artemidorus said:sogood, this is certainly cycling dogma, but have you any evidence to back it up? The wear point seems intuitively plausible, but the loss of efficiency ain't necessarily so.
I don't have any scientifically measured data to back that up. But the logic makes perfect sense and is consistent with all engineering principles. Added to that the extra grinding noise you hear when severely cross chaining, it's enough physical evidence that you don't need super accurate measurements. So the old saying goes... If it looks, smells and feels like [censored], then you don't exactly need to taste it.
Further, one can always bring out Sheldon Brown on these subjects matters,
"Try to avoid the gears that make the chain cross over at an extreme angle. These "criss-cross" gears are bad for the chain and sprockets. Especially bad is to combine the inside (small) front sprocket with the outside (small) rear sprocket. This noisy, inefficient gear causes the chain to wear out prematurely."
http://www.sheldonbrown.com/gears.html
And then there's the known benefit of fixies/single speed, where the straight chain line is a major selling point in terms of cycling efficiency.
So I think this so called dogma can be accepted and adopted for everyday riding, especially when you have an alternative combination of chainring and cog that can deliver the same gear ratio.