Triple to double
 

I've just ordered the sram etap wifli group and need to convert my FSA triple to a double. I see in the pic on the house of tandem website that they have done this by moving the (or buying proper) large chainring to the inside of the outer spider. For those of you who have converted triple to double how have you accomplished this?

thanks for any help on this!

Personally, I intend to keep my powder dry and fire only when SRAM comes out with an eTap triple. Your problem as I see it is that your present granny is around 30T and that is probably already too high, unless I way miss my guess. You could help things out with a new cassette, and they are coming out with 12 - 42 11sp cassettes which is the kind of point spread I'd want for a tandem, if my small ring was 30T. Chances are the paperwork will tell you that your present 52 (or 53) big ring has to go away with the new FD limited to 14 or so teeth capacity. I would try it out first before I ditch it. If it doesn't work it might actually work out cheaper to just by a complete unit double. You will almost definitely have to replace your cassette if you do this.

I moved the 52 to the inside position on the 130 BCD position and replaced the 30 with a 36 on the 74 inner position. Effectively I've made a compact crank.

I'm on Red22 with Hydro, not eTap. Shifting with double tap is a dream compared to the original 105.

I haven't tried this but it looks like what they did at house of tandem as well. Just wasn't sure you could attach that chainring to either side of the spider. Thanks. Cannot wait to get rid of 105 on the tandem!

I suspect your wait time will be infinite for that triple. We currently ride a 30 chainring with 28 rear cog successfully with regular 15%+ grades. If the triple-to-double doesn't work out then a double will be on its way. House of Tandem seems to be doing this modification so my bet is that it will work. Stay tuned ...

What brand chainring did you use? some chainrings are assymetrical and as I understand would not mount to the inside of a triple, did you have to change chainring bolts too?

Thank you

The conversion from triple to double should work fine. There are a few minor issue that you should consider. Your current low gear is a 30 x 28. To get the equivalent gearing with a 52/36 crankset, you need a 40T cassette. The 40T cassette has bigger gear jumps, and will require the use of something like the Road Link (the Red derailleur has 32T capacity). A triple crankset may not have the ideal Q factor compared to a double crankset (eg. Lightning or daVinci).

These are all minor issue but worth some thought when you're splurging on eTap. You'll love the shifting!

I changed from the FSA tandem crankset with a 52/39/30 at 170mm to a Shimano Ultegra 6603 Triple but mounted the timing chainring in the outer position, used the 52 from the FSA and imported a 36 stronglight from Mark at Precision.

The timing chain needs a 1mm spacer in each crankbolt as the chains are just too close for comfort and I added a 1mm spacer on the inner 36 too to get a little more space to stop rubbing on the 52 when the cassette is on a smaller sprocket.

Overall I'm very happy with the conversion.

If I am understanding it correctly you converted it to right side drive using the outer (normally where the 52 goes) as the timing ring?
Using a 36 as the granny and 36 too as tining? and what did you use as front crank?

Used 42 as the timing ring, not 36.

Front I used an Ultegra 6600 double, removed the 53/39 rings and mounted the 42 timing ring in the outer position with a 5mm spacer to get a slightly straighter chainline.

Overall the drivetrain changes to full 2x11 and one less timing spider saved me 396g. All I had to purchase was the 74 bcd 36T ring for $55 plus postage and local duties and 3 11 speed chains. The Shimano Ultegra cranks were lying around in the parts bin. Being a hoarder paid off for this project.

One problem with the Ultegra 6603 was the Q factor was not quite wide enough for the tandem frame so I machined an 8mm axle extension that bolted inside the axle.

What cassette are you using with the 36/52?

I modified a 12-25 to remove the 12, 13 and 14 and acquired a oneupcomponents.com mini driver and shark 10 tooth cluster (https://www.oneupcomponents.com/prod...t-cluster-1x11) so I'm running a 10, 12, 14, 15, 16, 17, 18, 19, 21, 23, 25. Nice close ratios with little steps until speed is really high, then we have big steps but a very high top ratio - like a 57-11.

