Need some advice!!!
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Joined: May 2005
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Need some advice!!!
I am fairly new to diesel ownership. I just bought a 2001 F-250 with the 7.3L. The truck has a 6" lift and 35" tires. The problem I am having is that on the 29 gal fuel tank I get about 250 miles not towing my trailer, and about 170 when I do. The trailer is a 23' toyhauler and only wieghs about 7000lbs when I tow it. The truck has no problem getting up to speed, but when it gets there it acts like it has a problem staying there. Even on strait flat runs it feels like something is draging back the trailer and the truck wants to downshift and run at about 2500 rpm.
Please, somebody either tell me I am crazy and this is normal or tell me what is wrong.
Please, somebody either tell me I am crazy and this is normal or tell me what is wrong.
Last edited by gmanatc; May 23, 2005 at 07:16 AM.
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Joined: May 2002
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From: College Station U.S.A.
Hello,
Well,t he first problem there might be is that the speedometer has not been adjusted. If so, it will show you did less miles than you normally did. PI x diameter is the old formula from elementary school for this. You might want to borrow a GPS and check how much your speedometer is off, that will be just as much as how your odometer is off too. If you have a lower gear ratio, like 3.73, with big tires, you are using more of the low end torque. Also, if you have an automatic, once it gets to the high overdrive and locks the torque converter, it will be a little more loaded because of the big tires. Those big tires will always hurt mileage, I had them on my old dodge and got very bad mileage too. if you want tall tires but good mileage, get Kelly Safari AWR or MSR, that will give you a 33.2" high tire that is narrower (and cheaper). I hope this helps.
Well,t he first problem there might be is that the speedometer has not been adjusted. If so, it will show you did less miles than you normally did. PI x diameter is the old formula from elementary school for this. You might want to borrow a GPS and check how much your speedometer is off, that will be just as much as how your odometer is off too. If you have a lower gear ratio, like 3.73, with big tires, you are using more of the low end torque. Also, if you have an automatic, once it gets to the high overdrive and locks the torque converter, it will be a little more loaded because of the big tires. Those big tires will always hurt mileage, I had them on my old dodge and got very bad mileage too. if you want tall tires but good mileage, get Kelly Safari AWR or MSR, that will give you a 33.2" high tire that is narrower (and cheaper). I hope this helps.
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From: College Station U.S.A.
Oops, I forgot to mention that those lifts put more stress in the u-joints, you can loose up to 12% of the power left once you do power x cosine (cos in a calculator) of the angle the shaft has with the axle of the pinion of the differential. The big tires confuse the computer and it doesn't know in what gear to go. As far as I know, the only ways to adjust for tire size is at the dealer or with a Hypermax tuner.
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From: Not this forum
Originally Posted by alalor
Oops, I forgot to mention that those lifts put more stress in the u-joints, you can loose up to 12% of the power left once you do power x cosine (cos in a calculator) of the angle the shaft has with the axle of the pinion of the differential. The big tires confuse the computer and it doesn't know in what gear to go. As far as I know, the only ways to adjust for tire size is at the dealer or with a Hypermax tuner.
*****edit******
I just realized you have a 2001.......mine is a 95, not sure if your's is diffrent or not......
Last edited by 3 of 7; May 23, 2005 at 10:51 AM.
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From: Dallas GA
Another way to regain lost power and return the RPM's back to stock is to do a gear change in the differentials. Since you have larger tires than stock you will have to go to a lower gear ratio. My dad and I just finished doing this to a Jeep.
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From: College Station U.S.A.
Yup, changing gears will add some pulling power, but it will lower mpg. But the odometer will still be wrong. On these trucks you don't need to change odometer settings when you change gears though because they measure rpms of the ring of the differential. On older Fords and on Chevrolets that measure rpms of the driveshaft, they need to be adjusted when you do a gear change.
