Tandem Cycling - why aren't both chains on the same side?

both my mini-twinn and my 26" SS twinn have both chains on the right-hand side.
why aren't high-end tandems similarly configured? [ARE some?]

I'm thinking torque...but to be honest I don't really know....

Reduces flex on frame . . .
Also gives you a 3rd chainring.

Early on, crossover cranksets (where the sync chain is on the left side / drive is on the right) were adopted to eliminate interference problems when front derailleurs and multiple chain rings found their way onto bicycles. Additionally, it usually meant that you would need to give up one of your chain rings such that a tandem that might otherwise have a triple crankset would be reduced to a double crankset. The latter wouldn't be a big deal to anyone who lives in relatively flat terrain, but created issues for touring tandems and tandems that were ridden in hilly terrain where that 3rd / granny chain ring would be necessary. Finally, even for those who could get by using only two of their three chain rings as drive rings with the third supporting the sync chain, using the inboard chain ring position would make for some pretty ugly chain lock-up and chain ring damage if the drive chain accidentally overshifted and landed on the sync chain. Using the outboard chain ring was a work-around for this, but it then limited the size of the inner chain ring due to interference with the right chainstay or required the use of a wider or offset bottom bracket spindle.

Now, it is possible to add a fourth chain ring on certain types of triple cranksets outboard of the big chainring, but they need to have a pretty wide 'Q' to accommodate the chain passing between the big chain ring and crank arm. The latter isn't all that desireable or even much more practical than simply using a crossover crankset.

So, they pretty much became the standard for higher-end touring tandems and have typically been fitted to tandems that use wide-range gearing.

As for current tandems, track tandems and tandems used for racing where the extra chain rings aren't used often times will use a same-side / right-side drive.

BTW, a same-side drive puts less wear and tear on the rear bottom bracket compared to a crossover.

BTW, a same-side drive puts less wear and tear on the rear bottom bracket compared to a crossover.

Why?

Why?

The left end of the rear spindle is being pulled towards the front of the tandem by the captain's pedal loads and the right end of the spindle is being pulled towards the back of the tandem by the combined pedal loads of captain and stoker acting on the rear wheel, causing the rear spindle to be twisted fore and aft against the bearings: Grab a pen, ruler or stick in your hands pointed straight up and down with one hand on each end and then move your hands away from each other and you'll see what's happening to the rear spindle.

Now, to be fair, you have this same asymetric load on a regular, single rider bike on the drive side, but with a tandem you're exacerbating the twisting condition with the captain's loads on the other end of the spindle. As you can imagine, triplets, quads, etc can be very hard on rear bottom brackets.

With a same-side drive, the loads from the captain's pedal inputs work directly against the loads generated by the rear crank to rear wheel drive chain (tie a string around one end of the pen with two long ends and pull those away from each other) to approximate something closer to the loads that a spindle would deal with on a single rider bike.

The left end of the rear spindle is being pulled towards the front of the tandem by the captain's pedal loads and the right end of the spindle is being pulled towards the back of the tandem by the combined pedal loads of captain and stoker acting on the rear wheel, causing the rear spindle to be twisted fore and aft against the bearings: Grab a pen, ruler or stick in your hands pointed straight up and down with one hand on each end and then move your hands away from each other and you'll see what's happening to the rear spindle.

Now, to be fair, you have this same asymetric load on a regular, single rider bike on the drive side, but with a tandem you're exacerbating the twisting condition with the captain's loads on the other end of the spindle. As you can imagine, triplets, quads, etc can be very hard on rear bottom brackets.

With a same-side drive, the loads from the captain's pedal inputs work directly against the loads generated by the rear crank to rear wheel drive chain (tie a string around one end of the pen with two long ends and pull those away from each other) to approximate something closer to the loads that a spindle would deal with on a single rider bike.

OK. I had to go look at the drive train to see what you were saying. Thanks.

There's three legs' worth of torque going through a rear BB spindle on a typical tandem...

Our early 90.s Santana Visa is set up as a direct drive, both chains on the right

4 Chainrings, with the receiving timing chainwheel outermost

Don't know why it was set up that way - it was 'new old stock', apparently overlooked in a bike shop attic for a number of years, and the price made it irresistible, so I bought it sight unseen

No problems with drive-train flex at all in 13 years of use.

Plus - all the greasy bits are on one side, an advantage when hefting it onto a car top carrier
Minus - all those cogs and chains on the same axle have a greedy appetite for stoker shoelaces!

I didn't go looking for these setups, but did notice a Calfee we were riding with at STR had a setup with outer ring timing and a double to the rear wheel.

Possibly for the weight savings.

PK

Possibly for the weight savings.

That, and because Gary G. and his lovely wife Kirsten live and ride where you don't need more than a double.

That, and because Gary G. and his lovely wife Kirsten live and ride where you don't need more than a double.

I believe they mentioned living South of us, I think they said Miami, if that's the same bike / team. Very nice folks.

PK