Few recumbent bikes or trikes can do without them. Idlers (or pulleys, as some call them) are essential to ensure that the chain passes between all the structural elements, from the cranks to the hub of the wheel it drives. They are extremely stressed parts that can easily cause unpleasant noises or take unnecessary power away from the rider.

Most manufacturers supply their own versions of idlers, but these can be replaced—either right after buying a new machine to make your new darling look and ride better or over time as the pulleys wear out.

The people at Terra Cycle in Portland, OR, USA, are the biggest experts in making pulleys for recumbent bikes. So, with their permission, we visited their website and compiled some basic information about pulleys.

Power, Return and Over/Under idlers

The chain that moves from back to front and does all the work is the power portion of the chain. It’s the line of chain on top and carries the load (all that muscular power you’re putting into each push of the pedal). This is where a Power Idler goes. In the old days, recumbent manufacturers used skateboard wheels for idlers, but because you’re pushing so powerfully, the chain would wear down the polyurethane with unnecessary friction. Today, thanks to a guy named Pat Franz, we put a toothed cog in our power idlers. The teeth keep your chain from wandering and, because the line is so taut, the chain spins the idler without any undue friction or slowing. 

The other half of the chain, the part that runs below the power, is the return. It’s the bottom and just kinda hangs out. Its job is to return back to the chainring. On this section of chain is where you find the (you guessed it) Return Idler. We don’t leave out the toothed cog in the return idler just because it’s extraneous; we do so because a lightly loaded chain (the return side) can skip over the teeth of the cog, causing noise and friction and possibly damage to your chain. 

Both instances (power and return) occur on any given chain, but, depending on the cycle, the chain can follow different paths and require different sets of idlers. For bikes whose power-side and return-side chain spin the idler in the same direction and run close together, an Over/Under Idler is perfect. The over/under is a two-in-one idler, serving both the power and return chain.

Terra Cycle Idlers: Sport vs. SportPlus vs. Elite

Originally designed as a cost-saver to help first-timers (or those with multiple bikes) to upgrade to T-Cycle quality, the T-Cycle Sport Series Power Side Idler, Return Side Idler, or Over/Under Idler will be the best (and only) idlers many riders ever need. Sport Series Idlers are designed for supreme function and durability. Made with a precisely crafted 7075 aluminum cog for the power side and an industrial urethane band on the return, with military-grade ballistic nylon side plates and with top quality ABEC 7 steel bearings, the Sport Series Idlers are built to last and do an exceptional job maintaining your chainline. 

Upgrading to Elite Series Idlers gives a slight boost in performance, further improvements to durability, and an MTV-worthy makeover in looks. When you upgrade, you find that what was an all-steel ABEC 7 bearing is now a smoother and more durable hybrid ceramic ball bearing; what were ballistic nylon are now two immaculately machined aluminum side plates whose beauty is only surpassed by their fortitude; and what was precision aluminum is now an indestructible titanium cog born of meticulous and unrelenting fidelity to the ideals of the perfect idler. In short, the Elite Series Idlers are the undisputed best idlers in the world in functionality, durability, and serious bling-factor.

The SportPlus series features the same specially designed beveled side plate shape as their Elite Series idler, but the sides aren’t machined from a solid block of aluminum, and it doesn’t have the Elite’s titanium cog or ceramic bearings. So you get exceptionally smooth chain flow, a very durable 7075 Aluminum cog, very nice ABEC 7 bearings, and super tough glass-filled nylon side plates, all at a much lower price.

Ceramic vs. Hybrid Bearings

Short answer: because better bearings—like those found in T-Cycle idlers—drastically increase the lifetime of your product. One customer has ridden for 50,000mi in the rain and mud of Oregon without his T-Cycle idler giving way! 

The Annular Bearing Engineering Committee (ABEC) is a group that was formed within the American Bearing Manufacturers Association in order to create an industry standard for the tolerances of ball bearings. On the ABEC scale a higher number means a more precise bearing. There are five grades: 1, 3, 5, 7, and 9. All T-Cycle idlers come with high-quality ABEC 7 bearings, with the exception of Elite idlers, which can be upgraded to hybrid ceramic bearings. 

In a hybrid ceramic bearing, ceramic balls are encased in the same steel rings as a standard bearing. The ceramic balls, however, are stronger and more friction-resistant than steel, giving the bearing a smoother and longer-lasting ride. Since the ball is what wears out when the bearings are used on cycles, the hybrid ceramic is a good match. 

How to get a new idler for your recumbent

The easiest way is of course to contact your recumbent dealer and ask them. You will probably be able to choose whether you want an original pulley from your recumbent bike manufacturer or whether you want an alternative from, say, Terra Cycle or another pulley manufacturer. You can also contact Terra Cycle directly, or you can choose from their e-store where they also have complete kits for particular models.

In any case, it will be important to match the pulley size and axle diameter. While you can order a larger pulley in some cases, which will improve the efficiency of power transfer and make the cycle quieter, you may find that the pulley won’t fit in the space you need. On rear-suspended recumbents, there’s a risk that a different pulley size will change the suspension geometry and you’ll “create” a pogo effect with the new different-size pulley. The pogo effect causes a portion of the pedaling or motor power to be lost in the spring and the bike to bounce when you ride. But that is another story.

Why are larger idlers quieter and more efficient?

Larger idlers are quieter because the geometry of a say 23-sided polygon is a closer approximation to a true circle than a say 15-sided polygon. It has to do with the arc error between a polygon with the same number of sides as the number of teeth of the idler. Larger idlers have less arc error, and the chain moves more smoothly over them. Larger idlers are more efficient primarily because each link of the chain doesn’t bend as much as it comes on and off the idler. The smaller the idler, the more each link has to bend.

Chain tubes are another important part of the entire power transmission system. However, we will look at these next time.