Speedometer calibration after tire and wheel size change?

[jamesavery22]

Has anyone else addressed this? SR5 with stock tires is consistently 2-3mph faster on the speedometer than GPS. I won't be putting larger tires on. Is there any calibration that can be done?

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[TrailAdventurer]

I doubt the speedometer is 100% GPS based, but maybe it can compare the speed based on wheel speed vs. the GPS speed periodically, and re-calibrate itself for a new wheel size?

Vehicle speedometer is not determined using GPS. It's determined using the same sensor used for ABS. The wheel speed sensor informs the ECU how fast each wheel's going at any moment in time.

For me, going from OEM to 34s on Riddick, I noticed a moderate change. Vehicle speed is consistently overstated 2-3 MPH compared to GPS.

There are various sites that discuss this, including Tacoma World, Toyota Parts Center, JD Power, and so on. In one article, it indicated it's a rear wheel that is used.

 

[DENNISD]

Has anyone else addressed this? SR5 with stock tires is consistently 2-3mph faster on the speedometer than GPS. I won't be putting larger tires on. Is there any calibration that can be done?

I have owned many Toyotas and all of them showed that I was going at least 1 mph faster than I actually was. I have heard that Toyota has engineered their vehicles to do this on all of their vehicles. Not sure this is totally true but it has been consistent on my end. I think they are erroring on the safe side so to speak for legal reasons.

In any event, if you are placing larger diameter tires/wheels on you vehicle you may actually be spot on with the MPH after the fact.

 

[24TacomaGirl]

All manufacturers always err on the side of caution and conservative readings for legal and liability reasons where mechanical systems are used. Because of this, yes, the factory reads high (overstated speed vs actual) when stock and in fact can become spot on with the larger tires removing the intentional slack from the readings. And then with larger and larger it will continue to deviate past spot-on as would be expected.

 

[HardCorTaco]

I just did a speedometer test on my truck. I have 34” tires on my truck. The tire size is 285/75/r17. When the truck said I was going 65 MPH I was actually going 68. I have a speedometer calibration tool on order. Is anyone interested in watching a full length video on the install?

 

[BLtheP]

The truck is calibrated for the Speedo to be accurate on 33’s and the odometer to be accurate on 32’s. It’s a compromise between all the stock tire sizes.

245/70R17 (31”) - 3.5-5 mph fast at 70, odometer slightly fast

265/70R17 (32”) - 2-3 mph fast at 70, odometer accurate

265/65R18 (32”) - same as above

265/70R18 (33”) - spot on Speedo, slightly slow odometer

Non stock:

285/75R17, 285/70R18, or 34” - Speedo 2-3 mph slow at 70, odometer a bit slower than 33’s


It’s really not that complicated of a concept but one has to be paying attention and catch it to understand the nuances.

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