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Old 01-14-08, 10:25 PM   #1
saturnhr
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why no 14-25 cassettes with with a front triple chainwheel?

Why does Shimano so avidly advice against the use of its 14-25 15-25 16-27 (Ultegra CS-6600 cassettes) in combination with a front triple chainwheel? Quote Shimano technical service instructions "gear shifting performance will drop, and the bicycle may fall over and serious injury may occur"
(14-25 and 14-27(self-mixed) cassettes are very popular in junior and youth cycle sport because of regulation implemented gear restrictions)
Thanks for any insight!
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Old 01-15-08, 01:36 AM   #2
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I remember reading that when I got my CS-6600 12-25T cassette. The only difference between my cassette and a 14-25T cassette is that the latter has the 14T, 15T, 16T, etc. cogs further out. Perhaps these larger sizes--when used with the inner chainring at the corresponding chain angles--are bad for the chain. But I still can't figure out why that would really matter. Maybe the outer plate of the front derailleur can't handle it.
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Old 01-15-08, 02:15 AM   #3
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Probably because a lot of people want to cruise in the 14, 15, or 16 while in the middle chainwheel/ring and there will be a lot of cross-chaining or wearing out of the outer cogs/chain. Shouldn't be a big deal if the chainlines are close to ideal and they are using the cogs that best match up, chainline wise, with whatever the front chainwheel/ring (for example: outer 3 cogs with the largest chainwheel/ring). Seen a lot of people with 9 to 10 speed cassettes and a single chainwheel and they shift without any problems and haven't heard them complain about wearing out the cassette or chain sooner than they expect or the chain jumping under power pedaling.
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Old 01-15-08, 04:24 AM   #4
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I asked this same question a couple of months ago and no one had a satisfactory answer. There was plenty of speculation, but no answers.

So I went ahead and bought a 16-27, mounted it on my winter wheelset with the studded snows and have put three hundred miles on the combination with no troubles whatsoever. I'm running a Bontrager 52/39/30 crankset with an Ultegra FD, 105 RD and a 105 chain.

When I switch between the winter wheelset and my three-season one with a 12-23 cassette, I have to make a half-turn cable adjustment at the RD, and a half-turn back when I switch back to the winter wheelset. And yes, I find myself shifting the FD much more often to minimize cross-chaining.

Still, the combination seems to work and I'm happy with it when the slush piles up and I have to push the studded snows into the winter winds on the climb home from work.

But no, my bicycle hasn't fallen over, nor have I sustained any injuries. I promise to report from my hospital bed if it should happen.
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Old 01-15-08, 05:15 AM   #5
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Why not go to the source and ask Shimano?
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Old 01-15-08, 07:17 PM   #6
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A while ago when I first mounted my fenders the rear drive side bolt stuck out a little on the inside. I thought it would be no big deal because it seemed well out of the way, but actually shifting to my smallest cog because really hard, and once my chain jammed (I sawed down the bolt to fix the problem).

I wonder if they're worried about something like that--obviously frame designs differ in the widths and spacing of the hanger vs the seatstay tube, so maybe they're afraid that on some frames big cogs would put the chain too close to the seatstay. And in that case it would make sense that on some bikes it's no problem.
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Old 01-15-08, 07:37 PM   #7
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The derailleur pulleys do not go straight sideways. They go up and down as they go in and out. This more or less keeps the guide pulley around the same distance from the cogs. They more or less go at about a 45 degree angle. When the derailleur is all the way out to the small cog it is built to be close enough to the 12 or even an 11 tooth pulley. It seems to me that the triple might not be able to take up all the chain slack and the guide pulley might hit the cog or even the lower pulley may go up and over the top pulley.

Road derailleurs and MTB derailleurs do actually have a little different travel distance. The MTB pulley goes farther down as it goes sideways to accomodate a 32 or 34 t cog. The road derailleur stays up where it should be for a 27 or 25 t cog. Even though the sideways travel, and the cog spacing, is the same the MTB derailleur goes father down as it goes sideways. That means it has to travel a longer path than the road derailleur.

The shifters have a slight difference in travel.

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Why not go to the source and ask Shimano?

I always wonder why people don't do things like that instead of going to another source.
It works !! Why ask in a forum? I found a lot of answers doing that. That's how I learned about the shifter travel being slightly different. You don't need to have all the answers, you just need to know where to find them.

And people don't read the instructions too! All the tech sheets are on line.

Last edited by 2manybikes; 01-15-08 at 07:42 PM.
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Old 01-16-08, 10:08 AM   #8
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For my wife I put together a 9-speed 14-28 cassette using all Shimano parts. The rest of the drivetrain was Ultegra triple with 52-42-30 chainrings. It always worked perfectly.

Al
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Old 01-16-08, 12:20 PM   #9
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For my wife I put together a 9-speed 14-28 cassette using all Shimano parts. The rest of the drivetrain was Ultegra triple with 52-42-30 chainrings. It always worked perfectly.

