What are car gears, are they like bicyle gears?

[scilearner]

Hello everyone,

 

In a bicycle, if I want to go uphill, I put gear 1, change the chain and it is easier to pedal and I move less. In a car also you have to put gear 1 up a hill. Now how can I relate bicycle gears to car gears, what does easier to pedal mean in terms of car gears. Thanks

[CaptainPanic]

It's pretty much the same idea.

 

Instead of your legs going up and down, in an engine the pistons move up and down.

And on a bike, there is a chain between the gears, but in a car the gears are in direct contact.

To change gear on a bike, you move the chain onto a different gear. In a car, you move part of the gearbox, so different gears come into direct contact with each other.

 

So, it completely relates. It's the same principle. It's only put together in a different way.

[Airbrush]

what does easier to pedal mean in terms of car gears. Thanks

 

It means the engine can run faster to go a shorter distance. That gives more power for going up hill. In exchange you burn gas faster.

[doG]

See http://auto.howstuffworks.com/gears2.htm

[ewmon]

A gear ratio (literally, a "tooth ratio") does two things:

1) It changes the rotation speed

2) It changes the torque

 

Hopefully all my math is correct.

 

On a bike, a 2.5 ratio means that for one revolution of the crank, the back wheel makes 2.5 revolutions. This is really helpful for going fast because we simply couldn't pedal as fast as the wheels turn at the fast speeds we want to go (otherwise we'd ride kiddy tricycles instead). At the same time, the torque on the pedals sprocket translates into 1/2.5 (or 40%) at the back wheel.

 

So, if you're pedaling at 1 rps (revolution per second), your back tire is spinning at 2.5 rps. At the same time, if you push straight down on the pedal with 100 pounds on a ½-ft crank that's horizontal, thus producing 100 lbs × ½ ft = 50 ft-lb of torque, the torque working the rear wheel will be 20 ft-lbs (that is, 50 ft-lb/2.5), and if the radius of the wheel is conveniently 1 ft, then that produces 20 lbs of thrust (20 ft-lbs / 1 ft = 20 lbs) at that instance.

 

Furthermore, 2.5 rps on a 1-ft radius wheel gives a road speed of 2.5 rev/sec × 2π ft/rev = 15.7 ft/sec (about 10.7 mph). Multiplying that by the 20-lb thrust gives you 314 ft-lb/sec (~0.57 horsepower). You're exerting 0.57 hp on the moving pedal, and the same power is coming out where the tire meets the road (if there are no losses in the system ... but there's always some losses).

 

Now, let's say you encounter a hill, so you need more thrust at the road to carry you up the hill. So you downshift to a ratio of 1.0. This means that the wheel spins at the same speed as the cranks. You're exerting yourself the same as before, so your 50 ft-lbs at the crank translates through the 1.0 ratio into 50 ft-lbs at the wheel whose 1-ft radius produces 50 lbs of thrust where the tire meets the road. You're now producing 50 lbs thrust instead of 20 lbs so that the bike can carry you up the hill. Your wheel is now spinning at only 1 rev/sec, equivalent to 6.28 ft/sec or 4.3 mph.

 

You changed gear ratios to sacrifice speed for increased thrust, but you're still pumping out the same power which is also what the wheel is exerting on the road.