Dirty:

Is there anywhere I can find a precise calculator to figure out the speedometer change? I recently went from 285/70R17s to 35x12.5s. I've found rough calculators, followed friends going at certain speeds and passed some radar signs, but can't get any closer than a 5-7mph difference.

 

requires java:

http://www.miata.net/garage/tirecalc.html

 

I put on 285/70/17's to replace my wimpy 245/70/17's too, only after I burned through them. [8D] I saw gas mileage go down some because the Toyo Open Country A/T's had much better traction, which equals more rolling restistance. But I think it's worth it since it adds to the usefulness of the truck as an offroad or bad weather vehicle. It added a noticeable height difference though I can't say for sure how much. It seems like a couple of inches since my truck used to be shorter than my father-in-law's Silverado 2500 but is now taller (and still taller even when he took off his toolboxes and ladder racks. Also it used to be noticeably shorter than Hemi Sport's with the 20 inch rims (33" outer diameter of tires), but is now the same height.

I have pics in the gallery on this forum:
https://dodgeforum.com/albumphoto.as...e=1&sortType=6

Also, you can go to the dealer to get the speedo/odo adjusted. They called it a "pinion factor" adjustment for bigger tires. It only cost me $33 - I thought it was worth it and recommend it. Shift points were off due to the change in RPMs at a given speed.

 

Woken, http://www.supermotors.net/vehicles/...tors/index.php
Java not required.

Looks like at 30 MPH, you're actually going 32.11 and at 65 MPH you're doing about 69.57 according to the calc. on that page. Of course, speedo's are all relative anyways, unless they're certified.

 

even certified speedos are relative. They are simply certified to be within a certain percentage of where they are supposed to be when new, wheras other speedo's aren't. Get an old 9c1 caprice and run it against GPS and i gaurantee you it will be off due to wear and tear, yadda yadda yadda. Most modern speedos run off of a system where a sensor creates a sine wave that is corellated to the roatational speed of some part of the driveline (in our case i belive it sits where an ABS sensor would sit on most cars) changes to any part of the drive line before or after the senso, to te sensor itself or in some instances to the cars electrical feild will throw any speedo way off. Hell a speedo reading will change between a tire being brand new and being bald...

 

True... good point(s)

 

I got Futura Dakota AT from pep-boys. I wasn't too sure about them at first, but I noticed handling is a thousand times better, and they look good too! Cost me $420.00 For all four (included lifetime road hazard, rotation, installation, and valve stems. And they are rated at 50,000 miles) It beats spending 1000.00 on 4 tires. I had a 02 Durango and I spend 200.00 a tire for it. I won't do that again.

 

I saw some futuras on a Chevy that looked sweet. Nice and wide. What size did you get and what is the load rating?

 

I replaced my 245's with 285's and absolutely love them. I went with Michelin M&S. About $180 per each. Well worth it though, they handle great in mud, snow, rain.

 

No offense to any one, but I would never buy Michellin tires again. That is what was on the truck when I got it, and I didn't evenget 25000 miles on them.