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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 02-21-14, 09:33 AM   #1
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Smoother shifting

Crunching through the numbers of the gear ratios I had a little epiphany this morning.

If every time I shift a chain ring, I do a simultaneous and opposite shift on the rear cog (double shifting?). That applies to either up or down shifting. That way the change in the cadence will be much smoother and not as abrupt.

Trying it out on my ride this morning, the shifting worked flawlessly.

This seems so simple and intuitive, it made me wonder if everyone is already doing it and I am just a little bit slow. Or are most people not bothered by the change in cadence and I am making a big deal over a non-issue?

On another note, can the DI2 system be programmed for this? It would be ideal if the buttons on either hand can be programmed to shift up and down and not linked to the individual derailleur. Can the gear choices and double shifting be made by the computer? Or does this still require a software hack at this point? It seems to me that this is an easily programmable advantage of the electronic system over the traditional mechanical system.
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Old 02-21-14, 09:58 AM   #2
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On flat road I usually shift two cogs in back when shifting a ring in front. It just depends on the gaps in your cogs and between chain rings. When going up hill I have to judge if cadence is dropping or rising fast maybe I just shift one cog in back. There is one steep hill our ride that as we start to climb I always just shift from big ring to middle because we need a lot more gear fast.
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Old 02-21-14, 10:07 AM   #3
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Smoother shifting

Yeah double shifting is a common practice. I'm right handed so I typically reach down, shift the left lever/frt derailleur with my thumb and shift the right lever/rear derailleur with my fingers.
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Old 02-21-14, 01:41 PM   #4
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I used to sometimes shift both ends at once until I dropped a chain... now I try and reduce the drivetrain disruption and shift one end at a time. I usually try and anticipate things and get the front shifting done before the grade requires it.
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Old 02-21-14, 05:18 PM   #5
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I almost always double-shift. Only time I don't is for an exceptionally rapid acceleration or deceleration. The deceleration might leave us spinning much too fast for a few seconds, but no big deal. With our 11-34 cassette, chainring shifts require 1-2 cogs in back. With a smaller cassette, the back has to be shifted even further. By now, it's a habit. I just do it and know how many cogs in back to shift almost automatically.
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Old 02-21-14, 05:38 PM   #6
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Don't double shift. The slack in the chain can be too much or the chain tensioning function of the derailleur to control. Eventually you will drop a chain, not good to push your luck. The chain could get caught between the small chain ring and the frame, of the small cog and the dropout.
This could lock the back wheel or damage something. Or you.

Just because some riders can do it successfully for a long time, does not make it right, or safe. The system is not designed for that. The total the derailleur can control is specified by the maker in sales and tech manuals. I could play Russian roulette for a year and not get shot. That does not prove anything except that I am an idiot.
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Old 02-21-14, 10:38 PM   #7
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We normally do not double shift.
Our legs tell and terrain tell us when to shift rear cog, or when ascending
descending the front chainrings.
After 38+ years of tandeming it's what we are used to doing.
As for re-programming DI2 . . . good luck.
Tried DI2 early on and after 1,800 miles the system quit; when the system was working properly, it was great.
We are now back to good old reliable barend shifting. Less complex, more reliable and much cheaper to boot.
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Old 02-22-14, 12:59 AM   #8
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Quote:
Originally Posted by zonatandem View Post
We normally do not double shift.
Our legs tell and terrain tell us when to shift rear cog, or when ascending
descending the front chainrings.
After 38+ years of tandeming it's what we are used to doing.
As for re-programming DI2 . . . good luck.
Tried DI2 early on and after 1,800 miles the system quit; when the system was working properly, it was great.
We are now back to good old reliable barend shifting. Less complex, more reliable and much cheaper to boot.
There is nothing in common with the original di2 system you tried and the present system except the external battery. Having said that you still can not get one shifter to shift both derailleurs at the same time. It is easy to program the shifters to work how you would like as in multiple shifts or single shifts when you push the buttons or have the left shifter control the rear derailleur etc. when doing double shifts the di2 is very fast so it works well even having to push both shifters.
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Old 02-24-14, 08:23 AM   #9
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Zonatandem,

I am also an admirer of the simplistic beauty of the bike.
I am at awe at how the human mind can transform metal into a machine that can more efficiently and swiftly aid our locomotion. To do so with our own capacity without the aid of external power is so much more elegant.

