Hello All,

I am currently running 255/75/17 tires on my JK w/auto trans. I plan on running either 285/70/17 or 33x12.5x17 tires...The difference in diameter between the tires are minimal...My question is, would I need to get the Jeep recalibrated (i.e using the Hypertech) to maintain the auto trans shift points or is it not necessary....Thanks...

 

The main reason to recalibrate would be for the speedo and odometer. If you're not liking the loss in power (which shouldn't be too bad) you need to start looking at gears.

 

As was stated new tires at 285/70/17 will not be that much larger then the old.
The 255's have a width of about 10" and a dia of about 32"
The 285's have a width of about 11.2" and a dia of about 32.7"
The speedometer reading 60 with the 255's will read about 58.8 with the 285's.
Although it doesn't seem like much the increase in dia and width will increase the resistance, and you will loose some power. The dealer could easily compensate for the speedometer and the shift points with a reflash.
I was not aware of any tires of 33x12.50 in the 17" size, and would not know how large a dia it would be. I do believe a 33x12.50x16 has a diameter of about 34.5" so I would believe if one were made in 17" size, it would most likely be around 35-36" dia.
This would be quite a large difference compaired to the original. I do not believe a reflash is possible. In addition quite a bit of power will be lost in getting those tires moving. Also alot of breaking force to get them stopped.l

 

I just asked my dealer's service manager about this while getting an oil change. He said that ANY time the tire size is changed, the warrantee will be voided unless the computer is recalibrated. He said that because of the change, the 'true mileage' of the vehicle can't be documented and reported to Chrysler.

He did say he could calibrate for 33s (which is contrary to many posts here). Then, he mentioned he'll match any tire store's price for tires just to get me to buy from the dealer. That sounds pretty good for a dealer. They'll reflash and know what the heck a TPMS is.

 

The dealer doing the tire recalibration sounds like a good deal and I'd prefer paying the dealer a small pittance versus paying a very stiff amount to Hypertech for a programmer that will only work on one vehicle with limited functionality.

As far as the quote above, did you point out to the service manager that you and the OP for this thread both have lifetime warranties (e.g., not based on mileage)?

 

Yes I did. I also asked him if it was necessary to bring the Jeep in every 5,000 miles for an inspection to keep the warantee valid (I saw this in an article about the warantee). He said no. Just keep consistent records that the maintenance schedule was kept (like reciepts for servicing or parts if you do your own oil changes). He did strongly suggest only using Mopar oil filters though...

 

I wouldn't advise that. An inaccurate odometer is ONE reason why the dealer CAN void the entire warranty. Especially if you do not recalibrate. It would be directly the fault of the customer.

 

There is a required inspection...but it is every 5 years.