Calculating Tyre sizes

**Disco_owner** · 27th April 2008, 08:48 PM

Could someone please post in here how to Calculate a tyre sizes , this has been bugging me for a while , for eg if someone says I've got a set of 265/75R/16 how does that actually equate to in inches "?

**dmdigital** · 27th April 2008, 08:57 PM

265mm width
75 percent of width in wall height
R implies radial
16" rim

1" = 25.4mm

So 265/75R16 is
265mm wide
803.9mm diameter = 2 x 75% of 265mm + 16" = 31.6"

See here: Tool

**Slunnie** · 27th April 2008, 09:00 PM

Originally Posted by Disco_owner

Could someone please post in here how to Calculate a tyre sizes , this has been bugging me for a while , for eg if someone says I've got a set of 265/75R/16 how does that actually equate to in inches "?

This is a good program to do it:
Tire size calculator

Admittedly you do just get to know what the metrics and imperial tyres convert over to after a while....

or then again, it may show how sad I am too.

**TimNZ** · 27th April 2008, 09:01 PM

Hi, have a look at: 4WDbits Tyre Size Calculator

**Disco_owner** · 27th April 2008, 09:07 PM

Thanks heaps Fellas,

I will be going to 315/75/16 shortly but according to the Tool it's not quite 35" ..But close

**Slunnie** · 27th April 2008, 09:17 PM

They're close enough to be commonly known as a 35 though.

Which tyre are you looking to fit? I can't wait to see them!

**dmdigital** · 27th April 2008, 09:17 PM

Here's the source for the conversion tool. I wrote this some years back when there weren't as many other conversion pages on the www.

Code:

<html> 
<head> 
<title>Tool</title> 
<script language=javascript> 
function tyreSize() 
{   var w = new Number(tWidth.value); 
   var p = new Number(tWall.value); 
   var r = new Number(tRim.value); 
    var Inch = new Number("25.4"); 
   var d = new Number(); 
   d = (w*(wBtn1.checked?1:Inch)*p*0.02) + (r*(rBtn1.checked?1:Inch)); 
   d /= (dBtn1.checked?1:Inch); 
   d = Math.round(d*10)/10; 
   tDmtr.innerText=d.toString(); 
   if(isNaN(tDmtr.innerText)) tDmtr.innerHTML = "<b>#ERR</b>"; 
} 
function reset() 
{   tWidth.value = ""; 
   tWall.value = ""; 
   tRim.value = ""; 
   tDmtr.innerHTML = "&nbsp;" 
} 
function convertToMpg() 
{   var l = new Number(fLitre.value); 
   var m = Math.round(62.5/(l/4.55)*100)/100; 
   fMpg.innerText = m.toString(); 
   if(isNaN(fMpg.innerText)) fMpg.innerHTML = "<b>#ERR</b>"; 
} 
function convertToLtr() 
{   var m = new Number(fMpg.value); 
   var l = Math.round(10000*(1/((m/4.55)/0.625)))/100; 
   fLitre.innerText = l.toString(); 
   if(isNaN(fLitre.innerText)) fLitre.innerHTML = "<b>#ERR</b>"; 
} 
</script> 
</head> 
<body> 
<table border="0" cellpadding="0" cellspacing="3" width="233"> 
    <tr> 
      <td width="50" align="right">Width: </td> 
      <td width="50"><input id="tWidth" type="text" name="tWidth" size="3"></td> 
      <td width="60" align="center"><input id="wBtn1" type="radio" value="true" checked name="wBtn">mm</td> 
      <td width="60" align="center"><input id="wBtn2" type="radio" value="false" name="wBtn">inch</td> 
    </tr> 
    <tr> 
      <td width="50" align="right">Wall: </td> 
      <td width="50"><input id="tWall" type="text" name="tWall" size="3"></td> 
      <td width="60" align="center">%</td> 
      <td width="60">&nbsp;</td> 
    </tr> 
    <tr> 
      <td width="50" align="right">Rim: </td> 
      <td width="50"><input id="tRim" type="text" name="tRim" size="3"></td> 
      <td width="60" align="center"><input id="rBtn1" type="radio" value="true" name="rBtn">mm</td> 
      <td width="60" align="center"><input id="rBtn2" type="radio" value="false" checked name="rBtn">inch</td> 
    </tr> 
    <tr> 
      <td width="50" align="right">Diameter: </td> 
      <td id="tDmtr" width="50" align="center">&nbsp;</td> 
      <td width="60" align="center"><input id="dBtn1" type="radio" value="true" checked name="dBtn">mm</td> 
      <td width="60" align="center"><input id="dBtn2" type="radio" value="false" name="dBtn">inch</td> 
    </tr> 
    <tr> 
      <td colspan=4 align="center"> 
     <span style="color:blue;text-decoration:underline;cursor:hand;" id="sbmt" onclick="tyreSize();">Calculate</span> 
     &nbsp;&nbsp;<span style="color:blue;text-decoration:underline;cursor:hand;" id="rst" onclick="reset();">Reset</span> 
     </td> 
  </table> 
  <br> 
  <table border="0" cellpadding="0" cellspacing="3" width="233"> 
    <tr> 
      <td width="100" align="right">litres/100km: </td> 
      <td width="70"><input id="fLitre" type="text" name="fLitre" size="5"></td> 
      <td width="30" align="center"> 
         <span style="color:blue;cursor:hand;" title="Convert to mpg" id="toMpg" onclick="convertToMpg();">&gt;&gt;<span></td> 
      <td width="30" align="center"> 
        <span style="color:blue;cursor:hand;" title="Convert to l/100km" id="toLtr" onclick="convertToLtr();">&lt;&lt;</td> 
      <td width="70"><input id="fMpg" type="text" name="fMpg" size="5"></td> 
    </tr> 
  </table> 
</body> 
</html>

**rick130** · 27th April 2008, 09:21 PM

Just remember that they aren't exact calculations, either. Tyres can be quite a bit either way of their 'calculated' size (usually significantly smaller) and can vary batch to batch too.

Some 35's are sometimes closer to 33.5's. (often the 'imperial' sized tyres)

**Disco_owner** · 27th April 2008, 09:41 PM

Originally Posted by Slunnie

They're close enough to be commonly known as a 35 though.

Which tyre are you looking to fit? I can't wait to see them!

Most Probably Maxxis or BFG MT's If price is right I'll go with Maxxis although I'm Told Maxxis are a BFG made tyre. when will you be back down to sydney next Simon ,Like to catch up with you very soon.

P.S dm_td5 that source code you're written , what Program was it written with? I studied a Java progamming language similar to that few years ago at UTS when i studied for my eng degree.

**Slunnie** · 27th April 2008, 09:52 PM

Originally Posted by Disco_owner

Most Probably Maxxis or BFG MT's If price is right I'll go with Maxxis although I'm Told Maxxis are a BFG made tyre. when will you be back down to sydney next Simon ,Like to catch up with you very soon.

Cool! You'll love them, the extra traction and the diff clearance.

I should be out on Tuskers next TT to Lithgow next weekend hopefully. Are you coming to that? He has a post on here somewhere about it.

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