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2007 Kia Sportage EX Luxury
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8 Posts
Discussion Starter #1
According to my speedometer, I was driving 65 MPH but my GPS said I was going 63 MPH. With my other SUVs, the GPS and the speedometer are more accurate.
 

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Cerato S Hatch Auto
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1,236 Posts
The roughly 3% error that you noticed is quite typical. Car makers are generally required to make sure that the speedo doesn't read slow, so they make it slightly optimistic. This also allows for the 1% variation that occurs due to wear during the life of the tyre.

And yes, the GPS speed is accurate; it's not a simplistic "point-to-point" speed (which would be inaccurate), but a continuously updated parameter. I've tested my GPS against accurate road markers and a stop-watch, and its well within ±1 km/h which is the readout precision of the GPS. My mobile phone gives a rather ambitious precision of ±0.1 km/h and this is in agreement as well.
 

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2008 Kia Sportage 2.0; 2000 F150 Lariat 4X4; 2006 Chevy Trailblazer
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57 Posts
The variance is why the police give you ten miles per hour over speed limit, before they start ticketing. You can not expect precision accuracy, from a mass produced analog speedo. I mean, it is a KIA for crying out loud, not exactly the top of the food chain.
 

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2009 Sportage LX V6 4WD, 2011 Mack GU813 405M
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62 Posts
i noticed the same thing after i put my magellan in the sportage, the focus i used to own and the gps were bang on (or close enough), but the speedo in the spoetage is about 5% optimistic. the tires had been replace before i bought it, so i figured their overall diameter was maybe smaller the the factory ones.

had a similar problem with my 88 YJ. took out the 3.73 gears and put in 4.10, which made the the speedo read high (due to higher driveline speed), then did the lift and 31" tires (to replace the 28's), and that leveled it out (according to the radar "your speed/posted speed signs" in my area at the time)
 

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Cerato S Hatch Auto
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1,236 Posts
Our KIA at +2% has the most accurate speedo in the fleet. Maxima is +7%, so paying twice the price doesn't help.
 

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2009 Sportage LX V6 4WD, 2011 Mack GU813 405M
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62 Posts
my mack roll off speedo reads 1kmh fast vs. the gps, so price isnt relevant, $250000 and its still wrong

im sure it the drive tires, but either way, same tire size that was on went back on,
 

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Cerato S Hatch Auto
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My mack roll off speedo reads 1kmh fast vs. the gps, so price isnt relevant, $250000 and it's still wrong

I'm sure it's the drive tires, but either way, same tire size that was on went back on.
1 km/h (1% at 100 km/h?) isn't much. Tyres wear by about 1% during their life, and different brands probably also vary a little. Inflation will vary effective diameter.
 

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2009 Sportage LX V6 4WD, 2011 Mack GU813 405M
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62 Posts
1 kmh regardless of speed (therefore, no percentage can be applied as it constanly changes), i know of the rotational difference in overall tires size, but consistantly 1 kmh, even after all the drives were redone. ever since i took over that truck(a year ago) the speedo has been off by 1 kmh. just trying to make the point, that regardless of vehicle price, discrepencies do exist
 
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