Speedometer Offset

[Lo Tek]

So - digital speedo reads consistently 1-2 mph faster than “analog”. Have ruled out parallax, etc. Difference does not appear to scale with speed - virtually the same difference from 10 mph to 80 mph. Analog is on the money with GPS, although set tire size is about an inch larger than actual (which I realize would count for about a mile per hour on the digital side, but should scale with speed…?)

Anyway just curious if anyone else else’s speedo have this apparent offset?

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[GuzziMoto]

So - digital speedo reads consistently 1-2 mph faster than “analog”. Have ruled out parallax, etc. Difference does not appear to scale with speed - virtually the same difference from 10 mph to 80 mph. Analog is on the money with GPS, although set tire size is about an inch larger than actual (which I realize would count for about a mile per hour on the digital side, but should scale with speed…?)

Anyway just curious if anyone else else’s speedo have this apparent offset?

Both our JKU and our JT do that, with the JT being slightly further off. It seems like it is just a matter of the needle being slightly offset, as you point out it is not off by a percentage but off by a couple mph.
My take is the digital reading is the actual reading, and the needle is just slightly off. If you reset your tire size for larger tires use the digital speed reading to confirm you are accurate, that way your odometer will also be accurate.

 

[Free2roam]

My tire size was .40 difference. Cop sai I was doing 75 in a 65. Yet I was on gps at exactly 71 on cruise at 71 and every road or construction sign said exact reading I was going. They dropped the ticket from speeding to illegal parking and no points. Cock suckers either way.

 

[Lo Tek]

If you reset your tire size for larger tires use the digital speed reading to confirm you are accurate, that way your odometer will also be accurate.

Well, yes … but factory tires were 31, current tires are 31, and the set size from the factory (and current) is 32.6 … guess I need to dig out the revs per mile calculator.

Thanks for the confirmation that you see the difference on yours, I think I’ll ignore it now.

 

[CrazyCooter]

My tire size was .40 difference. Cop sai I was doing 75 in a 65. Yet I was on gps at exactly 71 on cruise at 71 and every road or construction sign said exact reading I was going. They dropped the ticket from speeding to illegal parking and no points. Cock suckers either way.

That was better than speeding and a moving violation, but how can they justify a parking ticket when you were traveling at 71mph?

 

[GuzziMoto]

Well, yes … but factory tires were 31, current tires are 31, and the set size from the factory (and current) is 32.6 … guess I need to dig out the revs per mile calculator.

Thanks for the confirmation that you see the difference on yours, I think I’ll ignore it now.

If the digital reading is accurate, that is what I would be concerned with. The needle being off, that seems to be normal.
There is some grey area around tire sizes, from the tire size listed in the specs to the actual tire size to the size you need to enter into the vehicle to get the speedo to read right. Those three values are not the same values. For any given tire those three values are three different numbers.
As long as the digital speedo reading matches what a stand alone GPS says (don't trust the built in GPS for that, they tend to get their speed from the vehicle), you should be good.

 

[Lo Tek]

If the digital reading is accurate, that is what I would be concerned with.

I’m an old fuddy-duddy. I tend to ignore the digital most of the time other than setting cruise speed, and I’d rather be on the low side than high for that one.

 

[GuzziMoto]

Well, I would bet a donut that if your digital speedo matches the speed shown on a stand-alone GPS not only is your speed right but your odometer and tripmeters would be right. If your actual speed matches your needle and not the digital reading it is likely your odometer and tripmeters are off.
On ours, both of them have the needle reading slightly faster than actual. It sounds like you are saying your needle reads lower than what the digital reading is, which would mean your odometer and tripmeters are reading low.

 

[Bindul]

So - digital speedo reads consistently 1-2 mph faster than “analog”. Have ruled out parallax, etc. Difference does not appear to scale with speed - virtually the same difference from 10 mph to 80 mph. Analog is on the money with GPS, although set tire size is about an inch larger than actual (which I realize would count for about a mile per hour on the digital side, but should scale with speed…?)

Anyway just curious if anyone else else’s speedo have this apparent offset?

Yes, this fixed 1–2 mph offset is common, caused by a fixed integer rounding or display offset in the digital cluster rather than a scaling tire-size error.

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