Mustang Final Drive Ratios Spreadsheet

[aeropaul]

I've been deliberating switching rear end gears on the mustang. I am making an attempt to quantify the differences for myself between my stock 3.73 rear gears and the other available options. I plan on autocrossing next year when the weather warms up but 90-99% of my car's life is daily driving, so drivability is a major consideration for me. I also plan on upping the engine power over the car's life, so I can make up for taller rear gearing that way. I got a little bit carried away in making my spreadsheet though. So I thought I'd share it.

I've uploaded it to dropbox.com, so you can click the link and download it in .xls format.
https://www.dropbox.com/s/zvurnddwoixl1ii/Mustang Gear Ratios.xls?dl=0

A bit about the spreadsheet:
It contains the forward gear ratios for the stock Getrag MT82, as well as the ratios of the Tremec T-56 magnum (both the 2.66 and 2.97 version). I included these because it seemed like the best way to put some perspective on the gear ratios. It will also be helpful to those of us considering the T-56 swap as a viable option when it comes to fruition. The sheet calculates final drive ratio based on all the currently available rear end gear ratios for the S550 mustang (for all transmissions). It then displays the gear ratio spread between each shift.

The inputs are your tire diameter and ground speed (in MPH), highlighted in orange. The output tables are engine RPM in each gear, and RPM spread for each shift at the input speed. This way, you can easily see what the RPM drop between shifts is for a given speed and tire diameter.

Hopefully some of you may find this useful. If not, well at least I got to satisfy my OCD on a Saturday morning.

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[analogman]

Thank you Paul! I have a clone of your car on order, it should arrive next week.

So, after doing your analysis, what rear end gear ratio will you be using?

 

[aeropaul]

Thank you Paul! I have a clone of your car on order, it should arrive next week.

So, after doing your analysis, what rear end gear ratio will you be using?

Congrats! You're going to love it. I know I love mine!

I would maybe try 3.55, but the real issue is the spread in the transmission. I'm not totally convinced it's worth the trouble. I really should go drive a 3.55 equipped GT (non-PP) to get a real feel for it. Swapping in the lower (numerically) gear will put less space between gears (numerically), but everyday shift points will be lower RPM. Not something that can be easily seen with raw numbers. Plus, I want to get a good 4-6 months of driving before I really start to tweak things, so I can get a good feel for the car. TBH, swapping the trans is not something I'm going to do unless I break the stock unit, and unlike the chicken-littles, I'm not too worried about that happening.

 

[Jimdohc]

Nice calculator. Thanks for sharing it.

Driving a 3.55 non-PP is a great idea.

I suspect you won't notice the difference. During daily driving, probably shift at same rpm. Just traveling at a slightly different speed during the shift.

I think, 1st & 6th maybe the only noticeable difference. 1st due to change in acceleration. 6th for it's highway rpm/sound.

 

[S550guy]

Very cool spreadsheet Paul!

As for your final drive, yes the 3.73 offers the most acceleration but takes a hit on fuel economy (car needs to run at a higher RPM to maintain speed as compared to a taller final drive).

I'm interested to hear your thoughts on the 3.73 PP vs 3.55 non-PP (what I have) when talking about public road driving.

 

[Boff]

I currently have a 3.55:1 car (2013) and the main issue is that at 65-70 mph on the highway the car is truly gutless. The Track Cal I installed helped a lot. The 2015 I test drive with these rear gears (and the 20's) suffered the same problem.

My 2015 will be the PP...I'm hoping it will be a bit better.

For autocross, the 3.55:1 will be better on higher-speed courses because you won't have to shift to third. (we do a few airstrips where we get well into the 60's). But on slower and smaller courses, the 3.73:1 will help you dig out of the slowest corners in 2nd.

 

[fionic]

I've been deliberating switching rear end gears on the mustang. I am making an attempt to quantify the differences for myself between my stock 3.73 rear gears and the other available options. I plan on autocrossing next year when the weather warms up but 90-99% of my car's life is daily driving, so drivability is a major consideration for me. I also plan on upping the engine power over the car's life, so I can make up for taller rear gearing that way. I got a little bit carried away in making my spreadsheet though. So I thought I'd share it.

I've uploaded it to dropbox.com, so you can click the link and download it in .xls format.
https://www.dropbox.com/s/zvurnddwoixl1ii/Mustang Gear Ratios.xls?dl=0

A bit about the spreadsheet:
It contains the forward gear ratios for the stock Getrag MT82, as well as the ratios of the Tremec T-56 magnum (both the 2.66 and 2.97 version). I included these because it seemed like the best way to put some perspective on the gear ratios. It will also be helpful to those of us considering the T-56 swap as a viable option when it comes to fruition. The sheet calculates final drive ratio based on all the currently available rear end gear ratios for the S550 mustang (for all transmissions). It then displays the gear ratio spread between each shift.

The inputs are your tire diameter and ground speed (in MPH), highlighted in orange. The output tables are engine RPM in each gear, and RPM spread for each shift at the input speed. This way, you can easily see what the RPM drop between shifts is for a given speed and tire diameter.

Hopefully some of you may find this useful. If not, well at least I got to satisfy my OCD on a Saturday morning.

neato, thanks!

can you upload to google drive? dropbox always gives me problems at work.

 

[aeropaul]

neato, thanks!
can you upload to google drive? dropbox always gives me problems at work.

Done:
https://drive.google.com/file/d/0B2y8xN1c3KGvbHB5eGJMNWx2SEk/view?usp=sharing

Yeah, I'm on the fence right now. Auto-X is done for the season, with events starting back up in march, so I will probably wait till then (and do exhaust in the meantime) to really evaluate the track performance. With the 3.73, 6th actually has a decent amount of grunt while returning 24-25 MPG reliably. In fact, now that I've rolled around to 1000 miles, I'm seeing 15-16.5 with 90% city driving, and a solid 25 on the highway. I suspect it'll get just a little better by 2k miles but not much. I'm happy enough with that considering how satisfying the acceleration with 3.73 gears is. I drive 10k miles a year and considering the cost of replacing the diff gears, it is at best a zero sum game, and I'd have to drive about 15k or more a year to see a return on changing gears.

I'm glad you guys could get some use of my OCD.

 

[fionic]

Done:
https://drive.google.com/file/d/0B2y8xN1c3KGvbHB5eGJMNWx2SEk/view?usp=sharing

Yeah, I'm on the fence right now. Auto-X is done for the season, with events starting back up in march, so I will probably wait till then (and do exhaust in the meantime) to really evaluate the track performance. With the 3.73, 6th actually has a decent amount of grunt while returning 24-25 MPG reliably. In fact, now that I've rolled around to 1000 miles, I'm seeing 15-16.5 with 90% city driving, and a solid 25 on the highway. I suspect it'll get just a little better by 2k miles but not much. I'm happy enough with that considering how satisfying the acceleration with 3.73 gears is. I drive 10k miles a year and considering the cost of replacing the diff gears, it is at best a zero sum game, and I'd have to drive about 15k or more a year to see a return on changing gears.

I'm glad you guys could get some use of my OCD.

thanks!

I'm also happy with the mileage on the 3.73. Been getting ~20 average with all city driving. Not bad for a v8!

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