Speedometer Calibration
03-21-19, 04:45 AM
#1
Pit Crew
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Speedometer Calibration
I like to run winter tires on my car during winter, and right now I still have them on my stock 19" wheels. I need a new set of all season tires before I take them off, but I'm hesitant on getting a set of 19" tires then going through the process of having to swap every November and March. I have a set of 18" Continental all season tires (nearly new) in my garage, which I used for my wife's Acura TL. Luckily, I had placed winter tires on the car shortly before she totaled it back in December. My question is, if I decided to pick up a set of 18" wheels and just use those Continentals (outside of winter) is there a way to calibrate the speedometer to compensate for the size difference? I normally wouldn't care, but I do a lot of driving (usually 30-35k/year) and I'd rather not have the odometer adding extra miles when I'm using the 18" wheels.
03-21-19, 05:26 AM
#2
If you get the correct tires on your 18s, the overall diameter of your 18s should be about the same as your 19s.
For example, my 18s and 19s only have about 1% difference in speed. So at 100 mph, I'm only 1 mph off.
For example, my 18s and 19s only have about 1% difference in speed. So at 100 mph, I'm only 1 mph off.
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Cobra611 (03-21-19)
03-21-19, 06:34 AM
#3
Lead Lap
Don't believe there is any way to change how the speedometer operates. As fellow member @AsianxWu mentioned, keep it within the same OEM specs for the wheels/tires and you wont need to worry about the difference since it will be very minimal:
Just as reference, the AWD GS comes with the following non-staggered OEM tire sizes:
18": 235/45/18 (Premium & '13-'15 Lux Models)
19": 235/40/19 (F-Sport & 2015+ Lux Models)
1010 Calculator has a helpful tool that shows the speed difference between the OEM 19 and OEM 18 sizes as being "0.28% too fast"...that means that if you drove all 35,000 miles on the smaller 18s, you'd put an extra 100 miles total which even Lexus has deemed negligible:
https://www.1010tires.com/Tools/Tire...ismetric=False
Just as reference, the AWD GS comes with the following non-staggered OEM tire sizes:
18": 235/45/18 (Premium & '13-'15 Lux Models)
19": 235/40/19 (F-Sport & 2015+ Lux Models)
1010 Calculator has a helpful tool that shows the speed difference between the OEM 19 and OEM 18 sizes as being "0.28% too fast"...that means that if you drove all 35,000 miles on the smaller 18s, you'd put an extra 100 miles total which even Lexus has deemed negligible:
https://www.1010tires.com/Tools/Tire...ismetric=False
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Cobra611 (03-21-19)
03-21-19, 07:36 AM
#4
What is the size of those 18s?
03-21-19, 08:14 AM
#5
Pit Crew
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Cobra611 (03-21-19)
03-21-19, 08:49 AM
#7
Those 18s are actually taller than the 225/40/19s, and will actually add less to your odometer. Difference in circumference is approx +1.1%, which means that if your odometer reflected 30k miles driven, you actually travelled 30,330. Or vice versa, if you travelled 30k miles, your odometer would show 29,673. Not enough of a difference to be material.
Now these numbers are all academic and may not be realized in real world experiences, because there are variables that cannot be perfected.
- the tires may actually be a little taller or shorter depending on manufacturing tolerances, or
- the speedometer may not be accurate to begin with.
Don’t spend too much time analyzing this, just go out and enjoy your GS!
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Cobra611 (03-21-19)
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