4.10 or 4.56 on 31"

[troyniss]

Hello everyone,

New sub here.

I recently bought a 1997 Ranger 2.3l 5speed.
Upgraded the wheels to 31" BFG K1 A/T.

It's a dog in 5th gear and can barely maintain speed up a hill and lacks passing power. Usually have to drop it in 4th to get any noticeable acceleration to pass. I know the stock gear ratios for my truck are well below what they should be and with the added tire weight and height, I need something more plausible.

I've read that 4.10 or 4.56 gear ratios for 31"s are optimal, but having seen mixed reviews and discussions I'm currently in a bind as to what gears to go with. I looked at some posts in regards to gear ratios for larger tires, but they seem to be from 3-4 years ago and would like a fresh perspective.

Not planning on doing any towing, but would like to adventure out into mediocre trails and snow. I use the truck for city driving but occasionally go on highway across state. I need some advice as to what gears might fit my profile the best.


Thanks for the help

 

[BlackBII]

If you're sticking with the 2.3 and 31"s for a while I'd say absolutely 4.56.

 

[alwaysFlOoReD]

The 2.3 likes rpm. The following chart doesn't take into account an overdrive gear.

http://www.therangerstation.com/tech_library/gearandtirechart.shtml

I'd say 4.56 if you're buying gears anyway, but if you find used axles with 4.10 you could save some money.

 

[troyniss]

I suppose if I ever upgrade tire sizes too 4.56 would save me in the long run.

Thanks for the information.

 

[adsm08]

5.13 with stock tire size on a 2.3 sounds about right to me. I don't know if they make anything deep enough for a 31 to not suck.

 

[Captain Ledd]

As someone who went 4.56 with a meager 29" (235/75R15) tire with a 2.3L 5spd manual, go deep. Go at LEAST 4.56. And as ADSM08 suggests, do consider 5.13's.

Ha, mine's a 1997 as well.

 

[gw33gp]

I think 4.56 gears would be about right with 31" tires for a 2.3L engine. If you really like to spin the engine high at highway speeds go for the 5.13. I think 5.13 gears with 31" tires would be great around town and anything 55 mph and below but would be near useless for anything much faster. It would be like driving around in 3rd gear.

 

[DangerRanger37]

Can someone please explain this logic to me?

4.10's for 31's should be plenty right? That's my conventional thinking anyways....

 

[alwaysFlOoReD]

4.10/31"/4.0l is great, but the 4.0l is about double the torque [wag] of the 2.3l so more gear is needed.

 

[Captain Ledd]

I currently run right about 3,000 RPM at 70 mph. It's not as bad as you might think. Put it this way, that's the same number of power pulses and fuel/air intake as 4.6L V8 turning at 1,500 rpm. And with that higher rpm, you're actually in the powerband of the 4cyl engine.

I settled on 4.56's because 5th was useless and I spent all my time running in 4th, so why not make 4th into 5th? 4.56 gears would put things right about where I wanted to be.

For 31's, you're looking at roughly:

2,750 rpm @ 70mph in 5th w/ 4.56's

or

3,075 rpm @ 70mph in 5th w/5.13's

You're welcome to drive around for some sustained time at those RPM's to determine if one or the other is more acceptable.

 

[gw33gp]

Those numbers seem to be a little off. When I run my 31" street tires with my 4.56 gears, I am running 3,000 rpm at 70 mph in 5th gear. That is with a properly calibrated speedometer. I doubt the tach is reading wrong.

 

[Captain Ledd]

It works with my truck tire size. Although my speedometer is still off, I run a dashcam with GPS (the proper satellite kind) and it lists a speed that is pretty close to what I'm driving.

Granted those calculations don't take into account actual tire radius, unless you put that number in. I've used that excel sheet with lots of vehicles and it's generally pretty close.

I've got my 5th gear at .79 ratio.

But because I'm open to criticism, Here's now I'm figuring it:

(transmission gear ratio) x (axle gear ratio) x Tire rev per mile: (63360) ÷ (2 x 3.14159265 x (diameter of tire in inches ÷ 2)) x (speed in MPH ÷ 60)

Long equation I know, but it looks cleaner in Excel.

 

[gw33gp]

I am not going to criticize your equation because at a glance it looks right. I can simplify it for you though. The calculation for circumference (2 x 3.14........ x (diameter of the tire ÷ 2)) can be reduced to (3.14 x diameter of the tire). Circumference is normally calculated as (3.14 x d). In your equation the 2's cancel each other out anyway.

I have no explanation as to why calculating gives different numbers than what I get while driving. I know that tire diameters are usually smaller than the tire designation but I don't think it is enough to account for the discrepancy. I know that when I have the 33" tires on, the rpm is below 3,000 rpm at 70 mph in 5th. My 5th is also supposed to be 0.79. Maybe my tach is off a little at 3,000 rpm. I know at idle it is good.

 

[85_Ranger4x4]

When I fine tuned my speedo with my tuner in the '150 I learned fast you can't just go to BFG's website and plug in the tire dia. There is mush in it from the truck sitting on it and it is enough to count. So you have to measure the radius yourself and go from there. And then it still takes some tweaking.

I was going by mile markers.

Heck, my Ranger spins 2700rpm at 60mph with 3.73's and 31's.

 

[Spott]

A much more accurate calculation is obtained by using "roll-off distance" instead of calculating tire diameter.

Make sure your tires have the correct air pressure, and that you have half a tank of fuel. Park your truck in a driveway or parking lot, then make a chalk mark on a rear tire sidewall at the bottom of the tire, closest to the ground. Make a corresponding mark on the ground, adjacent to the tire mark. Now roll your truck straight forward or straight back until that chalk mark comes around once to the very bottom of the tire, and make a second chalk mark adjacent to the tire mark. (It's even better if you can sit in the driver's seat while you roll it.) Measure the distance between the center of those two marks on the ground.

The distance between those marks is the actual distance your truck travels in one tire revolution, call it the "actual effective circumference", for your tires, at your operating pressure, with your vehicle weight and equipment load. Use that number instead of (what the manufacturer advertises the tire diameter to be * pi) in your calculations.

If you want to be even more accurate, roll off 10 tire revolutions, and then divide the resulting distance between the chalk marks by 10, to reduce measurement error.