12-28 cassette

pm78

Im having trouble getting a new 12-28 cassette to sit properly without jumping. Previously, I had a 12-23 with a standard 52-39 chainset. Both the chain and cassette are quite new. Im just wandering would I have to change the derailler too to make it work?

Pinch Flat

pm78 wrote: »

Im having trouble getting a new 12-28 cassette to sit properly without jumping. Previously, I had a 12-23 with a standard 52-39 chainset. Both the chain and cassette are quite new. Im just wandering would I have to change the derailler too to make it work?

What's the spec in the derailleur? May be that 28 is outside its range

Mechanic365

Did you make sure that the top jockey wheel clears the 28t cog by the recommended amount (unsure but sram I think is 6-10mm)
You do this by adjusting the screw on the side of where it meets the hanger

07Lapierre

Chain and cassette are "quite" new? My guess is they are worn.

smacl

In addition to derailleur capacity, you may also want to check your chain length, as bigger rear sprockets may require a longer chain.

mamax

I had a 12-28 cassette recently and regardless of adjustment it would jump on 2nd and 3rd gear, from new up to 500 km
I tried a friends wheel with same type cassette and it worked perfectly so I just went and got a new cassette and chain, I'm putting it down to a faulty
Cassette, everything is perfect now.

Pinch Flat

smacl wrote: »

In addition to derailleur capacity, you may also want to check your chain length, as bigger rear sprockets may require a longer chain.

I'm with smacl on the dérailleur capacity. OP check the model of the RD. Is it Shimano? A lot of short reach RD's have max 27T. Although some seem to cater for 28T & 30T. Would need to establish exact model first.

Quick look at Shimano techdocs http://techdocs.shimano.com/media/techdocs/content/cycle/SI/105/RD-5500-5501/SI-5TK0D-En_v1_m56577569830603908.pdf

doozerie

Various possibilities that spring to mind, many of which have already been suggested:

* Derailleur capacity. Also as mentioned, some/many rear derailleurs can actually handle a larger cog than they are spec’ed for but in that scenario you usually have to be more fussy with your adjusting to the gears.

* B-screw adjustment - if you haven’t already adjusted the distance of the top jockey wheel from the cassette then you are likely to have problems. Usual result is that that top jockey wheel is either too close to the cog, and it makes contact causing the chain to skip a little, or it is too far away (less likely) which can make changing between gears less reliable.

* Chain length - if the chain is too short you’ll struggle to change into the lower gears, if it is too long it can flop about when in higher gears (particularly when in small chainring), either way you end up with gearing issues.

* Cross chaining - don’t use outermost chainring with innermost cog(s) or innermost chainring with outermost cog(s). If you cross-chain then the problems this leads too might be exacerbated with the new larger cog.

* Rear derailleur limit screws / cassette spacers - If the new cassette is positioned the same as the old one then this shouldn’t arise, but if you added or left out a spacer (or moved to a wider cassette for some reason) when installing the new cassette then the derailleur limit screws will need adjusting.

pm78

Thanks a lot for replies all very helpful. I have spent bit more time at it there. I tried the "B" screw and no real joy. I think it that my derailleur/chain is too short. From a bit of googling it seems that I should still be able to overcome the problem but it a bit beyond my mechanical know-how. I will stick with the 12-23 anyway im told "you should be able to get over anything in Ireland on 12-23". Thanks again. Anyone looking a 12-28 cassette used twice?

Carpenter

pm78 wrote: »

Thanks a lot for replies all very helpful. I have spent bit more time at it there. I tried the "B" screw and no real joy. I think it that my derailleur/chain is too short. From a bit of googling it seems that I should still be able to overcome the problem but it a bit beyond my mechanical know-how. I will stick with the 12-23 anyway im told "you should be able to get over anything in Ireland on 12-23". Thanks again. Anyone looking a 12-28 cassette used twice?

Would it fit ultregra 6800 if so I am interested

lismuse

I am looking for a good used 12/28 , how much do you want for it ?
6800 is 11 speed so not compatible AFAIK .

doozerie

pm78 wrote:

Thanks a lot for replies all very helpful. I have spent bit more time at it there. I tried the "B" screw and no real joy. I think it that my derailleur/chain is too short. From a bit of googling it seems that I should still be able to overcome the problem but it a bit beyond my mechanical know-how. I will stick with the 12-23 anyway im told "you should be able to get over anything in Ireland on 12-23". Thanks again. Anyone looking a 12-28 cassette used twice?

I was checking the specs of Ultegra 6700 recently and the rear mech in that groupset is spec’ed for a 28 tooth (but can handle a 30, according to anecdotes). If your groupset is a similar vintage then it might well be spec’ed for a 28 too so I wouldn’t give up hope until you’ve confirmed that one way or the other.

As regards being able to get over anything in Ireland on a 12-23, I rode a 12-23 for a few years a while back with a 39/53 up front. I rode those gears up the steepest Dublin/Wicklow climbs that I was aware of at the time (Old Long Hill, Luggala, The Wall, etc.) and it was manageable. It wasn’t pretty, and my knees grimace at the memory, but it was do-able. I weigh nothing though and always have done, gravity is kinder to my knees than to many, so I had every advantage I could have really. Now that I’m a few years older I’m much more careful about putting my knees in particular under that kind of stress and I wouldn’t recommend anybody else do it either.

So personally I’d ignore that glib advice you’ve been given that anything in Ireland is ride-able on a 23 cog, I’d give fitting the 28 another shot, starting with checking the online spec of your rear derailleur. If you can post here what make and model the rear derailleur is then we may be able to help further.

smacl

doozerie wrote: »

So personally I’d ignore that glib advice you’ve been given that anything in Ireland is ride-able on a 23 cog

+1, had some gearing issues on my triple a couple of years back and ended up going up the full wall in 42/25. Unlike Doozerie, I am carrying a few pounds and not hugely fit, and by the top was seeing tunnel vision, could hear the sound of capillaries popping on my forehead, and was spitting up bits of lung. So not really that pretty a sight...