stocks are 245 75r16 correct,i want to move up to maybe 265 75 r16 or 285 75 r16..if my understanding is correct i will only be changing the width of the tread not the height so the speed and all brake sesors should work fine,right?http://www.dieselplace.com/forum/smileys/Confused.gif


the reason i ask is i see alot of post about how bigger tires mess up the speedo and you need to buy a programmer so everything will be right again..i don't want to do that at this point.thanks and thsi site is awesome!!!http://www.dieselplace.com/forum/smileys/Big Smile.gif

toolman


given the aspec ratio "the second number, 75" and the wheel size "the third number, 16" stay the same, you will have a taller tire when you increase the first number, which refers to width.





reason is the aspec ratio refers to sidewall height. The 75 means 75 percent of the width of the tire. so in order to have a wider tire and stay the same height you must have a lower aspec ratio.


hope this helps.





Jason

got it..thanks for clearing that up..so would going to a 265 really change everything that much,i notice on some tire sites its called a step 1..and is listed as ok to do..(jason)thanks again for the quick reply..

Go From 245's to 265's you will be 1' tall !


ps.....yes go to 265 will mess up your speedo a littleEdited by: RUMAXED

You'll also be changing the overall diameter with the examples you have shown. What you're trying to do is called "plus sizing" where you keep the overall diameter the same by playing with the cross-section (width) of the tire versus the sidewall height.


The first number (265) is the width of the tread (in mm), but the second number (75) is the percentage of the first number that represents the sidewall height (also in mm), and finally the last number (16) is the diameter of the "hole" in the tire where the rim goes.


So, to calculate diameter, the following formula applies:


2(tread width * aspect ratio) + rim size


Example of 245 75r16:


2(245mm*75%) + 16" = 367.5mm + 16" = 367.5/25.4 + 16" = 30.5"


I divided 367.5mm by 25.4 to convert to inches.


Therefore, 245 75r16 has an outside diameter of 30.5" or a circumference of 95.7" (Circumference = 2*pi*radius)


The diameter of a 265 75r16 has an outside diameter of 31.5" or a circumference of 99.4" which equates to about 3.9% slower reading on the odometer than stock.


The diameter of a 285 75r16 has an outside diameter of 32.8" or a circumference of 103.1" which equates to about 7.8% slower than stock.


However, if you chose a 285 65r16 the outside diameter would be 30.6" or a circumference of 96.1" which equates to less than .5% slower than stock.


The bottom line is that you'll have to find a standard tire size that keeps the overall diameter and the rim size of 16" the same as the stock diameter.


There's actually a website that has a tire size calculator that is very useful for quickly calculating what I have illustrated above. The URL is: http://www.miata.net/garage/tirecalc.html


Hopefully this wasn't too longwinded and provided some useful information.

<FRAME src="http://errors.aol.com/vl5/error_dns.adp?host=dieselplace.com">It will just throw the speedo off about 3% across the range. It will vary some from tire mfgr. to tire mfgr. Edited by: Blue Max

thanks to all agian for the answers..and capt its never to long winded when i am learning something new..http://www.dieselplace.com/forum/smileys/Thumbs Up.gif