Rear gear questions.

[MSGia]

Good evening all,

I’m really thinking about doing the limited slip swap on my 2WD truck. I have the diff picked out and a decent bearing kit, but I’m trying to decide what rear gears to go with, and what brand aswell. Stock is 3.55, my options are 3.73, 4.10, and maybe 3.90, only one brand makes em. The main thing I’m concerned about is top speed, my truck only gets up to 98mph (which is less now bc smaller tires), so I don’t know what speed figure to go off, but I would hope to be going more than 90mph. Is that something a tuner can address? Other important info, my tire diameter is 27.2”, I have the 4.0 SOHC with the overdrive 5 speed. Also, can anyone with a 3.73 or 4.10 swap speak on gas mileage? It’s not my primary concern, but just curious. If I’m trying very hard I can get a 300 mile tank and 17-22mpg, that’s with my 3.55:1 open gears.

 

[Bgunner]

The higher the numbers are for gearing the lower the gear ratio. 3.55 is a higher ratio than the 4.10.

If top speed is an issue then the 3.45 ratio would be the way to go.

Some vehicles have speed limiters that a tuner could help with.

 

[alwaysFlOoReD]

Where are you traveling at 98mph? And how many times a day do you need that speed? Are you strictly driving the autobahn, or is there a % of city driving as well? Or is this a track only truck?

 

[MSGia]

Okay, okay, my concerns about top speed were a little exaggerated. I’m almost never going 98 miles per hour, I’ll go maybe 80 here and there. I just don’t want to be stuck with a 75mph top speed. My main goal is better acceleration. Now of course a 4.10 ratio would grant me this, but I don’t know if maybe 3.73 would be more modest for the street. It is not a track only truck, it’s mostly street.

Where are you traveling at 98mph? And how many times a day do you need that speed? Are you strictly driving the autobahn, or is there a % of city driving as well? Or is this a track only truck?

 

[alwaysFlOoReD]

Well, I had a b2 with a 4.0 and 5speed. I had 4:10's in it with 31" tires. It did great for me. With the tire size and gearing the speedo was bang on. It probably would have been a bit wound out at 80 but I never really traveled the freeway much. Did a fair amount of towing my work trailer with it tho. Fuel mileage was decent too. If you lean more towards freeway travel then 3.73 might make more sense. It really depends on tire size too.

 

[RonD]

Go here: https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

Plug in your numbers
2010 Ranger will have a 5R55E automatic which will have a 1 ratio 4th gear and a .75 Overdrive(5th gear)

4.0l SOHC engine has best power at 2,900rpm, when cruising you want to stay at about 2,300 for best MPG and quick power if needed

3.73 ratio
28" tires<<<<<<<<put in YOUR tire diameter
2300rpm
.75 OD
Calculate
68.5MPH

3.55 ratio would be 72MPH
4.10 Ratio 62.3MPH

And that's at 2,300rpm so barely above idle, lol
At 3,000rpm the 4.10 would be 81.3MPH

4.10 is best for towing and getting up to speed quicker
3.55 is best for MPG, lower RPM at 70MPH

 

[00t444e]

You will run out of power or hit the limiter before you hit top speed with 4.10 gears.

 

[rusty ol ranger]

Youre pry hitting the limiter at 98.

Even 4.10's with an O/D trans should have zero issue running 80.

My 97 F250 HD with 4.10s will run 80 all day. Itll do it in 3rd to but the engine is screaming and i dont wanna grenade it (460)...but its rare i ever run that fast...normally when empty going up north (limits 75 north of lansing and even at 80 you get passed 75% of the time)

 

[Josh B]

my 93 with 3.73 got 21 mpg when it had 265s, since going to 32 inch now it gets 7 percent less, which still isn't bad

 

[cbxer55]

I have a 98 3.0 auto. Fitted the rebuilt 7.5 axle with 4.10's a few years ago. Love it. It's actually faster now top speed, than it was with 3.73'.s Running ancient 50 year old Cragar Mag Master rims, 14 x7 front, 1`4 x 8.5 rear, with low profile BF Goodrich TA Radials. Rears are 25.4 inch diameter.

 

[Blmpkn]

Fitted the rebuilt 7.5 axle with 4.10's a few years ago. Love it. It's actually faster now top speed, than it was with 3.73'.s

I don't think that science can say no any more authoritatively to this statement than it already does.

 

[Roert42]

I have a sohc with an auto 3.73 rear. Got about 17 mpg before the super charger.

Shorter gears can actually help increase fuel economy if you do a lot of stop and go driving. More mechanical advantage so the engine has to do less work to get you rolling. Sacrificing by getting higher cruising rpm on the highway.

 

[Roert42]

I don't think that science can say no any more authoritatively to this statement than it already does.

What he forgot to say was that his truck couldn't get over 43mph before due to the 3.0, now with the 4.10s he can almost hit 50mph.

 

[Josh B]

It isn't unusual to gear something down and get more high end speed

 

[Ranger850]

From what I was told, 3.73 ratio with the 3.0 is "midlle of the road" gearing. Not sure if the 4.0 would be different, but it get's you decent acceleration and decent MPG, but not great for either. tire size would also play into the final ratio