That said, I also enjoy discovering new things and new ways of doing things.
Apparently, I was slow in learning the double shifts. The concept is so simple, I am trying to figure out why I have not discovered it before.

With regard to the DI2, I think electronic shifting is another inevitable path in the evolution of the bike. It holds some potential in making the machine more efficient and simpler to use, like the evolution of the automobile automatic transmission. Of course, with every evolution, the machine moves away from the original single gear machine.

Akexpress,

I am trying to decide for myself if the DI2 system is ready, or rather if I am ready for it. The electrical and mechanical component of the system seem to be sound. But the programmability is apparently in its early stage, although that is an easy problem to remedy. I am wondering if that issue will be addressed before the current generation becomes obsolete. Also, given that double shifting will give you two to three extra gears, do I really need to upgrade to an eleven speed system?

CJ
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Old 02-24-14, 12:24 PM   #10
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I also appreciate Rudy's (zonatandem) KISS approach and his wealth of experience but we won't give up the DI2. As far going with 11 speed there are two problems as I see it right now. The reason we can ride DI2 or for that matter any double setup is the availability of wide range cassettes in 10 speed due to the mountain bike components. At this time there is no 11 speed wide range cassettes Yet that go to 36. there are supposed to be 11-32 Ultegra cassettes soon in 11 speed. That still would push us a little to much where we ride as we do lots of big climbs. The second is you need different wheels or at least hubs that have 11 speed cassette bodies available. When cassettes are available it will be an easy change as the only component that will need to be replaced is the rear derailleur. The 10 speed front and shifters will work with 11 speed just fine. the software is maturing all the time and you can make just about any button do what you want except make one button shift both derailleurs at the same time. We started with DI2 on the tandem and have now converted all of our singles to it also. Right now there are some amazing deals on the 10 speed stuff since Shimano is moving toward 11 speed. My next purchase is the shimano R785 hydraulic shifter for the right side to run the new road hydraulic brake on the rear with a 203 mm rotor. They are now just becoming available.
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Old 02-24-14, 01:03 PM   #11
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Quote:
Originally Posted by chojn1 View Post
On another note, can the DI2 system be programmed for this? It would be ideal if the buttons on either hand can be programmed to shift up and down and not linked to the individual derailleur. Can the gear choices and double shifting be made by the computer? Or does this still require a software hack at this point? It seems to me that this is an easily programmable advantage of the electronic system over the traditional mechanical system.
Fairwheel Bikes hacked a mountain with Di2 to do sequential shifting with one shifter. So the bike shifted to the next ratio in the progression, shifting the front, rear, or both derailleurs as necessary.

Here's a video of a sequential shifting setup:

[video=youtube;eq_BgmJ3a-o]http://www.youtube.com/watch?feature=player_detailpage&v=eq_BgmJ3a-o[/video]
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Old 02-24-14, 01:09 PM   #12
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Quote:
Originally Posted by 2manybikes View Post
Don't double shift. The slack in the chain can be too much or the chain tensioning function of the derailleur to control. Eventually you will drop a chain, not good to push your luck. The chain could get caught between the small chain ring and the frame, of the small cog and the dropout.
This could lock the back wheel or damage something. Or you.

Just because some riders can do it successfully for a long time, does not make it right, or safe. The system is not designed for that. The total the derailleur can control is specified by the maker in sales and tech manuals. I could play Russian roulette for a year and not get shot. That does not prove anything except that I am an idiot.
Well adjusted modern drivetrains can handle a lot, that back in the day would have been risky, double shifts included.

Properly adjusted limit screws are going to prevent the chain from dropping. Also if you think about chain angle, a front shift from big to little, combined with a rear shift going to 2 smaller cogs is going to be less likely to drop the chain to inside because the rear shift is moving the chain angle the opposite direction.

If you're really worried about making a double shift, a slight bit of finess eliminates any theoretical risk by making the front shift a fraction of a second ahead of the rear shift.
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Old 02-24-14, 01:33 PM   #13
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It appears that Fairwheel did a sequential DI2 road bike but the pictures show it is the old Dura-Ace 7970 DI2 system and they had lots of glitches but in the end made it work. Hackers have complained that the new system is harder to hack ( at least the battery system due to the battery now having a chip) but the software already has more options for the shifting then the old system.
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Old 02-24-14, 01:46 PM   #14
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Quote:
Originally Posted by waynesulak View Post
On flat road I usually shift two cogs in back when shifting a ring in front. It just depends on the gaps in your cogs and between chain rings. When going up hill I have to judge if cadence is dropping or rising fast maybe I just shift one cog in back. There is one steep hill our ride that as we start to climb I always just shift from big ring to middle because we need a lot more gear fast.
This


Quote:
Originally Posted by vrooom3440 View Post
I used to sometimes shift both ends at once until I dropped a chain... now I try and reduce the drivetrain disruption and shift one end at a time. I usually try and anticipate things and get the front shifting done before the grade requires it.
It's not necessarily a matter of anticipation. It's a matter of spacing.

