Chevrolet Trail Blazer speedometer variance

[Gaurav]

Thanks guys, for all the help and yes indeed I will consider tire change to OEM size or slightly bigger to counter this speed variance.

Will only change the cluster, if it fails completely and not for this minor issue. Have a good day guys.

[salmanahmed]

On 6/24/2016 at 1:39 AM, taqir said:

Hi Gaurav, as I suspected it is true that your vehicle is fitted with slightly smaller height tire that might be resulting in this speed discrepancy.

Your tire size: 255/60R17    29.0x10R17    29.0"
Stock tire size: 245/65R17    29.5x9.7R17    29.5"

However this half inch must be causing lack of 2 kms plus the over-reading by default. My car over reads by 4-5 kms anyways.

I total agree with you on this one, if you increase the diameter of a tyre then that increases the speed of the car. The speedometer measures the rotation of tyre only, the diameter is already feed in its system. When the diameter increases that increases the total distance travelled per rotation. So depending on the increase in the diameter of the tyre, the actually speed can vary. If you use "low profile" tyres on a standard alloy rim then that will decrease the top speed of the car are the distance travelled per rotation will decrease. 

[Gaurav]

Thanks Salman for adding further useful information, that I'll remember while upgrading tires next time.