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Understanding gears #4517754
09/16/17 11:20 AM
09/16/17 11:20 AM
Joined: Feb 2008
Posts: 1,065
MA.
Camprunner Offline OP
Camprunner  Offline OP

Joined: Feb 2008
Posts: 1,065
MA.
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!

Re: Understanding gears [Re: Camprunner] #4517757
09/16/17 11:27 AM
09/16/17 11:27 AM
Joined: Sep 2010
Posts: 8,167
Texas
4WD Offline
4WD  Offline

Joined: Sep 2010
Posts: 8,167
Texas
Ring 41 teeth - pinion 10 teeth 41/10= 4.10 gear ratio

Re: Understanding gears [Re: Camprunner] #4517758
09/16/17 11:28 AM
09/16/17 11:28 AM
Joined: Sep 2015
Posts: 4,110
Connecticut
69GTX Offline
69GTX  Offline

Joined: Sep 2015
Posts: 4,110
Connecticut
Google is your friend

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


----------------

2001 Lincoln Cont 4.6L DOHC/ 39K mi / QS HM 5w30 / FUG XG2
1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF
1969 Ply GTX/RRs
Re: Understanding gears [Re: Camprunner] #4517764
09/16/17 11:45 AM
09/16/17 11:45 AM
Joined: May 2010
Posts: 9,846
out there
spasm3 Online content
spasm3  Online Content

Joined: May 2010
Posts: 9,846
out there
3.73 turns of the drive shaft for each 360 of the wheel/axle.


13 elantra 75k 5w30 QSUD
03 chevy avalanche 80k synpwr 5w30
17 mazda cx-5 9500 miles m1 0w30
Re: Understanding gears [Re: Camprunner] #4517772
09/16/17 11:53 AM
09/16/17 11:53 AM
Joined: Apr 2016
Posts: 1,202
Campbellsville, KY
Alex_V Offline
Alex_V  Offline

Joined: Apr 2016
Posts: 1,202
Campbellsville, KY
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.


To quote a friend, "Synthetics, man."

'85 GMC C3500, 454, 132K
'82 Mercedes 300CD, OM617 turbo, 173K (totaled 2018, in rehab)
'85 Mercedes 300TD, OM617 turbo, 217K (wife's)
'67 Suburban, 350, 331K
Re: Understanding gears [Re: 69GTX] #4517774
09/16/17 11:54 AM
09/16/17 11:54 AM
Joined: Jan 2017
Posts: 1,139
USA
ArcticDriver Offline
ArcticDriver  Offline

Joined: Jan 2017
Posts: 1,139
USA
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


Multiple Diesel and Gasoline vehicles
Re: Understanding gears [Re: Camprunner] #4517785
09/16/17 12:06 PM
09/16/17 12:06 PM
Joined: Oct 2005
Posts: 7,094
Colorado
Kuato Offline
Kuato  Offline

Joined: Oct 2005
Posts: 7,094
Colorado
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.


Thick vs Thin test: 15k / 43k miles complete
Re: Understanding gears [Re: Camprunner] #4517790
09/16/17 12:10 PM
09/16/17 12:10 PM
Joined: Oct 2008
Posts: 19,327
Sunny Florida
SteveSRT8 Offline
SteveSRT8  Offline

Joined: Oct 2008
Posts: 19,327
Sunny Florida
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.


"In a democracy, dissent is an act of faith."
J. William Fulbright
Best ET-12.79 @ 111 mph
4340 pounds, Street tires
Just like we go to Publix
Re: Understanding gears [Re: Camprunner] #4517816
09/16/17 12:36 PM
09/16/17 12:36 PM
Joined: Jan 2013
Posts: 2,488
Texas
WyrTwister Offline
WyrTwister  Offline

Joined: Jan 2013
Posts: 2,488
Texas
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 , :-)


Wyr
God bless
Re: Understanding gears [Re: SteveSRT8] #4517819
09/16/17 12:40 PM
09/16/17 12:40 PM
Joined: Jan 2013
Posts: 2,488
Texas
WyrTwister Offline
WyrTwister  Offline

Joined: Jan 2013
Posts: 2,488
Texas
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 , :-)


Wyr
God bless
Re: Understanding gears [Re: WyrTwister] #4517865
09/16/17 01:31 PM
09/16/17 01:31 PM
Joined: Aug 2010
Posts: 6,229
Champlain/Hudson Valley
Kira Offline
Kira  Offline

Joined: Aug 2010
Posts: 6,229
Champlain/Hudson Valley
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?

Re: Understanding gears [Re: Camprunner] #4517875
09/16/17 01:46 PM
09/16/17 01:46 PM
Joined: Dec 2005
Posts: 3,557
The Canyons
02SE Offline
02SE  Offline

Joined: Dec 2005
Posts: 3,557
The Canyons
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.

Re: Understanding gears [Re: Camprunner] #4517936
09/16/17 03:26 PM
09/16/17 03:26 PM
Joined: Jun 2003
Posts: 34,068
ME
eljefino Online content
eljefino  Online Content

Joined: Jun 2003
Posts: 34,068
ME
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.

Re: Understanding gears [Re: Kira] #4517959
09/16/17 04:14 PM
09/16/17 04:14 PM
Joined: Oct 2005
Posts: 7,094
Colorado
Kuato Offline
Kuato  Offline

Joined: Oct 2005
Posts: 7,094
Colorado
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.


Thick vs Thin test: 15k / 43k miles complete
Re: Understanding gears [Re: 02SE] #4518071
09/16/17 06:52 PM
09/16/17 06:52 PM
Joined: Jan 2013
Posts: 2,488
Texas
WyrTwister Offline
WyrTwister  Offline

Joined: Jan 2013
Posts: 2,488
Texas
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 , ;-)


Wyr
God bless
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