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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!

11-08-16, 07:21 PM   #101
carhillclimb
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 Originally Posted by Turbotandem Understood. But I was careful to say "for the same deceleration rate", not for the same force applied to the caliper. If one wants to decelerate, say approaching a stop light going from 20 to zero in 500 feet, the strain on the fork is the same regardless of the rotor size (assuming the caliper is mounted at the same point on both forks with just spacers out to the rotor edge. That is because the caliper pressure on a larger rotor need apply less pressure, thus less force on the larger radius rotor. A small rotor on the other hand has less leverage on the wheel so applies more force for the same deceleration; but in the end applies the SAME force on the fork. If you do the math, the force on the fork works out the same, the radius in a way cancels itself out. That said, if you apply equal braking power at the lever and caliper, you CAN decelerate faster with a larger rotor, such as coming to a stop in 300 feet instead of 500 feet, and that would impart more bending on the fork. Many forks only rate themselves to 185mm, so putting a 203mm rotor on, as we do on mtn tandems, can be over spec based on this thinking; in case one does brake real hard.
Same deceleration is the same force at the tire. The torque needed to create that force at the tire edge = tire radius X deceleration rate. The torque needed at the rotor is the same, and the radius is the rotor contact radius so the force at the caliper to create that tourque = deceleration rate X tire radius / rotor contact radius. This is clearly a larger force for a smaller rotor contact radius, which is approximately (rotor diameter - pad width) / 2, where my name for the pad dimension is bad.

What am I missing here? The caliper is further from the fork but the forces are lower, and I am pretty sure the distance to the fork is smaller than the rotor radius, so the torque on the brackets should also go down even as the distance goes up. This of course assuming that you are not moving the caliper so far out that the bracket is flexing too much.

11-08-16, 08:50 PM   #102
Turbotandem
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 Originally Posted by carhillclimb Same deceleration is the same force at the tire. The torque needed to create that force at the tire edge = tire radius X deceleration rate. The torque needed at the rotor is the same, and the radius is the rotor contact radius so the force at the caliper to create that tourque = deceleration rate X tire radius / rotor contact radius. This is clearly a larger force for a smaller rotor contact radius, which is approximately (rotor diameter - pad width) / 2, where my name for the pad dimension is bad. What am I missing here? The caliper is further from the fork but the forces are lower, and I am pretty sure the distance to the fork is smaller than the rotor radius, so the torque on the brackets should also go down even as the distance goes up. This of course assuming that you are not moving the caliper so far out that the bracket is flexing too much.
Since the caliper mounting point on the fork are always the same, when you move the caliper away from the mounts to accommodate a larger rotor, you are basically mounting the caliper on a lever are. So even thought the caliper force is less the bracket it's mounted to levers back to the same fork mounting point. This the force ends up the same from the forks point of view.

 11-09-16, 12:09 AM #103 geoffs Senior Member     Join Date: Sep 2004 Location: Sydney Bikes: Co-Motion Mocha Co-pilot, Santana Sovereign, Seven Axiom SL, Seven Axiom SLX, Blom Track Posts: 181 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 31 Post(s) HI Twocicle, I just read your post regarding Lightning cranks and Q-factor and realised you are using speedplay pedals. You can buy shorter pedal axles if that makes a difference. They are available from Speedplay but there is another manufacturer thats excellent quality at a better price.
11-09-16, 06:14 PM   #104
twocicle
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 Originally Posted by geoffs HI Twocicle, I just read your post regarding Lightning cranks and Q-factor and realised you are using speedplay pedals. You can buy shorter pedal axles if that makes a difference. They are available from Speedplay but there is another manufacturer thats excellent quality at a better price.
Yes, shorter pedal axles are one part of achieving a desired Q. Linda has been using the Zero Ti (which are as short as possible with minimum heel clearances) for over a decade. With the Lightning pedal axle spacers removed, her heels may just brush the crank arms, so we have "airplane tape" (clear "frame saver", etc) to act as a scuff shield. Can't get her feet any closer than that.

Last edited by twocicle; 11-28-16 at 11:00 AM.

