Supposedly the dealer reset the computer in my 05 CCSB 4x4 D-max to accomodate the 285 tires I put on it.
Based on my mileage and speedo reading I am doubtful that they did what they said.
So I come here for an objective non BS answer.

1) can the stock computer be changed for tire size ? If so would the tech have to guess at the diameter ?

2) If it cant be changed is there a simple reprogrammer that will do it ?

3) If it didnt get changed am I looking at creating trouble by running the bigger tires with the 245 settings in it ?


Thanks
Scott

No The Diesel Computor Will Only Recailrate For Tire Size 265 75 R16

You Will Have To Find An Aftermarket Calibrator To Accomodate Tire Size Change

sheldon27 didn't gm limit tech2 to only factory tires, thought remembered reading somewhere before, like 245/75-16, 215/85-16 and 235/85-16.

You can run without recalibrating.

If you want to correct your speedo, you need to get a PCM tuner.

Several people tried to get their dealer to correct speedo and have met very limited success.

You do not have to add HP to correct your tires.

If you have access to a GPS, I would run with that to find out just how much your speedo is off. If its not much, you might find you can live with it.

I tried setting the gear ratio and tire size for my truck with the Predator and when I checked it against the GPS, I was more than 10MPH off. I was only 3MPH off before the change. Needless to say, I reset the parameters and am happy to live with the 3MPH difference.

There are alot of guys here that do it and don't seem to have issues, guess maybe I'm just not as lucky as they are.

Thanks everyone for the help.
It looks like I am about 2 mph off at around 65 mph based on the stationary
"your speed" machines that you see in construction areas. A friend at work has a GPS and was telling me last week what it would do. I thought I would give that a try.
I figured I would loose some mpg with the 285's but they look so much better I cant resist :ro)

When I had my tires put on last weekend they were able to recalibrate my speedometer for the 285's. Also a buddy of mine had his 03 C/C long bed reprogrammed for the H2's as well.All work was done by dealerships.

William

I tried setting the gear ratio and tire size for my truck with the Predator and when I checked it against the GPS, I was more than 10MPH off. I was only 3MPH off before the change. Needless to say, I reset the parameters and am happy to live with the 3MPH difference.
With the Predator we can calibrate the speedo to 0 error with just tire size. With my stock tires I modified the tune with 243 R75 16 to remove error. You don't have to enter a "real" tire size. It may take a little experimenting.

My dealer service manager "claims" he can reste my speedo for larger tires as long as they are not too big. How big is too big I wonder.

At least I know that I can put 265's on without warranty issues at this dealer.
:D
I have found that either my GPS is wrong or the speedo on my D-Max and my company truck (a 2004 F-150 -:t junker) are off exactly the same amount because they both read about 2.5 mph slow according to the GPS so I don't know which to believe.

i think i would go with the GPS reading.

the gps is more accurate

If the dealer can put in a different gear ratio they could change that in addition to tire size to get you close. I just don't know if they can do gear ration changes.

I wouldnt trust the Dealer with that many things to accomplish.

The dealer can change for gear ratio and get you pretty close on the 285's. 315's on a 3500 is a different story.

According to the GPS I am pretty close.

40 MPH on truck = 40 mph on GPS
60mph on truck = 61.5 on Gps
80mph on truck = 82.5 on GPS

Apparently the dealer was right when they said they adjusted for the 285s

now if I could just get my mpg over 15

Thanks for the help

Scott

I just recently purchased 285's to replace the 245's that came with my '05. Stock

My mpg were 16.4 and now its 15.9 to 16 even.

I just read the Tacometer and it put me approx. 3 mphs off.