Understanding gears

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I was wondering about rear end gear ratios for example my 2013 Mustang GT has a 3:73 rear axle ratio so does that mean that the rear wheel turns 3:73 times for every one revolution of the engine? I know that 3:73 is a lower gear then the other ratios for the Mustang being 3:55 or 3:33 and it gives you more acceleration off the line with the negative being lower fuel millage. But I don't quite understand how to explain it? Is 3:73 where one wheel turns 3:73 times with one complete engine revolution?

Thanks!
 
It's the ratio of input vs. output speed of the differential - 3.73 tevs of the driveshaft to one of the wheels. Whether that correlates to engine RPM's depends what the transmission is. A manual transmission with no overdrive, in high gear? Yes. Non-overdrive automatic? Slightly higher engine speed. Overdrive? Engine RPM will be lower to the tune of whatever the transmission's OD ratio is.
 
Originally Posted By: 69GTX
Google is your friend

If your ratio is 3.73, the drive shaft turns 3.73 times for each turn of the rear wheel.


I say half right.

The explanation was right on the money but the part about Google being our friend is a claim I ambeginning to doubt.
A friend respects your privacy.
grin.gif
 
Originally Posted By: Camprunner
I was wondering about rear end gear ratios for example my 2013 Mustang GT has a 3:73 rear axle ratio so does that mean that the rear wheel turns 3:73 times for every one revolution of the engine? I know that 3:73 is a lower gear then the other ratios for the Mustang being 3:55 or 3:33 and it gives you more acceleration off the line with the negative being lower fuel millage. But I don't quite understand how to explain it? Is 3:73 where one wheel turns 3:73 times with one complete engine revolution?

Thanks!


Numbers above are correct....a higher ratio, say 4:11 to 1, allows the driveshaft to turn faster than a 3.73, so it is easier for the engine to accelerate the vehicle. You lose (potentially) some top speed and mpg at the expense of that performance.
 
Yep. Not as important today with multi speed transmissions. My 2014 RAM has a 3.91 rear gear and with two overdrives it is still happy at highway speeds.
 
Originally Posted By: Camprunner
I was wondering about rear end gear ratios for example my 2013 Mustang GT has a 3:73 rear axle ratio so does that mean that the rear wheel turns 3:73 times for every one revolution of the engine? I know that 3:73 is a lower gear then the other ratios for the Mustang being 3:55 or 3:33 and it gives you more acceleration off the line with the negative being lower fuel millage. But I don't quite understand how to explain it? Is 3:73 where one wheel turns 3:73 times with one complete engine revolution?

Thanks!


Drive shaft turns 3.73 times for each revolution of the axles .

Best wishes , :)
 
Originally Posted By: SteveSRT8
Yep. Not as important today with multi speed transmissions. My 2014 RAM has a 3.91 rear gear and with two overdrives it is still happy at highway speeds.


Tire diameter plays an important part , too . The larger the tire diameter , the further the car travels with each revolution of the tire .

As far as engine rpm , this has the same effect as a slightly lower numeric deferential ratio .

Best wishes , :)
 
Just to punctuate this thread-not to highjack it.

My Dad had a 1970 Mercury Monterey 400-2V (spelled OINK-OINK) which had a 1.75 rear end. It had the C6 transmission.

Even cars with "economy rear axles" (some Cadillacs were so marketed during a gas shortage) weren't as long legged as that Mercury.

Anybody experience a higher rear axle ratio?
 
I believe the tallest gear set Mercury offered was 2.50:1.

I know of taller custom gear sets in custom differentials, than 1.75:1, but they are in Landspeed vehicles.
 
I've always figured the actual proper terminology would be 1:3.73 but the 1: gets dropped in casual notation.

Motor trend etc when they do a car test will list a chart that includes "engine RPM at 60 MPH in high gear" to combine the cumulative effects of overdrive transmissions, tire size, and axle ratio.
 
Originally Posted By: Kira
Just to punctuate this thread-not to highjack it.

My Dad had a 1970 Mercury Monterey 400-2V (spelled OINK-OINK) which had a 1.75 rear end. It had the C6 transmission.

Even cars with "economy rear axles" (some Cadillacs were so marketed during a gas shortage) weren't as long legged as that Mercury.

Anybody experience a higher rear axle ratio?


That's the tallest ratio I've heard of. I know some Chrysler products from the 70s had 2.76.

My brother built a 440 into an early 70s Road Runner....727 automatic and 3.21, it would chirp leave long black streaks (as the rear end walked sideways a bit) on the road when it shifted into third gear. At around 120mph.
 
Originally Posted By: 02SE
I believe the tallest gear set Mercury offered was 2.50:1.

I know of taller custom gear sets in custom differentials, than 1.75:1, but they are in Landspeed vehicles.





As a teen ager , I drove a 1966 Comet 289 . The rear end ratio was numerically slightly smaller that 3 : 1 . Had 14" wheels which partially compensated for the high differential gearing .

Best wishes , ;-)
 
Did it do pretty good on gas ?

Must have had a fearsome top end , if it had the torque to red line in top gear .

Best to you and yours , :)
Wyr
God bless
 
Originally Posted By: WyrTwister
Did it do pretty good on gas ?

Must have had a fearsome top end , if it had the torque to red line in top gear .

Best to you and yours , :)
Wyr
God bless


Nope, 400 was no gas miser! But it did run a 13.08 with headers, carb, intake, and a recurved distributor.
 
Taking off , with that much hp & tall gears must have been pretty hard on the differential , and the rest of the drive line ? Ever " loose " any one of thos sub-systems ?

Best wishes , :)
Wyr
God bless
 
Originally Posted By: WyrTwister
Taking off , with that much hp & tall gears must have been pretty hard on the differential , and the rest of the drive line ? Ever " loose " any one of thos sub-systems ?

Best wishes , :)
Wyr
God bless


Yes. The stock Turbo 350 transmission was the weak point. Broke it three times before hitting the junkyard for a TH400 and having it professionally built. Never had a problem with it again. Overall it was a very tough car, just needed more brakes to go with its "go"...
 
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