I was wondering, are there any disadvantages of having an inaccurate speedometer other than not knowing your exact speed? I'm assuming the previous owner of my truck put on bigger tires and did not correct the speedometer.

 

the mileage wont read correctly either. my truck had 35s on it, now it has 31s. so every 1000 miles, it logs an extra 100 on the odometer. if you went from small tires to bigger, you will actually log less miles on the odometer. you can buy the plastic gear from the dealer, or a hypertech will correct on the 98 and newer trucks i beleive.

 

Not that I'm aware of...the mileage may be off a little tho...

My truck came with O.E. 265/75/16 and someone previously put 245's on (lucky me, 'cause I've only got 1 inch to clear the garage)...it's about 4 mph off...speedo says 75, true speed is 70-71 comparing with my wife's Monte Carlo and friend's Grand Marquis, both '03's...so obviously, say your truck came with 245's, and has 265's now, at 75 on your speedo, you're going about 79.

Yahoo for a "tire mph calculator" to get an 'estimated' idea of where your at. If you don't know the O.E. size, get a build sheet (search these forums) from Chrysler...don't bother with the door placard, DC only puts the minimum required size on the door instead of what actually came on the vehicle.

 

I'm with you on the door sticker issue. My 1500 came with a 2500 tire sticker.


What ever the pecentage your speedometer is off, add that percent to the miles for MPG. It's close. Me I'm running 77 with the speedometer reading 70.

 

My truck had small tires on it, then bigger tires were put on (285's), so my speedo reads lets say 30 but the actual speed is about 34. That means I am recording less milage on my odometer than what it should be and that would mean (with the 30 and 34 example) that I'm actually getting like, what, .1 more mpg than what I actually calculate due to inaccurate milage?