My Scangauge II displays readings 2-3 miles per hour less than the vehicle's speedometer. My vehicle is a 2007 Toyota Corolla with 13,000 miles, no modifications, original equipment tires kept at recommended 30psi. The ScanGauge is kept at 0% adjustment for speed. Is it likely that I should adjust the Scangauge's speed to match the vehicle's speedometer or is it more likely that the vehicle's speedometer is inaccurate? The odometer mileage for TANK vs. the vehicle's trip odometer agree within 1 mile over 325 miles between fillups. Anybody have a similar experience?
Scangauge II Speed readings
- Thread starter tigrpal
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MY Scan Gauge is about 1 mph and right on with my 05 Corolla. This is also verified using a GPS.
Let me guess, Your Corolla is a S or LE model?
Take care, bill
Let me guess, Your Corolla is a S or LE model?
Take care, bill
I can just about guarantee that in a 2007 model year vehicle the speedometer is electronic and driven off the same data source that the Scangauge gets it's data. So it is virtually assured that your vehicle's speedometer is inaccurate.
Put another way, when the Scanguage says you're going 55MPH, it's getting that data from the same place the dashboard is.
Digital data representing the vehicle's speed is sent to both the dashboard and the Scanguage.
The Scanguage decodes this data in accordance with SAE specifications and displays it on a digital display. There is no room for error in that conversion process, it's simple math.
The speedometer, on the other hand, is taking this data and converting it to a pointer position for an analog display. The needle could be off a little bit in either direction, the needle positioning mechanism could be non-linear, the point is, whenever you convert from digital to analog you do have a greater potential for errors in the conversion, it's not perfect.
When you convert from digital to digital, barring some sort of hardware malfunction or a programming error, it's going to be 100% accurate. The chances that your Scanguage is suffering from either a hardware malfunction or a programming error are very, very small.
There is, of course, the analog-to-digital conversion which converts the vehicle speed into digital data, but any inaccuracies here would affect both the Scanguage reading and the analog speedometer reading in the same way.
How would I know?
The LE and S models have larger tires.
Larger tires = speedo off more.
CE has smaller tires = speedo right on.
When I need to replace my tires, I'll stay with the smaller tires for a couple of reasons;
1. Cost (after all I'd rather spend the extra $20-30 for oil! (Thats 25-30k miles worth of oil changes)
2. Better MPG for me.
3. For the times that I get caught in the snow before I change over, a smaller tire works better in the slush.
The speedos are all the same through out the line and everyone that I have talked to about the speedo being off (slow) has a LE and S models.
Take care, bill
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How you know it's not:
LE tires = speedo right on
CE has smaller tires = speedo off more?
Because I've done the following;
Compaired the speedo to a stop watch and mile markers and used a very accurate GPS.
Both show my speedo to be within 1 mph.
And the larger tires do cause yours to do what others have reported.
Whatever. Just trying to help.
Take care, bill
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It is common for a speedometer to read high. We usually saw a ~2 mph difference between speedo indication and VSS signal. I was told it was due to liability reasons pertaining to speeding tickets etc. Better to err on the side of safety rather than be sued because someone got a speeding ticket and blaming it on a speedometer/tire diameter combo that was slightly out of tolerance.
A variation in tire size would cause the same error on both the Scanguage and the speedometer. That there is a difference between the readings on the two is NOT due to tire size. You would need some sort of external reference to determine any effect of tire size on speedometer accuracy, be it a GPS or a radar/laser gun.
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