ok, this post has been done over and over. but, no one can seem to give an outright answer. i see a lot of half answers and answers that avoid the actual question. so, the question is: will 4.10 gears improve gas mileage and highway rpms when tires are 35" or over? i'm not looking for people to say "if you are trying to save mileage it would take years to pay for the difference." i really just want a straight forward answer, if anybody knows. i did try this thread once before, several months ago. what tire size would it start to lower highway rpms? would it ever or am i confused?

also, when you go up in tire size, i've heard that you lose both low end and high end 'seat of your pants' power. i know larger (in number) gears will improve your low end, or take-off and acceleration, but will they also give back your higher end power? i guess basically what i am getting at, will going to a 4.10 or higher put you back to, or better than, stock performance after going to a larger tire? please keep in mind to try to keep ambiguity out of the answer.. its hard enough to decide whether or not to add the lift and tires (and still stay practical)

 

what do you have now 3.55 3.73 3.92?

Going to a lower gear like a 4.10 or 4.56 will of course give you better off the line power to the wheels, your rpms will be higher on the interstate as its taking the drive shaft more rpms to get 1 full turn of the tires. If you do more city than highway then a lower gear like 4.10 and 4.56 will help out because you're engine won't strain as much and there's less force/wear on your drive shaft. As for the highway you will lose mpg as once you're at speed it doesn't take much fuel to keep you going at that speed, but if your driveshaft is having to spin faster to maintain that speed you will lose mpg.

To make it simple try riding a 5 speed bike from a stand still in 4th gears, that'll make your muscles burn, next once you're at a fast speed, try maintaining that in 2nd gears, sure it'll require less force from your muscles but you will have to work them faster to keep your current speed.

Another issue, not so much for 4x4 since there's two drive shafts, but for the 2wd people that lift em and put big tires (personally think that's pretty queer) if you go down to a 4.56 and drive at fast speeds you can have your driveshaft snap due to harmonic resonance, one really long tube being spun at much higher rpms than originally designed can cause any uneveness in weight on the sides of the shaft to start to wobble and then kablamo you're stuck next to a ferd waiting on a flatbed.

 

The only way you can win in both worlds is wit a custom geared tranny, lower than standard 1st and second gears, normal 3rd, slightly higher 4th and a much higher 5th/OD

That and a TC that's worth a damn.

oh and for anyone reading this that doesn't know what the numbers mean, basically its how many times the pinion turns to make the ring turn once (or is it the other way around LOL) if you want to know yours go to dodges website and request a build sheet with the last 8 of your vin. Or if yer really bored, break open the pumpkin and count the teeth on the pin and divide by the number of teeth on the pinion.

 

i have 3.73. but what i am asking is if going to a larger tire, 35" or 37", would going to the 4.10 or taller be a correct compensation? i know with stock tires 3.73 are best all around, but you lose power and things change with larger tires. would the 4.10 still increase rpms at higher speeds or am i still thinking backwards?

 

even a 3.92 would increase hwy rpms but of course not by much, really going from 3.73 to 4.10 isn't much of a change, you might as well go with a 4.56.
Going to 4.10 is a 10% increase in driveshaft rpms, well 9.9xyz and 4.56 is about a 22% inrease in driveshaft rpms.

Either way youll need to go to a lower gear like a 4.10 cause a 35 would be pushing it with 3.73 and a 37" tire would just kill your mpg in the city without a lower gear.
So basically yeah a 4.10 is the closest increase % to compensate for a 35" tire, and a 4.56 will be needed for a 37" tire.
Go with 35"s,4.10 and with the money you save by not buying the 37" tire buy an edge.

 

im wondering about this too i got a 6spd,35' and 3.55 to get better leave from the line BUT mine 1rst is pretty useless,doesnt take long before having to swap into 2nd and 3nd after that its ok tough

 

if i lift though its gonna be 8", so 35" is pretty much outta the question. it would be 37"

 

Then go with 4.56

Woli your chassis cab may have a much lower granny gear. Not sure though. But can't imagine youd think you have good off the line with 3.55s.

 

Follow along, this gets a bit technical

Bigger tires are like going to numerically lower gears. Going from stock tires to say 35's is like going from 3.73's to 3.41's

This will effectively LOWER your highway RPM's by approx 9%. This will also reduce your available torque by 9%.

Overall effects are lower highway RPM, but also reduced power overall.

The effect on mileage is this, and I know this is not what you want...........IT DEPENDS.

IT DEPENDS on what the OPTIMUM RPM range is for YOUR engine. Low RPM's do not always equate to good fuel mileage, putting the engine in it's optimum RPM range for your specific traveling speed is where you get the best efficiency.

What you need to do is figure outat what RPM rangeyour truck gets it's best MPG right now and then when you decide on the tires, you select the gear accordingly.

To figure out the effects that specific gears and tires have on each other, use this formula.

Original Tire Diameter (inches) / New Tire Diameter (inches)x current gear ratio = Effective gear ratio to the ground

EXAMPLE

Original: 32"
New: 35"
Gears 3.73

(32/35) x 3.73 = gearing to the ground

(.914) x 3.73 = 3.41

Effective gearing to the ground = 3.41


Now to see what gears you need to use to REGAIN your ORIGINAL performance, you change the formula a bit.

New Tire Size / Original Tire Size x Current Gear Ratio = Gears you need to install to regain lost power.

EXAMPLE

(35 / 32) x 3.73 = Gears you need

(1.09) x 3.73 = 4.07 (closest match is 4.10's)

4.10's would get you back to NUMERICALLY the same power level. This does not take into account the tire mass, rolling resistance or aerodynamic drag.

Whenever I suggest gears to guys, I always say to go one gear ratio NUMERICALLY HIGHER than what the formula tells you to take the other factors into account.

Bottom line is this.....you must know the RPM range that YOUR engine operates most efficiently in when selecting gears for mileage.

Hope that helps

Rich

 

FYI yall 4.10 is a lower gear than 3.73. A lot of people mix it up simply because its a larger number.