3.55 or 3.73? What's the Difference?

[jslinkosky]

Can anyone tell me what the real difference between the 3.55 & 3.73 ratio axles? What's the advantage of one over the other?

[akirby]

Can anyone tell me what the real difference between the 3.55 & 3.73 ratio axles? What's the advantage of one over the other?

 

The real difference is 0.18.

 

The lower the number, the slower the rear wheels turn which yields slightly better highway fuel economy due to lower RPM but slower performance off the line.

 

Higher ratios (numerically) yield better off the line performance but worse highway fuel economy.

 

If you want performance off the line or for towing get 3.73s. If you want better fuel economy get 3.55. The difference won't be drastic though.

[NickF1011]

There isn't a whole lot of difference honestly. 3.73's will offer a bit better acceleration/pulling capability while 3.55's will give slightly better highway fuel economy. The difference between 3.55 and 3.73 is pretty marginal though.

[jslinkosky]

Ok, thank guys! I guess that makes sense. So, with the 3.55 ration, the vehicles EPA Fuel Estimates increase a little? Or is it too marginal to calculate?

[fordmantpw]

Ok, thank guys! I guess that makes sense. So, with the 3.55 ration, the vehicles EPA Fuel Estimates increase a little? Or is it too marginal to calculate?

 

Actual results, 3.55 will be a tad better on the highway and a tad worse in the city. But the results are marginal due to the very close ratio.

[akirby]

Ok, thank guys! I guess that makes sense. So, with the 3.55 ration, the vehicles EPA Fuel Estimates increase a little? Or is it too marginal to calculate?

 

They're factored together somehow but only one EPA number is produced. 3.55 vs. 3.73 is negligible. 3.31 vs. 4.10 would be a much more noticeable change.

[NickF1011]

3.31 vs. 4.10 would be a much more noticeable change.

 

Going from 3.27's to 4.10s was the first mod I ever did to my Cobra.

[lakeguy]

Can someone comment on the same questions with going from a 3.31 to a 3.55? Will the mileage change be noticable? Other factors to consider?

 

My need is for occasional (6-8 times year), low-mileage towing, otherwise mostly highway driving, and I don't need to beat everyone off the line at the stoplight. So, seems that the 3.31 would meet my needs. But at the same time, I'd rather not be on the lower edge of the range if there is a risk of things being under ratio. How close is the 3.31 to the lower edge of reasonable range, and given my normal use, what are the pros/cons of each?

 

Thanks

[NickF1011]

Can someone comment on the same questions with going from a 3.31 to a 3.55? Will the mileage change be noticable? Other factors to consider?

 

My need is for occasional (6-8 times year), low-mileage towing, otherwise mostly highway driving, and I don't need to beat everyone off the line at the stoplight. So, seems that the 3.31 would meet my needs. But at the same time, I'd rather not be on the lower edge of the range if there is a risk of things being under ratio. How close is the 3.31 to the lower edge of reasonable range, and given my normal use, what are the pros/cons of each?

 

Thanks

 

In all honesty, you would probably hardly notice it in most driving conditions. Going from 3.31 to 3.55 would probably raise RPM at any given speed by only around 100 or so. Over the long run, the 3.31's will give you marginally better fuel economy, and the 3.55 will give slightly better performance. The 3.31's certainly aren't a high enough gear to worry about it making the vehicle unusable or anything. It's not like they are 2.78's or something.

 

I would simply base the decision on this: Do you want another mpg here and there or do you want it to accelerate and tow just a little bit better? Neither option will really make or break the truck.

[johndeerefarmer]

In all honesty, you would probably hardly notice it in most driving conditions. Going from 3.31 to 3.55 would probably raise RPM at any given speed by only around 100 or so. Over the long run, the 3.31's will give you marginally better fuel economy, and the 3.55 will give slightly better performance. The 3.31's certainly aren't a high enough gear to worry about it making the vehicle unusable or anything. It's not like they are 2.78's or something.

 

I would simply base the decision on this: Do you want another mpg here and there or do you want it to accelerate and tow just a little bit better? Neither option will really make or break the truck.

 

 

I say buy the 3.73's. You will have the abilitity to tow more if needed. Also since you have more power off the line, you should get slightly better mpg in city driving. Now as far as highway driving goes, instead of driving your usually speed, slow down about 5 mph. RPMs will drop and you should get the same mpg as the other rear ends

[V8-X]

Personally, I'd opt for the 3.73's, as I have in my 2006 F150. Of course that has a 4spd auto, not the 6spd auto as the 2009+ has.

 

For your application as defined, I think you'd be fine with 3.55's. I had the 3.55 in my 2002 F150, but again, that had a 4spd auto.

 

From seeing others on F150 forums I frequent, the most popular ratio on 2009+ models is the 3.55.

 

Just make sure you get LS. Otherwise, find a dealer that has both options available and take each for a spin.

[bb37]

Going from 3.31 to 3.55 would probably raise RPM at any given speed by only around 100 or so.

Yep. If your engine had to turn 2000 rpm to go a given speed with the 3.31, it'd be turning 2145 rpm with the 3.55.