Gear Ratios

[Stallion]

gear ratio:
The relationship between the number of turns made by a driving gear to complete one full turn of the driven gear. If the driving gear turns four times to turn the driven gear once, the gear ratio would be 4 to 1. In most instances, the gear ratio is not even like 4:1 because the same teeth would be meshing with each other. Thus a ratio of 4.11:1, for instance, means that a particular tooth on one gear may eventually mesh with every one of the teeth on the other gear. Changing the tire size will change the effective gear ratio.

This is a quote from a definition of "gear ratios". I'm just not sure I understand these 100% but do we, as muscle car enthusiasts, want a closer ratio (say, 3.08:1) or do we want a larger one (4.11:1)? I figured that logically we would want a closer ratio because the smaller the driven gear would be the less bogged down the engine would be, right? Or do I have my logic wrong? Can somebody please correct me and set me straight? Thanks!!

 

[Ken]

Depends on what you want to accomplish. Are you shooting for top speed, or are you looking to drag race and get out of the hole (launch) more quickly? It all depends on what you're looking for; top speed = a high gear (lower numerically) ratio, bottom end pull = low gear (higher numerically) ratio.

_ken

 

[Stallion]

I see what you mean, Ken, but what's the science behind this idea? What makes one better for that, and another better for this? What's the cause to that?

Thanks!

 

[Vettelt193]

With a higher number ratio, like 4.00 gears, the input has to turn 4.1 times for the output to turn 1, this means the car moves slower at any given RPM (in the same gear) than a 3.00 gear. This also means the engine has an easier time getting up to higher RPM, because at a given RPM, the engine can do less work to maintain that speed, or in other terms, have more extra power to do something else... in our case the something else is get going faster. The lower gear numerically, 3.00 for example, is better for top end, because the engine only has to turn the imput shaft 3 times instead of 4, allowing the car to move faster per RPM... there is much more to it than this, like, you can't put a 2.00 rear in a car and expect it to go 300 MPH, but this is the basic info you may need.

 

[Stallion]

Okay, I think I see where you are coming from. Thanks for the info!!

 

[Geof180]

yep yep.. it's all about torque multiplication...

Geof

 

[Stallion]

yep yep.. it's all about torque multiplication...

Geof

I love torque, we were learning about it in AP Physics. Torque = Fd where F is the Force applied perpendicularly through a distance, d.

One thing I never understood was, why do people want big tires/wheels? If an engine puts out so much torque, and then to get the force applied to the surface (road) you would divide by the torque arm, d. If the wheel/tire is bigger, then the divisor will be bigger, lessening the force on the street. So with this theory, wouldn't we want smaller wheels/tires?

Can you explain this to me? Thanks!!

 

[JohnZ]

I love torque, we were learning about it in AP Physics. Torque = Fd where F is the Force applied perpendicularly through a distance, d.

One thing I never understood was, why do people want big tires/wheels? If an engine puts out so much torque, and then to get the force applied to the surface (road) you would divide by the torque arm, d. If the wheel/tire is bigger, then the divisor will be bigger, lessening the force on the street. So with this theory, wouldn't we want smaller wheels/tires?

Can you explain this to me? Thanks!!

The "big tire" thing is all about traction and grip; for drag racing, if you have enough power to spin the rear wheels, you just make tire smoke while the other guy is gone - so you put more rubber on the ground to get more of a tire contact patch to get more grip and put the power to the ground so the car will accelerate.

Same applies for road-racing - the more tire contact patch you can get on the ground, the more lateral grip you can get for faster cornering, and the more grip you can generate for more effective (harder/shorter distance) braking without locking the wheels.

It's all about the extremes of traction, grip, handling, and braking performance.