01-08-17, 11:16 AM   #105
kek
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 Originally Posted by twocicle XTR Di2 triple FD mount hacking... Moving to the XTR Di2 triple FD imposed some real headaches due to the wide offset they built into the default/standard mounting bracket system. Even at its inward-most setup, the inner cage plate of FD still mashed up against the outer chainring, or if raised enough, would travel too far outward and significantly interfere with the driveside crank arm. The XTR Di2 triple FD was a bust with the standard Shimano "high mount adapter" clamp. After much thought about options, I had an idea to try the Shimano "direct mount adapter" + 1 Problem Solvers 26mm offset direct mount adapter. This config allowed me to shave off a few mm from the Problem Solvers square chunk of metal, which pulled the FD in toward the seat tube up until the point where the Shimano direct mount adapter just brushed the seat tube. By reducing the standard direct mount offset, this provided just enough clearance (plus maybe 1mm to spare) for FD adjustment. The FD now shifts through all chainrings without any issue and misses our driveside crankarm by maybe 1mm (no contact under any shift scenario). To note, my adapter hacking was only needed because we insisted on a narrow set of cranks with basically a road triple chainline instead of a mtn chainline (wider cranks & wider chainline). Most tandems with standard tandem cranksets (FSA for example) will have enough chainring offset to work fine with the default XTR triple FD offset.
".. basically a road triple " - so, this trick is solution to install triple XTR di2 with shimano road triple crankset (BCD 130/74, chainline 45) ?

origin8 adapter looks close to problemsolvers, may be it can be used too?

Last edited by kek; 01-08-17 at 11:38 AM.

01-08-17, 09:50 PM   #106
twocicle
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 Originally Posted by kek ".. basically a road triple " - so, this trick is solution to install triple XTR di2 with shimano road triple crankset (BCD 130/74, chainline 45) ?
I was able to pull the XTR triple FD far enough inboard to work with ~48mm triple chainline. There seems to be only .5mm more space available before some of the FD mechanism (little swing arm on the rear) will hit the seat tube. A 45mm chainline is probably not achievable. The photos posted above in #82 might give you some idea of just how tightly inboard this hack positions the FD.

We have been running this setup for a few months now (wintering in CA and AZ) and really loving this triple setup. It isn't quite as precise shifting as the full Ultegra Di2 2x11 in some gear combos, and the setup tolerances are a PITA, but it's still very good and worth the pain.

Quote:
 Originally Posted by kek origin8 adapter looks close to problemsolvers, may be it can be used too?
There needed to be enough material on the PS direct mount adapter to shave down at least 3mm. Theirs was a more solid chunk of metal, so easy to rework and still have plenty of platform material left over. The Origin8 adapter appears to already have material removed from the thick part of the platform area, so there is not much there to start with... probably not enough to shave down.

Last edited by twocicle; 02-25-17 at 11:04 AM.

 01-24-17, 07:51 AM #107 racefacelefty Senior Member   Join Date: Oct 2016 Bikes: Posts: 59 Mentioned: 1 Post(s) Tagged: 0 Thread(s) Quoted: 28 Post(s) Earlier in this thread the transfer belt was on the right with a 2x system on your Calfee. I'd like to convert my Cannondale by moving the transfer chain drive side and go 2x. Is there any reason the inner triple mounted transfer chain ring cannot be same size or bigger than the middle ring? The FD will not interfere with the transfer chain if I use a 38/39 inner ring and a 42 for the transfer chain. I can use anything from a 30 to a 42 but prefer a 42 as that is what I have on the front crank that I want to use currently.
01-24-17, 09:48 AM   #108
twocicle
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 Originally Posted by racefacelefty Earlier in this thread the transfer belt was on the right with a 2x system on your Calfee. I'd like to convert my Cannondale by moving the transfer chain drive side and go 2x. Is there any reason the inner triple mounted transfer chain ring cannot be same size or bigger than the middle ring? The FD will not interfere with the transfer chain if I use a 38/39 inner ring and a 42 for the transfer chain. I can use anything from a 30 to a 42 but prefer a 42 as that is what I have on the front crank that I want to use currently.
Hi Raceface,

This would be a good discussion for a new thread, but to answer once here...

Option 1:
If you currently have a typical tandem crossover crankset (timing on left side and triple drive rings) then the simplest modification for a 2x drive ring setup is to use just two of the three chainring positions. This can be either the granny/middle, or the middle/outer. If you opt for the outer two positions, most double FD will need a special mount that positions the FD further outboard (most doubles do not have enough reach to span to the outer ring of a triple crank). The most practical setup is to use the inner/middle and ring sizes such as 30/48, or 34/52. The double Ultegra FD (mech or Di2) can easily handle the 18t spread of those chainrings, 10 or 11 speed. With an 11t cog on the rear, the top end ratio is enough for any team that does not go racing. Most teams badly overestimate their need for a top end gear and lose out on the low end for climbs. I am a Cat 2 road racer (single) and use a 52x11 as my top gear on that, but for our non-race tandem the 48x11 is plenty with our high avg cadence (anything over 37mph is usually downhill so we just rest/tuck).

