oldacura

Not sure that I understand you here. A tandem might be able to slow down faster than a single due to the fact that the rear tire is much harder to lock up. However, I'm pretty sure that I can accelerate faster on my single than we can on our tandem.

A couple on our last tour had a late model Paketa. It was outfitted as a Di2 triple. Somehow Dave Walker (Paketa) was able to "hack" Di2 to be able to use an XTR rear derailleur (11x40) and an Ultegra triple front derailleur (54x39x30 I think). This gave them a wide range and relatively small steps. Not sure how this was done. This is the only instance that I am aware of.

If I could have a wide-range Di2 triple, why would I choose a double? What compromise does having a triple cause one to make?

mtseymour

Sram is responding to demand rather than "push" riders to use 1x12 drivetrain. Like other users of the Sram 1x11 drivetrain, i use the 10-42 cassette with a single 28T ring. With this setup, I can climb the steepest trails in my area, but will spin out on certain downhills. I don't mind this trade-off because climbing is more important than descending. Riders who prefer a 30 or 32T chainring won't spin out but will struggle on steep climbs.

Despite this tradeoff, the 1x11 drive is very popular because it prevents dropped chains. With its "clutch" mechanism, the Sram rear derailleur won't drop a chain on very rough terrain. A chain tensioner near the front crank makes the drivetrain even more bombproof.

The Sram Eagle is a substantial improvement because it removes this trade-off between low and high gearing. With a 12sp 10-50T cassette, the Eagle can provide low AND high gearing for virtually all terrain. The Eagle is particularly useful for enduro racing.

Since dropped chains are uncommon (and less dangerous) on road bikes, I don't expect to see road version of the Eagle drivetrain due to the high cost and bigger gear jumps. It's more likely that Sram will launch a more affordable version of the Eagle for mtn bikers.

akexpress 

We have 4 Calfee's, 2 Tetra tandems and 2 Dragon Fly singles. They make great bikes but a word of caution in that they are overly optimistic on time frames All of our bikes were 30-60 days longer then originally promised. One tandem has a very custom shade shifting paint that looks amazing but with lots of travel has a few scratches that bummed me out at first. Our new tandem is nude and looks great also but in a different way and since we are planning on lots of loaded touring with it some of which will be on gravel I won't worry as much about scratches. The singles are nude with one having a gloss clear overcoat. Order your frame with DI2 internal routing even if you go with mechanical to start as most eventually go with electronic. There are a number of threads concerning DI2 but I will never own a tandem without it. Even our touring tandem is drop bar XTR triple DI2. I think tandems are the best application of electric shifting period. You can do a combo of having Calfee build your tandem frame and they will even allow you to supply some of the parts and Rob will do the build for you. Consider Middleburn cranks in that they are modular and go from double to triple easily,use standard bottom brackets and have many crank arm lengths, all in a good price point. We have thousands of miles on the tandem with 50/34 and 11-36 or 11-40 including a number of European and Colorado assents with plenty of range available. Feel free to PM if you want any other info.

pdlpsher

Due to the heavier weight and drivetrain inefficiencies, a tandem experiences a higher variability of speed as compared to a single bike. It has a much higher terminal velocity than a single. Similarly it reaches a lower speed when climbing a hill. So speed changes are more frequent and the rate of change is more drastic than a single. When dealing with a higher speed variability, it's desirable to have a wide-range cassette as opposed to a close-ratio, narrow-range cassette. A wide-range cassette reduces the amount of rear shifts. For example, if your speed slows down from 20mph to 8mph, you may only need four shifts on a wide-range cassette as opposed to five or six shifts on a close-ratio cassette.

The compromises of a triple is a significant increase in number of front shifts as compared to a double system equipped with a wide-range rear cassette. A front shift requires both the captain and stoker to back off the power, which disrupts the rhythm and hence the speed. On the double we find that we achieve a higher average speed, as we find ourselves spending more time pedaling due to the significant decrease in needing to execute front shifts. Last but not least, I don't have to ask the stoker whether I'm on the middle or the smallest ring anymore On the double I'm always aware which ring I'm on. On a triple it's easy to forget and be confused.

diabloridr

I'm going to gently push back on this argument, with the understanding that all teams are different and equipment needs will vary accordingly.

