do 4.10s hurt gas mileage?

[Robert]

The axle is always engaged on all 4WDs that use CV joints as opposed to hubs at all times. On '97 and up Explorers though the driveshaft is also always engaged (I'm sure this is what you meant though) unless it has been modified to force it into real 2WD such as mine has.

Since the NoSlip only locks when it is getting power through the driveshaft and I can eliminate 100% of the power going to my front driveshaft it is no different than having a 2WD truck until I put it into 4WD. My only concerns though were that I would loose my Auto mode for all practical purposes. I certainly wouldn't want to enable my Auto mode on the streets when traction was marginal. When my rear tires did slip, both front tires would then start pulling which would then reveal the downsides to having a front locker. My conern was if I was rounding a turn in the rain and happened to give it a bit too much gas. I didn't want it pulling me into the next lane as the fronts started to pull. The only way I could prevent that would be to keep it in 2WD mode.

It became a tradeoff no more Auto mode with the benefit of having front and rear lockers for hard-core 4 wheeling or leave my front open and just put a locker in the rear which allows me to keep using my Auto mode in the rain. I decided to keep my Auto mode and decided against putting the NoSlip in the front. I'm only putting it in the rear. I like the idea of a selectable locker though for the front and will look into this in more detail. This would let me keep my Auto for the street and have front and rear lockers for when it gets really bad.

 

[Hokie]

Originally posted by Robert
4.10s and 33" tires will get you worse mileage than your stock 30" tires with 4.10s. At least it has on my '97 4x4 SOHC.

I'm not doubting you, but what 33's did you put on? I just think its wierd that your mileage went up with 32's and dropped with 33's. Did you increase the tread width and put on a more aggressive tire? I would be that this is more likely the reason for your deacrease in mileage, that and a 33 will weigh more than a 32 or a 30. Also, did you regear your speedo? this would cause your mileage to appear lower due to your trip odometer being off.

 

[Robert]

I went from my stock 255 70R16 Firestone Wilderness AT's to 265 75R16 Michelin LTX ATs to 285 75R16 BFG All Terrain TA KOs. Each change, the tire size was increased slightly. All three tire brands were ATs, however the BFG are slightly more aggressive than the Michelins were. I suspect that the additional weight associated with the larger tires has played a small role in the decrease in mileage. What I suspect has the biggest affect though is the increase in diameter. An engine has a certain RPM range where it operates most efficiently. My SOHC gets better mileage at higher RPMs than lower. The best mileage I ever got out of it was cruising through an entire tank of gas across New Mexico with my CC set on 80 MPH. I got 20.5 MPG that time. I've touched 20 a couple of times but usually averaged 18-19 MPG. With my 33s now, my RPM is so low that my engine is lugging. When the engine starts to lug, I naturally give it more gas to prevent my Explorer from slowing down. This causes the torque conveter to unlock which is essentially the same thing as slipping a clutch. When the torque converter isn't locked up, the additional power is being used up in the form of heat in the transmission instead of mileage.

With my 32s, my engine was still in it's optimum RPM range for my daily commute (at the lower end though). Now with 33s, it has placed my engine outside of this range which I am paying for with fewer miles/tank. Right up until I put the tires on I was getting about 285 miles until my gauge was at about 1/8 tank. Now I am only getting to about 245 to the same point on my gauge.

Yes, my speedometer was recalibrated each time I increased my tire diameter.