One downside of using the inner/middle ring positions is that the effective chainline will be somewhat inboard of optimal, so you won't want to use the granny and outer 3-4 cogs on the cassette due to excessive chain angle. Should not be a big deal because those gear ratios will likely exist from the big ring and inner cogs. The inward chainline position of the big ring usually allows use of most of the biggest cogs (ie: big-to-big) without problem, though if you have a huge cog like a 40 or 42, that might not be optimal. The largest cassette we ever used was a 11-36 11spd, and that worked fine with the 48/30 rings, though I did not use the 48-36 combo while riding.

Option 2:
As far as moving the timing chain to the driveside, you would need a new regular front crankset plus a new regular triple crank for the rear if you don't want to reuse the existing rear w/crossover unused. Regarding inner ring sizes on the drive triple, a road triple usually has a 74mm BCD (granny) and you won't find many rings bigger than 34t in that BCD. A 42t 74mm is probably not available. Better to move the timing to the outside position as I did with the belt drive, but do note there is always the danger of having the timing chain snag with the drive chain when it is shifted up to the big (middle position) ring.

For the right side drive setup on our 2013 Calfee Tetra tandem, I used regular road FSK SL-K Light cranksets: double 175mm front, triple 170mm rear. I simply replaced the shipped chainrings with a Gates Belt ring on the outer position (plus some chainring spacers and longer bolts) and a pair of Stronglight 48/30 chainrings on the rear. Now that we have the Lightning tandem cranks, I'll be posting the complete FSK cranksets (w/original unused FSA rings) on eBay in a month or so after we get return from Tucson. PM me if interested and I'll let you know.

My suggestion is to stick with a typical tandem crossover crankset and implement your double chainring choices as per option 1 above.

Last edited by twocicle; 01-25-17 at 09:28 AM.

 02-24-17, 05:10 PM #109 twocicle Clipless in Coeur d'Alene Thread Starter     Join Date: Mar 2012 Location: Coeur d'Alene, Idaho Bikes: Tandems: Calfee Dragonfly S&S, Fandango 29er Mtb; Singles: Specialized Tarmac SL4 S-Works, Specialized Stumpjumper FSR, plus other misc Road & Mtb. Posts: 1,842 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 101 Post(s) Di2 triple w/Lightning update - 1200 miles later Just a quick follow up report... this setup is working great and no major issues. While in Tucson we had a wee problem with the Lightning spider lock ring coming loose on the drive side, and so I had to order up another Lightning lock ring tool for quick delivery (I had left our tool at home). To be fair, the lock ring probably came loose due to my initial fiddling and remounting various spiders without re-applying any additional thread lock compound (ie: blue Locktite). Once I got the new tool and blue Locktite applied, no further problem. No issues with the timing side SWorks spiders coming loose, just the drive side. For the entire 1200 miles we used the same gearing setup: 48/36/26 XT "Trekking" rings with a Ultegra 6800 11-28 cassette and chain. The XTR FD/RD did not seem to use any more battery than what we saw with the Ultegra road derailleurs, meaning, long long battery life of a couple months between charges... and that is with the original skinny "seatpost" battery, not the new beefier mtn version. The 48 x 11 would not be high enough for a race setup, but for our normal "quick" road rides the range of this triple is really good. Only a couple times we may have wanted a 11-32 cassette for really steep pitches. The middle 36t ring x 12-23 cogs get the majority of usage. We especially like the single tooth steps of the 12,13,14,15 (36x12 gets us rolling over 24mph) for smooth ratio progressions to match our high cadence style (typically 103-107rpm). There is a new 11-25 cassette waiting to be used, but now back home with the snow & ice in N. Idaho, it will have to wait. Bottom line, this setup looks like a long term keeper.
 02-24-17, 10:30 PM #110 racefacelefty Senior Member   Join Date: Oct 2016 Bikes: Posts: 59 Mentioned: 1 Post(s) Tagged: 0 Thread(s) Quoted: 28 Post(s) This build has been an inspiration. Thank you. After reading all your different configurations I realised how much one can modify a standard tandem to make meaningful improvements.
02-26-17, 08:26 PM   #111
Turbotandem
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 Originally Posted by twocicle While in Tucson we had a wee problem with the Lightning spider lock ring coming loose on the drive side, and so I had to order up another Lightning lock ring tool for quick delivery (I had left our tool at home). To be fair, the lock ring probably came loose due to my initial fiddling and remounting various spiders without re-applying any additional thread lock compound (ie: blue Locktite). Once I got the new tool and blue Locktite applied, no further problem. No issues with the timing side SWorks spiders coming loose, just the drive side.
Our expierence with lightning drive side spider is that the action of the captain's pedal stroke coming thru the spider in a CW force, then at time the captain's stroke pauses while the stoker pushes produces the usual CCW action on the lock ring. This Back and forth CW to CCW force are not anticipated in the Lock ring no matter how well the loctite is applied. We've had several work loose. The solution that seems to solve the tandem specific failure is to put an intervening very thin washer just below the lock ring. I cut my washer from a soda can, but there are standard washers like for bottom bracket spacers that fit.

