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exceeding derailleur range

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exceeding derailleur range

Old 07-22-20, 01:44 PM
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torger
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exceeding derailleur range

With the tandem we have a greater need of wide gear range than on the single bikes. We have an old school 10 speed triple chainset, Shimano 5700 with 52-39-30 in the front and 11-32 in the back. Already that is more than the max capacity (the 5700 is speced as chain wrap of 40, and we are running 43), but it works fine, except one minor quirk in extreme cross chaining: when on big to big and shifting to one easier gear the chain usually jumps two sprockets instead of one.

As long as the midde ring works fine, I'm ok with some quirkiness for cross-chaining on the biggest and smallest front ring. So I'm thinking of extending the range further, without spending to much money, which means keeping the triple chainset (otherwise I need to change the levers and chainset = expensive). Changing chainrings and cassette is relatively inexpensive, and we could get a Shimano Deore M6000 10 speed rear derailleur which have larger chain wrap, but I would prefer to keep the current.

We think we have enough high speed with 52 to 11, we would like to have more climbing gears though. In normal riding we use only the large and middle ring, the granny ring is the bailout on steep climbs.

One idea is to swap the 30 granny ring to a 26. Then there will be a large jump from 39 to 26 (big risk of chain drop? we have a chain catcher though), and possibly the rear derailleur won't be able to keep the chain taught small to small, but maybe that's okay. We don't need the crosschain gears to work well as they should not be used, but it's of course preferable if there are not catastrophic failures if one forgets and accidentally put in such a gear.

Any tips or experiences from these type of out-of-spec configurations?
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Old 07-22-20, 06:33 PM
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Both our tandems have 3x9 drivetrains using 2005-era Shimano derailleurs, road front and mountain rear. I use 11-34 cassettes and the triple on our Speedster is 52-39-26. I use the largest 3 or 4 cogs with the 26 chain ring on the steepest climbs. I try to avoid crossing the 52 with the 34 cog, but the chain is just long enough that nothing will break if I do. I have a chain catcher and the low limit screw on the FD is backed all the way out. The shifts all work perfectly. Once the chain drops onto the 26, I just trim the FD slightly to stop the cage from touching the chain. The total range is 6.18 and we use all of it.
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Old 07-22-20, 10:31 PM
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I have swapped out the 30T grannies on more road triples than I can remember clearly. Since 24T is the minimum possible size with the 74mm BCD of 5 arm road triples, that is what I buy. Last one I got for $9.99 on sale. Grannies are nothing fancy. No ramps, no pins, they can be found dirt cheap on sale. No derailleur made is going to wrap that kind of gear range with a 52/39/24 triple but I haven't found that it matters.
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Old 07-23-20, 02:21 PM
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I have dabbled in this endeavor on my tandems, road, and gravel bikes a fair amount. What I have learned is that as long as you can clear the largest cog with the derailleur jockey wheel, you can usual push 2 or 3 links over in capacity. Beyond that, things get a little dicey. Both of our Co-Mo's had 30-39-52 with 11-32 in the rear and I was able to change the 30 to 28 on both bikes (I didn't try 26), however, when I tried to go to a 11-34 in the rear, the capacity was too much and I couldn't get full coverage across all gears. For me, I need to be able to shift into any gear. I may not want to stay there, but I should be able shift into it, then out of it without problem. Many will say "It's OK, I don't need to go into those gear combinations" but my experience is when riding in a hilly area such was we do, that you find you can't anticipate every shift and you don't always know exactly what gear you are in and shifting into something that is going to skip when you're heading uphill is not fun.

With the 28-39-52 set up, I get good performance on my Primera with a Truvative crankset and 5700 RD. On the Carerra, with FSA Gossamer triple crank and Ultegra derailleur, my shifting performance was never good so I just upgraded to SRAM Red Etap with an aftermarket Digirit jockey cage with a 49T capacity. Front is 34-50, rear is 11-42. We lost a little on the high end and gained a little on the low end. This was not cheap, (but I have enough bikes, I could not justify selling the need for another bike to the stoker, but fixing our shifting woes was an easy sell). In full disclosure, I just received and installed the large cage yesterday and we haven't ridden it yet, but it does cover the range the bike has.

In your case, I personally would be hesitant to go to a 26, mainly due to the reasoning I made above. You probably can get away with 28, or you could try dropping on both low and high end such as: 26-39-50/11-32 (or 34) or 28-39-50/11-34 (or 36). Do the math on the capacity numbers and go with your comfort level on shifting issues given your riding conditions. If you and our stoker can handle a drivetrain where the chain starts skipping because it is too loose, then you should be OK (We cannot in our typical riding terrain) Going to a 34 or 36 cog in the rear will likely require a roadlink. I have these on the Carerra, and 2 of my half bikes with good results. The chainrings are realitively cheap and the roadlink will set you back $22 so it is not a lot of money.

If you are considering a mountain derailleur pay close attention to the pull ratios as there is not a lot of compatibility between Shimano road and mountain groups. Shimano has a compatibility chart but I don't believe it covers mixing families (i.e. road and mtn). There is pull ratio data online you should be able to find.

A lot of folks are striving for greater gear ranges and when Shimano came out with their GRX family I was excited that maybe they had recognized the market need, but alas, they did not.