My experience has been that teams often have a narrower "sweet spot" in cadence compared to single riders. Some teams may be well-matched in preferred cadence and have a relatively wide useful cadence range, but most teams will need to compromise their cadence due to differences between the riders.

This narrower range of useful cadence results in a need for closer - not wider - ratios. Di2 is great for this since shifts are flawless and require no effort.

While the low and high speed limits of a tandem are usually wider than a single, the higher momentum of the tandem results in lower - not higher - accellerations and decellerations.

An automotive analogy would be a a large diesel truck with a relatively low-reving engine (normally equipped with 18+ speed transmissions) vs. a high reving sports car with a 5 or 6 speed.


I'm basically in agreement here. Many tandems are operating gruppos significantly out of manufacturer's specifications (smaller chainrings or larger cogs), resulting in decreased shifting performance between the small and middle chainrings. The tooth difference between the small and middle rings can often be quite large.

This results in a need for coordination for these shifts so teams can be hesitant to use the small ring unless absolutely necessary. A wider ratio double-chainring drivetrain sidesteps this issue.

Di2 triples are such unicorns at this point that I have no idea if the limitations of mechanical triples also apply to electronic applications.

merlinextraligh

Our 2x11 setup gives us a lot of flexibility.


Our normal setup is a mid compact front 52/36, with an 11-25 cassette in the rear. That gives us low enough gearing for most of what we ride, and tight spacing.


For the mountains, we use an 11-36 rear cassette which gets us a 1-1 low. ( if we ever needed lower gearing we could go to a 34 inner chain ring, and/or an 11-40).


On the high end, we virtually never have a need for a higher gear. You can pedal to 50 mph (at 130 rpm) with a 52/11. Above that it's almost always more efficient to tuck and coast.


Couple of very rare occasions we've wanted a bigger gear. ( attacking downhill on Mt Bachelor in the Masters Nationals Road Race at 55mph), and doing the time trial the next year on Antelope Island in Utah, which had significant downhill sections.


On a TT course with downwind downhill sections, you can make use of a bigger gear than 53/11. It's not that you'll be spinning out the 53/11 at 130 rpm, but that a bigger gear can allow you pedal a lower, less lung busting cadence in those sections where conditions allow you to push into the mid 30's.


For that, the Lightning cranks on our bike have interchangeable spiders, allowing us to use 130bcd rings. So for a TT we can go 56/44.


With an extra spider, cassette, and chain rings, our 2x11 setup covers about the entire spectrum.

merlinextraligh

This is definitely the case for us, with the mechanical shifting on our Robusta with a triple.


We run it with 53,39, 26 up front and an 11-28 in the rear.


The 26 is a Salsa ring, and it and Praxis outer rings, are not setup to work together to shift up from small to middle.


However, the setup allows us to have tight spacing with an 11-28 cassette, and still have a very low gear.


So we accept the compromise of rough shifts on the infrequent shifts in and out of the small ring, for better shifting and spacing on the gears we regularly use.


But it is a compromise.

oldacura

Our Di2 is setup with 52/34 rings and an 11 speed 36/11 cassette. I have it setup with synchro shift. We usually ride on the big ring. Synchro helps avoid cross-chaining a lot. The display will beep twice on the shift before it initiates a front shift. This lets me know that before I do the next shift (either up or down) I announce to my stoker "shift". This lets her ease up in anticipation of the shift. A downshift to the smaller ring takes a second or two. The chainring engages the chain before the rear derailleur moves the chain 2 cogs smaller. If we ease up until this completes, all is good. When I forget to announce this shift the torque goes to zero and the stoker is not happy.

I find myself anticipating the terrain ahead and deciding when to move from high range to low or vice-versa. Once we have changed from the high range to the small, I try to stay there for a while. There is quite a bit of overlap between the ranges.

