Speedometer error

[smartxs]

Originally Posted by tonymcpa

Just wondering if everyone has the same experience....

I finally had a chance to get the GPS in my smart and noticed at 50+ mph or so the speedometer is 3 or 4 mph lower than the reading on the GPS.

Even the Scangauge reading is 2 mph higher than the speedo.

Am I imagining things? Anybody else?

reads Lower or Higher? On my recent trip from SF to LA, CA my GPS consistently read out slower than the Speedometer. When the Speedo read 92 actual speed was 90 on the money and governor was cutting in. the error seemed to remain constant from 60 on up to top speed, meaning the speedometer was 2 MPH faster than actual throughout the range.

Since I had a lot of time (about 6 hours), I also timed the miles to check the speedometer vs the GPS. Gps was correct. Yah know what I didn't think to check though was the Odometer! wait! the GPS reads 1633 miles and the ODO reads 1685. Now, don't think there is an error because of this, the car had over 48 miles on it when I installed the GPS, and it easily could have been 52 by the time I actually finished testing the head unit and fully connected the GOS antenna.

I think they are both so close, it shouldn't be a concern like it was with Honda. My CRV and Pilot were both wildly optimistic, just like their gas mileage estimates.

[tivoboy]

I have the feeling that the ODOMETER is off as well, I think the smart thinks I am putting MORE miles on it than ACTUAL. I don't mean this as a joke!

[meaux61]

As I said, my GPS and Scanguage say 2 or 3 miles faster than the speedometer does.
For instance, when the Speedometer says I am going 65, the other two say 62.
I wonder if I should add a few miles to my calculations when I figure gas mileage, at this rate, each hour of driving, I actually drive 3 miles more than it records. It could explain why I usually get 37-39 mpg eh?

Meaux

[Quagmire]

Soooo... Does this mean that the 10,000 mile oil change is actually only 7,000 miles? The 24,000 mile warranty is only 21,000? The car doesn't go as fast as we think it does?

[tivoboy]

so, I did a GPS test today, two GPS devices. the CAR reported about 1.5-2 mph FASTER than actual, I think this is their way of getting us to drive slower and save fuel.

[RussBarnes]

These errors, especially in the odometer, show that your calculated mpg is also wrong. After changing to larger tires my speedo is right on but odometer now reads 5.6% low so I multiply the reading by 1.056 to get real miles traveled.....I used GPS to check speedo and minimum of several 20 mile runs on interstates to verify odometer.

[NCC1701]

Just got my scangauge today. My speedometer reads a few MPH Higher than the scangauge.

[Karl Roth]

Originally Posted by wahi

My speedo reads 2 mph more than what my scangauge's telling me.

that is typical most (all cars not just our smarts) read less than actual speed
karl

[WickedMessenger]

The SAE (Society of Automotive Engineers) specifications for automotive speedometers and odometers allow a surprisingly large tolerance for accuracy. They allow a 4 mph variation (+/-2 mph) at any particular speed. Measuring speed (and therefore miles) is a difficult thing because of ambient temperature (+/-2.5% between 20 and 130 deg.), tire growth (3% change in revolutions per mile between 30 and 90 mph), centrifugal effects (-2mph at 90 mph), tire wear and resulting change in radius (+2.5 mph at 90 mph), speedometer design limits (+/-2 mph at 90mph), and tire inflation pressure (1mph for every 6 psi increase). Before you go adding all these together, remember that it wouldn't happen that all the extremes exist simultaneously. And some are self compensating. Nevertheless, measuring vehicle speed is hard to do. The GPS is very accurate. But don't expect too much from your dashboard.

[SmartWillie]

OKay, My Speedo shows 65 when the gps is 62. Thus I only really go 62 miles in an hour and my miles per gallon are less. If I burn 1.5 gallons per hour, then the mpg = 43.33 on the Speedo and I really get 41.33 via the gps.

This is a laugh any way, because I only get 33 to 37 mpg so far. Still fun to drive.

Willie