Anybody know the formula to figure out what size 285's are so I can have the attitude display my correct mpg??

It's for MPH and you will need to enter 2619.75 or as close to that # as you get. That is if your tires are 285-75-16.


Enjoy


DanEdited by: dwrat

Copied from a different thread about tire sizes, etc:



<span style="color: rgb(51, 51, 51);">
To find speedometer error between, say, </span><span style="color: rgb(51, 51, 51);" ="highlight">315</span><span style="color: rgb(51, 51, 51);">s and </span><span style="color: rgb(51, 51, 51);" ="highlight">245</span><span style="color: rgb(51, 51, 51);">s, you can just
calculate the difference in diameter and multiply by indicated speed. To figure out the actual tire diameter, you
have to take the tire width (the </span><span style="color: rgb(51, 51, 51);" ="highlight">315</span><span style="color: rgb(51, 51, 51);"> or </span><span style="color: rgb(51, 51, 51);" ="highlight">245</span><span style="color: rgb(51, 51, 51);"> or whatever), and multiply
by twice the sidewall ratio (70 or 75 or whatever), and add that to the
diameter of the wheel (but you have to convert either the wheel to
metric or the sidewall dimensions to inches).</span>







Examples: <span style="color: rgb(0, 0, 255);"><span ="highlight">315</span></span>/<span style="color: rgb(0, 255, 0);">70</span>-R<span style="color: rgb(153, 153, 153);">17</span>







<span style="color: rgb(0, 0, 255);"><span ="highlight">315</span></span>*<span style="color: rgb(0, 255, 0);">0.70</span>*2/(25.4 mm/in)+<span style="color: rgb(153, 153, 153);">17</span>=<span style="color: rgb(255, 0, 0);">34.6</span> inches







<span style="color: rgb(0, 255, 255);"><span ="highlight">245</span></span>/<span style="color: rgb(255, 153, 0);">75</span>-R<span style="color: rgb(0, 204, 153);">16</span>







<span style="color: rgb(0, 255, 255);"><span ="highlight">245</span></span>*<span style="color: rgb(255, 153, 0);">0.75</span>*2/(25.4 mm/in)+<span style="color: rgb(0, 204, 153);">16</span>=<span style="color: rgb(255, 0, 255);">30.5</span> inches







Now, once you have the actual diameter of your wheels, you can figure out the effective ratio:







(<span style="color: rgb(255, 0, 0);">34.6/</span><span dragover="true" style="color: rgb(255, 0, 255);">30.5</span><span dragover="true" style="color: rgb(255, 0, 0);"></span>)*indicated MPH=Actual MPH




If this doesn't make sense, let me know,



Dennis



Now to find out what number you have to put in the Edge Juice, you take
your tire diameter (34.6 or 30.5) and multiply pi*diameter*25.4mm/in



34.6*3.14*25.4=2761.0



30.5*3.14*25.4=2433.8


Edited by: baimpala

thanks B - so what is the tire height in inches and for the edge unit, running 305/70/16 ???? thanks again bro



on edit - i printed that out and wholla, got the numbers, thanks again for this info, makes things much easier


Edited by: tbone1227

For a 305/70/16, here's the calculation:



305/25.4*1.4+16=32.8



32.8*3.14*25.4=<span style="color: rgb(255, 0, 0);">2616</span>



Should be close enough for government work. . .



Dennis

Tbone for that size tire (305-70-16) you will need to enter 2713.99 or as close to that as you can get if you want your MPH to be correct.

Thanks, Baimpala, another one of life's mystery's solved.http://www.dieselplace.com/forum/smileys/smiley36.gif

For 285/75 -16 the numbers my Edge manual shows aren't what yall are putting, but I know ho to do it mathematically as yall did...





Bighttp://www.dieselplace.com/forum/smileys/smiley5.gif

Tbone for that size tire (305-70-16) you will need to
enter 2713.99 or as close to that as you can get if you want your MPH
to be correct.



dwrat, the numbers you are looking at in the Edge book are for a 305/75R-16.

I am not looking in any book but you are correct I did input 75 instead of 70http://www.dieselplace.com/forum/smileys/smiley5.gif. My calculations for the 70 is 2618.232.


Here is 2 links to figure all this out


1. http://www.discounttire.com/dtc/brochure/info/tireMath.jsp Use this to figure out the circumference.


2. http://convert.french-property.co.uk/index.htm (http://convert.french-property.co.uk/index.htm) And then use this one to convert it from inches to millimeters.


These work great and have my edge working GREAT!http://www.dieselplace.com/forum/smileys/smiley1.gif