The Importance of a Tachometer on a Motorcycle
It may not seem like it to most people but a motorcycle does have a dashboard. By dashboard, it is meant, an area that has instruments that tell you what the bike is doing. What gear you are in, if your blinker is on, low oil, speed, and the RPMs (revolutions per minute of the engine), and of course your speed. This is all important information when you are riding a motorcycle.
You need to know what the RPMs are so that you know when to shift the transmission into the next higher (or lower) gear. If you are an experienced rider (or have experience driving a car with a manual transmission) you can tell this by the sound and the feel of the engine.
Shifting by feel/sound is one of those scenarios that looks good on paper but can have serious consequences in real life. If you look at a tachometer, you will see numbers. They will usually be single digit numbers (1,2,3 etc). On some bikes that are capable of high revs you may get into double digits. The important thing to know is what these numbers signify. Whatever the number is, you have to multiply it by 1000. If the needle is on 3, you are actually running the motor at 3000 RPMs. The next logical question is “what exactly is an RPM”?
RPM stands for Revolutions Per Minute. That is more or less common knowledge. What does that really mean to you? For an internal combustion engine to work (it varies if you have a 2 stroke or a 4 stroke motor) it has to complete an entire cycle of operations. Fuel has to enter the cylinder, get compressed, get ignited by the spark plug (which pushes the piston back down and turns the crank shaft), and the exhaust gas has to leave the cylinder. That is 1 revolution. So, on the tach (the common term for the tachometer) you see the needle at 3. What is really happening is the entire process described above is happening 3000 times every minute.
That is a lot of moving parts that are moving at an extremely fast speed (and 3000 is a normal riding range). This is why a tachometer is so important. It tells you how much strain you are putting on the engine. The speedometer can be misleading because of the transmission. You can be riding very fast but still have low RPMs.
Another feature that you will see on the face of the tach is an area that is red (sometimes preceded by orange). They mean exactly what you would think. Danger. If you are revving the engine so high that the needle is going into the red (red lining it) you are running the risk of blowing up your motor. This isn’t a Hollywood thing. There won’t be a fire ball and loud boom. What is going to happen is you will have a mechanical failure. It may range from just blowing out a seal or a gasket all the way to breaking the crankshaft or cracking a piston. It is a good rule of thumb that the manufacturer knows what the capabilities of the motorcycle are.
For everyday riding, you shouldn’t have to worry about it. You won’t ever go anywhere near the red line. The main people that deal with it are racers that are pushing the bikes to their mechanical limits (and as a disclaimer, have the personal skill and experience to control the bike in those situations).
For the casual rider, you will shift somewhere between 3000 and maybe 5-6000 range. 6000 is high for bikes that are cruisers and choppers. If you are riding a sport bike it may not even redline before it gets into the 12,000 range. Remember, just because the motor CAN do it doesn’t mean you have to make it do it. Think about a car. The speedometer says 140mph. Have you ever driven you Honda Accord that fast?
So, to put it in simple terms, the tachometer tells you how many complete revolutions (or complete combustion cycles) that your engine is making every minute. There are a lot of big numbers being thrown around. Don’t let this scare you away. When you are sitting at a stop light in neutral the motorcycle is going to be idling somewhere between 800-1200 RPMs. Internal combustion engines are designed for the internal parts to take abuse (controlled explosions) at a high rate of speed.
If you don’t pay attention (and are doing 40mph in first gear, you may not make it back home on you beloved motorcycle. Pay attention to the speedometer and tachometer.
