Power upgrades.. what to do?

[J-Thompson]

Not sure what you are trying to simplify there. I fully grasp the concept of how gearing helps the engine. It changes RPMs which in turns puts it in a different part of the power curve. It also gives a mechanical advantage which is why a the old trucks and jeeps with 75 HP motors came stock with 5.13 gearing. What I was including for the original poster and what you don't seem to understand...is that along with gearing there is other things he can do to help with MPG. The width and weight of the tire will affect MPG, sorry but that is a fact. If he want's taller tires he can go taller but keep them skinny. A 235/85R16 would be tall skinny and give better MPG then a 265/70R16. Also less aggressive tread would help. An A/T vs. an M/T, never said that regearing was worthless....just that there are other things that contribute to lose of MPG.

roughly 80% of your loss due to tires is due to hight
if not then by your reasoning if I could find a 40" tall 9" wide tire that weighed 50# I would not need to regear

oh and for the proof
LTB's ,31 X 11.5 ,measured OD of right at 31"
weighed them on a certified scale ,that I serviced, at about 55#
I thought they were heavier
when I switched to the MTR-K'sI lost about 1-2 MPG
32 X 11.5
same weight ,same width ,less tread ,more air
measured 2" taller
go figure?????????????????

what I figured
my Loss was all OD because I gained some on tread and PSI

 

[tommudd]

I guess I should not be getting very good mileage then from my 265-75-16s according to one poster on here.
Just ran 246 miles from downtown Pittsburgh Pa to home running at an average of 75 MPH according to the GPS and got 22.3 MPG.
So with 235-85-16s bet I could of gotten 25-28 MPG

 

[05kj6spd]

Boy I am just not sure what is up with you guys. First the original poster of this thread asked how does re-gearing help gain MPG. No answers from you oh though you all seem to have them. Then when I give him an answer, that is fully correct you argue it with some half explained science only looking at part of the problem or outcome.

First off....tire height, width, weight all affect your MPG. Heavier tires get worst mileage then lighter tires, wide tires less then skinny, tall tires less than short, aggressive grippy tread less then a smoother tread design. When you factor all of these in the off-road tires that we choose to run makes more friction for our drivelines to overcome. One way to offset this is by re-gearing. What re-gearing does is increase the mechanical advantage of the drive-train over the tire. Simply put a object at rest will stay at rest until an equal or greater force acts on it. So a 75 pound tire requires more force to start rolling then a 40 pound tire.

As far as your whole reasoning of getting the RPM's back into the normal cruising range, if that was all that was required you could simply turn of your over drive. Bottom line the deeper the gears the more the mechanical advantage the easier time your drive-line is going to have.

Oh and yes you probably would have gotten better mileage with 235/85R16's since there would have been less rubber on the road therefore less friction. So that's it I am done hopefully someone got something out of this because I for sure did not.

 

[tjkj2002]

Boy I am just not sure what is up with you guys. First the original poster of this thread asked how does re-gearing help gain MPG. No answers from you oh though you all seem to have them. Then when I give him an answer, that is fully correct you argue it with some half explained science only looking at part of the problem or outcome.

First off....tire height, width, weight all affect your MPG. Heavier tires get worst mileage then lighter tires, wide tires less then skinny, tall tires less than short, aggressive grippy tread less then a smoother tread design. When you factor all of these in the off-road tires that we choose to run makes more friction for our drivelines to overcome. One way to offset this is by re-gearing. What re-gearing does is increase the mechanical advantage of the drive-train over the tire. Simply put a object at rest will stay at rest until an equal or greater force acts on it. So a 75 pound tire requires more force to start rolling then a 40 pound tire.

As far as your whole reasoning of getting the RPM's back into the normal cruising range, if that was all that was required you could simply turn of your over drive. Bottom line the deeper the gears the more the mechanical advantage the easier time your drive-line is going to have.

Oh and yes you probably would have gotten better mileage with 235/85R16's since there would have been less rubber on the road therefore less friction. So that's it I am done hopefully someone got something out of this because I for sure did not.

Some common sense is needed.

A tire that is 10.50" wide but 33" tall(load range C) is going weigh less then a 14.50" wide tire that also measures 33" tall0load range C),common sense as the 14.50 tire has more rubber.


Oh and since 235/85's are load range E and most 265/75's are load range D there would be little to no advantage to the 235's as it's a heavier tire(or as heavy) as the wider 265.Every 1lbs of rotaional weight added is about the same as adding 10lbs to the actual vehicle weight.So that 10lbs heavier tire is like adding 100lbs to the vehicle weight,then times that by 4.

 

[KJDevildog]

If you want power, get a B&G PCM flash, and do the usual drop in filter and exhaust mods.