Speedometer Error

[Shaf]

My 2020 4S seems to have an inaccurate speedometer. It reads about 3mph high. I’ve checked against several sources so I’m quite sure it is off. Has anyone else experienced this and do you know if there is any correction. The tire size is set correctly.

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[MartyMeatball]

Pretty common. Most manufacturers err on the high side so they don't get in trouble with the bureaucrats.

 

[ciaranob]

My 2020 4S seems to have an inaccurate speedometer. It reads about 3mph high. I’ve checked against several sources so I’m quite sure it is off. Has anyone else experienced this and do you know if there is any correction. The tire size is set correctly.

As above but a 1-3 mph difference not uncommon when swapping out tire-wheel combos (e.g. wider tires) w/o re-calibrating the speedo - no idea if relevant to your setup?

 

[whan]

Common - our Ferrari is 3mph different, and our Mazda is 2mph vs. what google maps GPS says

 

[Midlifecrisis]

You will probably find it gets more inaccurate the faster you go. Maybe 1 mph at 20-30 mph and 3 mph at 70 mph. I think that is normal, although if your 3mph out is at 30mph speed then that is a bit more than I would expect

 

[Skilly]

common. You will notice that your odometer is on point though; it doesn't move through miles at that same accelerated rate.

As folks mentioned above, it's pretty standard.

 

[cometguy]

All three of my non-BEV Porsches have their speedometers set about 3 mph high... Standard Porsche thing...

 

[Skilly]

As above but a 1-3 mph difference not uncommon when swapping out tire-wheel combos (e.g. wider tires) w/o re-calibrating the speedo - no idea if relevant to your setup?

This is an inaccurate statement. Wider tires dont impact speedometer readings.

I see this statement a lot - common misconception. In fact, it's the OD that has any impact on speed readings. For example, a 325/25/21 has the same OD (revs per mile) as a 275/30/21

 

[ciaranob]

This is an inaccurate statement. Wider tires dont impact speedometer readings.

I see this statement a lot - common misconception. In fact, it's the OD that has any impact on speed readings. For example, a 325/25/21 has the same OD (revs per mile) as a 275/30/21

Sorry you're incorrect - a taller tire (my 'bigger' tire) will require a speedo recalibration - here is an example:

https://www.discounttire.com/learn/...MIsZuetd799gIV0xPUAR0QXQ0rEAAYASAAEgLlBfD_BwE

 

[Skilly]

Sorry you're incorrect - a taller tire (my 'bigger' tire) will require a speedo recalibration - here is an example:

https://www.discounttire.com/learn/...MIsZuetd799gIV0xPUAR0QXQ0rEAAYASAAEgLlBfD_BwE

Don't be sorry.

Yes a taller tire would require calibration because it would have an OD that would be larger than a tire that was "shorter". There would be no reason to do this though,...at least I can't imagine a good one.

Note what you said - you specifically mentioned a "wider" tire, which has no direct impact on OD unless you aren't changing the other factors in tire size (again, can't think of a practical example of why). I provided you an example where the tires are substantially different in width, but OD remains the same.

Most people match tire OD instead of opting for a recalibration of your speedo. When you start messing with OD, even in the slightest (and especially on an all wheel drive vehicles) you are begging for problems.

 

[ciaranob]

Don't be sorry.

Yes a taller tire would require calibration because it would have an OD that would be larger than a tire that was "shorter". There would be no reason to do this though,...at least I can't imagine a good one.

Note what you said - you specifically mentioned a "wider" tire, which has no direct impact on OD unless you aren't changing the other factors in tire size (again, can't think of a practical example of why). I provided you an example where the tires are substantially different in width, but OD remains the same.

Most people match tire OD instead of opting for a recalibration of your speedo. When you start messing with OD, even in the slightest (and especially on an all wheel drive vehicles) you are begging for problems.

 

[Jhenson29]

Tires/wheels can definitely affect speedometer accuracy. For example, i removed my wheels and now the speedometer reads 0, which matches very closely with my physical observations of the car.

 

[Dee]

There is a slight difference here.
Is it in % or is it standard 3mls off?
You can test this:
At 50 GPS, does it say 53 or 55?
At 100 GPS, does it say 103 or 110?
Do you know what I mean?

In the first case the presentation is off, in the second case the calculation is off (but ~10% is common)
Like myself, when I'm doing 259 it says 269 on the odo.

 

[Dee]

Tires/wheels can definitely affect speedometer accuracy. For example, i removed my wheels and now the speedometer reads 0, which matches very closely with my physical observations of the car.

Try that at 100mph and I'm curious about your findings.
You may be on to something here. ??

 

[tbinmd]

For Porsches it's normal for the speedo to read high. On my 993, the rate was variable, and also affected the mileage.

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