Hello Everyone,
New member here with a new 2015 Mustang GT and already have a question regarding the correct rear axle ratio for my car. I think it's too low and need opinions/advice so I can address the issue with my dealer. Here are relevant facts.

• From the factory - 18' wheels (tire size unknown)
• Additional Equipment (among others) - 19" wheels with P22/40R19 W tires
• Manual six speed transmission
• Axle Ratio: 3.31
• Axle Code: GG
• Axle No: MT 82

My question is; Do I have the correct rear axle. I think the axle ratio should probably be 3.73 with these tires and rims, but I really have no idea. I only know my first gear is like having a "Grandma" gear in a two ton truck.

Can anyone provide any technical expertise?

Thanks, cehendy@gmail.com

 

Something must be very very wrong even with the 3.31 axle it still should be very quick off the line. The manual has a very low gear and the difference between the 3.31 and 3.73 should only be a tiny bit. I have a 2014 with the track pack and Wold like the 3.31.

 

As far as I can determine the only way to get a 3.73 axle is to order the PP. The optional axle without the PP is the 3.55.

 

Sorry. Make that a 3.31

 

Well, I guess it is quick up to 15 mph. I just though it should be quick up to 40-50 mph. Guess my reference was based on my '57 chev; it's been a while.
Thanks.

 

Sorry, what's the PP? I guess I was just expecting a faster start past 15 mph. I just learning about some of these things.
Thanks

 

There's a number of threads in the 11-14 section about the Getrag 6 spd and the axle ratios. The consensus I read was going from 3.31 to 3.55 was similar to 3.73's in the 05-10 Tremac 5 spd. I think 3.73's in the 6 spd will make 1st gear pretty useless as you redline in no time.

 

I hope all you will bear with me on some of these "stupid" questions. Just became a real Mustang owner and know not much technical wise. I do, however, have lots of other answers.
cehendy

 

Thanks, I check out 11-14. Guess I just don't understand all this axle stuff.

 

What complicates it is the different gear ratios of different transmissions. While I appreciate having a 6 spd for a little more choice in the middle gears for two lane twisties, combined with a top gear "overdrive" for better mileage, for some reason Ford made 1st gear pretty "short" and so you hit redline way too quick.

 

Pretty sure the PP gets the 373's. Base Gt gets 331 or 355 as an option. I love my 331's on my 14' Gt, its great on the fwy at 70mph my rpms slumber at around 2k. This gives better fuel economy and also better acceleration at fwy speed. Ill stick with my 331's.

 

I'm a little confused by your question. Are you asking from a technical standpoint if 3.31s are "incorrect" with 19" wheels? No, but depending on your application it may or may not be optimal.

I would think that if you feel like first is a grandma gear, then increasing the axle ratio would only make the effect worse, as it would increase the torque but shorten the gear even further. Meaning your top speed in first would be even lower.

I have 3.73s in my 14 track pack and 1st is pretty short. If I make a right turn from a dead stop, I have to shift out of first before the turn is competed. It's fun, but it's a little much for a daily driver.

Also, I'm wondering what your dealer can do for you? If you already bought the car, aren't they going to want money to swap the gear? Like $400+?

So... I think you should ask your dealer if they have a 3.73 GT on the lot somewhere that you can test drive. On the 2015s, the performance pack models will have it. If they have a used 2013-2014 track pack they will have it as well. There are other cars with it but aren't really identifiable without the window sticker. I think you will find 3.73s to have the opposite effect from what you want.

 

Thanks, I'm checking with the (out of town) dealer

 

Let me understand all this. The higher the ratio (3.31 up to 4.1) the less mph I would get out of first gear? Think I'm confusing axle ratio with gear ratio, as someone pointed out. I'll understand the difference, then return with new question.


Glad I joined; lots of quick help. Thanks, for now

 

I'm sensing you want to be left alone for now, but you should look at this spreadsheet. This helped me understand it much better.

https://themustangsource.com/forums/...dsheet-483731/

 

berzerk has good info. Higher the final drive ratio the easier it is for the engine to rev, thus faster acceleration in each gear, but lower top speed in each gear.

I love my 3.73s on the street, as the acceleration (particularly in 2nd) is awesome, but when I'm at the track I wish for 3.55s because I run out of gear with couple hundred yards left to the brake zone in some corners.

On the street I end up doing a lot of shifting. 1st is only meant to get the car moving, at 10mph I'm in 2nd already. And I'm in 6th by 45mph. Nice thing is if you drop to 2nd at 35mph it puts you right into the power band, and 2 seconds after you floor it you're at 60mph.

 

I'm still getting used to my '15 GT with the Performance Package and the 3.73 differential. First gear is now for uphill starts or cold mornings (as I fast-idle the car through my quiet neighborhood). It's done by 15mph. The notchy shifter makes getting through 2nd to 3rd not very fast. So I use 2nd gear for 'easy' start-offs. I'm hoping the notchy nature of the shift linkage lets up by a couple thousand miles. At 1015 miles I'm still shifting very slowly when the drive train is cold. Only a bit faster when everything is warm. Trying to shift too quickly results in a 'clunky-chunky' shift. No gear grinding or harsh sounds, just mechanically different from the quiet 'bump-thump' of a slow & smooth shift. Maybe Getrag designed the 'clunky-chunky' shift sensation into the new 6-sp tranny. I don't know. I'm just trying for the smoothest break-in possible. Any suggestions or wisdom is appreciated. Thanks.

 

I have a 2014, and in the mornings I have to double clutch second and third for about the first ten minutes of driving. I now have about 4500 miles on my car.

 

Harley, could you define "2nd gear for easy start offs". I'm getting ready to order a 2015 GT w/the PP next month. Can you start off from a dead stop in 2nd gear with yours (in that 1st gear is pretty much a granny gear), or by easy start offs, do you mean you're still rolling?? Just curious. I'm not convinced on the PP as yet & can't drive one til I get back down to the lower 48 right before I order one. Thx in Advance. Dennis

 

There's a spot on the door that's has a double letter like GG DD or whatever if it says GG you have the 3:31 gears. I just bought mine 2 weeks ago and traded in a 2014 GT base model with nothing on it except 3:55 gears. I liked the 355's but don't care much for the 331's on new one. With the 3:31's you should be able to get up to like 45 mph fully wound out in 1st and 68 in 2nd to if you had 355 it'd be 42mph in 1st and 63 in 2nd. If you had 3:73's it'd be 40 in 1st and 60 in 2nd. Search the internet and you can find the list of gear ratio's and speed of each gear.