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Discussion Starter · #1 ·
Does anyone know how far off the speedo is when compared to actual miles per hour when running stock tires in an 03? Also how did you come to this conclusion?



Thanks
Chris
 

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Seems to be around 5% or so from what i have noticed. I came to this conclusion as i have a scanguage installed which should be showing the speed as the ECU is reading it. At low speed it seems almost exactly what is showing on the guage but around 100kmph the guage is about 5-10kmph slower than what the scanguage shows. Cant say exactly as i prefer to watch where im going rather than watching the speed 100% of the time but there is a minor difference on the guage, which i have noticed on several cars i have used an OBD reader on and they all seem to have about the same % difference, and others have mentioned a similar difference in calibration.

Makes me think they are made this way on purpose to help you keep to the speed limit without getting a ticket if your needle is exactly on the mark.
 

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Mine reads 2mph faster, verified by gps.
 

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Discussion Starter · #5 ·
I realize that this is kinda a weird question but I have a speedo recalibrating box to compensated for different size tires and I am trying to get it as accurate as I can.



Thanks for the input
Chris
 

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Old school method.

If you have a safe area with a mile marked off,(like some states do on their highways) if you travel 1 mile in 60 seconds your speedometer should be reading sixty.
 

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... around 100kmph the guage is about 5-10kmph slower than what the scanguage shows.

Makes me think they are made this way on purpose to help you keep to the speed limit without getting a ticket if your needle is exactly on the mark.
If the speedo reads slow, that means you're going faster than you think (speed says you're doing the limit but you're actually speeding) and would therefore make you more likely to get a ticket....right?
 

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I got pulled over one time by a State Trooper for speeding. I had just replaced the tires on my CJ7 with a set one size larger. When I asked him if the different, i.e. larger, size tires had an effect on my speedometer he told me it would alter the reading by an average of 7-9 MPH. He clocked me at exactly 9 mph over the limit. He gave me a warning instead of the ticket because of my question and the obvious newness of the tires.
And BTW, when I first saw the title of this thread I thought it was going to be about swim wear.:confused:
 

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If the speedo reads slow, that means you're going faster than you think (speed says you're doing the limit but you're actually speeding) and would therefore make you more likely to get a ticket....right?
I wrote that the wrong way around... i meant the scanguage shows about 5-10kmph slower than the tacho. I have yet to confirm this difference with GPS however.
 
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