wn rider

After riding a friends Burley for a few hundred miles, my wife and I finished our first year on our Co-Motion. We have had a great time together and I have been really pleased with the bike with the exception of some frustration I have had regarding front-end shifting.

Despite continually adjusting and tweaking the FD (both me and LBS), I continue to have issues with dropping into the granny. Always seems great on the stand but the only way it will reliably drop into the granny is when I run high rpm and essentially zero torque. It is a 2012 and we have the stock Truvativ Elita Tandem crankset and 105 components.

One tandem shop I spoke with indicated that others had some shifting issues with the Truvativ Elita cranks so I don't know if it would make a significant difference if I replaced these with the FSA or Shimano. I am not running a chain catcher right now so maybe I just need to put one on and adjust the inner limit.

In the end it's one of those things that isn't a huge deal since I can compensate for this by making sure I shift plenty early but it seems like it should work better than this.

Anyone have any thoughts on how much impact the crankset actually makes?

Paul J

Front shifts are a weakness with tandems. I would highly encourage you putting a chain catcher on the bike to save from a dropped chain. Our bike is temperamental on the front shifts we have to give a very slight pause before adding pressure along with not shifting into the small ring with the chain too far down the rear cog. We've found that it doesn't take too much pressure on the peddles to create an issue on our front shift. We are using 9 speed Race Face cranks with a XTR front derailleur.

twocicle

FWIW, here is a link to a related thread concerning your crankset:
https://www.bikeforums.net/showthread...a-Tandem-crank

Since your CoMo is a 2012 model, likely you are running a 10spd config?

I would not look at the cranks themselves as playing much of a roll in your downshift->granny problems, but it could be related to chainline, ie: your driveside may be setup too far to the inside, an issue which could be resolved by using BB or axle/spindle spacers. Next, your cranks likely came OOTB setup for 9spd, which typically isn't much of a problem, but maybe that depends on the quality of the chainrings provided with those cranks. You may want to look at replacing your chainrings... not all are created equal. The best bet for 3rd party 5-arm rings is: 1) Shimano, 2) Specialites TA (go to Wiggle.com for these), 3) FSA N10 rings.

Other than chainrings, it could be your FD simply has a weak return spring. Perhaps have the shop let you test out a new triple FD.

Chain mfr & model? I have had great shifting performance and durability using Shimano Ultegra 10spd chains on our tandems.

Hope that helps.

Chris_W

Cranks are a hugely important part of a bike but also an expensive one, so bike companies often save money on them. Truvativ Elita cranks are a couple steps down in quality from the rest of your 105 equipment, in terms of weight and shifting quality; and as mentioned above, they are normally designed for 9-speed chains - although this normally doesn't make a difference it's certainly not optimal. FSA Gossamers are one step up but are still a little behind the quality of 105 components (the crankarms are not hollow and the chainrings are pretty basic), and all FSA stuff tends to be overpriced aftermarket, so I wouldn't think that the Gossamers are really worth the upgrade cost. The Shimano cranks are awesome quality, great weight and shifting if you are happy with the stock ring sizes, but they are obviously not cheap.

twocicle

Still, while the Truvativ Elita cranks may not be a top model, looking to replace those can be expensive. Other than a poor crank install resulting in a bad chainline you would be hard pressed to blame the cranks as the primary factor to the problem in the OP. If it does turn out to be a chainring issue, you can buy a set of 3 top quality chainrings for $100 and be done with it. for example see the "Shimano Ultegra FC-6603 Triple Chainrings 10spd".

B. Carfree

This may not be helpful, but when I changed my middle ring down from a 42- to a 38-tooth, my tiagra front derailleur no longer shifted well to the granny. The bulge in the derailleur stopped too high on the outer cage to push the chain off the 38-tooth and onto the granny. On the advice of people on this forum, I changed to an old dura ace triple front derailleur that I got on ebay and that solved my problem. If that had not worked, I would have had to go to a smaller big ring in order to be able to drop the front derailleur low enough to work.

Dean V

I have used Elita and Gossamer cranks with no shifting problems. Certainly does help if you don't leave the shift late so you are still at a good cadence and definitely need to make sure you or stoker aren't putting power through at the time.

