So a summer tire size change is next on my list of mods, but because I live in the great white north, I have a set of winter rubber mounted on their own rims.

The '11 raptor tire size is 315/70/17 according to Ford.ca and I am considering going with some Nitto Trail Grappler 295/70/18 mounted on my original factory FX4 wheels.

According to www.tiresizecalculator.info/ the raptor size tires are

Sidewall: 8.68 in
Radius: 17.18 in
Diameter: 34.36 in
Circumf: 107.95 in
Revs/mile: 586.93

And the 295/70/18 sized tires are

Sidewall: 8.13 in
Radius: 17.13 in
Diameter: 34.26 in
Circumf: 107.63 in
Revs/mile: 588.68


For a whole whopping difference of "
Speedometer reading with new tire is 0.30% too fast. When your speedometer is reading 60mph you are actually traveling 59.82mph."

Now nitto's website numbers for this specific tire are slightly off the sire zize calculator site, but close enough for arguments sake.

I called my dealer today and was told that it is an hour labor to re-configure the computer for the different tire size. If it wasn't for the fact that I have a set of winter rubber already, I wouldn't worry much about the switch, but an hr labor, twice a year at $136/hr is kind of a costly pain in the ***(ettes).

If I change tire size without the computer updates, I realize that my speedo will read slow. (According to that same site, Speedometer reading with new tire is 6.81% too slow. When your speedometer is reading 60mph you are actually traveling 63.83mph.)

How big a deal is this for the TCS system to handle? We have all read the threads about the TCS problems with bigger tires, but I'm not real clear as to why our trucks are having the issue in the first place. If nothing else, with the speedo reading slow, and therefore the trucks computers thinking that you are moving slower, I would be led to believe that the TCS should be less responsive.

I can add 7% to my spped in my head no problem. Actually might work well, to drive the posted limit according to my speedo, and not 10% over like I normally do. And the truck puts on less mileage than it reads. Win/Win.

What are the negatives of not programing the computers?

 

Not sure what your original tire you are starting with to get 7% (6.81) difference, but that is quit a bit and will affect your traction system. You'll notice when turning into a lot on a upgrade or bump, your ABS will activate. I had only a 3.7% difference and after I had my dealer reflash, my TCS problems were basically eliminated. It still occurs, but now I believe it is activating because I'm really am slipping up front when turning aggressively. The TSC is fairly sensitive.

Not sure if you thought about picking up a basic programmer to change your tire size. It would pay for itself in no time flat. Plus you can enter your exact tire size. Fords calibrations have fixed tire sizes in their which are released from production. So unless you have an aftermarket tire size which matched something from factory you'll never be exact (but shouldn't be that far off either if sticking with something reasonable).

 

HyperCrap makes a speedo calibrator/programmer that allows you to change tire size and GR (no other PCM modifications). http://www.hypertech.com/products-sp...alibrator.aspx

Don't know if it will work on your 2010.

 

I read somewhere that the dealer can only program for available tires sizes. Is this a limitation of the computer or programmer? In other words, can the Hypertech speedo calibrator calibrate what the dealer programmer can't? Or does it require additional parts (I see they make an "inline calibrator" accessory)?

 

I went through this fiasco with my '06 Ford F250 with an 8" suspension lift and 37" Toyo Open Country tires. I did a lot of research and BE CAREFUL WITH THE HAND HELD PROGRAMMERS CLAIMING THEY CAN FIX YOUR SPEEDO CALIBRATION. What most (if not all) actually do is change the shift points for the larger tire sizes. They DO NOT recalibrate the actual speedometer reading on your dash. I found this out with my SCT X3 programmer. I changed the tire size with the programmer and drove down the highway and it was still way off at 55 mph. It did, however, adjust the shift points at the correct RPM's for the larger tires. Innovative Diesel Performance unlocked certain end-user functions of the SCT X3 for me so I could dial in idle rpm, wheel size, gear ratio, shift points, and other functions.

Ford dealerships are limited to factory sized tires to correct your speedometer. All the dealerships I encountered in my area said they could only adjust up to a 35" tire.

I ended up going with a computer bundle package called AE (AutoEnginuity). With this program you can do much, much more to your vehicle and it will correctly adjust for tire sizes up to 40". You can do .25" increments up to a certain point and then only adjust in .50" increments. I was able to dial in the speedometer on my Super Duty perfectly with the 37" tires reading 55 mph compared to two separate GPS units. I also ran an exact 1 mile measured stretch of road with the odometer as that is what I was really concerned with...correct odometer reading.

Just FYI, call the various companies who claim to correct the speedometer with their programmer. Most will clarify it only corrects the shift points and not the actual dash reading.

 

That is weird. The SCT3, Edge and Gryphon has changed many on here just fine, including mine. The truck dash unit will always be 2-3 mph fast as Ford builds them that way, but my Edge monitor is dead on with the gps.

 

Mine was definitely more than 2-3 mph off. Mine was over 7 mph by 55 mph. I drove it before and after the adjustments and it read exactly the same on the dash, only difference was shift points by rpm indication. I called SCT and the tech rep on the phone confirmed it was only to change my shift points and not my gauge on the dash.

Also, I was running the SF3 and not sure if this had anything to do with it? If they are working and actually adjusting the speedometer, then awesome! I didn't have such luck.

 

Interesting. I have an Edge with the PHP custom tunes, so essentially the Gryphon. I change back and forth with tire size, so I have reprogrammed often and I have never had a difference in shift points. Obviously, if I entered a wrong tire size, the shift points would be affected, but if the tire size is entered correctly, regardless of what size they are, it shifts at the same points.

 

I got a response from hypertech today indicating their speedometers programmer will adjust the 2011 fine all engines except the ecoboost. Of course I have an ecoboost! Tech support did say their inline device would but that looks like a pain to switch back and forth between winter and summer. Anybody know of one that works for sure?