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Does the recommended "largest sprocket" matter?

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Does the recommended "largest sprocket" matter?

Old 12-08-12, 12:57 AM
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Does the recommended "largest sprocket" matter?

Just bought some (cheap) Shimano WH-R501s. The instructions recommend "largest sprocket: 21-30T". I was planning on putting my 12-36T cassette on for a stupidly steep hill climb tomorrow. Is there anything wrong with this?
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Old 12-08-12, 05:37 AM
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It's normally the RD which is the limiting factor. Most road mechs struggle with more than 29 or 30t big sprockets - the clearance just isn't there.

I'm not sure why Shimano recommends a maximum sprocket size for the wheel - I can't see any mechanical reason why the wheel could be a limiting factor, but I might be missing something.
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Old 12-08-12, 10:27 AM
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If your rear derailleur can handle it, put the cassette on, then bench test the arrangement to see that the derailleur cage doesn't interfere with the spokes on the largest cog. You may have to fiddle with a spacer to get enough clearance and then retune the derailleur.

But otherwise, it might just be Shimano covering its warranty butt; the wheel obviously is meant for road use and to match to a road group, and to step outside that "church" with an MTB cassette is like annointing the devil (in Shimano's eyes as far as warranty goes). So take care because if you bought it from an LBS, and something goes wrong, because your warranty might be annulled by the misuse clause.

It's why warranties mean almost nothing to me with bike stuff.
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Old 12-08-12, 11:57 AM
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as someone mentioned, it may be a warranty issue. all other things being equal, bigger rear sprockets have the potential to put more force on rim, spokes and hub. after all, at some point spokes can be pulled through the rim, strip through nipples and bust through the flanges on a hub.
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Old 12-09-12, 10:32 AM
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Also something bigger than a 30 means lots of stress by rider weight, loaded touring, and just monster climbs. In order words, big force at slow cadence. All of this means lots of stress on the rims and spokes, especially on the drive side.
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Old 12-09-12, 10:44 AM
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If you're putting on a cassette with a 34T, in addition to a long cage rear der, you may very well need a new and longer chain.
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Old 12-13-12, 04:07 AM
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Ok, so I put a 11-27t (I think) cassette on. Normally this bike has a 12-36t, which the derailleur (Deore LX) can handle fine.

Two problems:
1) I can't get to the smallest sprocket. Even with no tension in the derailleur cable, it sits on the second smallest.
2) When using the largest sprocket, the derailleur very lightly brushes against the spokes.

I'm guessing the answer is "spacers!" - I need to get a spacer and put it between the cassette and the hub? Doesn't that cause a problem at the other end of the cassette?

(Btw, thanks for the responses about forces. I didn't realise that a heavy load at low cadence creates more force than, say, mashing in a higher gear.

Also: I don't care about warranties. Warranties are for other people. )
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Old 12-13-12, 06:11 AM
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Originally Posted by stevage
Ok, so I put a 11-27t (I think) cassette on. Normally this bike has a 12-36t, which the derailleur (Deore LX) can handle fine.

Two problems:
1) I can't get to the smallest sprocket. Even with no tension in the derailleur cable, it sits on the second smallest.
2) When using the largest sprocket, the derailleur very lightly brushes against the spokes.

I'm guessing the answer is "spacers!" - I need to get a spacer and put it between the cassette and the hub? Doesn't that cause a problem at the other end of the cassette?

(Btw, thanks for the responses about forces. I didn't realise that a heavy load at low cadence creates more force than, say, mashing in a higher gear.

Also: I don't care about warranties. Warranties are for other people. )
Did you adjust the H and L limits? (as in following either Sheldon or Park?). Did the cassette retaining ring tighten properly? I only ask the latter since when I switched my single from 11-32 to 12-30 (Ultegra) I had to use the very thin spacer that came with the 12-30 cassette. I assume the bike shifted well with the 12-36 (or are you doing a change-out on a new, never ridden bike?). Tell us more.
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Old 12-13-12, 10:00 PM
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There is something not quite right here. The fact that the cassette is wide enough to have the derailleur brushing the spokes on the big cog, plus not being able to drop down at the other end into the smallest cog is odd.

The derailleur stop screw for the small cog certainly needs adjusting, but you also need to get that spacer on to the freehub to stop the spokes touching.

It's one of those things that I think I would need to see in person...
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Old 12-13-12, 10:13 PM
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yes, depending on the 10 spd cassette model, you may need a 1 mm spacer between the last cog (3 cog carrier) and the freehub. My CS6600 cassettes fit fine on my wh-R500 (same feehub...) and a recent new cs5700 required that 1 mm spacer to put the cassette in the proper position - most LBS have the spacers. WHy there are differences in the carrier which holds the 3 largest rear cogs, I don;t know, but there are. Even the guys at the LBS don;t know why the difference...
Once I put on the spacer, the setup was perfect and matched the prior cassette shifting, with no RD adjustment.
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Old 12-13-12, 10:44 PM
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Originally Posted by rdtompki
Did you adjust the H and L limits? (as in following either Sheldon or Park?). Did the cassette retaining ring tighten properly? I only ask the latter since when I switched my single from 11-32 to 12-30 (Ultegra) I had to use the very thin spacer that came with the 12-30 cassette. I assume the bike shifted well with the 12-36 (or are you doing a change-out on a new, never ridden bike?). Tell us more.
Ok, so this is my 9 speed cyclocross that I use for everything - touring, commuting etc. The 12-36 has been on there for 6 months or so, and shifts fine (well, apart from dirt in the housing...) I now get a new wheel, plus brand new cassette (which I think is 11-27, but I don't quite remember. Definitely 9 speed, 11-something).

I did have a little trouble with the lock ring at first, but eventually got it to sit nice and tight. I also dropped the cassette at one point, causing all the bits to separate - but I think I got it back in order. There were two kind of spacers that went between some of the smaller sprockets. There weren't any spares.

I haven't adjusted the high-low limit screws. My goal was to have two sets of wheels that I can readily swap between, so I'd rather not go down that path. (That is, I'd rather have only a 12-24 7 speed cassette than have to adjust the limit screws each time I swap wheels. Adjusting brakes is bad enough.) From memory, when I put the 12-36 on (replacing an 11-34), I had to adjust both screws - that time I had the problem of being able to reach neither biggest nor smallest sprocket.

Anyway, sounds like I should get a 1mm spacer or two (heh, third trip to the LBS in two days). I'll see how that goes.
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