Gear ratio change. Is it necessary?
- Thread starter eagle
- Start date
OffroadTaco4x4
Well-Known Member
Well I can tell you one thing, I've had my truck from stock tires, to 33s and now to 35s and I can say there is a big drop in mpg. I'm not sure how much better your mpg would be but I'm sure they would pay them selves back depending on how long you have the truck. I'm pretty sure most people go with 4.56
g_chandler85
Well-Known Member
Same problem with mine. 6" pro comp with 35s and it guzzles gas, especially on the highway.
I don't know that changing gear ratios is going to have any kind of impact on mpg. Most of the fuel is being burned to overcome aerodynamic drag. By raising your truck, through bigger tires and a lift kit, you are increasing the frontal area. Total drag is a function of frontal area and coefficient of drag. By raising your truck, you are increasing both. The increased frontal area is obvious, but the increased drag is there too. Tires are a big cause of aerodynamic drag. Bigger tires, more drag, higher truck, the tires are exposed more and this gives more drag. By increasing the space under the truck, you are passing more air under the truck, which is not very "clean" areodynamically, and therefore increasing drag.
Look at what they are doing to big trucks to increase mpg. They are putting skirts all around them, even on the trailers, to keep air from going under the truck. They are enclosing the wheels as much as possible and using flush hub covers because a rotating wheel is about the worst aerodynamic thing on the vehicle. In formula racing cars, which are required to have open wheels, the builders do whatever they can get away with to enclose the wheels to make the cars more aerodynamically efficient.
By lifting your truck, and putting bigger tires on it, you are basically doing the exact opposite of what designers do to increase mpg's.
Look at what they are doing to big trucks to increase mpg. They are putting skirts all around them, even on the trailers, to keep air from going under the truck. They are enclosing the wheels as much as possible and using flush hub covers because a rotating wheel is about the worst aerodynamic thing on the vehicle. In formula racing cars, which are required to have open wheels, the builders do whatever they can get away with to enclose the wheels to make the cars more aerodynamically efficient.
By lifting your truck, and putting bigger tires on it, you are basically doing the exact opposite of what designers do to increase mpg's.
texastacoma
Well-Known Member
Changing your gear ratio has everything to do with mpg, if you put more a heavy duty ratio in to it, something like a 4:10 for off roading or towing your mpg is gonna suck, if you put something smaller in it your mpg will have at least a couple mpg boost, if not more, yes drag has a lot to play in mpg, but the gear ratio has a lot more sway in the big picture, that's why trucks like duallys, 3/4 ton pick ups and commercial trucks get such bad gas mileage, the gear ratio is made to pull... A lot, it's also why cars nowadays are able to 30-40 mpg, they have a ratio that is specific for moving that vehicle and its passengers, nothing more, that's also why you'll burn straight through a rear end if you pull to much for to long, a vehicles towing capacity isn't rates by the engine or frame, it's rated to the rear diff in the vehicle
Well, for one thing, He is talking about shortening his final drive ratio (raising it), which is the opposite of what you are saying. Overall, the main issue is how much energy is takes to move the vehicle down the road. Increasing aerodynamic drag causes a tremendous increase in the energy required to move the vehicle since the majority of the energy used to move the vehicle is used to overcome the aerodynamic drag in the first place. Changing gear ratios does nothing to change the amount of energy required to move the vehicle.
Engines have a specific operating range (rpm's) that produces the highest engine efficiency. Shortening the ratio (raising it) a little here and there will not change the efficiency much. Secondly, by putting bigger tires on it, he is effectively lowering the final drive ration which should increase his efficiency. But, this engine efficiency issue is splitting hairs. If you drove the same speed in 5th vs 6th gear, the mpg's would be nearly identical. If you raise the ride height 5", you'll see a huge drop in mpg's because the thing has become such a pig aerodynamically speaking.
In short, lifting your truck, and discussing mpg's is like discussing which cigarette is best for your lungs.
PinkTaco
Well-Known Member
I think the marlboros are best for your lungs because cowboys smoke them and look how cool they are.......... Same applys to lifting
Joe Buroker
New Member
Anything above 35" and you might want to go to 5:13
burton8913
Member
when you put bigger tires on the truck are you bringing it to the dealer or a shop to have the ecu or the odometer recalibrated otherwise i dont see how anyone is getting an accurate mpg reading
Demo Man
Well-Known Member
Are you following me wisky? Lol. Remember the Subaru Justy? My shop teacher in HS had one. Total burn out. We picked it up and set it in between 2 telephone poles. I don't know why I told that story. Sounded good though.
The Justy, the first production CVT. We called it the 4 wheel snow mobile. Many a micro car has been "parked" sideways in a garage.
Demo Man
Well-Known Member
For a little 3 cylinder that thing would move.