Odometer accuracy vs. 18" tires

[Birdhunter]

Wondering if anyone else has noticed this. During my big road trip back east I checked the odometer versus the post miles on the interstate for a couple of 100 mile segments and noted that the odometer came up to 105 miles when the post miles said I had been 100 miles. I even did this in a couple of different states (boredom when you go 2000 miles in 3 days by yourself with nothing but the CD player cranked up). I know that on my old S15 I went from stock 185 tires to 235 tires and of course the odometer was off, by a bunch. So this begs the question of does Nissan do a stock calibration for the odometer and standard tires or is it recalibrated if they change tire size? Although this doesn't sound like it adds up to much, it makes over 1/2 mpg difference in mileage.


So who wants to tackle this one?

[Big Platinum]

Both rim/tire combo have the same overall diameter, the only difference would be the gears. I would hope Nissan thought of this and has two seperate calibrations for the different final drive ratio's.

[Slurppie]

I guess if you wanted to take this one step further you could say that by reporting more mileage that whats actual you are being cheated out of your 36K mile warranty.."Deep thoughts by Jack Handy"

[Big Platinum]

That actually happened to my mom in a car she owned and she got the odometer rolled back and warranty reinstated.

[PHOEBISIS]

The 18's and the 17 OR are about the same 32.6" height.The XE 17's 245/75 17 are about 31.4".
I would have them-dealer-check it out..Luck,Charlie

[Sammy Sandbag]

The 18" tires have a diameter of 32.6" the OR 17" have a diameter of 33.0"

[amati5]

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

[eakes]

I just completed a 1400 mile trip. The odometer on my KC LE, 4wd reads 4% low. That is, 100 miles on mile markers shows as 96 miles on the odometer. Looks like there may be a + or - 5% window for odometer accuracy.

[Sammy Sandbag]

Originally Posted by amati5

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

That is only a conversion, it doesn't give the exact specifications of the various manufacturers. The measurements I gave were from the actual companies for those listed size's overall diameters. For example, not all 33x12.50R15 are 33" diameter and have a section width of 12", most are smaller.

[jkp]

Mile markers don't always account for elevation changes, and some actually fudge a bit on horizontal (ie curves) changes. You might want to check it with a GPS on a flat, straight section of roadway if you're really interested in validating your concern.

[TerryTitan]

I noticed the same thing but it was getting less mileage on the truck the furhter I went down the hiway, and noticed that the speedometer was also off by 2mph. (Cruise @ 77mph, traveled 75 according to mile markers in 1 hour)

[NissanTech]

I checked mine with my gps and I am readiing on the speedometer 60 mph and my gps is saying 61.5.I have checked this at varing speeds.It seems the faster you go the more the seperation.Below 30 it is pretty close.At least that is what I am getting