Greetings fellas! I saw a thread a couple of days ago about the stock tire size. I had assumed I had stockers on my truck. But when I took a look at the door sticker, as was mentioned in the thread, I noticed the difference.

Stock size is P235/75 R15

Actual size is 31x10.5 R15

I am trying to calculate the differences to the two, but can't figure out how to get the aspect ratio.

I am using this link to calculate.

http://www.csgnetwork.com/tireinfo4calc.html

 

31's convert to the 267/76 size

give me a min to do some checking

 

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

go to this site.

type in the stock size then type in the size on my last post. it gives all the info you need.

 

Great thanks! I figured out how to get the width measurement, but I couldn't figure out how to do the math on the aspect ratio.

 

So when I put in the information and tell it a speed of 60MPH. It spits out with the different tire size I will be doing 55MPH? Does that sound right?

 

NO your speed will be 60 mph when your speedometer hits the 55mph line.

so if you look at your speedo and it says your doing 55mph your actually doing 60 mph

 

If you're lucky though you're speedo has enough error from the factory that going from 235s (29x9.25, for reference) to 31s will make it dead on accurate

 

But if you look at the chart, the stock is on the left and the 31's are on the right. Same with the speed.

I thought with larger tires, the speedo reads high. Aka, higher then actual speed.

Not that the speedo is legible at all. It bounces higher then ***** goin' down a staircase.

 

Ha! So I went to lunch in the truck and I started the GPS speedo I have on my Droid. This app seems to be very accurate at least when used in my other cars.

When driving it showed 60MPH, and the truck speedo showed 60 ish MPH as well. As I mentioned the speedometer bounces to high heaven. But when it finally settles down it seems to be plus or minus 1 or 2 MPH from the GPS. That is good news.

However if I do get pulled over for speeding, I will still use the excuse that the speedo is inaccurate.

 

So here are some shots of my tires.

Are these a good brand? I have never heard of them, and don't even know who makes them.