Rear axle ratios and impact on towing
Suppose you have a choice between two axle ratios, say they are a 3.09 and a 3.45. And let's say the vehicle has an 8 speed transmission, so there's plenty of gear flexibility. Ok, so there's roughl...
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Hey Turtle !!!....I've already lost all my hair so, save yours for another time.... ;)
I'll take a crack at this...
Take each component individually before adding them up....early one mentioned
if any one cycles...you can 'see' each gear that the chain is on and the other
gear that, that same chain is on...
Simple math from there dividing the gear teeth numbers...
Forget about HP and Torque for not...again why mentioned cycling...folks seem
to under stand better when they have their own skin in the game vs an inanimate
object
Gears change RPMs from one side to the other side (input to output) shafts
A 4.1 diff gear ratio will have the input pinion turn 4.1 times to *ONE* turn
of the crown gear...which is attached to the axle....which is attached to the
flange that the wheel bolts to....which will have a tire mounted on that to
connect that drive shaft turns to the pavement.
The tire is another variable, but save that for later down this thread
Hope that is clear that the drive shaft to pinion to crown gear has a ratio of
some sort that then turns the wheel
A 3.73 will have the drive shaft turn 3.73 times to *ONE* turn of the wheel
A 3.08 will have the drive shaft turn 3.08 times to *ONE* turn of the wheel
ETC
Same thing for the engine to tranny and let us us a manual instead of an automatic.
As an Automatic has a TC (torque converter that used hydraulic coupling...which
means that there is slippage in the TC and why there are now TC lockup to by
pass or remove thats slippage)
So if the the first gear is a 4.56:1, the engine will turn 4.56 times to *ONE*
turn of the tranny output shaft
And so one for the other gears in the tranny
The tranny output shaft is the drive shaft and we won't complicate this with
the mention of a transfer case and it's gears)
That drive shaft is connected to the diff input shaft, which is the pinion
from the above few paragraphs
So depending on which the gear is selected for the tranny and what the diff
ratio is...will determine the number of times the engine turns vs the wheel turns
That is the basis for all of this thread...how many times the engine turns vs
how many times the wheels turns
That is then factored by which gear ratios are selected or involved
All simple math folks
Now the variables that has folks messed up
One is gasoline vs diesel, which has different characteristics. Like that one
gallon of gasoline does NOT have as much BTU's as diesel.
Another is that one used compression ignition and the other spark. So their
componentry is different because of the stresses are different and a whole
lot more
Why, generally speaking, diesels have much more torque at lower RPMs than
gassers generally do.
Why gassers can spin to higher RPMs, generally speaking, than diesels can.
Now toss in Torque and HP to further confuse...
As for efficiency of any one gear ratio to another...it has more to
do with the pumping losses and how the gear set is designed. The
most efficient gear is a plain spur gear, but the noise from that
kind of gear would have most folks complain that something is wrong...
Everyone is used to helical gears these days, that they don't know
what a straight cut spur gear sounds like.
There is a Porsche racer who beats lots of folks and those others
have very similar 911's...he had a custom made set of straight cut
spur gears for his custom gear box. Fast, but NOISY !!!
I'll take a crack at this...
Take each component individually before adding them up....early one mentioned
if any one cycles...you can 'see' each gear that the chain is on and the other
gear that, that same chain is on...
Simple math from there dividing the gear teeth numbers...
Forget about HP and Torque for not...again why mentioned cycling...folks seem
to under stand better when they have their own skin in the game vs an inanimate
object
Gears change RPMs from one side to the other side (input to output) shafts
A 4.1 diff gear ratio will have the input pinion turn 4.1 times to *ONE* turn
of the crown gear...which is attached to the axle....which is attached to the
flange that the wheel bolts to....which will have a tire mounted on that to
connect that drive shaft turns to the pavement.
The tire is another variable, but save that for later down this thread
Hope that is clear that the drive shaft to pinion to crown gear has a ratio of
some sort that then turns the wheel
A 3.73 will have the drive shaft turn 3.73 times to *ONE* turn of the wheel
A 3.08 will have the drive shaft turn 3.08 times to *ONE* turn of the wheel
ETC
Same thing for the engine to tranny and let us us a manual instead of an automatic.
As an Automatic has a TC (torque converter that used hydraulic coupling...which
means that there is slippage in the TC and why there are now TC lockup to by
pass or remove thats slippage)
So if the the first gear is a 4.56:1, the engine will turn 4.56 times to *ONE*
turn of the tranny output shaft
And so one for the other gears in the tranny
The tranny output shaft is the drive shaft and we won't complicate this with
the mention of a transfer case and it's gears)
That drive shaft is connected to the diff input shaft, which is the pinion
from the above few paragraphs
So depending on which the gear is selected for the tranny and what the diff
ratio is...will determine the number of times the engine turns vs the wheel turns
That is the basis for all of this thread...how many times the engine turns vs
how many times the wheels turns
That is then factored by which gear ratios are selected or involved
All simple math folks
Now the variables that has folks messed up
One is gasoline vs diesel, which has different characteristics. Like that one
gallon of gasoline does NOT have as much BTU's as diesel.
Another is that one used compression ignition and the other spark. So their
componentry is different because of the stresses are different and a whole
lot more
Why, generally speaking, diesels have much more torque at lower RPMs than
gassers generally do.
Why gassers can spin to higher RPMs, generally speaking, than diesels can.
Now toss in Torque and HP to further confuse...
As for efficiency of any one gear ratio to another...it has more to
do with the pumping losses and how the gear set is designed. The
most efficient gear is a plain spur gear, but the noise from that
kind of gear would have most folks complain that something is wrong...
Everyone is used to helical gears these days, that they don't know
what a straight cut spur gear sounds like.
There is a Porsche racer who beats lots of folks and those others
have very similar 911's...he had a custom made set of straight cut
spur gears for his custom gear box. Fast, but NOISY !!!
