I have a 1997 Expedition with a 5.4 and 3.73 gears. Currently I have the stock wheels and stock 255-70R-16 tires. I would like to go up to 265-75R-16 tires. Will these fit without a lift and will there be tire rubbing when turning into driveways and such? Also will the tire size change cause the computer to make the engine run poorly and the tranny to shift at the wrong time? What about the speedometer? Will I need to change something there and if I do make a gear change in the speedometer will it correct the computer problem? Is an aftermarket speedometer tuner necessary? Thanks.

 

Just put on 265 X 70 X 16 Mich Cross Terrains on my 99EB. Went up from 255 X 70 X 16. No problem on clearance. Had GY Wrangler RT/S's. HUGE HUGE HUGE difference! Can turn the wheel at slow speeds with one finger. Go for it. Mich has a deal with a free Palm Pilot until the middle of May.

Keith

 

Thanks for the reply. Did you have any problems with engine computer or speedometer?

 

Not yet. Down here in South Florida I think they give you a 10mph window. Need to find one of those portable radar/readout trailers. I'll let you know. Can't see that small of a change in size causing a huge discrepency.

 

Thanks, I'll look into those.

 

davet

We can now solve the problem of reseting our speedometer, odometer, and partial throttle shift points due to changing our tire sizes.

Hypertech has stepped up and updated the capabilities of their PowerPorgrammerIII product (product code 41023) .

www.hypertech.com

I spoke with Jim at Hypertech today and he confirmed the PPIII now supports upgrades to these parameters on our 5.4L Expeditions and F150s. IMPORTANT, this is a new capability in the PPIII as of March 2003. You MUST make sure the PPIII is at least revision 23.13.01 or it won't support this function.

I just bought a PPIII at 4Wheel Parts today. It's expensive but 4Wheel is running a sale this week: ~$350.

I used it to reset the parameters on my 2000 Expy this evening. I selected the harder shifts option and reset my tire diameter to 31.25 inches (thats a LT265/75 15). Thirty minutes and I was done. Just back from the test drive and I notice the difference immediately.

The PPIII can do other types of updates on your 5.4L if you want to go that route; optimize tuning for 91 Octane, optimize WOT shift points etc.

No worries on the warranties according to Hypertech .

Hope this helps.

 

After almost 40,000 miles of highway and city driving, I just replaced my 255/70R16 Michelin CrossTerrains with 275/70/R16 Crossterrains. I love these tires!

I have no problems with rubbing, they fill out the wheel well much better than the OEM size, and my speedo is about 3.2% slower.

If I have my truck back into the dealer for anything, I will probably have them reprogam the brain (after I remove my Superchip! ) for the new tire size. Which leads me to a follow-up question. Given that I only went up a relative small amount in tire size, is it worth it to have Mike T. and his gang reprogram my chip?

 

Jeff,

Let me know what you decide to do. I only went up one size to 265's. I had looked at 275, but all the tire reps said not a good idea? I'm more than happy with their response and performance. If you're only off a little over 3%, then mine is probably negligible. Did you fall into the window for the free Palm Pilot?

Keith

 

davet, are you a 4x4?

I've got 285/75/16's on my '00 4x4 and don't have any problems. After installing the taller tires, I cranked my torsion bars a bit to level-out the truck. It looks awesome compared to stock. Speedo is off 10%, so your speedo will be off around 5% with 265's. I've got a Superchip programmer that will also correct the speedo error but it's no big deal adding 10% to the shown mph.

The swap will result in a higher rear gear ratio, again by about 5% so with your 3.73's your new ratio will be around 3.55:1.

 

Keith-

I went with the 275/70R16's and they are great! My speedo is off by 3.2% (by the way, with your 265/70/R16 and assuming your OEM tires are 255/70/R16's, your speedo is off only 1.8%). Nice cornering ability and the usual great ride. I did not a hair of slowness(drag) off the accelerator. Makes sense since it a bigger tire, but it's not enough to worry about.

Not sure why the tires reps said it was a bad idea to go with the 275's, maybe because they aren't as common as the 265's?

Yes, I fell into the free Palm Pilot, but my wife already put the clamps on it. That's okay thought, since I'm in the computer biz... don't need it!

Hope this helps...
Jeff

 

Yes mine is a 4X4. I will use whatever tires I get year round. These 255's are great summer tires and about as wide as I would want to go for winter here in MN. I also have a Banks Trans-Command so I don't think I have any options for correcting the speedo other than what the dealer can do or by changing ring and pinions. Is that correct? I don't really mind the speedometer being off but will the computer cause the engine to run differently or just change the shift points on me. Does the engine computer and trans shift points use the speedometer reading to vary engine settings and shift points? If so a speedometer recalibration is required to get everything back in line is that correct? And if I need an aftermarket chip to get it back in line I may have to stick with the stock size tire since I have the Trans-Command which is already altering my line pressure based on load on the engine. Bigger tires could open Pandora's Box for me I think.
Thanks for all the input. I'm new to these Fords.

 

I'm no expert on what affects what when mods are made and frankly don't know what the Banks Trans Command is, but by installing larger tires (285/75/16) my transmission shift points were a little different but I got use to them almost immediately. Now 30,000 miles later I'm still glad I put the larger tires on.

 

jimmsimm. Do you do any heavy towing with it and if so do you still have the power you need?

 

You can see from my mod list that I have shorter gears and taller tires. I started with 265/70-17's and 3.55's.

I had Mike T add speedo correction to my Superchip flip chip.

BTW - I tow a 6500 # TT in the mountains - the LT tires are much better than the P's for towing.

Ian

 

No towing here, but if I did, I would certainly install 4.10 gears.