I hoped that Di2 would make me less aware of front shifts. That I could just decide that I wanted a harder (or easier) gear. Instead, it makes me more aware of front shifts (than our old bar-end mechanical shift bike with 3 rings). If a road Di2 setup could be made to work with a front triple, I could pre-program the synchro shift points and likely be less aware of front shifts because they would be less dramatic. We rode the old bike mostly with the big & middle rings saving the small ring as a bail-out. The jump between the big & middle rings on that bike were pretty small (54-44 I recall).

merlinextraligh

What happens if you just ignore the beeps and hammer through the shift without letting up?


I haven't found any need to let up on front shifts running 52/36 rings.


The 52/34 setup could be a little bit more finicky given the larger gap, and that the rings are not ramped to match each other.

pdlpsher

Shifting on a tandem is inherently a difficult task and should be minimized whether you have mechanical or Di2. The issue isn't so much mechanical vs. Di2. I have Dura Ace Di2 on my single bike and Ultegra mechanical on my tandem. From an execution standpoint there's no difference between the two. I can execute perfect and accurate shifts on the Ultegra mechanical. The issue with the tandem is that there are two riders and hence twice the power output. A cleanly executed shift on a tandem could result in a horrible-sounding shift because the shifting was done with too much power applied (AKA shifting under load). This can happen on either Di2 or mechanical. Every team probably has their own unique shift strategy. In my case I never communicate to the stoker when I execute a rear shift. I just back off my power momentarily. Using this method results in good shifts 90% of the time. The other 10% just sounds horrible even when my lever execution was perfect. That's because the stoker applied too much power at that particular instant. If my goal was to preserve and extend the life of my components I should communicate with my stoker on every rear shift. But that's unrealistic due to the wind noise, extra effort, etc. So with that in mind, shifting on a tandem should be minimized, even if that results in a compromised cadence due to lack of a close-ratio cassette. By the way I always communicate when executing a front shift. A front shift is usually accompanied by one or two rear shifts.

I recently switched from a triple to a double and much prefer the double. Has anyone here also switched from a triple to a double with a wide-range cassette and then went back to a triple because they didn't like the double with a wide-range cassette? I'd like to hear from those who have spent time on both.

twocicle

Yes, after riding a Di2 2x11 for a couple years we much prefer and are happy with the 3x11 (also Di2) for the close gear ratios.

Contrary to the notion that a triple ring requires more front shifting, the gearing we are using allows us to ride in the middle ring for the majority of time, ranging from 11-25mph with nice tight shift steps and no front shifting required. The 48/36/26 x 11-28 works great for us over most of our typical terrain and have used it in the Los Gatos/Morgan Hill hills and Tucson too up to 14%. Easy enough to toss on a 11-32 or bigger cassette if/when needed (XTR SGS long cage RD capacity). Shifting is smooth and flawless.

This is my main thread on the topic: https://www.bikeforums.net/tandem-cyc...l#post19079472

mtseymour

I think every team that has tried Di2 feels the same way that we do: Di2 offers a big gain for tandems.

We've been using Ultegra 6870 Di2 for 3 years on our tandem. We also have Dura Ace 9070 Di2 and mechanical drivetrains (Ultegra 6800 and Sram Red) on our single bikes. On a single bike, Di2 is very nice but not essential. On a tandem, Di2 is really beneficial for these reasons:

1. Di2 is fast and precise
Di2 and eTap use powerful motors that can shift more quickly and precisely than a mechanical drivetrain. With Di2, the shift speed can be changed from "slow" to "very fast". It's also possible to "sweep" 2 or 3 gears. The key feature is that the front derailleur will slightly overshoot when moving from the small to big ring (and then retract). The result is fast, flawless shifts from the small to big, and big to small. This is simply not possible with a mechanical derailleur. As a bonus, the front Di2 derailleur will automatically move with the rear derailleur to avoid chain rub.

2. Di2 was designed for shifting under load
It's a bit of a myth that tandems generate a lot of power, and can overload Di2. Keep in mind that Di2 and eTap were designed to handle racing at the highest level. According to Bicycling mag, a Tour de France rider will "average 200-300 watts for a four-hour stage; that’s an intensity most recreational riders can sustain for only an hour or so." A mixed tandem team would be hard-pressed to average 200-250 watts over several hours.

