Mentioned this in another thread but figure I would start my own. I upgraded my wheels/tires from 275/65/r18 to 275/60/r20. I knew my speedometer would be off since I went with a slightly larger diameter tire than oem size. I downloaded an app to show my speed based off my cell phones GPS. My digital speedometer is right on with the gps speed on my cell phone app. My regular speedometer (with the needle) is off by a little over 1 MPH. This is what I was expecting and expected my digital speedometer to also be off by as much.

I'm not sure why they're off and leads me to this question, is the digital speedometer read in a different location than the regular speedometer? Why would they be different if not? Has anyone else noticed this when going with a larger tire? I specifically remember that the digital and regular speedometer read the same before I switched to different wheels/tires.

 

I've noticed my digital readout is different then the needle as well, this is with stock tires. I've never bothered to check with a gps to see which is correct though. It's probably off by around 3km/hr.

 

Digital speedometer vs GPS.. Analog speedometer matches digital speedometer exactly.

Digital speedometer:




GPS:

 

Stock tires and mine are different as well. Figured one was GPS and the other was of the truck. Doesn't bother me add I don't leave it up so never tried to figure it out.

 

Doesn’t really bother me either since I mainly use the digital speedometer anyways. Just thought it was strange.

 

Analog speedometer is as close to being correct as they can get it, that's why most police will let you away with a few MPH/KM HR if you are speeding. Digital is much more accurate as they do not have to adjust cables, springs, figure in width of a needle ect.

 

Mine is off too, I have seen several threads on this, seems to be very common. My truck was originally canadian so the digital speedo always defaults to KPH every time I start the truck so I never use it.

 

Digital to analog conversion is why your analog speedo is different. This is normal.

 

I think it's actually A to D (Analog to Digital). The difference would be in the error of the analog speedometer.

 

I wouldn't say that its "normal" as my wifes grand cherokee is identical between the two, as have been a couple other vehicles that ive owned.