Readers have been tantalized by cryptic descriptions of the sprockets on the 2019 Honda CRF450L with its electric start, rearview mirrors, and LED lighting. "Front and rear sprockets, produced in durable steel material, feature a damper system for smooth, quiet running." And, "Final-drive sprocket damper…designed to keep your bike quieter." Some interpreted this to mean the bike has a hub cush drive, which is hardly breakthrough tech.

Okay, imagine you have just been assigned as project leader on a program to make a dual-sport version of Honda’s long-serving four-stroke 450cc motocrosser, the CRF450R. What would be your absolute priority? Sure, you’d want to re-cam the engine for street and trail use and give it more flywheel too, but what’s the biggie?

Sound.

Remember the “less sound equals more ground” campaign of the 1970s? Bikes for use away from closed-course racing have to meet strict noise emissions, and with one big booming 450cc cylinder that won’t be easy. The old boom-box mufflers on 750cc flat-track racers only had to quiet 375cc cylinders. So no matter what muffler you design for this CRF450L, every other sound source on the bike will have to be studied, identified, and quieted as well. A quick phone call to the “Noise, Vibration, and Harshness” department brings a study team equipped with microphones, recorders, and analytical software.

They come up with sound-absorbing right and left crankcase covers (lots of streetbikes already have these) and they also suggest injecting a urethane slush-molding compound into the swingarm, whose large panels would otherwise vibrate like shiny aluminum loudspeakers. Sounds strange, but the mikes and the software don’t lie.

And one other thing: We don’t usually think of a chain drive as a sound source, but it is one. Old-time racers making a plug chop accelerated on full throttle, then simultaneously cut the engine and pulled the clutch to preserve the max-power evidence on their spark plugs. As they coasted to a stop, they could hear the zzzhh of the chain and sprockets.

Honda rubber sockets
Urethane rubber sprocket dampers are one of several measures adopted to enable the 2019 Honda CRF450L to meet noise emissions.Courtesy of Honda

A chain sprocket is a polygon with as many sides as it has teeth. As each roller hits the rotating sprocket there is an impact. Sound is radiated, and the sound meters of the Environmental Protection Agency will detect it and add it to engine and other sounds.

If you look at a photo of the rear wheel of this new Honda CRF450L, you will see that black urethane rubber is bonded to both sides of its sprocket. Just as each roller is about to impact its snug place in the sprocket, the chain’s inner side plates make a soft landing on those circular urethane surfaces, preventing the endless muted clicks that would otherwise result. Sound emissions are reduced and a certificate is issued to the model.