qspencer

This is related to the recent separate thread I started about getting a custom frame built. It will be piloted by my wife, who has a strong preference for SRAM, which means 2x11 gearing. A 34-32 low gear is fine for the flatland where we live, but we do anticipate taking it to hillier locales and we're not that fast anyway, so what I really want is something like 46/30 or even 44/28 chainrings with 11-32 cassette. Neither of these are possible with 110 BCD. As far as I can tell that leaves me doing something like using the inner and middle positions of a triple. Has anyone done this? Are there any negative consequences of putting a ramped/pinned 46t outer ring in the middle position? (I understand the recesses in the holes will face the wrong way and I would probably need a different bolt length as a result.) I've read about some makers of cranks making "micro" or "sub" compact cranks with 48/32 or 46/30 combinations, but does anyone know if something like that is available in tandem-specific cranks?

akexpress 

Check out Middleburn cranks as they are very modular and have tandem options. Alex at MTBtandems is the US distributor. Middleburn went away for a while but has apparently been bought and resurrected. You can also rethink options and use wider range rear cassettes for those trips with hills. We very successfully run 11-40 rear cassettes with 50/34 chainrings on mountainous trips and go back to 11-32 or 11-36 for less arduous trips. We are doing this with Shimano Di2

qspencer

That's also something I'm considering. I think 50/34 with 11-36 is probably sufficient, but I'm uncertain whether that will work with SRAM 2x11. SRAM's documentation claims their 11-36 cassette is meant only for 1x road rear derailleurs. I assume their mid-cage road rear derailleurs aren't designed to handle a 36 but I wonder if I could push one past its design parameters just a little. I think I read on some forum that SRAM road and MTB derailleurs use the same cable pull, so in theory I might be able to use a 9 or 10 speed SRAM MTB derailleur with road shifters.

akexpress 

You can use a Wolf components Road Link to extend the rear derailleur cassette capacity. A cassette is a cassette whether SRAM or Shimano and it is the rear derailleur that limits the size. I don't see why a SRAM 11-36 would only work on a 1x system ?

OneIsAllYouNeed

This works great. We've used it for a wide variety of hill climbing setups with triple cranks, double shifters, and double front derailleurs. Any normal tandem triple crankset can be converted to a double like you've suggested. You'll need "track" or "single speed" chainring bolts for the outer ring.

OneIsAllYouNeed

...
SRAM Force 1, Rival 1, and 10-speed MTB rear derailleurs can accommodate an 11-speed 11-36 or 10-42 cassette.

bwebel

[QUOTE=qspencer;19524984]This is related to the recent separate thread I started about getting a custom frame built. It will be piloted by my wife, who has a strong preference for SRAM, which means 2x11 gearing./QUOTE]

if she doesn't mind using a bar end shifter for the front, you don't _have_ to go 2x11. I have our tandems set up 3x11 with a SRAM 11 speed right lever and then the single speed left brake lever without any shifting capability. Then I use a single bar end shifter to shift a triple shimano front derailleur. We actually only use the triple only for the very occasional mountain ride, so most of the year I have it set up as 2x11, but leave the bar end as I find it shifts better than the indexed front shifting.

merlinextraligh

I'm guessing chain wrap capacity. But just a guess, given that a 2x setup with the same 11-36 cassette would require more capacity than a one x

qspencer

I suspect you're right. I couldn't find it on SRAM's site, but I found another source claiming total capacity on SRAM mid-cage derailleurs of 37. A 50/34 with 11-32 would need a total capacity of 37, while a 50/34 with a 11-36 would need 41.

Road Fan

I'm thinking of something like this as well for my Meridian build. But does the chain drag on the big ring when you are in the small ring? With a 145 mm OLD rear hub, don't you need a front chainline that is 7.5 mm or so larger than if the bike is a 130 mm single? And hence (if you're in square taper world) a BB cartridge 15 mm longer than in a single application?

Eddie50

In the process of completing my build and that is the main issue I have on the double setup with a rear standard triple crank and 145mm rear spacing.

It works but on the small ring, I can't use the last tree small cogs because the chain rubs on the big chainring.

Would work better on a 135mm rear spacing or 130mm.

B. Carfree

Just putting it out there; I don't know how well these would work. I think the rings are somewhat classic and thus missing all those wonderful ramps and pins. There had been some discussion on Jan's blog about them working fine on 11-speed, but they have not been formally vetted for that yet. If they work, they do allow you to use any even tooth number rings you want from 24-52.

https://www.compasscycle.com/shop/co...-double-crank/

BNB

I was told by our custom single bike manufacturer that the Wolf Road Link was designed for Shimano cassettes. The mechanic at this particular builder had to modify the design to get the Road Link to work with Sram etap. I do not understand what the issue was but I can guess that it might be that the sram micro adjust does not go far enough in the required direction to properly align. I am going to try this as we are suffering right now in the New Hampshire mountains with our 32 (with etap wifli) given that our home is on an 18% grade. Oh, and loving etap wifli and highly recommend.

TigerMom

I'm about to buy a new Santana road tandem. The bike shop double checked with the Santana manufacturer. They said that they can do a 2x11 Ultegra 52T/36T front crankset paired with a 10-42t rear cassette because in 3 weeks, they will be making new wheels that can accommodate the larger rear cassettes.

Any thoughts on this before we pull the trigger?

diabloridr

Do you have confidence your team will be happy with the relatively large jumps inherent in this cassette?

