Bicycle Mechanics - Rival RD with 12-32t cassette

Hi,

Somewhere in this forum (don't remember where) I read that with some fiddling you can get a Shimano RD meant for max 27t work with bigger cogs. I have a Rival RD, could I use a 12-32t cassette with this? Or would the largest cog hit the upper derailleur wheel?

Thanks!

My long DR will take a 11-34: 9 spd
http://i256.photobucket.com/albums/hh187/10wheels/50-39-24/5-39-24002.jpg

Short one:12/30 10 spd
http://i256.photobucket.com/albums/hh187/10wheels/50-39-24/BMCBag1230003.jpg

Sometimes you can fudge a bit cranking in the B screw.

you need a longer chain, with the bigger cog, and big ring needing it.
then it will go slack on small ring/smaller-cog combos
the long-cage RD will take up that slack.. so you pick..

[Maybe-Not if you fit a smaller outer chain ring, too,
with the same number less, as you add teeth on the back]

[10 wheels went with a longer cage type]

This is exactly what I was wondering, I have a 42 teeth as an outer ring. So am I correct if I say that means that chain length wont cause a problem and that therefore cage length is not a problem?

That means the only issue is whether I can fit the 32t to not touch the upper derailleur wheel.

This is exactly what I was wondering, I have a 42 teeth as an outer ring. So am I correct if I say that means that chain length wont cause a problem and that therefore cage length is not a problem?

That means the only issue is whether I can fit the 32t to not touch the upper derailleur wheel.

Not exactly. There are two separate specifications for rear derailleurs.

The first is the maximum cog size that the derailleur will clear which, as has been mentioned before may not be a hard limit and can possibly be slightly exceeded.

The second is the chain take up. It is not the size of the large outer ring which matters for this but the difference of the largest and smallest front chain rings' teeth (if not a single) PLUS the difference of the largest and smallest cogs. This limit can also be exceeded slightly with the understanding that the smallest cogs will not be able to be used with the small chain ring since the chain will go slack. You shouldn't be using those combinations anyway.

You will still have to size the chain to fit on the big-big combination even though you shouldn't use that one either. If you forget, and you will, and shift to that combo you risk damage to your derailleur and/or frame.

Thank you, that's a very clear explanation! I have 34/42 chainrings and the cogs would be 12-32, can you say anything about whether this would be a problem?

I'm aware of the importance of keeping a straight chain, I always keep a close eye on it. Actually, one of the reasons I have the 34/42 is because that way I can keep the chain quite straight while riding the speeds I usually ride on the flat.

You don't say what spec of RD you have, SRAM make a WiFLi version for their road range which is designed to use the larger capacity cassette (11-32) http://www.sram.com/sram/road/technologies/wifli_tm

I have a normal Rival RD with a short cage. I'm aware of SRAM's WiFLi RD, it's just that since I read it might be possible to get away with the short cage RD, it would save me some money!

SRAM's 210 Technical Manual - downloaded from this page http://www.sram.com/service/sram/3,381
states that the Rival rear derailleur is rated for 28 teeth max cog and 33 teeth takeup. So you are 4 teeth over the rating with the 32 tooth cog but OK with the takeup (42-34) + (32-12) = 8 + 20 = 28 teeth. So I would expect that your problem would be having the derailleur clear the large cog but it would take up the chain OK.

SRAM's 210 Technical Manual - downloaded from this page http://www.sram.com/service/sram/3,381
states that the Rival rear derailleur is rated for 28 teeth max cog and 33 teeth takeup. So you are 4 teeth over the rating with the 32 tooth cog but OK with the takeup (42-34) + (32-12) = 8 + 20 = 28 teeth. So I would expect that your problem would be having the derailleur clear the large cog but it would take up the chain OK.

I'm running an 11-32 with Rival RD on my single without problem. It's probably a long cage to achieve the take-up with my 50-34 chainrings, but the LBS did nothing special to get the RD to work flawlessly. I will change to an X9 to give me an 11-36 option when nasty climbs are contemplated.

Thanks dsbrantjr for showing me how to calculate it. So now I guess that with a short RD, it is possible to put a 30t (like 10Wheels shows) but like you say, 4 teeth is probably too much.


I'm running an 11-32 with Rival RD on my single without problem. It's probably a long cage to achieve the take-up with my 50-34 chainrings, but the LBS did nothing special to get the RD to work flawlessly. I will change to an X9 to give me an 11-36 option when nasty climbs are contemplated.

I've been studying the pictures on SRAM's website and it looks like the WiFLi RIVAL RD not only has a longer cage but also a longer parallelogram (is that what it's called?). I guess that's required then to clear the large cog. But when I look at 10Wheel's first picture, the parallelogram doesn't look longer than normal.