Al
For my wife I got an Ultegra 12-27, swapped an 11 for the 12, dumped one of the middle cogs and added a 30 on the end. This is being used with an Ultegra 6500 RD.

The crankset is an Ultegra 6503 triple with the small ring (30t) swapped out for a Specialized SS 26t and it all works great.

Shimano tends to be conservative on all their specs. My policy is always "try it and see."
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Old 03-30-12, 01:06 PM   #10
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I know this thread is 4 years old, but it's still quite relevant to me. My chainwheel is a 105 50-39-30, and the cassette is a 105 11-28. I recently bought a 16-27 CS-6600 junior cassette, and read the Technical Service Instructions that came with it. I Googled and reached this thread. So, to follow 2manybikes' advice, I called up Shimano at 949.951.5003 (a half hour ago) and had a Shimano representative named Kyle to talk about it. The Shimano official explanation is that when the chain is on the 16-27 cassette's 16 cog, the long cage rear derailleur might not take up enough of the chain slack, and this is why "the bicycle may fall over and serious injury may result." I am not an expert, but I would think that the 16 cog would cause less of a chain slack than say a 12 cog or an 11 cog would (or am I mistaken?), and I told Kyle so. Kyle stuck to the Shimano official explanation though. So, can the experts in this forum comment on the Shimano official explanation? And does tsl's experience mean that Shimano is conservatively wrong? What about what 2manybikes said about the guide pulley hitting the 16 cog since it's much bigger than a 12 cog or an 11 cog? tsl mentioned doing "a half-turn cable adjustment at the RD," and what does this exactly do? Does it result in how much chain slack is taken up, or does it result in how near (or farther than for an 11 cog) the guide pulley comes up towards the 16 cog, or both of these? Thanks in advance for your expert thoughts on this.
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Old 03-30-12, 01:26 PM   #11
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Doesn't make sense to me, either. In theory, you'd be spending more time in the biggest ring with a 16-27T (or 14-25T) cassette, so excess chain shouldn't be a problem.

I'm not aware of any hospital-bed reports from tsl, either.
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Old 03-30-12, 02:10 PM   #12
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..... It seems to me that the triple might not be able to take up all the chain slack and the guide pulley might hit the cog or even the lower pulley may go up and over the top pulley......
I thought that's what the B screw adjustment was for???
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Old 03-30-12, 11:16 PM   #13
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As said by the OP, there Was a Juvenile Gearing limitation, for racing, in the past.
But IDK about whether the remaining suppliers because of consolidation,
serve that market niche, any more ..
check with your Nearest racing organization's youth training coaches.

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Old 03-30-12, 11:55 PM   #14
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Unlike Sram where the jockey wheel is on center with the lower pivot and there of fixed height (in any gear) regardless of cage angle, Shimano and Campagnolo jockey wheels rise or fall with changes in cage angle.

That makes the B screw setting more complicated (pre2001 Campy) because it has to be OK for all sprockets on both the largest and smallest chainrings. Certain chainring size spreads combined with certain cassettes, especially those with larger smallest sprockets can therefore be extremely sensitive to B screw setting and chain length.

If everything isn't dialed in correctly the jockey wheel will bump a sprocket pushing the RD back and possibly breaking the hanger or the RD itself. I'm sure that with care these dis-allowed combinations can be made to work carefully, but it imposes an added burden on the mechanic, and Shimano rightfully wants to protect itself from liability if it isn't done correctly.
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Old 04-01-12, 04:39 PM   #15
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For the past 5 years I've been using Tiagra 14-25 nine speed cassettes with 28-38-48 chainrings on three different bikes. Front deraillers are 105 triples and rears are 105 short cage. I have about 35,000 miles total on these combinations (about a dozen cassettes in all) with zero problems. The one-tooth steps from 14 through 19 are very convenient given the flat but windy riding conditions in east-central Florida, and I'm careful to avoid cross-chaining when using the large and small chainrings.

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Old 04-01-12, 06:17 PM   #16
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I started racing when I was 17, which was before Shimano was dominant in the market. Suntour was the major player then and 14-24t 6-spd freewheels were pretty common. Shimano had just come out with 7-spd on their 600AX & Dura-Ace AX lines and I looked at those as well.

Aside from the jockey-wheel alignment and B-screw adjustments mentioned earlier, I found on some bikes, the 14t sprocket actually caused interference with the end of the chainstay and/or between the chain & seatstay. When a 126mm wheel is built to minimize dish and maximize strength & stiffness, the outermost cog is pushed as close to the drop-outs as possible. Typically just 4mm or so or so the chain barely clears the dropouts. One some bikes, mostly custom jobs with small dropouts to save weight, the 14t cog is large enough to cause rubbing.

