speedometer correction
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My Nitto Terragrappler 285/65/18s give me pretty much perfect actual/indicated.
You probably know all this but by default the factory set safety margin the speedo over-reads by approx 3% (higher than actual road speed.) This means with standard 18" rims on 285/60 tires you only travel 63 miles in one hour when your speedo suggests you should have travelled 65 miles. (as a matter of interest your odometer is corrected to actual distance)
So you need to increase total wheel perimeter length by 3% over stock perimeter to make actual speed equal indicated speed.
Stock perimeter 285/60/18 is about 99 inches. So you need to add about 3 inches to perimeter length. This works out to about 1.1 inches of overall tire height. Increasing profile by 5% on a 285 wide tire gives you this almost exactly. i.e 285/65/18 profile.
275/70/18 should make it under-read by a very small margin.
Only downside is a small deterioration in fuel economy I guess.
You probably know all this but by default the factory set safety margin the speedo over-reads by approx 3% (higher than actual road speed.) This means with standard 18" rims on 285/60 tires you only travel 63 miles in one hour when your speedo suggests you should have travelled 65 miles. (as a matter of interest your odometer is corrected to actual distance)
So you need to increase total wheel perimeter length by 3% over stock perimeter to make actual speed equal indicated speed.
Stock perimeter 285/60/18 is about 99 inches. So you need to add about 3 inches to perimeter length. This works out to about 1.1 inches of overall tire height. Increasing profile by 5% on a 285 wide tire gives you this almost exactly. i.e 285/65/18 profile.
275/70/18 should make it under-read by a very small margin.
Only downside is a small deterioration in fuel economy I guess.
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gaijin
GOLD Star
My experience is the same as Billfish.
With my stock tires, the speedo indicated faster than actual speed.
With my 285/70-17 tires, the speedo is within 1 mph at 65 - indicates 64mph for actual 65mph.
Actual speeds are verified with a stand alone Garmin GPS.
I just tell the cop that my tires are bigger and it's the tire manufacturer's fault.
John
Next Toy
I've got 285 bfg ko and friendly neighborhood radar has mine pegged perfectly.
Did you know you can set up the GPS on board to display your speed in real time?
gaijin
GOLD Star
No. How do I do that?
I know I can select current speed on the CID, but that is the same (incorrect) speed as the speedometer.
For testing actual road speed against speedo indicated speed do the following:
Turn the ignition off. Then without putting foot on brake turn ignition on. Now hold down the 'Display' button on the head unit and turn your parking lights on and off 3 times quickly. Oh and remember to pinch your right ear lobe in your left hand while you do this.
The head unit will now go into full setup mode and you can option quite a few things. One of them allows you to display the current speed as read by the GPS. Sitting still it will obviously read as zero. But you can now start the car (yes, you can let go of your ear now) and it will stay in this mode. Now as you move the actual speed will be displayed and you can check it against your speedo. (I think it returns to normal mode by pushing the setup button again or when you turn the ignition off. - can't remeber but one or the other.)
Note: For forum members that live in Southern Hemsphere like me you need to reverse the 'pinch procedure' and pinch your left ear lobe with right hand since we are upside down compared to that lot up there.
Would I lie to you?
Turn the ignition off. Then without putting foot on brake turn ignition on. Now hold down the 'Display' button on the head unit and turn your parking lights on and off 3 times quickly. Oh and remember to pinch your right ear lobe in your left hand while you do this.
The head unit will now go into full setup mode and you can option quite a few things. One of them allows you to display the current speed as read by the GPS. Sitting still it will obviously read as zero. But you can now start the car (yes, you can let go of your ear now) and it will stay in this mode. Now as you move the actual speed will be displayed and you can check it against your speedo. (I think it returns to normal mode by pushing the setup button again or when you turn the ignition off. - can't remeber but one or the other.)
Note: For forum members that live in Southern Hemsphere like me you need to reverse the 'pinch procedure' and pinch your left ear lobe with right hand since we are upside down compared to that lot up there.
Would I lie to you?
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Bill how about that diagnostic / setup mode for those of use without a setup button? 2008 version. Any ideas?
Probably one of the other buttons I'd guess. You could try Youtube or Google.
I think the forerunners or 08 lexus models have a similar procedure. Most toyota head units work the same although some require you to hold your finger on a point on the screen (lower left or something.)
I think the forerunners or 08 lexus models have a similar procedure. Most toyota head units work the same although some require you to hold your finger on a point on the screen (lower left or something.)
gaijin
GOLD Star
Not sure if this applies, but in my '13 there is an option in the settings for speedo calibration and my speed is dead on with the radar readouts now
are you serious? I have a 13, where is it in the settings?
Hard to find...
Setup > Navigation > detailed Navi settings > calibration > tire change
Setup > Navigation > detailed Navi settings > calibration > tire change
gaijin
GOLD Star
Based on my experience, all that calibration does is adjust the "Dead Reckoning" feature of the NAV display. When there is no GPS signal, like in a tunnel for example, the NAV display will continue to display vehicle position based on dead reckoning data calculated from wheel sensors and steering angle sensors. This "Calibration" fine tunes this data after installing a new set of tires.
It does nothing to affect the speed displayed by the speedometer or the CID.
That may be the case, but my speedo is matching exactly with the radar speed units put up around town. I'm 1.5" larger than stock which is approx 5%. So it could be that the factory unit was 5% over, but is suspect that is wrong given the electric odometers. I'd bet they get verified against actual gps data to protect against mileage tampering for warranty issues. Also these come with various sizes across the models & packages globally, so it would make sense that there would be an easy way to update the setting without a programmer
I'm guessing it would only change the "Dead Reckoning" like gaijin suggested, otherwise people could manipulate mileage by choosing different size tires and extending their factory warrenty...
the flip side to that coin is by putting on larger tires and not resetting the mileage you actually extend your warrenty also
gaijin
GOLD Star
It would make sense, but unfortunately is not the case.
I run two complete sets of wheels/tires.
Set #1 is the stock 285/60-18 wheels/tires that came with the truck when new. Tirerack.com says they do 661 revolutions/mile: http://www.tirerack.com/tires/tires.jsp?tireMake=Bridgestone&tireModel=Dueler+H%2FT+D684+II&partnum=86VR8HT684II&vehicleSearch=false&fromCompare1=yes
Set #2 are the 285/70-17 wheels/tires in my sig. Tirerack.com says they do 635 revolutions/mile: http://www.tirerack.com/tires/tires.jsp?tireMake=BFGoodrich&tireModel=All-Terrain+T%2FA+KO&partnum=87R7ATAKORWLV2&vehicleSearch=false&fromCompare1=yes
Even though I do the calibration each time I change the sets, the speedometer readout is always the same - Set #1 reads faster than my Garmin GPS and Set #2 reads slightly slower than my Garmin GPS.
I can determine no evidence that the speedometer/odometer are "adjusted" or "calibrated" in any way after performing the calibration procedure on the NAV.
In a 2010 LC I still cannot find the MPH in Nav. Was this setup feature available in 2010?