With many typical gearing setups, if you don't switch front and back, you're going to have a big jump in gear ratios, which often will be bigger than you need or want.

For example, with a 53/39 front and an 11-23 rear, the shift over point is going to be from the 39/13 to the 53/17.

http://www.gear-calculator.com/#

So if you're in the 53/17, and shift only the front to the 39, you'll be in the 39/17. You're speed will have dropped from 22mph to 16mph at 90 rpm, or to maintain the same speed your cadence would have to rise to 125 rpm. You're effectively jumping 5 increments. Unless the terrain changes suddenly and dramatically, that's going to be abrupt one way or the other.

However, if you go from the 53 to the 39, and go from the 17 to the 14 in the back at the same time, your speed only goes down from 22 to 20, making for a much smoother transition.

Going the other direction if you're in the 39/13 and shift to the 53/13, you're going to have to pick it up from 21mph to 29 mph in a hurry, or your cadence is going to drop from 90rpm to 65.


If you look at the gear calculator link, you graphically see the appropriate cross over points, and the compensating rear shifts necessary to work through the ratios sequentially.
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Old 02-24-14, 02:07 PM   #15
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Thanks Merlin,
That sequential shifting with the double shifts is exactly what I was hoping for. I wonder why Shimano has not gotten around to it?
CJ
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Old 02-24-14, 02:11 PM   #16
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Quote:
Originally Posted by merlinextraligh View Post
This

It's not necessarily a matter of anticipation. It's a matter of spacing.

With many typical gearing setups, if you don't switch front and back, you're going to have a big jump in gear ratios, which often will be bigger than you need or want.

For example, with a 53/39 front and an 11-23 rear, the shift over point is going to be from the 39/13 to the 53/17.

http://www.gear-calculator.com/#

So if you're in the 53/17, and shift only the front to the 39, you'll be in the 39/17. You're speed will have dropped from 22mph to 16mph at 90 rpm, or to maintain the same speed your cadence would have to rise to 125 rpm. You're effectively jumping 5 increments. Unless the terrain changes suddenly and dramatically, that's going to be abrupt one way or the other.

However, if you go from the 53 to the 39, and go from the 17 to the 14 in the back at the same time, your speed only goes down from 22 to 20, making for a much smoother transition.

Going the other direction if you're in the 39/13 and shift to the 53/13, you're going to have to pick it up from 21mph to 29 mph in a hurry, or your cadence is going to drop from 90rpm to 65.

If you look at the gear calculator link, you graphically see the appropriate cross over points, and the compensating rear shifts necessary to work through the ratios sequentially.
Agreed that front often results in too large a change. It is not that I do not shift both ends I just do not hit both levers at the same time, I instead cycle through a sequence as you alluded to.

There is a situational aspect to this as well. There is a key hill I often ride that goes from flat to 8% or better grade quite quickly that exemplifies the use model. If I know I am going to be needing to go lower up front before the top, that is when I will anticipate and shift front followed by quickly shifting rear to rematch cadence and speed. In this way I am able to work the hill on the rear derailleur. This is also running a compact double and close ratio rear cassette. If I were running wider ratios on the cassette (ala mountain bike style) it might be a different story.

There are limits to what limit screws can to... if the FD can move far enough for the outer guide to push the chain to the next chainring, then there is going to be some over-shoot room before the chain is stopped by the inner guide. Conversely if the inner guide is right there at "zero" clearance the outer guide may not cleanly push the chain over. It is a very crude but effective shifting system after all.
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Old 02-24-14, 02:48 PM   #17
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Quote:
Originally Posted by merlinextraligh View Post
This




It's not necessarily a matter of anticipation. It's a matter of spacing.

With many typical gearing setups, if you don't switch front and back, you're going to have a big jump in gear ratios, which often will be bigger than you need or want.

