Join Date: Jan 2008
Location: Prescott, AZ
Feedback Score: 0 reviews
2011 Super Duty and larger tires
My 2011 Super Duty has a 10" Ultimate Air Ride air suspension and 37X12.50X20 Nitto Trail Grappler tires on Pro Comp Black Chrome Wheels. I have stock 3.31 gears. I saw 22.1 mpg when stock on flat ground, sea level and 75 - 80 mph. After tires and lift the truck is at a best of 16.2 mpg under same conditions. The truck has ample torque and the tires are not creating a burden on the engine with 800 lb/ft.
After talking with numerous other shops and chip manufacturers we have concluded the following: The new trucks have very sensitive engine controls and sensors. When larger tires are installed, the truck thinks it is going slower than it actually is and "de-fuels" the engine. The result is an unfelt loss of speed when driving. The driver then gives the truck more acceleration, which actually "over-fuels" the engine and creates a fairly dramatic loss of mileage. The dealership can change the size of your new tires in the computer up to a new diameter of 34" or so (I was told). A technician and I fooled with it for awhile one day and were attempting to also fool it by changing the gear ratio in the computer as well, so that the overall tire size was compensated for. We were also doing the 400 hp/800 trq. flash. He ended up giving up after the computer began objecting to both being done at the same time, he thought.
The last I checked (month or so ago) no manufacturer has still been able to "crack" the Ford computer system and change the tire size, gear size and correct the speedo with resulting better fuel mileage. We are on the edge of changing axle gears to solve the problem, but are lazily investigating the correct gear ratio to go to.
We are also waiting to ship out a system to a shop up in Nevada that has a customer with same size tires, 4.30 gears, H&S programmer w. DPF delete and getting around 22mpg. I have not personally spoken to that customer.
On a final note I have had to have to DPF replaced at around 6000 miles. The dealer said they have heard of a few from their rep, who have had to do this. I suspect the larger tires are causing this. I have lately been having the "Drvie to Clean Exhaust" light coming on, which was the symptom before, along with the "wrench" picture. This truck sees a lot of short around town trips and I suspect that may also be contributing or causing the whole problem.
2011 Ford F250 Super Duty, CC SB SRW, 6.7L Scorpion, 3.31 gears, 10" Ultimate Air Ride suspension system, Accu-Pro Air Management System, 37X12.50X20 Nitto Terra Graplers, 20X9" Pro Comp Knight Chrome wheels, Custom through body exhaust, Custom aluminum rocker panels.
2003 Ford F250, 6.0 PS, 5spd Auto, 4.30 gears, 8" Ultimate Air Ride Air Suspension/Lift, 37" Toys on 20" Weld Velocitys, MBRP Dual Exhaust, Edge Chip, Propane Injection, Bullydog Intake.
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