Pulling the Grade w/Lifted PSD F250

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DesertDogs
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Pulling the Grade w/Lifted PSD F250

Post by DesertDogs »

OK Folks, I need some info here to see if my truck is doing what I paid all the Frickin' $$$ for:

Got a 2002 PSD250, has exhaust, gauges, K&N, and recently added the 4" lift with 315/75R16s on it. Ford recalibrated the computer for the lift, and the tranny has been totally rebuilt and had a TransGo kit installed (4r100 Auto tranny)

Towing the 30' Warrior, with just quads in it, and dry or nearly dry tanks, the best the truck does is around 40-45 on the hills. IN the flats, I push it to 60-65, but start experiencing a sway in the front end, and the truck is being pushed to make that power anyways.

What sucks, is that with the stock tires...55 easyily up the hills and 70 on the flats, without a sway.

So what's everybosy else experiencing?

And yeah, I know.."Put in a chip" problem is when I had a Superchips Microtuner hooked up to the truck...it killed the computer. Faulty Supertuner, and had to beg with Ford to cover under warranty.

So hit me with your info guys...I like the truck, gotta keep the trailer for the 4 seater that will make it's way in there. But I feel like the truck isn't doing it's job.....am I right or wrong?
Last edited by DesertDogs on Tue Apr 22, 2003 12:18 pm, edited 1 time in total.
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Post by AlxCook »

31.5" tire size???? That shouldn't make that big of a difference, especially with the desiel. I put bigger tires on my F250 (V10 though), and I couldn't notice any change in towing speeds. Isn't the stock size 30.5"????
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Post by YFZ Bob »

From Superlift site... :arrow:
Whenever larger-than-stock tires are installed on a truck, it will have a direct effect on the truck's performance. Why? It has to do with the effective gear ratio. Your truck comes from the factory with the optimum axle gear ratio to work with the truck's engine, transmission, and stock tire combination as well as provide a good balance between acceleration and fuel economy. When taller tires are installed on a truck but the axle ratios stay the same; the effective gear ratio is reduced. This means the engine is forced to operate below its power band, and performance and fuel economy suffer as a result. In order to restore the effective gear ratio (and the truck's performance), you'll need to have the axle gears swapped to lower (numerically higher) ratios. Read more.....http://www.superlift.com/geartire.asp

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Post by realbadlarry »

change the rear end to match the tires. Call transform in anaheim. They did it for my niegbor, after he wasted 2k and 2yrs building the motor to pull the rubber.

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Post by Dune Shredder »

i've got a f-250 v-10 with 285/75/16's no lift though don't want to flip the axles. Ican do 65 up the hills and belive it or not i've hit 85 on the flats with a 30ft 5th whl 2 quads and misc stuff. The milage sucks towing but the power is awsome. The only thing i'm going to add is air assist in the rear and a flowmaster. I know it's no help to you probably but hey. Keep on dunnin :D
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Post by LTZ 400 »

I have a 1990 F-150 that came with 235/75/15 tires and 3.55 gears. A few months ago I stepped up to 33/12.50/15s. Power went straight down the tubes. Turned 1500 rpms at 60 mph. Overdrive was almost unusable. Last month I changed to 4.10 gears. What a difference! The engine is turning faster BUT I'm getting better gas mileage due to not straining the little 302. The only problem I have towing now is hills. Not quite enough motor for the toybox. Next is a cam change.

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Post by LILHILL »

I have 2002 f250 no lift 285/75/16 and tow 30ft weekend warrior. I get sway only because tires are load range D so when tires wear down I will drop the size to get a load range E tire.
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Post by deviousracing »

hey said 315 wide tires not 31.5 inch tires

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Post by kev »

315/75R16 = 34.7/10.7. I would say the gearing is wrong for 35 inch tires.

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Post by xjruss »

I'm guessing you have 3.73 axle ratio from the factory so you'll probably need to drop down to 4.10 to get your power back. Should cost between around $600 per axle to do a gear swap. Or you could fork out a bunch of cash for engine mods and still end up swapping gears anyway... Start with gears, then turn up the power if your still not satisfied.

