gear ratios
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gear ratios
can anyone explain to me just how the different gear ratios work? how does the different ratios affect the engine output, gas milage etc. i know lower ratios = more take off power but why do you get better gas mileage with a say 3:55 compared to a 3:73. also why are higher ratios better for highway driving than lower ones.
thanks,
umphlettm
thanks,
umphlettm
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The axle ratio tells how many turns of the drive shaft for each turn of the axle.
3.55 : 1 = 3.55 turns of the drive shaft for one turn of the axle/wheel.
Most transmissions used to be 1:1 in high, so the ratio would translate also to turns of the engine. Overdrive transmissions reduce engine rpm to less than driveshaft rpm.
Read up:
HowStuffWorks "How Gear Ratios Work"
3.55 : 1 = 3.55 turns of the drive shaft for one turn of the axle/wheel.
Most transmissions used to be 1:1 in high, so the ratio would translate also to turns of the engine. Overdrive transmissions reduce engine rpm to less than driveshaft rpm.
Read up:
HowStuffWorks "How Gear Ratios Work"
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Joined: May 2009
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From: Skyway, WA
Nascar drivers want a really high gear ratio (2:75.1) to go really high speeds.
Drag racers want a really low gear ratio (4.10:1)to get from zero to 1/4 mile as quickly as possible.
Heavy duty trucks want an extremely low gear (6:1) ratio to allow them to get massive amounts of weight into motion. (Don't take the examples as actual gear ratio's as I don't really know how high Nascar uses or how low big trucks use... meant to be in the neighborhood of)
A Nascar racer would get smoked in a drag race starting from a stop. It would melt it's tires off trying to get started. A drag racer wants maximum traction at takeoff and doesn't want to spin it's tires. A drag racer could never get close to a Nascars top speed because it can't rev that high.
For the rest of us......
our engines have torque and horsepower
our engines might be able to rev to high rpm's (or not so much)
our vehicles have weight and air resistance to overcome.
Ever ridden on a 10 speed bike (or 18 speed for those younger )
Use the big sprocket in front with the little sprocket in back and you can go really fast if you have the muscles to get going... this is like the Nascar car
Use the little sprocket in front with the biggest sprocket in back and you can start out quickly and easily or go up a hill more easily You'd find yourself pedalling as fast as your able but not be going very fast. This is more like the drag racer. So you shift gears as you go.
Economy cars or even luxury cars that want to maximize gas mileage, have more gears. Think of horsepower as how strong your legs are, and Torque as how quick your legs are at applying strength.
Finding the right balance between an engine's strength vs how steeply geared it is helps balance between gas economy and power. More gears helps allow for a steeper (higher geared) rear end, by giving intermediate steps from being stopped to going fast. Some engines could rev to high RPM's if not loaded down too much. Ask too much from a motor by having a high rear gear ratio might result in it having to suck too much gas to overcome the load and in a sluggish acceleration. On the other hand, if you have a high torque motor in low RPM range, then having a low rear end gearing might result in it revving way higher than neccessary resulting in sucking too much gas or running out of usable RPM's.
A 4cylinder going through the same gear ratio's will go exactly the same speed as a V8 at the same RPM. The question would be, what is the vaccuum load (how much gas it wants to use) between the two engines.
Does this help? This is how I understand gearing
Drag racers want a really low gear ratio (4.10:1)to get from zero to 1/4 mile as quickly as possible.
Heavy duty trucks want an extremely low gear (6:1) ratio to allow them to get massive amounts of weight into motion. (Don't take the examples as actual gear ratio's as I don't really know how high Nascar uses or how low big trucks use... meant to be in the neighborhood of)
A Nascar racer would get smoked in a drag race starting from a stop. It would melt it's tires off trying to get started. A drag racer wants maximum traction at takeoff and doesn't want to spin it's tires. A drag racer could never get close to a Nascars top speed because it can't rev that high.
For the rest of us......
our engines have torque and horsepower
our engines might be able to rev to high rpm's (or not so much)
our vehicles have weight and air resistance to overcome.
Ever ridden on a 10 speed bike (or 18 speed for those younger )
Use the big sprocket in front with the little sprocket in back and you can go really fast if you have the muscles to get going... this is like the Nascar car
Use the little sprocket in front with the biggest sprocket in back and you can start out quickly and easily or go up a hill more easily You'd find yourself pedalling as fast as your able but not be going very fast. This is more like the drag racer. So you shift gears as you go.
Economy cars or even luxury cars that want to maximize gas mileage, have more gears. Think of horsepower as how strong your legs are, and Torque as how quick your legs are at applying strength.
Finding the right balance between an engine's strength vs how steeply geared it is helps balance between gas economy and power. More gears helps allow for a steeper (higher geared) rear end, by giving intermediate steps from being stopped to going fast. Some engines could rev to high RPM's if not loaded down too much. Ask too much from a motor by having a high rear gear ratio might result in it having to suck too much gas to overcome the load and in a sluggish acceleration. On the other hand, if you have a high torque motor in low RPM range, then having a low rear end gearing might result in it revving way higher than neccessary resulting in sucking too much gas or running out of usable RPM's.
A 4cylinder going through the same gear ratio's will go exactly the same speed as a V8 at the same RPM. The question would be, what is the vaccuum load (how much gas it wants to use) between the two engines.
Does this help? This is how I understand gearing
