2002 Pathfinder SE speedo error and implications

[wildpig]

I am sure I m not the first one to notice this, but it seems like there is a speedometer error in the SE maybe part of Nissan being lazy and not calibrating SE speedo to the standard 16 inch tires instead of the 17 in tires standard in the LE. I notice that my GPS was showing 68-69 mph but my pathy SE speedo was indicating 73 mph. 17in/16in is 1.0625. Multiply that by 68-69 gives you 73....

I know, you probably say that this is "the safety factor" built into the car by nissan so you don't end up getting speeding tickets as much? But i did notice that on my old 97 pathy when i was using the correct 16 inch tires the speedo and gps reading was right on with each other. Of course a couple of time i got the 15 inch tires just because they were cheap on sale and got the expected difference in reading.....

So I am wondering if anyone with a 2002 pathy LE have compared their speedo and gps reading to see if they match or not. Also just wondering if any other 2002 pathy SE owners can confirm my findings..

So stupid question: say if i change the two back tires to 17 inch on my pathy, would i get improved mileage to a tank of gas? I am getting about 380 miles to a tank highway so would that means putting on 17 inch in the rear i would get 404? Stupid question I know, why don't all of us put 20 in wheels and get even better mileage. I am sure at some point, the increased drag and weight will work against it....

[korbeano89]

im not 100% sure but a gps mph gauge is not really that accurate, the gps i think uses a point to point to calculate how fast your going, which takes where you where and where you are as points, and calculates how fast you went from when it started and ended its point to point. it just does that constantly. i dont think one inch would be noticeable on a gauge that wasnt setup for that size tire anyways.

[wildpig]

i did notice the speedo and gps difference on my old 97 pathy when i use the 15 in tires in the back. when i had the correct 16 in in the back there was no difference between gps and speedo reading.

So seeing that 17/16 giving 1.0625 and applying that ratio to the difference in the speedo (73) and gps (68-69) reading which calculates out exactly, I figure it might just be more than just coincidental ....

Let me know what you see the next time you drive comparing to gps

btw, 1 inch does make a difference if you think about it considering that the circumference of the tires (henc distance traveled) is directly proportional to the diameter so going from 16 to 17 inch, that's a 6.25% difference. It adds up....

[Chris.m]

btw, 1 inch does make a difference if you think about it considering that the circumference of the tires (henc distance traveled) is directly proportional to the diameter so going from 16 to 17 inch, that's a 6.25% difference. It adds up....

One thing I think you may be over-looking is a difference in tire size,

I found that in 2002, the Le was 245/65/R17
So, 245mm x .65 x 1inch/25.4mm x 2(for top and bottom) = 12.54 inches + 17(rim) =29.54 inches

While the Se was 255/65/R16
So, 255mm x .65 x 1inch/25.4mm x 2(for top and bottom)= 13.05 inches + 16(rim) = 29.05 inches

Putting it all together;
29.54/29.05 = 1.0169 or a 1.69% differnce in diameter and therfore circumference.

Tire size source(http://www.vehix.com/car-reviews/2002/n ... ifications)

As for a bigger wheel size improving fuel economy, I think all it would do would effectivley increase your gearing, which theoretically would improve fuel economy but I'm guessing would not be directly proportional. Also it would cause slower acceleration.

[Chuck Tribolet]

im not 100% sure but a gps mph gauge is not really that accurate, the gps i think uses a point to point to calculate how fast your going, which takes where you where and where you are as points, and calculates how fast you went from when it started and ended its point to point. it just does that constantly. i dont think one inch would be noticeable on a gauge that wasnt setup for that size tire anyways.

Modern WAAS-enabled GPS is accurate to about 0.1 MPH. Much better than your speedometer.

I've compared GPS to speedometer on several cars. ALL the speedometers read about 2-3 MPH higher than the GPS. I've also
checked a couple of cars with a stopwatch, mile posts, and cruise control, and that agreed with the GPS.

[wildpig]

Well, i guess the speedo reading is always a little higher to help us from getting tickets? Doesn't make that much sense in that way either because you don't get ticketed most of the time unless you are at least 10mph faster than posted limited. Oh well, no idea why they always calibrated it a little higher. Guess better than calibrated it too low?

[Pwnin O'Brien]

Yeah, the GPS is actually extremely accurate. Chuck is right, there is always a 2-3mph difference in GPS speed and the speedometer speed regardless of vehicle make or model. Nothing to worry about, your speedo isn't broken.

[Chuck Tribolet]

Well, i guess the speedo reading is always a little higher to help us from getting tickets? Doesn't make that much sense in that way either because you don't get ticketed most of the time unless you are at least 10mph faster than posted limited. Oh well, no idea why they always calibrated it a little higher. Guess better than calibrated it too low?

My theory is that it's to keep you from suing Nissan if you get a ticket. Theory only, no known facts.