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Post by YFZ Bob »

My neighbor has the 2000 3500 PDS. Stock setup we would run between 65-70 mph cruise speed but after he lifted his truck with 35" tires, our first run to Dumont I was following his lead, I glanced at my GPS mounted on the dash and it read between 75-80+ Mph, I called him on the CB and asked him what's all the Rush to get there, he had forgotten the Speedo reading was different from the ground speed and backed off, doing just that also got the motor out of the power band and felt his truck was loosing power on the hill climbs.
Last edited by YFZ Bob on Sun Apr 27, 2003 8:28 pm, edited 1 time in total.

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Post by Rooster »

Excellent point, Bansheebob! What Desertdogs isn't considering is the speedometer is now way off. A 315 tire is very close in diameter to a 35" tire so there is the problem. We replaced the stock tires on our '02 Ford PSD with 305's and the speedometer did read wrong - for a while. Whether the computer re-calibrates itself or not is my question because we've noticed that it's no longer off. I've checked it numerous times with my GPS and it's spot on now. :?

As far as losing power goes, our tire size increase wasn't even enough to notice since the 305's are 70 series which makes them only 33" tall. I was thinking about going to 315's next but after hearing this I'm going to reconsider. Hum?

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Post by BHenry »

For what its worth, I went from 285/75/16 to 305/75/16, or roughly the equivalent of going from 31's to 33's. My speedometer seems to more accurate now, as my change was withing 10% of the orginal factory size tire. All speedometers from the factory are off, with the European vehicles being the worst. I think I saw this article in Car and Driver or Road & Track a few months back while waiting for an oil change in the company van.

By the way, I'm running Nitto Terra Grapplers. Two reasons I went with this particular tire is because in this size, it carries an E load range rating. Its overkill for my 1/2 ton Dodge, but it did make a HUGE difference when towing my 6,000# trailer. The other reason is the increased tread width keeps me from having to air down as much (I made it out of Comp Valley at the clean up, with a bed full of trash, at street pressures).
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Post by Smiley »

I pull a 3300 pound trailer with a 5200 pound Bronco on it with a 2001 F350 running on 38s. The truck has a stock v10 and 4.30 gear ratio, the dealer recalibrated the speedo to the max setting, which is still 7 mph slower then true speed. These tires with the 4.30 ratio gets me a final ratio similar to a 3.70. I've very rarely gotten slower than 55 mph (gps speed) on long steep hills and I can cruise 75 (gps speed) all day long on flats and smaller hills.

Before I stuck money in an engine I'd get it re-geared lower.

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Post by THE BOMB »

My 2001 SD F-250, v-10, has 4.30 rearend, at first I thought I made a mistake, but after towing I know I made the right choice. It really helps in town getting the heavy truck moving (even supprises a few cars at the lights), I very rarely get slower than 50 MPH towing 8000 lbs toy trailer. No lift, no mods, but run 33x12.50x16.5, if you're going to spend the money on gears-go with the 4.30's.
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Post by sduncan »

285/75/16 tires are approx 33.4 in tall ans 11.5 in wide.
305/70/16 are 33 in tall and 12.5 wide.
315/75/16 are 34.9 in tall and 12.5 wide.
Your problem is with gear ratio. I would go with the 4:30s to make up the difference. It'll feel like you've added 50hp to the motor and make life much easier on the tranny(if its an auto).
Also, just what did Ford do to "re-calibrate for the lift" ? If they just re-flashed your computer, then that is not calibrating or compensating for the lift no matter what anyone says.
As far as the sway goes, did you set up the truck "L.A. style" with the frontend higher than the rear so that it looks like a pre-runner? If you did, then thats your sway problem. Truck and trailer are supposed to sit as level as possible. Even if the truck is lifted, it should still sit level. It could also be caused by incorrect caster angle.
Also keep in mind that when you went to a free flowing exhaust and intake, that you more than likely moved the torque curve higher in the RPM range. There is nothing wrong with this, as the parts will help keep the EGTs under control, but its something to think about.

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