Here's a cool link to calculate the tire size change and how it will affect the speedo. I switched to 20" wheels when I took delivery and was curious myself.

Tire Size Speedo Calculator

60mph showing on speedo, my truck is actually going 56.4mph. That should give me more bang for my buck on the warranty...hehe

 

Dusty1 and others....

According to my calcualtions......with my new YOKO 285/6018 "Geolandar" H/T-S tires installed.....my speedometer will read 3.096 MPH slower than I am ACTUALLY driving.

I have a friend who is a NC Highway Patrol State Trooper and I will have him do a side-by-side speedo check with me driving at all common, posted speed limits to verify my calculations.

I'll keep you posted on my EXPECTED gas MPG increase....and the speedometer "error" caused by these new, larger diameter tires.

Fred

 

OOPS......Brain Fart!!!

My apologies to one and all!!

I accidentally had my mix all talked up when I last posted above. What I meant to say is that with the new, larger diameter tires installed on my truck.....my speedometer reading will be 3.096% HIGHER than I am ACTUALLY driving.

Sorry for the confusion.....

Fred

 

I would have thought with larger diameter tires your speedo would read slower than you are actually going. I tried to use the tire calculator provided in a link, but the web site keeps timing out.

 

Dusty,

Just worked for me if you wish to try it again.

 

Thanks,

Yeah, the computer system at the office is slower than a dead dog. Half the time this forum times out too.

 

On a trip recently, with a SC Lariat, 3.73 gears, tonneau cover, 5 people for about 300 miles. I achieved 16.5 mpg, mostly highway, at average highway speed of 75-80 mph. I'm happy with that but I anticipate it wil get better, as it only has 3000 miles on it, and yet to has fully break in.

 

At 4000 miles my mileage seems to be increasing. I started new at high 12's but am now at high 14's. I drive interstate most of the time, 70-75 miles per hour. Also put a tonneau cover on, maybe some of the difference.

 

4.6 , 4 by, 17.5 local driving, only interstate trip (200 Miles) 19.5, satisfied

 

16.6 mixed driving.

BTW, how accurate is the computer?

 

I have found the computer to be off by 2 to 5 tenths every time I check and it has always read higher than actual mileage.

 

Just took a trip to the Blue Ridge Mountains from Chesapeake, VA yesterday. Round trip 479 miles, 24.7 gallons = 19.39 mpg. The gas gauge read a little over 1/4 tank left when I got back. This was computed by topping off before I left and topping off when I got back, then manually calculating the mileage. The computer mpg guesstimator said my mileage for the trip was 18.6.

This was with the A/C running the whole time, two passengers, and limited gear. It got up to 88 degrees, and the EATC system in full auto set to 68 was very comfortable. When the truck turned so that the full sun was on the dash sun load sensor, you could feel the air being diverted to the panel vents to compensate. Very cool.

I was very happy with the milege, considering the engine was dropping out of overdrive on the really steep hills so much that I just turned it off. Driving through the hills, I averaged about 35 mph. On the freeway to and from the B.R.M. I averaged 60 mph.

Another interesting tidbit. Turning Overdrive off really helped when going down the hills. The engine did a lot of the braking for me (I'm always trying to brake as little as possible to cut down on the dust!).

5.4L 3.73 LS 4x4.

 

I just passed 7,000 miles in my 5.4L XLT SCab 2wd with 3.55. I have made two highway trips over 200 miles each and got just over 18 mpg on each of those, there was also some around town driving in the mix. When I use a tank in around small town driving I get right at 14.5.
Same Shell gas station, although there is no way to know if it is the same gas.
I think that is going to be the gas mileage story on my truck.
No load on any trips. Just a couple of pretty girls (co-workers) riding with me on the highway trips. I know that they helped my spirits, maybe they perked the truck up a little, too. Hmmm?
Jimmyj

 

I have over 12,000 on my Lariat 5.4 SCab 4x2 with 3.73. A 50/50 mix of highway/city is usually 16 - 16.5 mpg. City driving is closer to 14. Mileage steadily improved from the 11.5 it was getting when new but I think it's reached its peak. Haven't tried a long highway trip as the vibration problem would drive me nuts.

 

Made my frist short trip towing 6500 lbs, 11360 total truck and trailer. I got 8.8 MPG, 200 miles and 22.5 gallons. It was a slightly hilly trip had the o/d off the whole way. I averaged 60 mph with at pretty good head wind going, and a tail wind returning. This is slightly worse then my GMC 1ton CC dually 4x4 with the 8.1 Gas motor towing the same load. I have a reg cab 4x2 5.4 and 3.55's, I maintained an average speed of 65 and the RPM's were around 2800. I think I'll try to run in o/d on my next trip and turn the O/D off when the truck starts to hunt for a gear as stated in the Manual "Use when driving conditions cause excessive shifting from O/D to other gears. Examples: city traffic, ......trailer towing and when engine braking is required." Maybe I'll see and increase in the mileage. I just hope I don't burn up the tranny. Has anyone put an aftermarket transmission temp guage in their truck? The truck averages 16 mpg around town without any load, I'll expect a slight increase as the motor wears in and I change all my fluids to Amsoil.