During short bursts, a pro rider may exceed 1,000 watts for 30 seconds or more. A strong male, recreational would be challenged to reach 600 watts. For example, I've never heard Peter Sagan or Chris Froome complain about Di2 mis-shifting during an attack or sprint. Not surprisingly, recreational teams like us can't get Di2 to mis-behave under full power. Since momentum is so important for a tandem, we can downshift at full power during a steep climb, or upshift to stay with a fast paceline.

Guide to Power Meter Metrics | Bicycling


3. Di2 requires minimal maintenance
Once Di2 is calibrated, it will stay in adjustment indefinitely because it's un-affected by cable friction, wear, and long cable run. I've only had to re-calibrate our Di2 derailleurs once in 3 years.

After switching to Di2 on our tandem, we shift more often (not less) to find the best gear combination. Synchronized shifting also makes it easier to find the right gear when navigating heavy traffic or a fast paceline. We don't miss the "horrible" noise or loss of momentum when mis-shifting on mechanical Ultegra. Di2 or eTap offer essentially flawless shifting, and their only downside is price.

pdlpsher

I found your other post where you mentioned you find the steps being too large on a 11-36 cassette. Personally I find it most difficult to maintain an optimal cadence when riding on the flats, where the primary opposing force is wind resistance. On rolling terrain and on climbs I find larger steps to be better as the primary opposing force is gravity. This may explain why larger gaps feel good on mountain bikes. So perhaps one's personal gear step preference can depend on the terrain type. I looked at my Strava stats for 2017 to see how hilly my rides are. Year-to-date I've ridden 6,763 miles and climbed 416,414 vertical feet. That works out to be a 61.5 foot gain for every mile, or 6,157 feet gain per 100 miles. This is perhaps above average in terms of elevation gain, hence my personal preference on wider gaps. FWIW I use a 11-speed 11-28 cassette on my single bike. I specifically chose a Sram 1190 11-28 cassette over the Shimano 11-28, because on the Shimano it's missing the 16th cog. With a 50 tooth chainring the 16th cog gives a speed of around 18-20mph. On my single bike I find that I cannot live with a 2 tooth gap between 15 and 17. While on the tandem I find no issues with 2 tooth gaps starting at 11 (11-13-15-17-19-21-24-27-31-35-40). I still think the gearing requirements on a tandem is far different from that of a single bike, in that a wider range cassette will track the frequent speed changes better, resulting in minimized shifting.

pdlpsher

There's no dispute Di2 is better I have the 9070 on my single bike and I will never go back to a mechanical group on that bike. I'm not arguing which is better, Di2 or mechanical. I'm merely suggesting that minimized shifting on a tandem is a good thing even if you have Di2

When we ordered our new Santana tandem I did't opt for the Di2 option for one simple reason, factory options are most often over-priced. I'm a home mechanic and I prefer to install purchased components myself. On the Santana there's also a $750 upcharge for internal Di2 wiring. I didn't go for that option as I do see wireless shifting as the inevitable. Since I don't have internal routing (I think it's not just holes on the frame....the eccentrics are different too), my only options are to do external wiring with Di2 or go with the new Sram eTap. Between Di2 and eTap I like the Di2 better, as I can execute a front shift in conjunction with a rear shift. I do that on my single bike all the time and I'm quite good at it. I don't think I can tolerate the delay of shifting the front and the rear in sequence on the eTap. Plus the eTap lacks the front derailleur auto-trim, which is a Shimano patented feature.
But if I go with Di2 I have no choice but leave the wires hanging on the frame. So I'm left with several options and I'm not quite sure what route to take. Waiting for wireless Di2 might be several years away. For those of you with Di2 I'd like to know how you get the wires over the two bottom brackets. I'd really prefer a wireless system as it'll be a very clean installation. So maybe I need to consider the eTap as well.

mtseymour

I'm surprised at Santana's $750 upcharge. Calfee only charges $300 but carbon fiber is easier to modify than titanium.

