Speedo Discrepancy

mjonesjr84

WTF was that?
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I recently put a 4" lift and 33" tires on my 2000 (including SYE & driveshaft). At the same time I installed the green, 31-tooth speedo gear for 33" tires and 3.73 gears. According to the Torque App and GPS, my speeds are dead on. However, the gauge cluster is off by 1-3 mph depending on the speed. I would assume the Speedo is getting the same signal that the OBD2 port is for the Torque App to read.

Is there any way to make the speedo in the dash more accurate?
 
That 31 tooth speedometer is the right choice for 33's and 3.73, you're not going to get it any closer than that with a speedometer gear change.
 
That 31 tooth speedometer is the right choice for 33's and 3.73, you're not going to get it any closer than that with a speedometer gear change.

The speedo and GPS is dead on with the 31-tooth. My problem is that the dash isn't reading the same that the OBD2 port is seeing. I'm reading speed via the Torque app and a OBD2 Bluetooth adapter. However, the dash itself is off. That's what I want to fix.
 
The speedo and GPS is dead on with the 31-tooth. My problem is that the dash isn't reading the same that the OBD2 port is seeing. I'm reading speed via the Torque app and a OBD2 Bluetooth adapter. However, the dash itself is off. That's what I want to fix.
I realize it was your speedometer itself that is off, it's as good as it's gonna get since you have the right speedometer gear installed. Tire circumferences can vary slightly which affect the speedometer, I would not look for or expect perfection at the speedometer.
 
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I realize it was your speedometer itself that is off, it's as good as it's gonna get since you have the right speedometer gear installed. Tire circumferences can vary slightly which affect the speedometer, I would not look for or expect perfection at the speedometer.

Thanks. I wasn't sure if there was something else I could do to make the dash more accurate since the reading it is getting is. Appreciate it.
 
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I would imagine there's a company or two out there that do instrument cluster repair. The speedo is essentially a motor that responds from signals from the PCM.

Question of course is how expensive would that repair be vs living with the discrepancy.

-Mac
 
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I can't speak specifically to the TJ as I have not tested it, but in other vehicles, specifically Nissan and Toyota trucks, there is a discrepancy between the odometer and speedometer. They both come from the same source (speed sensors), but in my trucks, an accurate odometer (based on GPS tracking miles for 30 minutes or more), ends up with the speedometer reading fast by about 2-3 mph at highway speeds. On those same vehicles, when the odometer is correct (and dash speedometer subsequently reading a bit fast), the OBD speed reading is actually correct. So the vehicle knows what the correct speed is, yet the dash gauge reads a bit fast.

I believe this is fully intentional by the manufacturers to help provide a speeding buffer. I would assume the same happens on the TJ. Where a perfectly accurate odometer (likely accurate in stock form) ends up with the speedo itself reading a bit fast. I would assume this is what you are facing and it is probably the same on all TJs, folks just don't notice it because they usually correct the speedo to where the speedo itself is accurate and don't pay attention to the OBD speed itself, or the odometer and how many miles it tracks vs actual logged by GPS.
 
I recently put a 4" lift and 33" tires on my 2000 (including SYE & driveshaft). At the same time I installed the green, 31-tooth speedo gear for 33" tires and 3.73 gears. According to the Torque App and GPS, my speeds are dead on. However, the gauge cluster is off by 1-3 mph depending on the speed. I would assume the Speedo is getting the same signal that the OBD2 port is for the Torque App to read.

Is there any way to make the speedo in the dash more accurate?

Ignore it and drive, why sweat the small stuff.

Mine is off by 5mph and I just adjust my driving habits.
 
I believe this is fully intentional by the manufacturers to help provide a speeding buffer...

I agree with this assessment. On 100% of the vehicles I've checked with a GPS, probably two dozen, the speedo reads dead accurate or higher, but never lower. A manufacturer can't get sued for a speedo which gets you a speeding ticket if the speedo is always off in the "safe" direction.

I believe the US standard for speedometer accuracy has words to that effect, but since those standards seem to live behind a paywall, I can't verify that. SAE J2976_201602 and SAE J2976_202205
 
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