I find using a 13x48t combination works just as well for rollouts. This was way before the current compact-crank trend came out and I just used a 48/36t 110mm crankset from a touring-bike. Sugino VP/VT/GT, or something like that.
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Old 04-01-12, 09:24 PM   #17
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Quote:
Originally Posted by saturnhr View Post
Why does Shimano so avidly advice against the use of its 14-25 15-25 16-27 (Ultegra CS-6600 cassettes) in combination with a front triple chainwheel? Quote Shimano technical service instructions "gear shifting performance will drop, and the bicycle may fall over and serious injury may occur"
Now for the real answer, it's called total chain-wrap capacity of the rear-derailleur. The rear-derailleur cage has to swing forward & backwards using spring-tension to keep the chain tight in each gear. When the bike is the small-chainring (and/or small cogs in back), you may notice that the rear-derailleur's lower-pulley aims towards the back:



Then when the bike is in large-chainring (and/or large cogs in rear), the derailleur cage is rotated and lower-pulley is aimed fowards:



There is a limit to how much difference in chain-length a rear-derailleur can handle at its maximum rearward to maximum forward rotation. This is the total capacity given in tooth-count listed in the specs. This is calculated as:

total tooth capacity = (BiggestChainring-SmallestChainring) + (BiggestCassetteCog-SmallestCassetteCog).

For a 14-27t cassette combined with a 52/39/30t crankset, that's a total-capacity of 35t. That exceeds the capacity of the RD-6700 derailleur by just a little bit. What happens when you have a combination like this with an "unsupported" rear-derailleur is you may end up in a gear combination where the rear-derailleur is fully rotated back with minimal spring-tension (30f/15r). Trying to shift while being shoved in a bumpy corner going over railroad tracks may cause the chain to skip and drop off the front chainring. No, this doesn't ever happen in a race...

Similarly, if you get caught behind a fading rider 1/10th of the way up a hill in your 52/23t gear, the rear-derailleur cage may be fully stretched out. Not knowing that you're only one gear from max in rear and doing that emergency shift to a 52/25t combination may actually snap the rear-derailleur resulting in the RD and chain wound up in your rear-wheel. Nah, I've never, ever done anything like this...

So if you want to use any of those cassettes with a front-triple, you're better off with a medium-cage rear-deraileur with 39t capacity.

Last edited by DannoXYZ; 04-01-12 at 09:31 PM.
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Old 04-01-12, 09:40 PM   #18
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Quote:
Originally Posted by skylla View Post
A while ago when I first mounted my fenders the rear drive side bolt stuck out a little on the inside. I thought it would be no big deal because it seemed well out of the way, but actually shifting to my smallest cog because really hard, and once my chain jammed (I sawed down the bolt to fix the problem).
It's usually easier to use a few extra washers
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Old 04-01-12, 11:18 PM   #19
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Quote:
Originally Posted by DannoXYZ View Post
Now for the real answer, it's called total chain-wrap capacity of the rear-derailleur. The rear-derailleur cage has to swing forward & backwards using spring-tension to keep the chain tight in each gear. When the bike is the small-chainring (and/or small cogs in back), you may notice that the rear-derailleur's lower-pulley aims towards the back:



Then when the bike is in large-chainring (and/or large cogs in rear), the derailleur cage is rotated and lower-pulley is aimed fowards:



There is a limit to how much difference in chain-length a rear-derailleur can handle at its maximum rearward to maximum forward rotation. This is the total capacity given in tooth-count listed in the specs. This is calculated as:

total tooth capacity = (BiggestChainring-SmallestChainring) + (BiggestCassetteCog-SmallestCassetteCog).

For a 14-27t cassette combined with a 52/39/30t crankset, that's a total-capacity of 35t. That exceeds the capacity of the RD-6700 derailleur by just a little bit. What happens when you have a combination like this with an "unsupported" rear-derailleur is you may end up in a gear combination where the rear-derailleur is fully rotated back with minimal spring-tension (30f/15r). Trying to shift while being shoved in a bumpy corner going over railroad tracks may cause the chain to skip and drop off the front chainring. No, this doesn't ever happen in a race...

Similarly, if you get caught behind a fading rider 1/10th of the way up a hill in your 52/23t gear, the rear-derailleur cage may be fully stretched out. Not knowing that you're only one gear from max in rear and doing that emergency shift to a 52/25t combination may actually snap the rear-derailleur resulting in the RD and chain wound up in your rear-wheel. Nah, I've never, ever done anything like this...

So if you want to use any of those cassettes with a front-triple, you're better off with a medium-cage rear-deraileur with 39t capacity.
That explanation makes sense, but the cassettes the OP listed (14-25, 15-25, and 16-27) would all be within the RD-6700's 33T capacity if used with a 52/39/30T triple. (Or other standard triples like a 48/38/28 or 52/42/32...)

- Scott
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