So I know how to calculate my mileage, but what do I have to do to the equation to compensate for the 285's?

multiply how many miles your odometer says by 1.08 and then divide by the number of gallons. thats what i do

multiply how many miles your odometer says by 1.08 and then divide by the number of gallons. thats what i do

Well that's easy enough. Thanks

Thanks for the info

Just remember that you are also going 8% faster than your speedo says too, so if the speed limit says 65 and you are going a "safe 70", you are really doing about 76. Just something to keep in mind. I just use 10% so i can figure out in my head about how fast im really goin.

If your stock tires were 245/75/16 and your new tires are 285/75r16 Toyo M/Ts. You are going 15% faster than your speedo reads.
multiply how many miles your odometer reads by 15% and then divide by the number of gallons.
http://www.rims-n-tires.com/rt_specs.jsp

Or just buy a programmer that adjusts for tire size!
Wanna buy my Tow-safe load it and forget it Hypertech PPIII?! :cool:

If your stock tires were 245/75/16 and your new tires are 285/75r16 Toyo M/Ts. You are going 15% faster than your speedo reads.
multiply how many miles your odometer reads by 15% and then divide by the number of gallons.
http://www.rims-n-tires.com/rt_specs.jsp

No, he will be going 7.8% faster than the speedo reads with 285's.

Just remember that you are also going 8% faster than your speedo says too, so if the speed limit says 65 and you are going a "safe 70", you are really doing about 76. Just something to keep in mind. I just use 10% so i can figure out in my head about how fast im really goin.

^found that out the hard way with a few tickets in the burb:mad:

Or just buy a programmer that adjusts for tire size!
Wanna buy my Tow-safe load it and forget it Hypertech PPIII?! :cool:

How do you like it? Why looking to sell? EFI live I'm guessing...

If your stock tires were 245/75/16 and your new tires are 285/75r16 Toyo M/Ts. You are going 15% faster than your speedo reads.
multiply how many miles your odometer reads by 15% and then divide by the number of gallons.
http://www.rims-n-tires.com/rt_specs.jsp

15% seems like an awful lot when stepping up two tires sizes....


Thanks for all the input guys! So would my calculations be correct if I multiply my miles by 1.08 as mentioned above?

Its not 15%, It is 7.8%, i rounded up to 8% in my first post. Simple math to find it. New tire circumference/original tire circumference. If you do the math to find these values, it comes to 1.078, so multiply your miles by 1.08 and you will be very close.

245mm=9.65in
From width to height:
9.65in*.75=7.23in
16in wheel +7.23*2=30.46in tall tire
30.46*3.14=95.644in diameter tire

285mm=11.22in
w->h
11.22*.75=8.415in
8.415in*2+16in=32.83in tall
32.83*3.14=103.088in diameter

103.088/95.644=1.0778

Its not 15%, It is 7.8%, i rounded up to 8% in my first post. Simple math to find it. New tire circumference/original tire circumference. If you do the math to find these values, it comes to 1.078, so multiply your miles by 1.08 and you will be very close.

245mm=9.65in
From width to height:
9.65in*.75=7.23in
16in wheel +7.23*2=30.46in tall tire
30.46*3.14=95.644in diameter tire

285mm=11.22in
w->h
11.22*.75=8.415in
8.415in*2+16in=32.83in tall
32.83*3.14=103.088in diameter

103.088/95.644=1.0778

Perfect, just what I needed. Thanks JD

multiply how many miles your odometer says by 1.08 and then divide by the number of gallons. thats what i do

What about with 265/75/16s; would you multipy by 1.04%??

Yep, 1.04 will be very close.

dam and here i was allways useing 1.07 when i ran 285's dam my mileage was better than i thought haha

i been useing 1.1 for the 295's that sound rite?

close enough 1.095 would be the exact theoretical. Just remember that the actual tire size can be off by a lot from theory. Some are smaller and some larger.

jb

Plus tread wear. There's no way to calculate your mpg exactly due to so many variables, but it's close.

What would it be for 295 70 17 and does my edge evo change my speedo for me when I set the tire size?

1.092, assuming your stock tires were 245/75/16

thanks raizor

no problem, i just saw the second part of your original post, i would assume if you set the tire size in the programmer it would adjust for you, but i have no programmer so i cant say for sure.

Adding 12% makes me feel better about my milage!

Here is the calculator I use. You may want to verify your odometer with a GPS.

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