The 39 was on the border of just usable with the 25 but the 36 leaves us hardly using the 25.

This is a clever conversion to 2x11 and right-side timing chain. The advantage is that you can use non-tandem cranks on the front and rear. You must be a strong team to climb on 36 x 25!

What are your thoughts on a right sided drive and a SRAM Eagle setup? Looking at gear calculator, an Eagle setup would actually be very similar to my current tandem setup, but it would be a 1x (I know, a lot of tandem folks cringe at moving from a triple to a double, but I've used a double for years without problems and I'm looking at a single!). This would open up a pretty simple right sided drive.

Anyway, this link lays out the gear ratios:

HTML5 Gear Calculator

What I'm wondering is, would I need to use a SRAM mountain crank to get a long enough spindle for the stoker? I'm not sure I can machine a part to extend my spindle like you did! I was thinking I'd use the inner ring to do the timing chain and outer for the drivetrain.

I wanted to use the inner for timing but twocircle advised against it based on chainline from the outer position and 2x rear dérailleur positioning. I'm glad I took his advice, the inner and middle are perfect with the inner positioned 52 sitting in line with the 5th cog. The cassette did move 1.85mm to the spoke side going to 11 speed on my hub. The Eagle will move further inboard as the shape of the cassette puts the 42 and 50 inside of the freehub body. And you won't have a RD.

My real problem with using the triple was the 52 on the inner gets very close to the chainstay and rubbing. My clearance is currently 3.5mm, I'm thinking or removing 2mm of that to improve the Q factor a little more.

However, I believe the only limiting factor on your choice of crank is the potential rubbing by the chainring on the chainstay. A 50 ring would have solved my problem with a standard crank axle. I suggest measuring up with a standard double crank to see your clearances with the chainrings you want to use. If there is adequate clearance with a standard double and you can mount the left side crank properly you are in the clear.

And then you just have to get used to the big jumps between gears.

This is really helpful, thank you very much! I found SRAMs tech documents and I think I nailed down how to put this together. I made a separate post for the build, so I don't derail this thread any more (sorry!).

One other issue I have is pickins up a crakset with enough clearance to put the timing ring on the outer position, if I take a double compact crank and use longer bots and spacers.

some models that I have seen have too little clearance between whre the ring an timing chain would pass and the crank arm.

Any suggestions on a double, compact lightweight crankset that would work?

Based on that SRAM tech document, I think the wide axle SRAM cranks will probably work for you but you can get the extact measurements from there and measure out on your tandem to be sure.

Robusta converted to DI2.

FSA Gossamer crankset with FSA Fr Der hanger.

Removed the inner ring, installed both BB spacers to left side to position DI2 Der correctly. Works great as a standard 53/39 setup.

FYI, we wanted a "compact" setup for the summer as we train for Leadville, which will involve lots more climbing. I moved the spacers back to standard (one each side). Then installed a 50t ring on the INNER 130mm BCD position, and a 34t on the 74mm BCD position. Installed a standard Shimano Fr Der hanger (moved der back inboard to standard). Works great as well.

We are using Di2 2x11 on our triplet. Using the House of Tandems 34T inner and either a 52 or 53 big mounted on the middle chainring position. 11-40 rear cassette with a road link.

Works great. Have a d-fly unit linked up with the Garmin so I can see what gear combination we are in. Gone are the days of asking the rear most rider "What gear are we in?"

I cant wait for DI2 for this alone. I am using the Di2 display junction myself.
The rest of the system (hydro discs and electronic shifting to avoid cable adjustments) will be a welcome change in our home too.


Now I will need to remember to charge it I suppose.

Both the SC-M9050 and SC-MT800 display show the battery level and gear position. The battery lasts a long time too.

showing battery level and remembering to charge it (especially being that it lasts a long time) are not mutually exclusive. ;)

Yeah, the battery lasts almost too long. LOL.

Ours has been on 50% forever it seems. No need to run out and charge it, but if I forget and we get stuck limping home, I'm sure my stoker would be impressed.