Know this has been asked many times before but could someone tell me again. Put new TOYO AT 265's on yesterday and wondered what the speedometer erro is. Drive out price for the tires was $540, is that good. Seems likke a good price compared to most tires of equal quality. Like the looks of the truck more now and hope wet traction is much improved over the OE Bridgestones with passanger tire tread. Edited by: Bill Gisse

Search the internet. There's ton's of info. See a few sites below.



http://www.performanceprobe.com/index2.php?redirect=http://w (http://www.performanceprobe.com/index2.php?redirect=http://www.performanceprobe.com/misc/calculators/tire.htm) ww.performanceprobe.com/misc/calculators/tire.htm
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http://www.ricksontruck.com/calculators.html (http://www.ricksontruck.com/calculators.html)

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

If you want to be able to figure it out yourself, you can do it pretty
easily. I copied this from another thread about gear ratios, but
speedo error is the same, so I modified the quote a little to suit your
needs. . .



Dennis




Here goes:




To find speedometer error between, say, 315s and 245s, 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 315 or 245 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).





Examples: <span style="color: rgb(0, 0, 255);">315</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);">315</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);">245</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);">245</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






Edited by: baimpala

According to 1010tires tire calculator: http://www.1010tires.com/tiresizecalculator.asp


At 60 mph, the 265's will cause your speedo to read 57.7 mph.


That's a 3.73% difference. Hmmmm......same as our gear ratio, thats kind of odd.


Tom http://www.dieselplace.com/forum/smileys/smiley30.gif

The speedometer with stock tires isn't right either ... any of you with a GPS can prove that. Mine is bare stock, and it is off by 2-3 MPH, according to my GPS (WAAS enabled).

Your speedo's easy to check on the interstate with a watch. Using mile markers, 60 MPH = 1 mile in 60 seconds.

265s will put you off approx 3-4 % whatever your indicated speed is.

Ditto what TheBac said. Later! Frank

The best way to check your speedo for accuracy is with a handheld GPS. I've only had a couple of vehicles that were right on the money. And a couple that were way off! (With OEM tires and wheels too).

For me, the speedo is more accurate with the 265 AT's than it was with the stock 245 passenger treads. It was off at least 5% with the OEM tires. My mileage was bogus before and I ate up my warranty 5% faster. My warranty lasted for 34,200 miles instead of 36K miles.


If you have the stock 245's, be warned, yours is probably reading 5% over as well, eating up your warranty 5% (1800 miles) faster. If you have a problem at 37,000 miles, you might want to mention that to the dealer...


Tim

305 Nittos on stock wheels. GPS, local radar signs have shown my speedo to be spot on.