PMK

FWIW, sometimes it possible to easily modify the chainring by changing the tooth profile at two locations 180 apart from the other. For the off-road tandem that ran single speed full profile tooth patterns for a middle ring, I copied the location and tooth profile from a chainring known to shift well. 5 minutes of modification and the chain easily is walked from middle to granny, where before it was as the op mentioned, not consistent and required little or no pedal pressure.

PK

zonatandem

Setting up shifting on a work stand for a tandem is always a bit of a gamble.
Works perfectly when testing it on the stand but adding the weight of 2 riders in actually riding it will likely screw things up.
Usually some minor tweaking while on the road will set things right.
It helps that you ease up a bit on the pedal pressure when shifting to small chain ring and to be far enough back on the cassette also helps.

bikeinxs

Friction is your biggest enemy to good shifting performance, we suffered through bad shifting on our speedster for years until I solved all the problems. Over the years I've found three main points of friction;

1) Particularly on the tandem for some reason I find that over time the cable housing will deform where it enters the shifter. This allows the inner reinforcing wire to partially enter the shifter and squeeze the shift cable. Check the ends of the housing and if you see bare wires just trim it back a bit and reinstall the housing.

2) the point where the cable wraps around the bottom bracket is a huge source of friction. The cable should not be running on bare metal. I take a section of shift cable housing and strip away the outer casing and reinforcing wires so I am left with just the smooth inner liner. Slip a 6 inch piece under the bottom bracket and run your shift cable through this. Makes a massive difference in performance.


3) Cable housings are the obvious source of friction but most tandem setups don't have much housed cable. Still, it doesn't hurt to just replace it regularly. I buy in bulk and it's quite cheap.

We run a race face crankset with a mix of brands of chainrings and a gearing range far outside that recommended by Shimano with excellent performance.

Onegun

You've basically answered your own question. Although adjusting front derailleurs on any given bike is an art akin to voodoo, I'm going to assume that after both you and your LBS have futzed with it, adjustment is not the issue.

Given that, I would start with an N-gear Jumpstop. The difference between the Jumpstop and the dog fang type chain catchers is that dog fangs are designed to simply catch the chain as it derails off the granny to protect the BB/cranks/chain, and to enable you to shift it back on. The Jumpstop is designed to stop the chain from derailling, so you can, in fact, over adjust the inner limit screw, readjust the cable, and get more reliable shifting.

Our 2005 trek T2000 has Shimano Ultegra cranks/rings, and our Burley Tosa has Truvative Elita cranks/rings. Both have Jumpstops, both are over-adjusted to the inside, and both will hit the granny reliably, although you do have to back off pressure a bit longer on the Elita setup.

So, if the $10 Jumpstop fix doesn't fully satisfy and you don't have PMK's metallurgical skills and tools, a change to the Ultegra rings may well be in order. However, do note above where I said, "more reliable shifting", not "perfect" shifting. Perfect front shifting is only available on two systems that I am aware of. One is Di2, which is not yet available for triple cranks, and the other is a two cable, push-me-pull-you system designed/manufactured/ridden by my friend Wyatt out in NoCal. It handles 4 chainrings flawlessly, but sadly, he only makes them for his own tandems!

wn rider

I appreciate the responses and suggestions. Its been icy and cold in the midwest lately so I will have some time to try a few things over the holidays. Thanks folks.

fietsbob

In the 50s the FD was on the front seat tube, not the rear. so a shorter cable but longer chain..

seems the cross chain issue becomes Moot, then..

Rambetter

I seem to have had almost the same problem on my '87 Santana. After fiddling with it for a while I decided to go with the chain catcher approach and it has worked elegantly for me. That is, have the front derailleur increase its throw towards the small ring by adjusting its limiting screw, and add a chain catcher in case of overthrows.

I'll state the obvious here, but there are many parameters in adjusting a front derailleur.
- the height of the front derailleur, meaning how high or low it's clamped onto the rear seat tube
- the angle at which the front derailleur is clamped
- the state of the limiting screws
- the cable "tension" - combination of where the cable is clamped, the length of the housings, the state of barrel adjusters, etc.
- (might be a small factor) things like the chain design and chainring design

In my case, I did not want to get rid of some of the original parts partly because they are rather "classic". So after trying to adjust the first four parameters above, and not succeeding after some amount of time, the chain catcher seemed like the best option.

dfcas

Shimano front Derailleur shifting is sketchy at best. I would replace the front shifter with either an older Campy ergolever with 11 clicks or a friction downtube shifter, both of which allow good trim options.

