12 speed cassette, 24t sprocket "ticking"?

[AlanW]

So my current gear configuration on my Ti bike is 12sp Di2, with Hunt 40mm carbon wheels and a 11/30 cassette, and it all works perfect. No issues, perfect gear changing, no ticking etc

I've just fitted another pair of new Hunt Four Season wheels but with a 11/34 cassette fitted, which was also new to the same bike. Pleased to report that its all good, its changing gears as it should on every gear option and the only adjustment required was a couple of turns to the B screw. Even the original chain fitted which really surprised me! That is apart from the 24t sprocket, either on the big ring or small ring and it sounds like it's not quite aligned perfectly and "ticks" slightly, which suggests that it's not quite adjusted right. Its certainly more pronounced and noticeable on the big ring as I guess there is more tension on the chain. Both cassettes are Ultegra.

All the other sprockets, and possible gear combinations are not a problem at all, its just the 24t one that is giving me grief?

Certainly a new scenario on me. If it was several sprockets, then yes, the rear mech would need trimming, but only one sprocket and not the top or bottom sprocket at that?

The master plan was to have one pair of wheels for faster riding and one set for audax events, hence the different cassette and the stronger wheels. So I didn't really want to have to adjust the rear mech each time I changed over wheels, hence the reason why the second pair are also Hunt wheels

Any ideas anyone?

 

[Kbrook]

Hi, I presume you know that with the 12speed cassette one of the sprockets has half a spacer built in and you need to put the thinner spacer with that. Not sure off the top of my head which sprocket it is I think it’s a smaller one than the 24 but is it possible you have used the thinner spacer in the wrong place?

 

[Kbrook]

 

[AlanW]

It did cross my mind and I simply slid the cassette from the white plastic cassette carrier straight over onto the freehub, so if any spacers were incorrect then it would have left the factory like that!

However, I have since removed the cassette in question and the first five sprockets are all riveted together on one carrier, so that rules out any potential spacer issues, so that's 34-30-27-24-21.

So it still remains an utter mystery at the moment?

 

[AlanW]

Update and this rather bizarre and somewhat baffling occurrence!

I removed the "ticking" 11/34 cassette from my Hunt Four Season wheels and fitted it to my Hunt 40mm carbon wheels. Went out for a test ride of around 30 miles, and not a tick to be heard?

Likewise, the 11/30 cassette that was on the Hunt 40mm carbon wheels I then fitted to the Hunt Four Season wheels, another test ride and again no ticking.

Swapped cassettes back, so the 11/34 was now back on the Hunt Four Season wheels, test ride and dam it, the tick returns and on the 24T sprocket , albeit intermittently now as opposed to all the time before. Not that it should make any difference, but both cassettes are Ultegra

But how utterly bizarre, as mentioned above, it cannot be a spacer issue as the last five sprockets are all riveted together on the same plastic spider.

In truth I have absolutely no idea at all, utterly baffled by it.......