good thing about this issue is that when you've got the chain in a set up the drivetrain doesn't like the noise increases. So if you're putting substantial wear/stress on the system, the bike will tell you if you listen.

Cross chaining for a brief period of time is perfectly ok. I can't see ever using the small/small combo, but I'll occasionally use the big/big combo on a hill if the group is going fast uphill.

Just be sure to test the big/big under high torque, low cadence conditions. On the stand, it will probably shift perfectly, but in the real world, when you are on climb cranking on the pedals and shifting to that combo could either throw the chain into the spokes, or it might balk at shifting.