Onegun

Doesn't really solve the OP's issue, although the trim options are nice. I run Campy ergo levers on our T2000 with Shimano running gear, and still had the issue until I installed the Jumpstop and over-adjusted the derailleur. One day I might try a Campy front mech and see if that solves it.

waynesulak

A chain catcher is helpful in all situations to prevent the chain going inside of the granny ring.

I have found that bar ends and Campy left shifters result in an incremental small movements of the FD which helps reliably move the chain off the middle ring onto the small ring. The Shimano design makes one spring release movement which is more likely to fail to move the chain. I like a Shimano 105 FD for its large stiff cage but any modern FD will work.

I have not used one but it seems to me that an electronic system would by its nature move the FD smoothly like a bar end and have that benefit in addition to higher force than a spring release. It is only the one step spring release of the Shimano mechanical FD that causes the most problems with shifting under loans.

Another factor that helps shifting into the granny easily are lower cadence/higher chain tension. Shifting into the granny is more difficult for any system at low cadence and high chain load adds to the problem. Often teams get trapped grinding up a hill at 80 or lower cadence and can't let up making it hard for the FD to move the chain. Even at full power I can shift the chain into the granny easily if the cadence is 90 or above. I often don't announce double shifts for this reason. Then again my stoker could pick up on the RD shifting up a couple gears and knows that is happening just as I start to move the FD. She may be letting up on the power just a little but I don't notice it.

dfcas

I bought a new Cannondale tandem that had Ultegra shifters, Truvativ Elita cranks and a 105 front derailleur. The problem was the amount of cable travel from the Ultegra shifters limited the amount the d could travel. If I moved it to where if would shift down to the granny, it didn't pull enough cable to shift up onto the big ring.

A shifter that allows more derailleur travel will be better at forcing the chain off the middle ring and down to the granny. A chain catcher or such may help with dropping the chain, but as I understand the OP thats not the problem yet.

Onegun

Interesting observation.

It seems to be a trend that, within reason, the farther down Shimano's line you go, the better suited the component is to tandem usage. I found that their $35 "below grouppo level" calipers work better for tandem brakes than Dura Ace. I suppose it's just the old adage, "Strong, light, cheap. Pick two." They have to be competitive with each other in both weight and price, so ...

Boy, howdy! The Di2 front mech comes with a warning about having your fingers ANYWHERE around the chainrings when you're operating it! Apparently it WILL take your finger off!

Onegun

I originally had Ultegra shifters on the T2000, but don't remember experiencing that. They were 6503s, (9speed), mated with an Ultegra front mech and Ultegra cranks. Probably just a difference in our setups.

With mine, I overadjusted without losing the big ring, but wanted the multitude of trim positions with the Campy plus a couple of features available with the Ergobrain that the Flightdeck didn't offer.

dfcas

"I continue to have issues with dropping into the granny"

I think This choice of words is confusing. As I understand it, the chain wants to stay on the middle ring and not fall onto the granny ring. As most others understand it, the chain is falling inside the granny ring onto the bottom bracket shell,thus the suggestions for a jump stop/chain catcher type device.

We need the original poster to clear up what the problem is.

Dean V

The problem is it won't shift to the granny from the middle ring. The others are suggesting having the lower limit screw wound back further to allow greater front mech travel to help drop the chain on to the granny. This in conjunction with a chain catcher due to the increased risk of the chain coming off the inside of the granny ring.

Onegun

You are correct in your understanding. What everyone else, (including me), is saying is that to solve the problem you have to loosen the inner front derailleur limit screw and readjust the cable to make it shift. In doing so you will, in all probability, now have a problem with the chain dropping if you don't have a chain catcher.

Onegun

Oops! Didn't see Dean's post before I wrote mine!

dfcas

What I am saying is that the STI shifters I used did not allow enough cable travel and therefore derailleur travel to overadjust toward the inside and still be able to shift up onto the big ring. If that is the OP case, then a different shifter that allows more travel may solve the problem. A bar end or downtube shifter or older Campy ergo may solve the problem and he should try that. It may need a chaincatcher, may not.

In answer to the OP question about the Truvatic elita crankset, I think it is fine and is not the problem. I used one without issue after I switched shifters. If it is ISIS, thats a bigger problem as finding BB's that last longer than ice cream is difficult.