I don't think that wireless Di2 is inevitable. Shimano will stay with wired Di2 because it has a large installed base with inter-changeable 11sp components (Ultegra & Dura Ace). My non-scientific estimate is that Shimano has about 80% of the electronic shifting market. Just look at how many new bikes are equipped with Di2 vs eTap. Why would Shimano copy Sram when its current design is so successful? Also, Di2 has longer battery life, lower price, and other unique features (eg. synchronized shifting, display).

With synchronized shifting, there's no need to coordinate front & rear shifting. Attached is a comparison of Di2 & eTap prices (retail or street price). Your best bet may to ask a local framebuilder to modify your frame for internal Di2 routing. External cable routing is a bad idea.

merlinextraligh

we have not had an issue of shifting under load. One of the advantages racing with Di2 is not having to hesitate just a fraction shifting up to the big ring on a top of a climb.

And I agree your typical mixed tandem team is not going to overpower it.

A top sprinter in the TDF like Marcel Kittel, or Andrei Greipel produces about 2000 watts for 5 second power.

I'm pretty big, and a decent sprinter for a Cat 3. Our combined maximum power is pretty close to that 2000 watts.

So I figure we're not capable of doing any damage to the equipment that Greipel or Kittel don't.

pdlpsher

It really depends on how one defines 'issue' with regards to shifting under load. As I stated earlier some of my rear shifts are accompanied by a loud crunch sound. I see this as something that should be minimized while some of you see it as just part of a normal bike operation, even when shifting at 2,000 watts

My view still remains the same. When I'm riding on my single bike I never consider shifting as bad for the drivetrain. But on the tandem I see the benefit to minimize the frequency of shifts. And by using a wide-range cassette I've noticed a significant decrease in rear and front shifts.

With regards to Di2, recently I was on a website and one of the online retailer was having a fire sale on the 9070 front derailleur for $140 At that price I almost pulled the trigger. I just checked the site and it's still available

Shimano Dura-Ace FD-9070 Di2 Front Der > Components > Drivetrain > Electronic Derailleurs | Jenson USA

mtseymour

We've never heard any "loud crunch sound" when shifting under power. Di2 is quiet while mechanical Ultegra will occasionally mis-shift due to long cable run. Here's a typical review of 6870 Di2 series from Bicycling:

"In my four-month test of the second generation of the Shimano Ultegra Di2 drivetrain, I haven't suffered a single missed, delayed, under-shift, or overshift. I haven't experienced any chain rub on the front derailleur. I have not had to change a derailleur cable or housing (or put up with sluggish shifting from dirty cables and housing I didn't have time to change)."

BTW, that's a great deal on the FD-9070 front derailleur. This is a good time to buy Di2 because retailers are clearing old stock to make way for the new R8070 and R9170 series. The 2016 & 2017 Di2 components should be compatible.

TCW2

Pushing or responding to demand matters not to me, I like what SRAM is doing. I've been using XX1/X01 on my mtb for a couple years now (26 ring for Colorado adventures). Before that I had 1-by with an 11-42 cassette using a Leonardi General Lee cassette adapter with XT cassettes (shaved 15 grams with the adapter and shifts great with a Wolftooth Goatlink). The 11 speed 10-42 cassette from SRAM is amazing. Eagle 12 speed is even better and now available in the GX level. My wife just got a new Tallboy CC warranty replacement frame and I'll likely put X01 Eagle on it eventually.

For our tandem we recently moved from 3x9 Ultegra, 11-28 cassette, to 2x11 Ultegra, 11-32, 52-39 rings. I much prefer the the 2x11 set up. Our Trek T2000 has SRAM/Bontrager carbon cranks that are similar to X0 cranks. A Force 110BCD spider might fit on the crank which would allow us to move to semi-compact 52-36 rings. A Roadlink with an 11-36 cassette would give us plenty of gearing for mountainous adventures.

Cross, adventure, tandem, mtb, etc. is helping with more gearing options for tandems. It would be nice if Shimano would make their stuff cross-compatible, XT-Ultegra derailleur-Shifter, for example. At least Wolftooth has that issue solved with the Tanpan adapter. Perhaps 2x12 tandem gearing is just pushing the envelope too far. We'll see, I suppose.

waynesulak

I agree some comments made earlier in the thread:

It depends on the power of the team. Lower power teams need more gears. This is even more so because they often also are riders with narrow cadence ranges.