TigerMom

Do you mean jumping from the 52T to 36T or do you mean the rear cassette? Would a 10-40 rear cassette be better?

diabloridr

I'm concerned about the cassette. My experience is that front shifts are relatively infrequent so the team is prepared for them, but rear shifts happen often.


We currently use an 11-36 cassette, but could likely accommodate an 11-40 if we needed lower gears.
A 10-40 might excessively compromise our comfort, but all teams are different.


What are you using now?

pdlpsher

I don't really see the need of a 10-tooth cog in the cassette. The 10-42 cassette was invented for 1x11 drivetrains. A 50/34 and 11/40 cassette is more appropriate. The slightly smaller 50 ring allows us to climb as slow as 9mph while still having two more gears left on the cassette. As such we don't need to shift down to a 34 ring unless we are on an extended climb. A 10/42 cassette requires an XD drive hub which is not a widely available standard. A 11/40 or 11/42 uses a standard hub body. I'd stick with 50/34 and 11/40 or 11/42.

TigerMom

For our single bikes, we use the 50/34 front chain ring. However, on the Tandem, we run out of hard gears on the mild 2% grade downhills/flats with 52T front chain ring and 11t rear cassette. So, with a 52T in front, we need the smaller tooth 10t rear cassette. The 50T/34T would definitely not work for us on the tandem...We would just be spinning in place on the flats without much resistance.

So for us, the best 2x11 combination would either be 53T/39T with 11-40 cassette or the 52T/36T with 10-42 rear cassette (The bike shop says that a 10-40 rear cassette doesn't exit). The bike shop says that they can put in the 10-42 rear cassette.

We're currently leaning towards the 52T/36T with 10-42 rear cassette. We do a lot of prolonged 10% grade climbs and are worried about running out of gears for the rare occasion of 15% grade.

Although I'm slightly concerned about the jumping cadence with a 2x11 with large cassette, we rather have consistent shifting instead of a triple crankset which doesn't seem to shift uphill on load very well.

TigerMom

We had to return our Cannondale Road tandem 2 that we bought used. We had a triple front 52T/39T/30T with a 11-34 rear cassette. But, we just could not shift to the granny 30T front chain ring at 5-7% grade uphill, even with soft pedaling. It would be wasted effort for us to shift to the granny ring at less than 5% grade. So, we were just using the 39T middle ring with the 34t rear cog to go up 8-10% grades (8% grade comfortably, 10%grade uncomfortably). We know for sure that we wouldn't survive more than 10% grade with the 39Tfront and 34t rear. We also didn't have enough hard gears for the 2% downhill grades. So, since we decided to purchase a new Santana tandem, we might as well get one extra hard gear for those mild downhills

pdlpsher

After recently switched from a triple to a double with a wide range cassette, I agree the double is a far better choice. The large gaps between gears on the cassette isn't an issue. The tandem speeds up and slows down much faster than on a single bike. So the large gear gaps actually minimizes rear shifts.

One benefit of having a 50 front ring is that I can leave the chain on the 50 and still have usable gearings (with a 11-40 cassette) that cover speeds between 8-35mph. This allows us to not have to shift down to the 34 except on extended steep climbs. If we had a 52 or 53 ring we may incur more shifting on the front. We have lots of rollies around here and it's very nice not have to shift down to a 34 on all but the steepest rollies. There's no free lunch. If you need a 53 for top-end speed then you will give up a bit of low-end gear range when on the 53. We do occasionally spin out with a 53-11 but the tradeoff seems worth it to us.

Dean V

I have never had any trouble shifting to the granny gear. It is just a matter of doing the shift early when cadence is reasonably high and you can unload the drive train completely.
Also thought 50/11 was high enough for us except for maybe racing and Strava bashing down 5% + grades, both of which we don't bother with anymore.

qspencer

I have now built the tandem that I was referring to when I started this thread. I've got SRAM 2x11 road shifters and yaw front derailleur. On the Sugino triple cranks, I have a 30t inner chainring and 46t outer chainring in the middle position, with nothing on the outside. I'm having trouble getting the shifting to the large ring to work. The 46t ring is ramped and pinned, but it doesn't seem to be enough to catch the chain. If I tighten the cable slightly so the derailleur pushes the chain over more aggressively, it will shift to the 46t, but with an unacceptably high probability of overshooting and dropping the chain on the outside. The 30-46t jump is big, so maybe I'm pushing the limits here and need to settle for a smaller gap.

The other solution I'm considering is installing a chain guard in the outer ring position in hopes that it would avoid the overshifting. Does anyone here have experience with a setup like that? I've found some chain guards marketed as "48t", but I don't know what that means in terms of the size relative to a 46t chainring.

pdlpsher

You may want to experiment with using a MTB front derailleur. The cage of a MTB derailleur is designed for smaller chainrings. I looked up the spec. for this model (X7) and it says it's compatible with 42/28 chainrings. It might work for your 46/30 combination. I found this derailleur for sale for $10. You have little to lose at this price.



SRAM X7 Front Derailleur 2X10 > Components > Drivetrain > Front Derailleurs | Jenson USA

qspencer

I had avoided this because newer SRAM road shifters do not have trim clicks for the front derailleur, with the idea that the yaw derailleur makes them unnecessary. The ability of the yaw derailleur to avoid chain rub compared to other road setups is impressive to me, but I'm now coming to see that it probably requires the right chainrings to get the shifting to work smoothly. It's possible the MTB derailleur doesn't need the trim clicks. It all depends on the shape of the cage and how it interacts with my particular setup. Like you said, it can't hurt to try, so I will probably do so.