What up? I just went to 315's on my truck. I immediatly noticed the change in MPG (I expected it) but I had a guy tell me that I should change the gearing on it to help MPG's. I am looking for someone who has done this or knows something about it. Changing gears and getting the speedo adjusted? Also, am I right to think the overhead computer will be off on the MPG estimate? Looking for replies....Thanks

 

Yep, it will decrease your fuel economy, is harder on the trans... tends to lug in OD. I'm going to chg to 4.10's as soon as possible... (if I keep my truck).

 

I bought my truck with 4.10s specifically for the purpose of fitting bigger tires. 4.10s with 315s is pretty close to stock tires and 3.73s.

 

Im not seeing a problem with any Gen3 running a 315. Your city MPG will drop, but at a steady cruise on the highway you may pick up a little.

 

with a 6spd 315's and 3.73's is right on the money my mileage is actually up at higway speeds 1700-1800 rpm vs 2000 rpm before and the mileage has not changed in town. I miss the 3.54's and 315's on my old 12 valve but this common rail truck is defiantely a step up for me.

i will never install 4.10s ever again. ive had em before and they jsut didnt fit anything i was doing.

 

Did you correct for odometer error? Going from stock 265s to 315s can change your odometer by 10-12%. You should be multiplying your miles by at least 10% and then dividing by gallons used.

Also, the overhead reads less mileage then actual, lowering your #s. But they read high usually anyways, so sometimes you break even.

I had 3.55s, 6 speed and 315s on my 01. I thought the gearing was great for highway(2000 RPM = 80 MPH), especially since the speed limit in MT is 75 MPH on the highway and 70 MPH on two lane.

I don't see a need for 4.10s unless you tow real heavy all the time.

I plan on going to 315s on my 03 Auto.

 

315's will not be that hard on the truck to spend money for 4.10s unless you really want them. You will lower mpg in town but higher on the highway so it works out.

 

I'm happy with 315's and 3.73's on my '05. I don't pull that heavy over the road, tho, about 8000 lbs. A little HP adder from Quad more than makes up for any reduction in torque multiplication.

I had the speedo recalibrated.

 

I was thinking of some type of HP add on. Just not sure what to go with. Just want to offset a small loss in fuel eco...... will the dealer charge an arm and leg to recalibrate the speedo???

 

My truck came with factory 4.10s.

With the LT315s, I did not notice any power difference, but there was a slight 1-2 MPG drop.

 

DC,

Add a Smarty and you will get the HP adder and be able to set the ECM for the tires size so that your speedo and MPG and again correct.