Riding style and goals are very important. If the team likes to do some riding at threshold then narrow spacing is required to get that last little bit of power and still be able to stay on top of the gear. It is very frustrating to be able to spin out a gear and not get on top of the next one. Teams with wider cadence ranges or that don't ride on the edge do not need that close spacing.

The combination of budget constraints, team weight, team power, riding goals and terrain combine to make it a very individual choice. It seems to me that the best advice is for a team to try various gearing setups and decide what works for them before ordering that dream bike.

For us now a triple is the best option. I cannot see spending all that extra money for nice shifting and less functional capability. I did order our last tandem to be Di2 internal wiring compatible.

diabloridr

My experience is that a smaller number of shifts with a large change in torque (due to differences in cog sizes) will be "worse" for the drivetrain than a larger number of shifts with a small change in torque.


Bottom line for our team is our drivetrain wear rates are small enough regardless of the drivetrain design that our best choice is to design the drivetrain to suit the limitations of the motors.


YMMV

oldacura

I'd agree that even if shifting under load is possible, it should be avoided (front or rear). It is just plain hard on the mechanism. If I were a racer and someone else was buying me new equipment every season, maybe I wouldn't care. But we buy our own equipment and I do most of my own wrenching so I don't like to abuse the equipment. I good shift is one that is almost silent.

mtseymour

I doubt that most tandem teams will prematurely wear out a quality cassette from Shimano, Campy or Sram. These all-steel cassettes (eg. SRAM XG-1190 & Ultegra CS-6800) use ramps and profiled teeth to provide quiet, fast shifts under full power. I would only be concerned about wear & tear with steel/Ti cassettes like the Dura Ace R9100. Although it's preferable to ease up while shifting, it's not practical while climbing or in a fast paceline. I'm not aware of any long-term testing to show that shifting under power or frequent shifts will "abuse" the drivetrain.

The reality is that most tandem teams generate less power than fit single riders (or racers). Also, tandem drivetrains are not usually exposed to rain and mud. I'm more likely to upgrade a road cassette (different ratio or lighter design) than replace a worn one. Besides, a CS-6800 is only around $60.

Alan_F

I found this thread interesting as we're currently looking at the impact of dropping down to "only" 3 rings to go electronic on our next DaVinci. Having just returned from a week in the New York Finger Lakes region and also regularly visiting the green hills of Vermont, we're not looking to give up anything at either end.

Our current setup (34 tooth timing rings, 18 tooth freewheels, 12/18/24/30 chainrings = effective 22.7, 34, 45.3, 56.7, and 9 speed 11-34 cassette) gives us 18 to 139 gear inches. We are a reasonably fit team but when climbing grades above 15% late in the ride that granny gear is appreciated. We try to maintain 85-95 rpm up even the steepest grades. One the way down the other side we were regularly spinning the big gear at 100 rpm at over 40 mph. As to why we would want to pedal rather than coast and tuck at that speed - I find the bike more stable, especially in cross-winds, when we're pedaling rather than coasting.

Luckily with the DaVinci drivetrain we'll be able to get just slightly tighter rear spacing and almost the same range with Di2 using 34 timing rings, 17 freewheels, and 13/24/28 rings (effective 26/48/56) with an 11-40 cassette. We'll probably run an 11-36 when not riding the big hills which will give up a little bit of granny gear but tighten up the rear gaps.

Alan
2010 DaVinci Joint Venture
2016 DaVinci Symbiosis XC 29'er
Lots of half bikes

pdlpsher

When you lose a chainring you will also lose gearing range. There's no free lunch. When we went from three to two rings we lost a high gear (53x11). This is a compromise. But we love our new setup because we end up shifting less and our average speed has increased despite the loss of the 53x11. With the introduction of the 10x40 or 10x42 cassette it solves the gearing range problem but it also creates large gaps between gears. Once again there's no free lunch. Each team has to decide what's their priority. For us we won't ever go back to a triple.