Originally Posted by bb700092

Thanks for sharing this useful thread. I have a similar issue as reported in the above thread by many.

My 2016 GS (purchased brand new) came from the factory with 225/50R17 tires. Most non-F-Sport 4GS come with 235/45R18 tires. The circumferences of the 17" and 18" tires are 81.24" and 82.71" respectively (ref. http://www.1010tires.com/Tools/Tire-...5R18/235-50R17), i.e. the difference in circumferences is almost 1.5" which is not insignificant.

To go one mile, the 235/45R18 revolves 14.3 times less than the 225/50R17. Thus, if the speedometer/odometer of my GS is tuned for the 235/45R18, it will show 1 mile has been covered when 14.3 times the circumference of 225/50R17 is still left to go. That is, my GS's speedometer/odometer is calculating 1.78% too fast. Therefore, when my speedometer shows 70 mph, I am actually traveling at 68.74 mph. However, I tested with two Garmin GPS systems and cell phone Waze app, and they showed even more difference. They consistently showed 66-67 mph when I am traveling at 70 mph on cruise control; this observation is in line with the thread above.

Last time when I went to my Lexus dealership for service, the loaner RX I received had a much more accurate speedometer than my GS. In the RX, I set the cruise at 70 mph and my GPSes showed 69 mph while my cell phone app Waze varied between 69 and 70 mph. So not all Lexus vehicles are equally affected.

If my odometer is off by 5% (i.e. shows 70 miles when it is actually 66.5 miles), I will lose 0.05x60,000 miles = 3,000 miles from my warranty which concerns me. I have reported this to Lexus corporate and they advised me to talk to my local dealership and get my odometer checked. When I requested my local dealership, they did not check anything (did not even touch my car) and said that what I am stating is within specifications and the odometer and speedometer get data from different sensors (so an error in the speedometer does not imply an error in the odometer) and that I am just being too nitpicky. At that time, my GS had about 2000 miles on the odometer, so tire wear is not a factor in the above observations. I had given up since that is the only Lexus dealership within three hours from my home until I came across the above thread.

To be continued ...

Originally Posted by bb700092

Here is my post from a related thread on this issue: https://www.clublexus.com/forums/gs-...0-f-sport.html

Originally Posted by Knucklebus

Testing that theory is pretty easy. If the speedo is off and the odo is correct, you lose nothing in warranty. Pick a stretch of road the next time you start a trip and at a mile marker, rest the odo trip to 0. After 10 miles see if 10.0 miles is with the 10th mile marker. If you can go 100 miles, your accuracy will improve.

I've done this on trips from KY to FL and the odo does seem to be closer than the speedo.

Originally Posted by bb700092

In your experiment from KY to FL, who decided the 10 (or 100) mile mark -- Garmin GPS, Waze app, Google Maps, or ...? In other words, what was your ground truth?