For example, with a 53/39 front and an 11-23 rear, the shift over point is going to be from the 39/13 to the 53/17.

http://www.gear-calculator.com/#

So if you're in the 53/17, and shift only the front to the 39, you'll be in the 39/17. You're speed will have dropped from 22mph to 16mph at 90 rpm, or to maintain the same speed your cadence would have to rise to 125 rpm. You're effectively jumping 5 increments. Unless the terrain changes suddenly and dramatically, that's going to be abrupt one way or the other.

However, if you go from the 53 to the 39, and go from the 17 to the 14 in the back at the same time, your speed only goes down from 22 to 20, making for a much smoother transition.

Going the other direction if you're in the 39/13 and shift to the 53/13, you're going to have to pick it up from 21mph to 29 mph in a hurry, or your cadence is going to drop from 90rpm to 65.


If you look at the gear calculator link, you graphically see the appropriate cross over points, and the compensating rear shifts necessary to work through the ratios sequentially.
You guys are studs and studettes if you can ride 53/39 with 11-23 cassettes. We ride 50/34 and 11-36 and sometimes wish for a little more. We do ride mostly in the mountains with 5-10% grades for miles at times. We can ride the 50 and use the full range of the cassette for everything up to 6% without using the small chainring and then we do many times the double shift to maintain cadence and pressure.
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Old 02-24-14, 03:20 PM   #18
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You guys are studs and studettes if you can ride 53/39 with 11-23 cassettes. .
We live in Florida, rarely out of the big ring.

11-28 goes on when we head north.
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Old 02-24-14, 04:04 PM   #19
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I tried to read all the posts but it was a tough assignment. What I'm getting though is the idea that if you know your system well enough you just intuitively know when two rear shifts are necessary or just one, or a front shift and an immediate drop of one (two?) teeth in back... a double shift if done simultaneously. I double shifted our Raleigh Couple all the time. Shimano 105 RD is the most advanced component in the drivetrain! We have an 'N-gear' chain catcher installed and it makes double shifting and worse a no-brainer. For the up-coming season I have upgraded to drop-bars but also downgraded(?) the shifting to down-tube. High end down-tube (Dura-ace) but down-tube is down-tube and I cannot double-shift DT to save my life. Maybe its me but in order to minimize the need for double-shifting one should at least have a triple up front and a close ratio cassette in back. We have a 52/39/24 and 12-27 9sp. I've ridden that combination for several seasons so I know what needs to be done when. I should think that a progression could be programmed into a DI2 system but it would be no better (or worse) than some of the IG (Rohloff, P?) systems where you get several 10 or 13% changes everytime you shift.

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Old 02-24-14, 04:55 PM   #20
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Sequential shifting is not for me. We run normal road cassettes like a 12-25 or at most 12-28. Sequential shifting would mean I have to shift two or three times to get the shift I want and not the shift Shimano wants me to make. I often shift two or three gears because a) we are topping a steep little hill and need a big gear change b) we are about to stand, c) we have just ceased standing.

Chain drop issues:

Chain drops are reduced because limit screws are set after some testing under load on the road. After once a year cable replacement I adjust the tandem in the stand and then it usually takes a couple adjustments and sometimes a dropped chain to get it really dialed in then it never drops. We have a pretty flexible tandem and this contributes to the fine tuning needed.

Chain drops are a minor annoyance only.

- Steel gear chain catcher on the front inside the granny ring prevents any drop to the inside regardless of where the limit screw is set.
- I have a 5mm bolt in the fender mount of the right rear drop out that prevents the chain from falling between the drop out and the small cog. Think chain catcher for the small rear cog.
- My chains do not fit between the front rings. Worse that has happened there is the chain not engaging and FD movement will then drop it to the next smaller ring.
- The only place we ever drop a chain is to the outside of the big ring. These can often be remounted with careful pedal action while coasting and I don't have to stop the bike or touch the chain. Sometimes stopping and remounting chain is needed and then I am glad to have waxed my chain.

Anticipation:

It helps to know the route and the hill you are about to climb. On a new route there is some guessing involved and if I guess wrong we may have to stand, or shifting up or down while already standing. Yeah a RISKY shift. Unlike other shifts I always call out standing shifts and my stoker knows to have her arms and hands ready to catch herself by supporting her weight on the handle bars should a mishap occur.

Modern rear cogs and chains are really great.

Last edited by waynesulak; 02-24-14 at 05:05 PM.
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