xlDooM

Hi guys. I recently replaced my Shimano HG30 11-32 mtb cassette on my commuter with a Sram PG-970 11-21 road cassette. Both are 9 speed. Chain is KMC 9 speed. Derailer is Shimano XT long cage. Front is Blackspire monoveloce, which worked fine with all gears of the hg30 cassette except for the biggest sprocket (cross-chain).

Let's say the largest sprocket is 1, smallest is 9. Then the sprockets 2,3,4,7,8,9 run sweetly, but in 1,5,6 I can 'feel' the cassette, i.e. I feel some rumble through the pedals. Sprocket 1 I put down to cross chaining, but 5 and 6 have me puzzled. How can there be cogs on both sides that run smoothly but those two don't?

I've adjusted the b screw on the derailer to bring it in closer, but obviously with this being a large capacity mtb derailer it's not exactly snug all over the cassette. Regardless, it shifts up and down crisply. I've shortened the chain so that in the largest sprocket on the rear, the derailer is angled forward slightly from vertical. The chain is not stretched, I measured it and it is definitely under 1mm stretched (chain has 1100 miles).

Any ideas why my drivetrain is less than perfect, even though all components should be compatible and the cassette is much more expensive than the one I replaced?

I've been contemplating a 10 speed chain, thinking perhaps the side of the chain rubs on the next-larger sprocket for some reason. All suggestions welcome!

jland

I had a SRAM OG 1070 cassette (the one with a tooth missing on each cog) which I found to be quite noisy (KMC chain, Shimano 105 RD). I switched to a Shimano 105 cassette because I needed a different gearing setup and the thing purrs like a kitten compared to the SRAM. The OG is supposedly noisy compared to the PG, but I remember also feeling the chain running over the cassette teeth in some gears.

shelbyfv

I used 970 cassettes w/o problems for years. The last one I bought had an issue similar to yours. The chain really didn't seat well on one of the larger cogs. IIRC, it got better after I used it awhile. I think the quality control for those cassettes is not what it once was. Maybe since it's not the latest product, SRAM has changed suppliers or cheapened it in some way. They don't seem to be as well finished as they once were.

Kimmo 

It could simply be the dies that stamp them out are getting a bit tired.

xlDooM

I rechecked it and the problem is indeed that the chain is simply not seating well on those cogs. Nothing I can do about it except hope it wears smooth.

Next time I'll pay the extra 15 for the shimano ultegra counterpart I guess. Thanks for the input.

shelbyfv

Maybe hold a file up against the teeth of the offending cogs while turning the crank. Just a little smoothing might be enough.

ThermionicScott 

IME, even if a chain doesn't have much stretch, it can run a little rough with a brand-new cassette. I'd buy a new chain and rotate the old one back in after another 1000 miles.

xlDooM

I was kind of hoping the chain would be stretched enough to warrant a replacement, but I really can't measure any stretch. It has 1100 miles, but I mostly ride in the 100-150W bracket and I'm a spinner so I'm not putting enormous stress on it. Also, it runs fine on most of the cassette, just not those two sprockets...

ThermionicScott 

I'm in much the same boat -- I don't put out a lot of power so I mostly spin. And I take good care of chains! Still, when I switched from a 13-26 cassette to a 13-23 cassette on my "go-fast" bike, the smaller half of the cassette ran a little rough. The chain was at 1500 miles or so but had no more than 1/32" stretch. Everything ran smoothly once I installed a brand-new chain.

My thinking is that some element of wear was causing the rough feeling -- perhaps roller clearances had increased, so each roller could shift a little in the tooth pocket as the sprocket went around. And my plan is not to throw away the 1500-mile chain, but to clean and lube it, and rotate it back on to the bike once I've put 1000 miles onto this combo of new parts.

xlDooM

Ok you have me convinced, I'll be getting a new chain and will report back! Comes the question: SRAM chain to go with the cassette or Shimano chain to go with the derailer, or KMC chain because it's cheaper? I'm leaning towards SRAM because of the power link. I broke the KMC missing link within a month, but I do like the ease of use of the special link...

ThermionicScott 

I prefer the SRAM links, too. The derailleur doesn't care what brand of chain you use, but you want to use approximately the same "speed".

Hope the new chain does the trick!

TallRider

a side-observation that may or may not apply to your question: using an XT rear derailer (designed to track with a wide-range cassette) on a more "flat" cassette means that as you get to the larger cogs, the rear derailer is further away from the cassette than it is supposed to be.
(that said, I ran an XT rear derailer on a Shimano 11-23 8-speed cassette for years with no problems, so you're probably okay here)

VELOSURANCE

I learned the hard way and wasted rides so when I swap out a cassette I do the chain also. If it's time to replace a chain ring or cassette it's also time for the chain. IMHO. Dave

xlDooM

Yes I actually wrote much the same thing in my original post Shifting is crisp enough though, no complaints there.

I would do the same, it's just that I swapped the cassette because I wanted different ratios, not because it was worn. It looked just fine, and it bloody well should after just 1100 miles

xlDooM

Update to this problem: we will never know if the new chain would have fixed it, because in the 200 miles I rode before I got around to ordering a new chain, the problem gradually disappeared. I guess the cassette had a few slightly out of shape teeth on those two sprockets that have now worn smooth.