Most of you know from the pics I posted that I now have 15x10 wheels as opposed to the stock 16x7 wheels. My questions are:

How do I know what the speedometer is off by, cause I know I'm going faster than its actually reading?

When calculating mpg's, I have heard that will be different as well...can someone tell me the equation or whatever it is to accurately calculate mpg's?

Thanks.

 

well its not all about the rim size,,,, it all about the height of the tire.......... so stock is about 30.5in and your is 33's so your speedo is going to read slow than your going

 

I apologize....Previous tire size: 225-75-16.....New tire size: 33-12.50-15 (305-70-15?)

Thanks for any help.

 

plug your sizes in here.......remember its not going to be one set # that youre gonna be off by.....its a % of whatever youre going

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

 

Its hard to imagine your truck came with 225's from the factory, but I have heard crazier things. Most came with 265's and some with 245's.

If they were 265's, then they were roughly 31.5" tall. Your 33" BFG's probably only measure 32.5" at max (probably actually 32"). Soooo, your new tires are approximately 3% taller, which will throw your speedo (and MPG's) of by 3% as well... which is not very much.

Examples:

55 MPH on your speedo is probably more like 56 or 57 MPH.
70 MPH " " 72 or 73 MPH.
When it shows 245 miles to a tank, it is really more like 252 (to correctly figure MPG).




Now if the speedo really is set up for 225's, then it will be more drastic as that tire only measures about 29" tall, which is roughly 11% shorter than you BFG's.

55 would be more like 61, and 70 would be more like 78.

 

MPG's may be a bit more difficult to equate, I think it would be worthwhile in the longrun to re-calibrate the odometer, trip, and speedo.

 

Its actually pretty simple. Once you get the percentage that new tires are bigger, then you just multiply that into the overall mileage of the tank of gas.

If the odometer shows you traveled 245 miles and the new tires are 12% larger, than it would really be 274.4 miles.

 

haha i know man i completely agree, but the inside door jam of the truck says "225" for stock tires, and believe me, they were the wimpiest things i had ever seen! My last ram had 265's, much better looking. Thanks for the info!

And as far as a recalibration that someone else had mentioned in the thread, how much would that be and what's involved? I didn't know that could be done, sounds like that would fix everything, the mph, mpg, etc.

 

Weird, My truck says it came w/245's but i just cant see that. I bought the truck used, but i have the off road edition and it coming with 245's just dont seem right to me!

 

i got my ram back in the day with the original tires they were 245/75/16 and the door also says 225/75/16 werid....

you have 97 so if you want to correct you speedo look into a tuner(sct or superchips i believe you can correct tire size on superchips but not a 1000% sure)


sorry if i rubed you the wrong way on the my frist post,sorry
)