Originally Posted by becnal
I just got a new Tandem, and I put my spd clipless pedals on, but, is it my imagination, or is the front crankset backwards from normal because the chain is on the left side********** Will I be able to clip in, or is everything off now???
Here's the deal. There are two types of tandem crank systems:
a. A Cross-Over Crankset: A cross-over crank uses a pair of left-side cranks with chain rings to transmit power from the front rider's cranks to the rear rider's cranks via the sync chain. The front right crank is a simple crankarm that looks just like a non-drive side single bike's crankarm, except that it's got right-handed threading... the same as you find on a single or tandem bike's drive side cranks. The left-side cranks both have single chain rings and are left-hand threaded. The power from the front rider's cranks literally "crosses-over" from the left to the right side of the bike through the rear bottom bracket, hence the name.
b. A Same-Side Drive Crankset: A same side crankset is basically two triple cranksets like the ones used on a single bike where the inner-most ring position (the granny or alpine ring) is used for the sync chain. The chain sits o the same-side of the bike as the drive side chain (that would be the right side on most every bike I've ever seen) and the crank arms are threaded just as they are on a single bike: the right side cranks are right-hand threaded and the plain crankarms on the left side are left-hand threaded. Unless you do some interesting modifications to hang a fourth chain ring, most same-side drive tandems are limited to two chainrings on the drive chain.
So, given this knowledge, there are three ways to create a crankset for a tandem, well actually four....
1. You combine two single bike cranksets to create a same-side drive that has only two chain rings for the drive chain.
2. You buy a tandem-specific cross-over crankset that has the correct right and left-hand threading for the cranks that belong on the respective front, rear, right, and left-hand sides of the tandem.
3. You get a hold of three one-piece or square-taper spindle, single bike cranksets with the same length of crank arms and use two of the drive-side cranks on the wrong side of the bike with a lone, single left-hand crank arm mounted to the right front of the tandem. This is where it gets interesting as there are two ways to deal with the three sets of incorrectly threaded crank arms:
a. Cheap & Easy: You can simply use three right side / right-hand threaded platform pedals and one left side / left-hand threaded platform pedal and Loctite keep the three backwards-threaded pedals from unscrewing themselves. A tell-tale sign that this has been done is that your left-side "timing" rings have two chainrings, where there should only be one.
b. Correct & Permanent: You drill-out the three incorrectly threaded crank arm pedal holes, then use the correct tap and helicoil inserts to create the correct right-hand / left-hand threading orientation for the pedals. When done correctly and with pedals installed, you'll never know that the cranks have been modified and they'll work just as well as any new cranks that were produced with the correct threading.
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Bottom Line: If what you're conveying is that you have discovered the left-side cranks are right hand threaded, then you've got a "cheap and easy" cross over crankset on your new, used tandem. As for using SPD pedals backwards, I don't think I've ever seen any where it should work: the left and right hand pedal engagment and release mechanisms are asymetrical.