112 with 3.73 is almost 6900 rpm in 4th. If you get that far, just shift into 5th at 6800, it will only drop back to 5100-5200 after the shift and should continue to pull.

 

I've been debating this too for several months.
decided to just leave the 3.73's see how they are..
im thinking the 3.73's are going to be a little steep with 3.66 1st gear..
worse case swap to 3.55's later.
not that expensive to swap. unless prices have changed recently.

 

1. You need 2 mph extra speed because trap speed is an average over the last 60' not true terminal speed.
2. Lots of bad math above.
3. Im using the 769.5 tire rpm figure for the 255/40R19 presented above. I have not checked it.
4. Never use tire height when you can get tire rpm. it can vary for tires of the same height.

3.55 w/ 255/40R19
1.32 x 3.55 x 769.5 / 60 = 60.098
6850 / 60.098 = 114.0 mph (112.0 mph trap) at Soft Limiter
7000 / 60.098 = 116.5 mph (114.5 mph trap) at Hard Limiter

3.73 w/ 255/40R19
1.32 x 3.73 x 769.5 / 60 = 64.766 rpm per mph.
6850 / 64.766 = 105.8 mph (103.8 mph trap) at Soft Limiter
7000 / 64.766 = 108.1 mph (106.1 mph trap) at Hard Limiter

I put a lot of faith in Bob's comments (He is by far the most knowledgable individual to post). However I suspect Bob's comments apply primarily to a car with Stickies. I know the limiter has little effect because we rode it for the last 60' on the 13.27 Pass on a Showroom Stock 2005.

That said I chose 3.55 because I feel the 3.73 will offer very little advantage off the line.
The 3.55 will mutiply more than enough torque to overcome the factory street tires.

I almost took the standard 3.31 as I could make a case for it on standard street tires. Abillity Spin 1st all the way through 60' so should be capable of simlar 60'. Not as likely to break the tires loose on the 1-2 shift. Carry 3rd longer. Still turn almost 6500 rpm in really good air. Of course that only applies to a 100% Showroom Stock Car.

In true Showroom Stock trim their was only 1/10 difference between 3.31 and 3.55 (13.49 vs 13.39 same day) on the 2005-2009 and that pretty much all occured in the 60' at 1.92 vs 1.99. With the 5.0's 8.3% Lower 1st and 22% Torque Increase I expect very little difference.

 

I'll readily admit to being a gear *****. My 99 Cobra wore 4.56s most of its life (also 4.30s and 4.88s). I'll also readily admit to sucking on hard-compound street tires. My driving style is just too aggressive, and I don't have the patience!

I've always used and had good success with simple mph/rpm gear calculations using tire height. It looks like this will be one of those times where we'll just have to wait and see with real-world cars. With all that first gear, the car might end up going quickest with less vice more gear in stock trim, simply because of the 60 ft. On stickies, the opposite would be true.

In the end, I wouldn't actually do a gear change till I'd had considerable seat time (see original comment). However, I would almost certainly opt for the factory 3.73s, as I *think* that is going to be the ticket.

BTW...Tirerack lists those tires as 763 revs/mile. That would change your calculations a bit (for example, making 3.73s run to 109.4 @ 6850 rpm).

Finally....I'd rather be on the limiter going through the traps than shifting to 5th going thru the traps.

 

I originally ordered mine with 3.73s but changed the order after the big discussion on mustangforums to 3.55s. Mine will be a DD, and will spend far more time on the street than on a drag strip. I switched because of the lower cruising RPMs and more usable 1st with the 3.55s. I will increase power on mine to make up for the higher gearing. lol

 

most folks are gonna race with drag radials. i know i am .so the gearing for stock tires is irrelevant. im going to get DR's with a 29" height anyway. 3.73's.

just change your tires to a taller profile when you replace them if you fell like you have to shift.

 

If I were to buy one, I would run 26" tires and move the rev limiter up to 7500. 29" tires add too much unnecessary rolling weight and rolling resistance, IMO.

 

tirerack shows variations in the same size (255/40/19) from 763 to 771 revolutions/mile on some that i checked.

that being said, i'm with assasinator and bob cosby on this choice of gearing and as for the solution
for street tires i will be changing to a 275/40/19 on the same rim when the stockers wear out

for the dragstrip, the nitto 555r in 305/45/18 will net 4-5 mph higher at the limiter in 4th gear

another alternative is to increase the limiter to say 7200 rpm through a tune which everybody that strips this car is going to get anyway

if FI is in your plans and you think you'll be at a 120+ trap then 3.55s are the way to go, for a bolt-on car which may trap 114-115 mph what i wrote above will work well IMO

 

another thought to this thread

i applaud Ford for giving the customer these gear options, it seems that they diligently tested to get this car to trap at or near the limiter with the 3.73 gear option

years past the car would be undergeared and it would have to be aftermarket to get what was wanted or needed

 

Noted Bob. I dont have the actual Tire RPM for the factory 255/40R19 Summer Rubber. I dont believe the OEM MB Spec 255/40R19 XL that is 763 RPM is the same spec but it may be the same rpm. I cant really seem to get good info on the OEM Mustang Spec 255/40R19.

