moman89

Hi,

I ordered my first ever mustang, a 2015 GT Premium with an automatic transmission (I spend time in traffic everyday to commute to work so manual just wasn't a practical option for me) and initially I ordered it with the stock 3.15:1 Limited Slip Rear Axel and was wondering what people advise if I should upgrade to the 3.55:1 while I might be able to? I will be using the car mainly as a DD and might hit the track once or twice a year. My drive is usually 50-50 city and highway.

Does anyone have an automatic with 3.15's? How are they enjoying it? My biggest concern about the 3.55's is traction/wheel spin on take off and to a much lesser extent, major affects to fuel economy.

Thanks

AMWill

Hey moman,

First of all, congrats on the order, I'm sure you're crazy excited! I know just how it feels.

In regards the gears, it is really up to you! The fuel MPG you will get with the 3.15's will definitely be a sight for soar eyes, but you can't beat the 3.55's compared to the 3.15's when it comes to the get up and go.

We were actually at the track with a buddy's S550 equipped with a 3.55 gear auto and we went 12.8 Bone Stock and 12.5 tuned! His car hooked and went even on stock tires, consistent 1.9 60's all day.

If It was my choice, I would go 3.55's all the way but at the end of the day, you will be happy regardless of which way you go.

Hope this helps!

-Will

redass02gt

I have the auto with 3.15s, because that's what they had on the lot. I test drove a car with the 3.55s, and I would've chosen the 3.55s if I had the opportunity to do so. I can't speak to the fuel economy part, but the 3.55s didn't seem to have traction problems and I definitely got on it during the test drive.

Now that I've had the 3.15s for a couple weeks, I don't know that it would be worth it to pay to change them. It's not like the car has any trouble accelerating, and it keeps RPMs low on the freeways.

AMWill

I completely agree with you red,

Pretty much spot on. If you were going to upgrade, I would probably jump to a 3.73 right away! I run 3.73's on my personal 2014 Track Pack GT and love them but I do miss having a 3.15/3.31 car for highway cruises!

-Will

thezonster

I'd like to hear from someone what kind of highway mileage they are getting with the 355's.

Picked up my car on Friday, with the 315's, and would consider changing, if not too great an impact to mileage.

I know that Ford is putting the same mileage ratings on the window sticker for the 355 cars, as for the 315 cars, and I know that cant be.

lwilliams

I took delivery of mine with 3:55 under it on Friday night. It has only got 95 miles on it right now, so I certainly can't say what it will do. But I will be watching this thread. I will report mine later on, but I would like to see what others are getting, both 3:15 and 3:55.

Congrats on placing your order....hope you get it soon!

AMWill

Congrats on your pickup Zonster!

Unfortunately we don't have any 3.15 cars here to get you an answer but I will definitely keep my eye out for you.

-Will

moman89

Hi Will!

Thanks for the replay! Is there any data out there about the difference between the 3.15 and 3.55 on the GT when it comes to 0-60 times?

I tried to change my order to a 3.55 and the dealer told me it's too late as the car is in production however if I want he can put in a new order but I would have to wait an extra month and to be honest I don't know if the difference between the two gears is worth an extra months wait.

However the way people are talking about the 3.15s I'm imagining a very slow accelerating car and I'm almost worried I will have this big powerful engine that doesn't use the torque

Camster

With a six speed auto,I think that it will scoot fine.

bluebeastsrt

I just ordered a Automatic with the 3.55. Just knowing I'm not paying 4-6 hundred dollars for an install is enough motivation to get the 3.55s from the factory.