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Tire Pressure question

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  #1  
Old 11-04-2008, 07:33 PM
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Tire Pressure question

Ok, so here's the deal.....

I just bought a used 97 F-150 S Cab XLT 4X4
4.6 and 3.55LS

The previous owner replaced the original 16 inch wheels with the 17 inch wheels that were the off road option for that year.

The tire size is the stock 265-70/17.

What are the recommended air pressures for that size tire.
My door sticker lists 29F 32R for 255-70/16 tires.

Also he never changed the speed sensor gear when he changed the wheel size, so the speedo now reads 5MPH low at 70....that will eventually ge me into trouble...

I've been to several dealers and they say they can't just look up a part number for the speedo gear, they need to know how many teeth are on the one I have so they can figure what I need for the correction.

Does anybody know how many teeth are on the speedo gear for 17 inch wheels and 3.55 gears?
That was a factory offered combo...

I really don't want to crawl under the truck right now just to pull the sensor and count the teeth.....
 
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Old 11-04-2008, 08:35 PM
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look on the tires for the correct air pressure as far as the teeth i'm not sure sure someone here will know good luck
 
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Old 11-04-2008, 08:44 PM
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For tire pressure, I would run em at around 35 empty, bump them up accordingly as you put weight in the bed, or tow.

The pressure on the tires is the maximum tire pressure, and its not always the best idea to run a tire in its max pressure, when not needed.
 
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Old 11-05-2008, 05:41 AM
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X2^^

Im curious about speedo tooth count also, Im going to need to change mine soon.
 
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Old 11-05-2008, 12:46 PM
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The dealership here told me that in 97 these trucks didn't have speedo gears they have a magnetic ring on the ring gear and a sensor in the rear diff. housing they also said they didn't think they could correct for tire size in the computer either unless it was a tire size offered on that truck, and I don't have an extra $75 laying around for them to tell me it can't be done. So if the local dealership is correct, you can't correct a speedo in 97.
 
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Old 11-05-2008, 12:57 PM
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You must be able to with a programmer or something.
 
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Old 11-05-2008, 01:11 PM
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ok, so i crawled under my truck when i got home from the dealer and sure enough there is a VSS in the tailshaft of the t-case, imagine that the dealer lied to me. Other than the dealer I was completely unsuccessful at finding a place to purchase the gears from, however I will be dropping the t-case out of this truck soon and If you havn't gotten an answer by then I will count the teeth and report back.
 
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Old 11-05-2008, 02:59 PM
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The speed sensor is on the transfercase (or transmission on 2WD's) until 99 I believe.
2000 and up you change the speedo calibration in the ECM.

The speed sensor on the rear is for the rear ABS, even my 91 F-250 has a sensor there.

I did a search on speedometer gears and found at least one company other than ford that appears to have the gears.

I'm just a little peeved that the dealer can't look up the part number for the speedo gear for a stock option....
I could see if I was putting a tire/wheel size on the truck that was not offered from the factory.

3 different dealers, including one that only sells Ford Trucks, all told me that I have to pull mine out and count the teeth.

I really didn't want to make a multiple day operation out of changing the darn thing....

Anybody here got a 97 with the factory off road option?
Can you look on the door sticker and get the tire pressures?
 
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Old 11-05-2008, 03:35 PM
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The tire size is the stock 265-70/17.

What are the recommended air pressures for that size tire.
My door sticker lists 29F 32R for 255-70/16 tires.
My truck came with the 255/70r16 and now has 265/70r17. "Google" tire calculator, I think you'll find it only makes about a 3mph difference at 60. I did not change my speedo gears, and have not gotten a ticket.
 
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Old 11-05-2008, 05:33 PM
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I have a monitor where I can see my road speed accurately and when I check it against the speedo guage the guage reads 1.5mph high. I guess the error is to keep you actually under what you think you're going.
 
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Old 11-05-2008, 07:41 PM
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go to a different dealer. they should be able to figure it out for you.
 
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Old 11-05-2008, 08:53 PM
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Agreed it really isn't that difficult for a dealer to know all of the part numbers. You definitely have a VSS gear you cannot change the speedo with a tuner. FWIW your speedo and odo are reading 5.2% slower/less than what you are actually doing.
 
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Old 11-06-2008, 09:34 AM
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i went from 265/70/r17 to 33x12.5xr17, and i havent noticed a difference in speed change.
 
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