If they are the 763 rpm you will start to bump the hard limiter at about 111.8 mph so it will start to hit it around 110 mph Trap.

I have also seen evidence that most peaople dont turn their cars high enough. I shift between 6500-6750 rpm (Depending On Gear) and trap as high as 6600 rpm (3rd) in my 4.6L 3V. Its not very fast (High 12's @ 105-107) but it does okay for stock tires, gears and suspension with just a CAI/Tune. I get repeated grief form others for going that high but the proof is in the time slips and thats what it likes.

In the 4.6L 3V we could never get the 4.10 to run any quicker than 3.73 on factory tires. That made me a bit hesitant to go over 3.55 with the new gearing (equivalent to 3.84 Rear at Launch) especially given the extra torque. With the MT82 4th w/ 3.55 now being equivalent to TR3650 4th w/ 4.69 and enough power to spin 1st I just felt it was enough.

Oh well at worst I spend $150 for a set of gears. The only reason I didnt take the base 3.31 Gears is I didnt know how long it would take to get programming. It does really stick in my craw to pay $395 for gears. They used to be a No Cost Option on Fox Bodies. The only extra cost to Ford is certification and I bet its minimal spread over 10's of thousands of cars.

Bottom line use your own best jusdgement. I do still believe the relative difference in gears is going to be tiny in a true Showroom Stock 5.0.

 

Concur completely on difference in Showroom Stock ETs with different gearing.

I look forward to seeing what you can get out of your new 5.0, as you obviously are quite skilled in getting a stock-tired car to ET!

 

As I understand from different threads on different forums..

3.31s were used for max advertised MPG.

3.55s were used for shortest 0-100kph (62mph) times. You may notice that these gears are standard in Canada, who apparently does not care about advertised MPG (and rightly so, they use, like, unicorn farts/100km or something like that).

3.73s were used for shortest 0-60mph times. If you look at the gearing charts, top speed in second is like 60.2mph.

 

Hawkeye, I think that was one of my post. It was intended to be a bit tongue in cheek.
I do agree that if we didnt have CAFE Standards the 5.0 M6 3.31 Combo would likely not exist.
I think we would have 3.55 Standard (Like Export Models) with a 3.73 Performance Axle Option.

Im getting old and cynical and somtimes tend to see conspiracies where none exist.
That said it really doesnt hurt Fords 0-100 kmh numbers if they can get away with one shift.

 

Bob, some are skilled and some just have to use pure persistence and determination.
I think I tend to fall into the later camp. All the same I appreciate the flowers.

I have a feeling you started out skilled and added a lot of pure bull headedness.
If its in the way and you cant go around you go through it.
I have much enjoyed watching you.

 

If you go with 20 inch rims and tires say 275 35 20 rear or 275 rears doesn't that help keep the rpms down a little?

 

Sorry i meant to say 285/35 20

 

one way to look at this especially if coming from the previous gen car is the 3.55 on the new 6 speed is the same overall first gear ratio as the 3.73 on the old 5 speed and the same OD ratio as the 3.31 on the old five speed. seems like the best of both worlds for a DD.

 

On street tires on stock or near stock power levels I'd go (and I went) with
3.55's

The need to shift into 5th during the last 66' of the 1/4 and inside the trap box will surely cost you equal (if not more time) than you will gain from the slightly more aggressive 3.73 gears.

Further, say you simply want to add a tune and gain 30 hp to your 5.0
With the 3.55's you would still be able to finish the 1/4 mile in 4th, and now do it right at or slightly below the rev limiter.

Further still, add the tune and with 3.73's on street tires and traction becomes more of a problem. Makes it harder to launch, and makes for more tire spin going into 2nd.
Tire spin = slower times
With the 3.55's you'll be able to launch at a slightly higher rpm with equal or less tire spin you'd see on the 3.73's and you would experience less spinning going into 2nd too.

I feel the 3.73's would be more advantageous for those running slicks who can take more advantage of the traction and therefore launch harder and not get as much (if any) tire spin going into 2nd either.

 

3.73s