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Equalizer Chainring Story

Balancing the Loads when Using a Block for the Shorter Leg

History of the Problem

For years, cyclist have known that unequal leg lengths mean less efficient pedaling, sore lower back, knees and hips. They have tried various methods to bring themselves into balance. Blocking up the short leg or using different length cranks are the most common solutions. Unfortunately, as you may have learned through experience, these methods not only do not solve the problem, but in fact often make thing worse!

To understand how the chainring works, think of a rider making a normal pedal stroke, where the power zone is between 2 and 5 o'clock. We'll assume that the riders right leg is shorter than the left and that this problem has been compensated for with a block under the right foot. Take a look at Figure 1.The solid line shows the pedal circle made by the left bottom of shoe and the dotted line traces the blocked right shoe.

Leverage increases as the distance from the bottom of the shoe to the bottom bracket spindle increases. That's not really new -- it's just another way of saying that longer cranks give more leverage, which decreases the pedal load. As you con see from the diagram, the right foot at 12 o'clock is turning a crank that is effectively longer than the left at the same 12 o'clock position. The length difference is equal to the thickness of the block. Since the load is constant, the right leg has more leverage than the left leg does at the same position, creating an imbalance.

In Figure 2, the cranks have turned 180 degrees. In this position the left leg has less leverage and is therefore pushing more load. With proper pedaling technique (where the left foot is pushing over the top as the right foot is pulling back), you see the right aside also has less leverage.

So in figure 1 you have the right and left with more leverage while pushing less load and Figure 2 you have the left and right leg with less leverage and pushing more load. This imbalance is what causes the problem for riders who are using a block only.

The Solution

Since blocks are the easiest and most economical way of compensating for leg length difference, the problem isn't what to use instead of a block, but rather how to equalize the leverage. Because the block forces the leverage to change at various points on the pedal circle. The solution is to compensate for this leverage variance by varying the loads.

This is accomplished by using round chainrings which are placed off center on the crank a precise amount depending on the size of the block. The Equalizer Chainring increases the load as leverage increases and decreases the load as leverage decreases, so that effective gearing and power output are constant throughout the pedal stroke.

Figure 3 show the blocked foot at 12 o'clock. Because there is more leverage at this point, the offset chainring (indicated by lines and arrows boardering the words more load): increases the leverage, keeping the load constant. Figure 4 show the left foot at 12 o'clock of the stroke. Here the leverage is decreased and the chainring decreases the load to compensate for the deceased leverage.

The result is that the loads are equal and in balance. Load is constant and steady throughout the stroke: as the block increases leverage, the chainring automatically increases the load and as leverage drop off, the load decreases right along with it. Both legs are now working with equal loads.

You're probably wondering how our system can work for you. Please feel free to call us at 1-800-438-4399 with any questions you may have.


High Sierra Cycle Center, Inc..

E-mail: hscc@Qnet.com

Call: 1-800-438-4399