Rear end gearing, what to get?

[callahan318]

Ok, so the 2011 is offered with 3.31, 3.55, and 3.73 gears.

Which one do you choose and why?

I am not planning on being a drag racer, but want something that gets up and goes.

Is fuel mileage that big of a difference between gears?

What about overall acceleration?

RPM top end and max speeed top end? What is the correlation?

(I am new to all of this so please help me out..., looking to buy when I come back off of my deployment.)

Edit- typo...and its late in the evening.

 

[KungFuHamster]

3.73's is looking like a good all around gear again.

 

[Mike@PowerHouse]

I have the 3.31, gone 12.58@112 on the factory wheels and tires, as delivered with all the crap in the trunk.
The car traps around 64-6500 rpm in 4th gear. I would suggest the 3.55 to put you spot on, 3.73 will require you to make a gear change to 5th, but your trap rpm would be a little low.

 

[Shaffe]

my question is why are the options only on the manual.. thats bs

 

[Alter Ego Trip]

my question is why are the options only on the manual.. thats bs

Cause us auto guys aren't into performance.

 

[GrnBullitt08]

3.73s....my bullitt came out of the factory with them and I love them. Good all-around gear.

 

[BSell]

I have the 3.31, gone 12.58@112 on the factory wheels and tires, as delivered with all the crap in the trunk.
The car traps around 64-6500 rpm in 4th gear. I would suggest the 3.55 to put you spot on, 3.73 will require you to make a gear change to 5th, but your trap rpm would be a little low.

Isn't 6500 rpm the stock engine's HP peak?

Looks like Ford goes drag racing, no?

So if you add more power, don't you need a taller tire to keep from over-revving in the lights at the big end?

 

[Shaffe]

Cause us auto guys aren't into performance.

haha if thats truely their thinking they making a big mistake

 

[Mike@PowerHouse]

Isn't 6500 rpm the stock engine's HP peak?

Looks like Ford goes drag racing, no?

So if you add more power, don't you need a taller tire to keep from over-revving in the lights at the big end?

Yes and no, you have to keep in mind that this trans has 5 forward gears plus 6th which is the only overdrive, so you can use 5th as another option.

But you run the risk of another gear change error.

 

[s8v4o]

3.73s....my bullitt came out of the factory with them and I love them. Good all-around gear.

Yeah but your car has a totally different transmission. 3.37s in the new mustang is probably pretty similar to 4.10 in the 2005 mustang.

 

[BSell]

Yes and no, you have to keep in mind that this trans has 5 forward gears plus 6th which is the only overdrive, so you can use 5th as another option.

But you run the risk of another gear change error.

Which would add more feet down the track with no power applied...not what we're going for here, right?

Hence, the Ford goes drag racing comment. They geared the car to top out fourth in the traps with the 'economy' gear in the rear end.

My other Mustang was an '86 5.0 manual trans sedan with the 3.55s. Folks complained that combo put the engine over its power peak short of the traps, causing a dive into the ugly overdrive 5th...not good. So Ford avoiding it this go around, even with another gear or two to use is good news, right?

 

[19COBRA93]

Yeah but your car has a totally different transmission. 3.37s in the new mustang is probably pretty similar to 4.10 in the 2005 mustang.

You'd be surprised. With the higher RPM capability, the '11 GT with 3.73's actually still feels like it has 3.55's (the one I drove anyway).

Personally, in an '11 GT I'd go 4.10's.

But for the guy who isn't going to drag race it, I'd still probably go 3.73's.

 

[s8v4o]

You'd be surprised. With the higher RPM capability, the '11 GT with 3.73's actually still feels like it has 3.55's (the one I drove anyway).

Personally, in an '11 GT I'd go 4.10's.

But for the guy who isn't going to drag race it, I'd still probably go 3.73's.

I'm talking shear numbers. For example..

First gear 2005
3.38 x 4.10 = 13.858

First gear 2011
3.66 x 3.73 = 13.6518

So from a first gear standpoint they are nearly identical.

 

[BSell]

I'm talking shear numbers. For example..

First gear 2005
3.38 x 4.10 = 13.858

First gear 2011
3.66 x 3.73 = 13.6518

So from a first gear standpoint they are nearly identical.

What gear gets you through the lights at redline in fourth then?

 

[s8v4o]

Assuming ...

27.25" tire (235/50/18 factory size)
7000 RPM
4th gear
3.73 gears

= 115.27 MPH which shouldn't be too far from where the car would be trapping right?

Now trying to get there in 5th gear (1:1) would take 4.88 gears and would be trapping 116.30 mph at 7000 rpm.

So, 4.10s at the top of 4th puts you at 104.87mph (not ideal)
And, 4.10s at the top of 5th (1:1) puts you at 138.43 mph (again not ideal in near factory trim)

So if trapping in 4th is what you want then possibly go with the 3.73s or 3.55s as Mike mentioned. 3.55s will allow for trapping close to 121 MPH in 4th gear if you're making more power then stock.

 

[s8v4o]

I have the 3.31, gone 12.58@112 on the factory wheels and tires, as delivered with all the crap in the trunk.
The car traps around 64-6500 rpm in 4th gear. I would suggest the 3.55 to put you spot on, 3.73 will require you to make a gear change to 5th, but your trap rpm would be a little low.

Hey Mike what size tire was that?

 

[Beauch]

Shifting at Max. Power RPM (6500 RPM), with 3.73:1 you would be:

1st - 39mph
2nd - 59mph
3rd - 85mph
4th - 109mph
5th - 144 mph

Right now an '05 - '09 with 3.73s and a 5-spd will go 104 in 3rd. Typically I shift the '06 at 5800rpm and go out the back in the 105 to 108 range in 4th.

The 3.55s in the '11 will get you to 115 at max power in 4th and you could hold 4th to 124 if you wanted at the big end.

All that said, I think the more gear the better. These things are heavy and if you can get enough tire to handle the gear in 1st, by all means, go big.

What I like to look at is the crossover curve for Hp/Tq on the downshift and try to make 65mph in 3rd the peak. That way if you are running down a highway and you want to pass something, you can simply drop it in 3rd and get around anything. The '05 - '09s love 4400rpm. Power starts building at 3600 rpm, but it's all there by 4400 and rolls on to 5800 pretty linearly. With 3.73s, the car pulls great from 65 to 100 in 3rd.