02-27-17, 10:13 AM   #112
twocicle
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 Originally Posted by Turbotandem Our expierence with lightning drive side spider is that the action of the captain's pedal stroke coming thru the spider in a CW force, then at time the captain's stroke pauses while the stoker pushes produces the usual CCW action on the lock ring. This Back and forth CW to CCW force are not anticipated in the Lock ring no matter how well the loctite is applied. We've had several work loose. The solution that seems to solve the tandem specific failure is to put an intervening very thin washer just below the lock ring. I cut my washer from a soda can, but there are standard washers like for bottom bracket spacers that fit.
Thanks Andy. I had a brain gap in my last post.

While in Tucson and ordering the 2nd Lightning lock ring tool from Tim, I mentioned your suggestion to use a thin spacer to him and he sent a couple spacers to me at no charge. I used one of those spacers, the thinnest one, plus blue locktite, and that has all held without any issue.

I'm not sure why, but the timing spiders (I'm using flipped S-Works road double spiders) seem to be fine without lockring issue and did not need any tightening or spacers. I opted for a pair of flipped S-Works spiders instead of the provided road triple spiders, to provide the best offset spacing for the Gates timing belt in combination with our "special" narrow Q-factor crankset. I never had a set of road double spiders to try out, but as I understand it, the Lightning road double spiders may not be strong enough for tandem use and some teams may have broken those.

Last edited by twocicle; 02-27-17 at 10:17 AM.

02-27-17, 10:33 AM   #113
Turbotandem
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 Originally Posted by twocicle Thanks Andy. I had a brain gap in my last post. While in Tucson and ordering the 2nd Lightning lock ring tool from Tim, I mentioned your suggestion to use a thin spacer to him and he sent a couple spacers to me at no charge. I used one of those spacers, the thinnest one, plus blue locktite, and that has all held without any issue. I'm not sure why, but the timing spiders (I'm using flipped S-Works road double spiders) seem to be fine without lockring issue and did not need any tightening or spacers. I opted for a pair of flipped S-Works spiders instead of the provided road triple spiders, to provide the best offset spacing for the Gates timing belt in combination with our "special" narrow Q-factor crankset. I never had a set of road double spiders to try out, but as I understand it, the Lightning road double spiders may not be strong enough for tandem use and some teams may have broken those.
Yes, I would think the timing spiders would undergo the same see-saw action as the captain and stokers pedal strokes potentially counter each other at times. But you're right, for some reason I've not had the failures on the timing spiders. Albeit, my failures have been on a right side drive tandem. Regardless there is something I don't fully understand about the dynamics, beyond the fact that the drive spider undergoes the most forces. Or it's dumb luck the timing spiders have not loosened.
I am one of those teams that have broken the lightning double spider, although not an especially powerful team nor loaded for touring. That spider is the one with a bit of a bowl shape to it and thin material between the arms as they span around the large crank connection hole. The thinness, and the flex in the bowl shaped (rather than planar shape of the triple spider) we think incur the breakage. I believe the planar double spider offered performs well enough, although we too have gone with NOS S-Works spiders. FYI, for our triple spider we had a circumferential ring fabricated/milled/tapped to strengthen the spider our on back-country gravel explore tandem (I may have failed to include a picture in the "gravel tandem project" post in this forum). Basically a contiguous 9mm bolt spacer, simply because we had suffered a breakage of another spider I was being cautious. Let me know if you want a picture.

 02-28-17, 09:39 PM #114 Turbotandem Senior Member     Join Date: Nov 2011 Location: Boulder, CO Bikes: Paketa V2r di2, C-Dale MT 3000, Teesdale, 1963 Huffy Daisey Posts: 225 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 12 Post(s) FD slim mount Thanks for the research and helping with my modification to the FD mount. I've posted pictures of this work in my gravel tandem project here: gravel tandem project The "BDSM" Bryan's Direct Slim Mount. Last edited by Turbotandem; 03-21-17 at 09:25 AM.
03-21-17, 12:08 AM   #115
twocicle
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 Originally Posted by Turbotandem Thanks for the research and helping with my modification to the FD mount. I've posted pictures of this work in my gravel tandem project here: gravel tandem project The "BSDM" Bryan's Direct Slim Mount.
Make that "BDSM" or do I need to send a whip-o-gram?