Speedo off by 4-5 mph

[rhino1csm]

2001 NSX speedo reads 4-5 mph faster than actual speed. Running original wheels. Any thoughts on a fix? Is there a fix?


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[Old Guy]

Original wheels and tire sizes? If you can find your tires on Tire Rack, you should be able to find the revolutions per mile for the tire. You can compare that to the original RE010 tires. Just because the tire size is the same doesn't mean that the revolutions per mile is the same.

If the discrepancy in speed is not due to a change in tires, then there is a calibration potentiometer for the speedo on the back of the instrument cluster. The speedo cluster has to come out for the adjustment and you need a pulse source to calibrate the speedo (the service manual provides the pulse rate versus speedo reading). If you are the least bit tech savvy, getting a calibrated / adjustable pulse source is the easy part. You could use something like an Arduino to generate any kind of pulse rate you want. Getting the cluster out of the dash would be the painful part - my neck starts twinging just thinking about it.

 

[docjohn]

what are your tire sizes?.....how are you measuring actual speed?

 

[rhino1csm]

what are your tire sizes?.....how are you measuring actual speed?

Oem tires and wheels. Measuring speed with my phone GPS speedometer and my radar detector GPS speed indicator.


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[docjohn]

If your tires are worn down with little tread depth you might see that difference.

 

[jwmelvin]

That type of discrepancy is common. Can't have the speedo read lower than actual speed.