# Tachometer vs Gear change

When your transmission shifts to a lower gear, the engine speed, as measured by the tachometer, increases. And when your transmission shifts to a higher gear, the engine speed decreases. Why?

Uh, that’s the reason for having more than one gear ratio in the transmission: to keep the engine speed within acceptable limits at different road speeds and load demands.

Here’s an excellent site to help explain the fundamentals of transmissions- http://auto.howstuffworks.com/transmission.htm

Torque = force x radius

To get a 2000 lb car moving from a standstill, the small first gear will spin [the engine] up to 3500-4000 RPM before no more effective horsepower is being generated, and at this point the car may be going only 15-20 MPH. When moving 50-60 MPH, the large fifth gear needs not spin as fast because momentum sustains the car speed as well.

If you’ve ever ridden a mountain bike, same concept.

I hope I explained this well enough, i’m no Physics major.

Because when you say a "higher or “lower” gear you’re refering to the ratio of rotations going into the transmission to the ones going out and eventually to the wheels. A “higher” gear will have more wheel revolutions per engine revolutions, so thus when you go into a higher gear the engine doesn’t have to turn as much to keep your car going at a given speed.

Oh boy…I wouldn’t want to own this car after it gets sold someday…

My son when he was 15 asked me the same question when I was teaching him how to drive. The example I gave him was his mountain bike. When you need to go up hill…you shift to a lower gear and peddle like h*ll…but the bike isn’t moving very fast…and it takes a lot less strength to move the bike…but a lot more revolutions. Then when you’re on a straight away…you shift to a higher gear…You shift to a higher gear…Now you don’t have to peddle as fast…but the bike is going much faster…and it it doesn’t take a lot of strength to move the bike since you’re not going up hill.

Mountain bike and…numbers. Think of the engine as 0 thru 9 ( 0,1,2,3,4,5,6,7,8,9 ), it can’t go any higher than 9 until the transmission comes along and adds a 1 in front so the engine starts back at 0 up to it’s 9 limit ( 10,11,12,13,14,15,16,17,18,19 ). Now the engine can’t go any higher again until the transmission changes it’s 1 to a 2 ( 20,21,22,23,24,24,26,27,28,29 ) . and so on . The engine has it’s range of RPMs and the transmission has changeable gear ratios to get you moving.