Last edited by Alcanbrad; 07-23-20 at 02:34 PM.
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Old 07-24-20, 01:01 PM
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Thanks for the responses. Seems like Ihave to try for myself and see how it works on our bike with our shifting style. I just ordered a 24T and a 26T. If none of those work I may order a 28T or just stick with the 30T.
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Old 07-26-20, 07:24 AM
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Go with the new, smaller ring and just avoid shifting to big-to-big and you should be fine.
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Old 07-26-20, 09:54 PM
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On our tandem, we have been running 53-39-26 in front and 11-40 in back for a few thousand miles. We use a Shimano 10-speed FD and a Shimano RXL M971 RD, now attached to a link. This all works very well. I don't usually shift beyond the 3rd largest cog in back when in the big ring, though it will shift into all cogs. The middle ring works on all cogs. I don't usually shift into smaller cogs than the 5th largest in back. We have a 10-speed Ultegra left brifter and an Ultegra 9-speed right brifter. When the right brifter finally gives up someday, I have a 10-speed in waiting. The RD works fine with 9 or 10 speeds. This has been an excellent setup. I also run 26T grannies on my single triples, thus getting closer spaced gearing for climbing, where it's most needed. I use chain catchers on all my bikes.

IME chain wrap is the least important variable.
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Old 07-27-20, 08:32 AM
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Originally Posted by Tony Marley View Post
Go with the new, smaller ring and just avoid shifting to big-to-big and you should be fine.
IMHO, a gearing setup that based on staying out of the Big/big is a recipe for eventual disaster. Someday in a forgetful moment youíll shift into the big/big under load. If the chain isnít sized for that catastrophic failure can result.

Much better to size for the big/big, and stay out of the small/small. Inadvertently shifting into small/small with a chain too long for the derailleur to wrap well wonít cause the kind of damage a too short chain can.

As for the 26 we put a 26 on our Robusta, with an 11-28 on the back. It worked pretty well. However, the shifts out of the little ring were a bit slow and sloppy because the 26 ring wasnít ramped and pinned to work with the 39 middle ring. Given that we didnít tend to shift in and out of the small ring frequently, it was an acceptable trade off.
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Old 07-27-20, 10:46 AM
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Originally Posted by merlinextraligh View Post
IMHO, a gearing setup that based on staying out of the Big/big is a recipe for eventual disaster. Someday in a forgetful moment youíll shift into the big/big under load. If the chain isnít sized for that catastrophic failure can result.

Much better to size for the big/big, and stay out of the small/small. Inadvertently shifting into small/small with a chain too long for the derailleur to wrap well wonít cause the kind of damage a too short chain can.

As for the 26 we put a 26 on our Robusta, with an 11-28 on the back. It worked pretty well. However, the shifts out of the little ring were a bit slow and sloppy because the 26 ring wasnít ramped and pinned to work with the 39 middle ring. Given that we didnít tend to shift in and out of the small ring frequently, it was an acceptable trade off.
I don't think ramps and pins do anything to improve shifting from a ring, only onto a ring. It's just the big jump. Captain goes, "Spin it up!" We accelerate a few strokes then ease off and captain shifts. Works like a charm. As you say, granny ring shifts are infrequent, just once at the top of a steep hill. We do wear out the pins on middle rings. I replace that ring almost once a year.
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Old 07-27-20, 03:59 PM
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Actually, my explanation was backwards, the ramps on the middle 39 ring are matched to work with the 30 ring that came on the crankset, not so much the 26 replacement. So it’s the ramps on the middle not be optimized for the setup, along with the size of the jump that affects the shifting.
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Old 07-30-20, 05:00 AM
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Below some images for the change from 30T to 24T, so now I have 52-39-24 in the front and 11-32 in the back. The chain is kept the same length, so the behavior on the middle (where most riding is made) and big ring is unchanged. The 52 to 32 gear is quite extreme still, the derailleur officially supports 30 as max on the cassette. I think I still could shorten the chain 1 - 2 links, but I kept it to keep shifting performance on the two larger rings optimal.

When dropping down to the 24T and 11 in the back the derailleur cannot wrap the chain fully. The chain will actually not go slack, but it will rub on itself on the front roller on the derailleur. Of course not optimal, but it still works. There is some rubbing on the three smallest cogs, no problem on the easier gears. As the rubbing gears still work and you get suitable audible noise feedback that you are crosschaining I think this setup is a perfectly acceptable hack .

The front derailleur can shift fine up and down from the small ring. Probably it's a little bit larger risk of chain drop and general mess, but I have a chain catcher there. I've only tested it briefly, we'll see over time how it works in panic power shifts etc.

So the non-rubbing range on the 24T front is 24 to 16 - 32 (11,12,14 cogs rub). The easiest gear on the middle ring is 39 to 32 so there still is plenty overlap of non-rubbing gears. Total range from 24->32 to 52->11 is 630%, more than most mountain bikes.


52 to 32

24 to 11

Changed from 30T to 24T inner

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Old 07-30-20, 06:08 AM
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I think you’re asking for trouble if you shortened that chain. The derailleur cage appears to be unwound just about as far as it will go I the big big. Taking out links and you increase the chance of jamming everything up.

Since there’s really no need to ride in the small small combo, just stay on larger cogs when on the small ring and you’re fine.
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Old 07-30-20, 08:35 AM
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Originally Posted by merlinextraligh View Post
I think youíre asking for trouble if you shortened that chain. The derailleur cage appears to be unwound just about as far as it will go I the big big. Taking out links and you increase the chance of jamming everything up.

Since thereís really no need to ride in the small small combo, just stay on larger cogs when on the small ring and youíre fine.
Yeah, I'll keep the chain length. I just tried to pull it a bit more with my hand and it seemed to be a bit more range left, but it's anyway not worth reducing shifting performance or increasing risk of jam in the normal range to avoid a bit of rubbing small-small.
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