Originally Posted by mtbikerinpa
By the numbers, 9 spd cogs and chains are not that much smaller than 7 or 8 spd as far as load capacity is concerned. The differece is probbably in the quality level you chose. Regardless of the ammount of gears I will only use steel cassettes. I have had numerous probs with alloy cogs, a lot of which would be corrected by a spider equipped set, but thats too much dough for me.
If the cogs are made of steel and chrome or nickel plated(as a lot of the lower level ones are and a lot of Sram's are) and the chain is XT(if shimano but not my choice) or Sram PC-68 or better, you should be able to get a full season or more out of it. I get a a full XC season and a winter on my chains and 2 seasons on the cogs before I change out(and that is before they are truly worn).
I hear what you are saying. I do not completely understand why I am having so many difficulties. I was using a mid level sram chromed steel cassette, and high end sram chain. I think what is happening is excessive roller wear, due to the smaller load bearing surface on the 9s chain. As I noted, the length of the chain has not changed much, maybe 1/16" over 20 link pairs. The cogs themselves are very similar in thickness to the 7 speed stuff...maybe 5% difference according to my micrometer. As you point out, that is not a significant difference in terms of load bearing on the tooth face. I am really surprised. For reference, we are talking about the same trail, same rider, same bike, same milage and same maintenance routine. The only thing that is significantly different is the 9s driveline. I've had 9s 3 cassettes and 3 chains of various branding wear out in short order, so I know it is not a fluke. I am a fairly strong, heavy rider, and I do a lot of climbing in the granny gear which probably exagerates the wear of the weaker 9s stuff. I'm done with it.