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Any tire experts?

J

JBMac

Member
Just bought a new set of Nitto Terra Grapplers for my 2500 Chevy Duramax. The last set gave me 80,000 miles. I decided with the price of tires and fuel, I would downsize to 265/75/16's. The old set was 285-75-16's, new ones are 265's. Can anyone tell me how many inches in diameter these tires are? I need to reset my speedometer to account for the change in size. I asked the titre shop and they gave me a blank stare. Should I just use a tape measure?
 
(quoted from post at 18:53:56 06/28/11) Just bought a new set of Nitto Terra Grapplers for my 2500 Chevy Duramax. The last set gave me 80,000 miles. I decided with the price of tires and fuel, I would downsize to 265/75/16's. The old set was 285-75-16's, new ones are 265's. Can anyone tell me how many inches in diameter these tires are? I need to reset my speedometer to account for the change in size. I asked the titre shop and they gave me a blank stare. Should I just use a tape measure?
Click to expand...
What you want is the rolling circumference while mounted on vehicle of both old & new tires. Mark pavement & tire, roll one revolution to get tire mark back to pavement & measure mark to mark.
 
31.6 in diameter your speedometer would be 3.6% to fast. When your are doing 60 on your spedo, you are traveling 57.8 mph.

Hope this helps
 
the rolling circumference of that tire would be 99.4 inches, the old
one would be 103.1.

Old tire = 614 rev's per mile
New tire= 637 rev's per mile
 
have u checked your speed with a gps? I know with my Jeep, the speedometer was out from the factory. When i Went from a 225/75/15 to a 31x10.50x15, the speedo was now smack dab on. And yes i checked it with 3 different GPS's just to be sure. But yes a 265 is 31.6"
 
(quoted from post at 19:15:42 06/28/11) can you tell me where to look to see how old my tractor is
Click to expand...
omeone probably can, but it would help if you could narrow it down a bit....American, Russian, Jap, English, whatever????? Make, model, anything you know about it including pictures.
 
Why would any one go to smaller tires, you are probably going to loose enough mileage to pay for the bigger tires, and the bigger tires would last longer!
 
An old fashson way is to drive 60 on the interstate and time your self between the mile markers. If your speedo is right it should take 60 seconds. 58 sec. would be 62mph. 62 sec. would be 58 mph and so on. That would give you a rough idea where your at with your speedo.
 
The truck came with 245's. The jump to 285's caused a noticable fuel mileage "dent". You would think that the taller tires would lower RPM's and make better mileage but it didn't. I use a fuel card and enter my odometer at every fill-up. I try to fill up to the same level each time, two clicks. On unloaded interstate trips in the mid-70 MPH range, I average 17 mpg. Pulling any load gets me in the 10-14 range. I'll report back how this affected my mileage. I get a weekly report that's pretty accurate. I'll burn about 5 tanks on the highway over the next 2 weeks, so it should be a fair comparison.
 
Actually it makes no difference what speed you drive. Just count the seconds it takes to drive a mile at a steady speed then take the seconds into 3600 and it will tell you the speed.

Jim
 
It doesn't matter.You reset the tire size with a GM Tech 2 scanner.I do it all the time for customers changing the tire size.
 
Don't forget your odometer is off also. Mileage is going to look really good. Might peel out better. That is if you do that sort of thing. Dave
 
I was just looking at a set of Terra Grapplers yesterday. Was concerned about road noise. How do they compare, in your experience? Thanks in advance!
 
the 265s are 31.7" tall...the 285s are 32.8" tall. Actually, the 285's are just a bit too wide for the factory GM wheel (should be on a 7.5" wheel), but seemed to wear evenly regardless and certainly handled any load issues.
FYI, I saw no discernable difference in fuel economy with these two sizes on my 2500HD duramax.
 
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