Motorcycle Council of NSW Recreational Trail Bike Riders Sub-Committee

Loud & Clear, noise is our main issue!

Trail Tips

Remember that making a racket only limits riding options

Ask any non-rider what annoys them the most about dirt bikes and they’ll bark out ‘noise!’ every time. They’re out in the bush, taking a break from the hustle, and suddenly they’re assaulted by a racket that drowns out even the thought of a little serenity. If riders are to continue to share the bush, something has to be done to curb sound levels.

The Source

Back when Adam was a teenager with a Brando haircut, trail bikes had two inches of suspension travel and big cast-iron 650cc engines that made all of 35hp, and the term ‘muffler technology’ was very much in its infancy. The engines were designed to make as much power as possible, then mufflers were added in a casual and half-hearted attempt to make the bikes street-legal. The result was predictable; riders took the mufflers off to regain the lost horses and bikes were habitually run loud.

As legislation was tightened to control noise levels, the design of motorcycle engines changed, with probably the most rapid development happening between 1985 and 1995. During this period, manufacturers began building bikes that performed to noise emission levels that were being increasingly lowered in Australia and Europe. To do this, the engines were tuned to work with effective mufflers, and advances in four-stroke technology in particular went hand-in-hand with increases in back-pressure from accurately tuned headers and mufflers.
Getting More

This situation reached the point about 10 years ago where after-market muffler manufacturers were having difficulty matching the power outputs of the stock systems, even when they strayed above the legal noise limits. What they most commonly found was that gains could be made in the top end of the rev-range, but this came at the cost of bottom-end and mid-range. Dirt bike riders predominantly rely on a meaty bottom-end and mid-range, and rarely wind the motor right out, so this explosive top-end delivery was doomed. On a muddy trail or a killer hill a hard hitting top-end is completely useless, and even dangerous, and this where the rider who wisely spent his money to tune his suspension will reap the rewards while his noisy buddy will end up on the ground.

Some after-market mufflers do spread an increased power output, especially when combined with a header tuned specifically for it, but the thing is that these pipes are as quiet as the stock systems, because the engine is built to perform best at that same degree of restriction. Remove the baffle from such a system and you’ll get an increase in noise, but no increase in power or acceleration.
Playing with Fire

Given the above, unless you’re riding a dinosaur or a dunga, noise does not equal speed. In fact noise equals numb-nuts, and the bloke on the loud bike will find it hard to round up riding mates who tuned their suspension instead. That said, many bikes are too quiet off the showroom floor and a little extra sound output aids the safety of both the rider and other bush users. Getting this balance is the crucial part.

Like so many other aspects of dirt bikes, the management of sound is all about appropriate use. The sound of a dirt bike alerts others to your presence, which is a good thing on a tight mountain firetrail. That purr of mighty four-stroke gives people just a bit more than a few seconds before you appear, which is a good thing.

That same sound, the beat of the engine mid-flight, is not appropriate near picnickers at the car park, or when transporting through a camping area or small town. Idle through these types of areas, keeping the muffler at a burble, and no-one will care that you were there. This goes for starting and warming a bike up as well. Engines like to warm slowly and gently, so a slightly high idle is the go. Revving the bejezzus out of a cold engine says a lot about the IQ of the perpetrator, none of which he’d be happy to hear, so keep the revs down and idle away gently.
Noise Types

Some noises are more annoying than others, even at similar output levels. Sharp, harsh sounds are more offensive than deeper, more mellow tones, and high-pitched noises are disturbing at close quarters. Generally, the sound of a two-stroke will carry further than that of a four-stroke, so back off a little earlier if you’re riding one into a populated area. Avoid after-market mufflers that produce sharp barks, because like two strokes these tend to bounce off hills and carry for long distances.
Duration

Putting up with the sound of a passing vehicle rarely upsets the normal Australian bush user. It comes, it goes, a wave to the rider, not a drama. The problems come from repetition. Riding a bike of any description in small circles within ear-shot of Joe Public will cause problems. You are, in effect, assaulting him. Stealing his peace. Rattling his desire to rest and relax. No wonder he gets grouchy. If you want to practice on a small, tight track, find one away from other people. Don’t spend all day riding in and out of the same car park, and don’t let your kids run around camp grounds on mini bikes. These things cause more complaints than all the other riding activities combined, and they are completely unnecessary.

There are thousands of hectares of bush and ride parks to ride in, most of which have no people. Out there, no-one really cares what you do, as long as you are registered and licensed, stay safe, and don’t trash the bush, so head into the wilds away from other bush users. For the few minutes of each day that you need to share some ear-space with others, back off and keep the noise down. It’s so little to ask and there is so much to gain.
Suspension before power

A Short Note: Buy an after-market muffler with care and remember the money would be much better spent tuning your suspension. Some after market mufflers require regular repacking with fibreglass or a similar material, so unless you’re good with maintenance these types get loud quickly and leave you with a drop in power. Rivets are common, but in such a high-vibration area they will rattle loose over time and require replacement. Extremely light mufflers are very tempting, but are easy to damage. Steel components rust. Watch too for imports from countries with lax noise laws. These pipes are big on bark and little else, and the fact that mufflers with a dB output that makes them illegal to race with, let alone use on the road, are even allowed into the country is amazing. Don’t be caught with a muffler you can’t use.