Ok guys, im curious. I am running 285's on my truck, which came stock with 245's. Now i know you can measure the circumfrence, and do all this other stuff, but does anyone know what you multiply your miles by to make up for the tire size difference. I thought i heard you multiply the miles you have gone by .20 for 285's, but im not sure. Im sure someone on here knows. Thanks

Eric

 

Use a GPS and set accordingly.

 

Get a Smarty!

 

hes got a 12v

 

good correction! I was waiting for the misguided help to run rampent. Not sure of the formula, but back in the dark ages we used to run at 60mph and use a stop watch to count from milepost "A" to "B".....unfortunatley I'm not sure of the formula. The gal in the parts department would know what gear it needed as soon as you told her the time you ran.

 

yeah the smarty was the first think that i thought of when i saw the thread title.

 

285's are 8% larger than 245's. Multiply your mileage by 1.08, and you will have the correct numbers.

 

Exactly what I was lookin for. Thanks a bunch! And i have a 12 valve, so i dont need a smarty. We have throttle response stock J/K

Eric

 

The tire rack site also used to have the formula and calculator for figuring this out.

 

at least with a lil free afc and plate adjustment

 

You're speedo would be 7.20% slower with the 285's.

 

+1 for the 8% difference. With my gps over 20 miles I found that I was traveling 8.5% faster and further than my speedo and odometer indicated.

 

i have 285 tires and when i was driving down the interstate, one mile marker was .9 on my odometer, so i just added the first numbers on to the total to get an idea of my milage (250 miles on odometer- add 25)

 

Most speedometer correction companies suggest you drive a five mile marked stretch of highway several times, resetting your odometer each time. Then you can figure the exact percentage difference and correct accordingly. Google speedometer correction and you will find a ton of companies. I just talked to these guys last week about my jeep. I will be getting one of the Stewart Warner adapeters as soon as I figure out where some of my slippage is occuring in the transfer case in the Jeep.

http://texasindustrialelectric.com/speedo.asp