It’s common knowledge that engine upgrades like a cam, carburetor, or bigger cubes can increase torque to the rear wheel. But the easiest and most inexpensive way to increase torque to the rear wheel, with no sacrifice in dependability, is to change your primary gearing by changing the compensating sprocket.
|155-56||21 tooth sprocket||1985-2006 Big Twin (Except 2006 Dyna Models)||19%|
|156-56||22 tooth sprocket||1985-2006 Big Twin (Except 2006 Dyna Models)||14%|
|157-56||23 tooth sprocket||1985-2006 Big Twin (Except 2006 Dyna Models)||9%|
To view our chain fitment matrix chart Click Here
– Torque increases shown above apply to 1994-up applications
– PN 155-56 requires a shorter primary chain, call for details
– 156-56 and 157-56 require a 39990-01 adjuster bracket and fat tensioner shoe
WHY CHANGE THE COMPENSATING SPROCKET?
A short course in torque multiplication is required to understand the reason why. A traditional rear wheel drive car has a rear axle with a specifi c axle ratio number. An axle ratio of 4.11 is generally recognized as a performance ratio. A 4.11 axle ratio means that the torque from the engine transmitted to the rear axle is multiplied by 4.11 before it goes to the rear wheels. An axle ratio of 2.08 is generally recognized as not desirable for performance applications. The motorcycle equivalent to a rear axle in a car is separated into two elements: the primary drive and the secondary drive. The engine transmits torque to the transmission via the primary drive chain and the transmission transmits torque to the rear wheel via the secondary drive belt. The primary drive number must be multiplied by the secondary drive number to calculate the ‘rear axle’ equivalent to a car, also called the overall drive ratio.
Today’s Big Twin primary drive system was introduced in the mid-1980s. Over the years, the factory used two primary drive ratios. The 37/24 (1.54 ratio) was used from 1985-93. From 1994 and up the 36/25 (1.44 ratio) was used, except for the 1999-up fuel injected FLTs which have the 1.54 ratio for improved acceleration. The traditional way to change the overall drive ratio is to go to a smaller transmission pulley or larger rear wheel pulley. This usually requires changing the belt; it’s a nasty job. If you have access to a 1/2” impact air gun, a compensating sprocket change is a 1 hour job.
You have a stock 1999 carbureted Road King. By going from a stock 25 to a BAKER 23 tooth compensating sprocket, the torque at the rear wheel will increase by 9%. This eliminates the overall drive ratio performance advantage of fuel injected Road Kings. Changing the primary drive ratio affects the overall torque multiplication to the rear wheel. Decreasing the number of teeth on the compensating sprocket increases torque to the rear wheel and improves acceleration and performance. The trade-off for this performance improvement is an increase in the highway cruising RPM with no transmission change. If a BAKER 6-speed transmission is installed along with a new compensating sprocket, the increase in performance will be realized along with a lower highway cruising RPM than with a stock 5-speed.