You do know that most aftermarket tuners come with a feature to recalibrate the speedo, don't you. Lots of other benefits to a tuner, hell an economy tune may get you back all of the gas mileage a tire increase will lose...

 

I am a noob when it comes to tuners. Any suggestions? And is it an easy thing to do?
Of course we leave in less than a month and I don't want to go with a speedo that is not accurate.
I did see a thread somewhere that said the 285's which are LT's with more belts wont ride as nice as P's... don't know one way or another.

 

Honestly, I wouldn't have a "P" rated tire on a full size truck. The "P" stands for passenger car rated, the "LT" stands for light truck. Weak sidewalls in a "P" tire, but yeah the thinner sidewalls flex easier making for a softer, more car-like ride.

An LT tire with a load range C wouldn't be very noticeable over the ride of a "P" tire.
Now as you get into a D or E tire, with the higher hauling/towing capacity and firmer sidewalls and thicker plys, now you'll start to significantly harshen the ride.

For a stock to mildly modded truck, I'd suggest looking at a Superchips tuner. Hell, the discontinued 3815 would do everything you need such as speedo recalc, have an 87 octane, max gas mileage, towing and performance tune, read and clear CELs, etc. and people are selling them all over the place who want the extended transmission scheduling of the 3865 that replaced it. I sold mine last year for $175, have seen them around for $150 and under now.

 

Okay... the Michelin LTX M/S2 in 285/70-17 are LT's I think... load range D. So "D" will be a noticable ride difference? I have a bed cover so I never haul anything heavy.
Also, the used 3815's on Ebay... some say "locked" and they will cost $100 to unlock. What is up with that?

 

Can't be locked, that means some a$$hole has tuned his truck with it and hasn't returned the unit to stock but is trying to sell it. A tuner only works on one vehicle at a time. Technically, Superchips doesn't have to unlock it for you, but often will for a $100 fee.

If a tuner were allowed to tune multiple vehicles at once, there would be no stopping guys from sharing one tuner among multiple vehicles, as a safeguard tuner companies "lock" the tuner when it's used to tune a vehicle. The unit is "unlocked" when the vehicle is returned to stock settings...

It's not any good to you if it's locked...

 

Makes sense.

 

Called the dealer on calibrating the speedo. They said $113 plus tax. They also said that they will get it "close"... within 3-4mph.
That didn't seem right as the difference between 245's and 285's at 60mph is 4.04mph off.

What am I to think about this??

 

For that price and what they told you I would look into getting a used tuner from the classifieds here, on dodge talk, or ebay.

 

i agree look for a tuner that dealership is going to charge you $113 and not do crap

 

They obviously intend to charge you $113 (I'm assuming that's their one hour rate + tax) and ain't gonna touch the PCM. That service manager knows damn well that going from a 245 to a 285 tire is about 3-4 mph off without touching the speedo.

My Superchips has my speedo about a half mile per hour off at 70 mph (according to my GPS) and that's only because the SC tuner goes by 1/4" increments and my "35 inch" Cepeks are actually 34.15 inches in diameter.

Put the $113 towards a tuner and have ALL the extra benefits a tuner offers besides the speedo re-calibration. My pig weighs in at almost 7000 lbs, runs 35" tires and I get within a mpg or two of what I got when the truck was BONE STOCK, running the Superchips Performance Tune with 100% (no ethanol) 93 octane gas, not to mention the 18 RWHP and 26 lb./ft. of Torque gains and the firmer transmission shifts that the tuner provides...