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When I had a Grand Cherokee I had 2 sizes over factory tires, my GPS showed a difference of less than 2 mph vs my speedometer, I brought my Garmin along one day and it was within 1 mph of factory navigation, so I stopped worrying about tire size and speedometers, Also got a warning ticket for 65 in a 55 mph zone, when I saw him I looked at my GPS, 65 MPH,,lol
 

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I use those LEO radar units that post your speed as you drive by as another source. Funny thing is that my dash speedometer consistently reads about 3mph too high...and my OBD data displayed on my Kenwood headunit reads right on w/ the LEO radar unit. So...go figure.

Folks around here often assume their speedo & odo are calibrated together, and I'm saying they're somewhat independent of each other. ALL of this is confused by the 4x4 CC Frontiers that share the same axle ratios, yet are shod w/ different sized tires. P4X w/ 265/75-16 vs SV w/ 265/70-16. I don't think this issue is as black & white as one may hope it to be. .02
 

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My S with the 15" tires always indicated 3mph faster then actual, I've now got 255-70-16's on it and waiting to find one of those hi-way radar signs at construction areas so I can see if I'm closer to actual speed now.
 

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my dash speedometer consistently reads about 3mph too high
If it consistently reads 3mph too high as opposed to being a percentage too high, the needle on your cluster might be mis-positioned on the stepper motor. Have you ever compared the "parked" position of your speedometer needle to another Frontier?
 

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I use those LEO radar units that post your speed as you drive by as another source. Funny thing is that my dash speedometer consistently reads about 3mph too high...and my OBD data displayed on my Kenwood headunit reads right on w/ the LEO radar unit. So...go figure.
On my P4x with stock tires my analog speedo is dead on with the LEO and GPS. However, OBD speed reported is 3mph lower :) (i.e. 60mph on analog needle shows as 57mph on OBD). Seems like there may be a standard 3mph visual offset on the needle.
 

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On my P4x with stock tires my analog speedo is dead on with the LEO and GPS. However, OBD speed reported is 3mph lower :) (i.e. 60mph on analog needle shows as 57mph on OBD). Seems like there may be a standard 3mph visual offset on the needle.
VERY interesting.
How does your GPS vs dash Odo compare?
 

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VERY interesting.
How does your GPS vs dash Odo compare?
GPS matches analog needle. Analog needle seems exactly centered on 0 when stopped.


Sent from my iPhone using Tapatalk
 

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How about carefully watching the mileage markers whiz by on the hwy vs how far traveled using odo?
 
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How about carefully watching the mileage markers whiz by on the hwy vs how far traveled using odo?
I rode 11 miles on the interstate, staying in the right lane so I didn’t wander, using the small green markers. The odometer trip meter read 10.7 miles. I guess that tells us the odometer is using my OBD speed? I picked 11 miles so I could use markers that I hoped were accurately placed. (Like not near exit ramps or in active construction zones etc)
 

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I rode 11 miles on the interstate, staying in the right lane so I didn’t wander, using the small green markers. The odometer trip meter read 10.7 miles. I guess that tells us the odometer is using my OBD speed? I picked 11 miles so I could use markers that I hoped were accurately placed. (Like not near exit ramps or in active construction zones etc)
That's a ~3% difference that accounts for the slightly taller tires. Is it then safe to say the P4X is the exception and the SV's are the rule? (Tricky inference to say the least.) And, therefore your MPGs need a slight correction to be accurate since you are traveling a bit further than your odo indicates.

I'm in the same but different boat w/ my 4x2/6-sp/3.54 rear axle SV.
Rehash: my speedo overreports my actual speed by 3 mph while my OBD reports actual speed and odo is correct.

And then there's all the other iterations of Frontiers w/ different axle ratios that will vary (at times) w/ KC vs CC vs 4x2 vs 4x4 vs AT vs MT. Oh yeah = 🤪
 
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Yer all wrong. The ECM will calculate speed and send the signal to your speedometer and odometer by using engine RPM, Transmission rpm, and differential rpm to calculate vehicle speed, there is no mechanical equipment measuring speed on modern vehicles, the difference you see in tire size speeds is due to the parameters set in your ECM, speedometers in production vehicles are only accurate to with-in 3-5 mph, this is why LEO's cannot or do not ticket you for 5 mph or less over the posted limits, if they do and you don't fight that ticket you are crazy.
 

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by using engine RPM, Transmission rpm, and differential rpm to calculate vehicle speed
Huh. I figured the vehicle uses the ABS wheel speed sensors. My '98 F-150 had a mechanical odometer and used a speedometer gear. My '02 had a digital odometer. It had an interesting set up from what I recall. It had one wheel speed sensor in each front wheel, and a speed sensor on the rear driveshaft. Regearing it caused an ABS light until I got a Hypertech programmer to change the rear axle ratio in the ECM.
 

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Huh. I figured the vehicle uses the ABS wheel speed sensors. My '98 F-150 had a mechanical odometer and used a speedometer gear. My '02 had a digital odometer. It had an interesting set up from what I recall. It had one wheel speed sensor in each front wheel, and a speed sensor on the rear driveshaft. Regearing it caused an ABS light until I got a Hypertech programmer to change the rear axle ratio in the ECM.
Yea but it sounded good didn't it, ;=) What I posted was "in genera;" its done several ways, S10 I had was digital signal from the ring gear,,
 
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