Hi,

I usually ride a 12/25 cassette but have planned a more hilly ride this weekend.
I wanted to mount that 12/28 SRAM cassette I had in stock and the speeds were just skipping all the time never staying except on the smaller sprockets.
I then mounted a 12/27 Shimano a friend lent me to try it out and it worked perfectly.

Both cassettes are almost brand new (the club bought them and no one really rode them yet), and my chain is not completely new but has minimal wear (and is a Shimano one if it has any importance)_

What would explain this difference in behavior?

I am positive it is *not* the 1 extra tooth: I voluntarily let a couple of extra links when sizing the chain so on my regular 12/25, it is a bit long so when using 27 or 28 make no difference and it fits just fine.

Could it be the Shimano chain? the SRAM derailleur (then why does it work with Shimano and not with SRAM... lol)?
And, by the way, SRAM states the derailleur can handle as many as 28 t on large sprocket, and yes, I set the B-screw properly.

I always thought Shimano and SRAM were fully compatible whereas Campagnolo had its own specificities...

Also, is the spacer required to fit 10sp cassette on 11sp freehub the same for Shimano and SRAM?

Most likely the SRAM sits a tiny bit closer (or further away from) the hub. So you probably just need a slight cable "tension" adjustment to line the rear derailleur up with the cogs.

Rumor has it they copied the Shimano freehub spline pattern

(it happens a lot Shimano sets a new standard then if everyone else uses it they change to something else and the game starts again)

That's the only thing I can think of.

They are compatible within 9/10/11 groups and I run a SRAM cassette on my tandem with everything else Shimano.

Did you attempt to adjust the derailleur at all?

Is your derailleur capable of a 28-tooth cassette? Not all are.

I always count on readjusting my derailleur whenever I change cassettes, even like for like, due to manufacturing tolerances.

It is likely that your B-screw adjustment needs to be changed when you change the cassette for one with different numbers of cog teeth; perhaps this is why the 27-tooth cassette ran OK but not the 28.

If you are going to put a larger cassette on you must be sure that your chain is long enough that you can comfortably shift to your large ring/large cog combination without straining anything. Test this while pedaling gently by hand.

ok thanks for confirming,... I might try to play around with derailleur adjustements after this weekend's ride,... or just go back to my 12/25 and forget about this all until my next hilly ride

Not really, I mean, not beyond the B-screw setting.

Yes, SRAM documentation says maximum is 28t.
The B-Screw had been adjusted.
The chain is long enough. As I said, I voluntarily sized it a few links too long when sizing it for the 12/25 (thinking about using it with larger cassettes). And, FWIW, when I put the 53/28 speed which is the one requiring the most chain length, the rear derailleur is extended but not fully, there is still some room for a little more (which is one of the criteria for a perfect chain length sizing, though there are several methods, I know..)

The fact that the 12x27 Shimano cassette shifted perfectly for you was really just good luck. As a general rule, when you change cassettes, even for one by the same manufacturer and the same configuration, you may have to make minor adjustments to the rear derailleur's cable tension and/or limit screws. There are manufacturing tolerances that may have to be corrected for.

On 11 speed Shimano-style hubs (except Mavic), most Shimano 10 speed cassettes require 2.85mm of spacers, while SRAM cassettes need 1mm less (1.85mm). There are exceptions (one being 10 speed Tiagra cassettes which, like SRAM, don't need the extra 1mm).

I had a SRAM 10sp that came with the 1.85 spacer installed in place of the very first inter-cassette spacer. I think it was between cogs 6&7. Chain kept trying to shift into lower gear. That was fun to find. I stuck a 10sp Shimano spacer in and it works perfect.

That's interesting... Is there a link to a documentation I could find to support this?

And how about that mavic hubs? I gave a mavic wheel so what happens on those?

I replaced a 6800 cassette with an 1190 and shifting was terrible for about a hundred miles. Going up the cassette was fine. But going down was like *click*...pause...*clunk*. No amount of tension adjustment helped.

I almost sold the thing. Then it just got better. Now it's clickclunk. Which I can live with.

Answer to myself, in case anyone else is interested: Cassette How-To - Part 2 - Slowtwitch.com

I have swapped them out several times on many bikes, sounds like a simple RD adjustment.