I have a 2014 stock LC with about 39K miles. I haven't done any major modifications and still have the stock 285/60/18 tires and wheels (no lift, bumper, rack, etc.). I run the tires at the recommended 33 psi. Only modifications have been dual batteries and a compressor.
I've noticed in the 4-5 months since I've had my 200 that my GPS apps haven't lined up with the LC odometer. In particular, Waze consistently reads 2-3 miles under my LC odometer when I'm cruising on the highway. I had attributed the Waze app being a little off to just thinking it's not as accurate as the LC odometer. But, after this past weekend, I'm not so sure anymore. I was on cruise at 75 mph and went through a section of highway that had a few of the electronic radar signs with your speed readout. The two I passed through both read 72 mph (as did my Waze app). Assuming the Waze app and external radars were correct, what are some things that could be causing this discrepancy? Anything to be concerned about or no big deal?
You have independently discovered what I have been reporting for the past four years - your speedo reads fast while your odo is correct.
I have done a lot of speed/distance comparisons using various outboard GPS units (Garmin) of the onboard speedometer and onboard odometer with the equivalent values reported by GPS.
Observations:
1. With OEM P285/60-18 tires the Speedometer reads 2-3 mph faster than GPS; i.e. when GPS shows 72mph the onboard speedometer will show 74-75mph.
2. With OEM P285/60-18 tires the Odometer reads the same as GPS; i.e. when GPS shows 500 miles travelled the onboard odometer will also show 500 miles.
Interim conclusion #1:
With the OEM P285/60-18 tires the onboard odometer displays correctly the distance travelled, but the onboard speedometer reads faster than actual speed.
3. With larger diameter tires, specifically the LT285/70-17 tires, the onboard speedometer reads the same as GPS; i.e. when GPS shows 75mph the onboard speedometer also shows 75mph.
4. With larger diameter tires, specifically the LT285/70-17 tires, the onboard odometer reads fewer miles travelled than GPS; i.e. when GPS shows 500 miles travelled the onboard odometer will show only about 482 miles.
Interim conclusion #2:
With larger LT285/70-17 tires the onboard speedometer displays correctly the speed, but the onboard odometer displays fewer than actual miles travelled.
The simple explanation for this is that Japanese law mandates that auto makers in Japan design speedometers such that under no circumstances, with any tire recommended for use with their vehicles, shall the speedometer display a speed lower than the actual speed.
In our case, Toyota recommends two tire sizes for use with the Land Cruiser - P285/60-18 and LT285/70-17. The LT285/70-17 tire is approximately 3.8% larger in circumference than the OEM P285/70-18 tire.
The calculations:
72mph (GPS) * 103.8% = 74.7mph (Speedometer)
500 miles (GPS) / 103.8% = 482 miles (Odometer)
The reason the onboard odometer is accurate with the OEM P285/60-18 tires is probably because Toyota wants the odometer to be as accurate as possible when the OEM tires are used - expecting that very few owners (they obviously are not figuring in IH8MUD members in this) would fit different size tires.
My takeaway from all this is that with my LT285/70-17 tires, my speedo is displaying accurately and I'm enjoying more miles under warranty. Also, if one wants to accurately calculate gas mileage, one must correct the onboard odometer miles by the difference between the tires being used and the OEM P285/60-18 tires. In all cases, even stock tires, I have never found the onboard calculated mileage to be accurate - it is always optimistic, and by variable amounts. GPS miles / gas pump gallons is the best way to measure mileage.
HTH
