Originally Posted by
Paniolo
If your rear derailleur is getting damaged by your spokes it was not adjusted right. An excessively worn chain can jump a tooth on the cassette, but I've never seen it damage the derailleur. I have seen that result in a broken chain which can cause a crash that damaged the derailleur.
It is good to avoid the Big/little and little/big cross chaining. Though the only practical implication with modern drive lines is increased chain wear.
Um, no. Big (53[standard double] or 50[compact], and little (11 or 12 depending on your cassette) are the gear ratios used when descending or riding flat terrain.
Little (39 or 34) and big (25, 27, or 28, again, depending on your cassette) are the gear ratios generally used when ascending (going up hill.)
Cross chaining is when you are in your big/big (53/27) or little/little (39/12). You should avoid this configuration but only because it wears out your chain prematurely. It should not cause your derailleur to break.