Downgrading cassette from 32 to 28

alexul

Hi all,
Maybe this one has been answered before but all my searches get me results for the opposite. I have a new bike which came with a 11-32 cassette Ultegra long derraileur. On another bike I have much better wheels but with a 11-28 cassette. For convenience I would like just to change the wheelsets. Will the long derailleur function the same or do I have to make some adjustments like tightening the b screw? Maybe adjusting the chain length?
Thanks

sandyballs

My logic considers it this way, you already have a rear sprocket within the 11-32 that will be 28 teeth so no adjustments are necessary less potentially a little turn of the barrel adjuster to compensate for freehub differences.

The weight weenies will tell you that you do now have a couple of unecessary chain links and you could save yourself a few grams by removing them. I would just leave the set up as is and you will still have the ability to run the 11-32 if you are going somewhere particularly hilly.

Mad_Malx

Straight swap will work fine. Think about it - your old 2nd gear was a 28, so your derailleur will function pretty much as it did before.
You get slightly less chain slap and maybe slightly crisper shifting if you take off two links and tweak the b screw, but it's not essential and you may not even notice.

Mad_Malx

^like wot sandyballs said faster than me.

gethinceri

:shock: "Downgrading"

The Rookie

Will work fine, you may need to wind the b-screw out a little and tweak the indexing, ideally you would remove a pair of links in the chain but it's not essential.

sandyballs

Can someone please genuinely explain why they think the b screw would need to be adjusted? The cassettes spacing for the 11-28 (Shimano or Sram) would be,

11-12-13-14-15-17-19-21-24-28

Slightly larger jumps on the 11-32

11-12-13-15-17-19-22- 25-28-32

So in my head of the 10 sprockets 7 are exactly the same, less for the trim I think everything is fine as is. Cheers.

964cup

Because the B-screw adjusts the distance between the top jockey wheel and the cassette, and now that your largest cog will be smaller, you might want to unwind the B-screw a bit to get the jockey wheel closer in, for best shift quality. I wouldn't bother, though, as if you leave it alone you'll be able to swap wheelsets without faffing. I have 11-26, 11-28 and 11-32 on various wheels and swap between them as needed without issue.

sandyballs

But the derailleur works on the principle of a parellelagram and remains equidistant from the cassette throughout its movement. Should it be already correctly adjusted on the 11-32 then adjusting it closer would surely bring it too close on 7 of the sprockets that remain exactly the same.

Mad_Malx

I think you're right Sandyballs.

Bobbinogs

Nah, the b stop has no function for all the cogs except the last one on any cassette where the extension of the cage is greatest. The guide wheel needs to be far enough away from the biggest cog such that it doesn't snag or interfere...too far away and the chain between the guide and cog will flex (very slightly) such that shifting is not as snappy as it could be. So, 2 things to consider but the former is critical whereas the latter is just preferable.

timothyw

I'd recommend checking the chain length and reducing as appropriate.

If you get chain-suck and scratch your brand new bike's chainstay, you might wish you had earlier. Certainly I did.

The Rookie

Chain length doesn't create chain suck though, that's worn parts or crud.