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I have been noticing now for a while and I was just curious if anyone knows the answer. When driving, if my speedometer reads, 55, and I set the cruise control, its says 56. It always seems to be a mile an hour slower then what I'm doing. Is it because the car is setup for 17" tires?
 

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The speedometer is calibrated but the needle is stuck on and can have some variation.
The right number is the cruise control. So your speedometer needle is off by one mph.
No one would care.
 

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The speedometer is calibrated but the needle is stuck on and can have some variation.
The right number is the cruise control. So your speedometer needle is off by one mph.
No one would care.
UNcalibrated from the factory!

“Speedometers are designed to never show speeds lower than actual speed.” Thomas Tetzlaff, Volkswagen Canada’s media relations manager, wrote in an email. “In order to do this... they will necessarily always show speeds slightly in excess of actual speeds.”

While speedometers are calibrated to fudge the numbers a little, odometers are designed to reflect accurate mileage, Tetzlaff says.
Source: http://www.theglobeandmail.com/glob...driving-as-fast-as-you-think/article11487709/


That's why when you compared GPS Speed vs Car... or worst motorcycle speedo (mine digital is 8% off from day 1 on my bike).

When it shows 60 mph you are never dead on... always slower (see US people suing car maker for a speeding ticket because speedo was off )

They voluntary make it show high speed... make you feel you go fast but in reality that's the reason you don't have a lot of overspeeding tickets issued.

Tolerance (displayed) is around 0% to + 10%
 

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That's why when you compared GPS Speed vs Car... or worst motorcycle speedo (mine digital is 8% off from day 1 on my bike).
My motorcycle was off 10%. I also had a Civic that was off 10%.
 

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IIRC, Germany has strict rules about speedometer error, even to the point that putting on any wheel/tire combination cannot allow the speedometer to show a lower speed than the vehicle is actually traveling. Consequently, speedometers in German marques like VW read "higher" than in most competing makes. So, given the source, you may not want to read too much into this comment.

Whenever I drive through a radar zone that displays speed with my domestic cars, the speedometer is spot-on.
 

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The speedometer is calibrated but the needle is stuck on and can have some variation.
The right number is the cruise control. So your speedometer needle is off by one mph.
No one would care.
First speeding ticket I ever got was doing 56 in a 55. Not doing 70 in a 55 and I'll reduce it to 56 in a 55, but an honest to goodness 56 in a 55.

I was too busy with college courses to try to fight it in court arguing about variance in mechanical speedometer readings.
 

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First speeding ticket I ever got was doing 56 in a 55. Not doing 70 in a 55 and I'll reduce it to 56 in a 55, but an honest to goodness 56 in a 55.

I was too busy with college courses to try to fight it in court arguing about variance in mechanical speedometer readings.
What city? Most police departments in Texas will not write unless you are at least 5 over and most I know are 10+ over. The judge would have thrown your ticket out. Judge threw out one of mine for 90/55.
 

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What city? Most police departments in Texas will not write unless you are at least 5 over and most I know are 10+ over. The judge would have thrown your ticket out. Judge threw out one of mine for 90/55.
Illinois at the time.
 

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My 2012 SE speedometer was exactly correct also.
I would say my ST speedo may be slightly off.. I have not really watched it vs the cruise enough to make the claim it is a certain 1mph over.. bit it may be close to that. say 1/2mph to 1mph over..
As for the 1mph speeding ticket. harassment.Plain and simple. For whatever reason the cop thought he was stopping you, he needed an excuse, and so the ticket. Maybe he thought you were someone else, or he hated college kids, or the make of car you drove... Most cops feel the need to give some sort of ticket if they stop a car.
Wayyyy back in the 1960s,, 5mph over was the limit or a cop could give one a ticket. Then by the 1980's it was ten mph over. Around here that is the 'unwritten law' 11 over and a ticket is possible..
 

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....
 

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Hi Guys,

well here in Aus my MK3 has 18" rims and to do 100kph I set me cruise control to 106. Does anyone know how to calibrate. I've looked at FoCCus but no luck with changes there.
 

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Hi Guys,

well here in Aus my MK3 has 18" rims and to do 100kph I set me cruise control to 106. Does anyone know how to calibrate. I've looked at FoCCus but no luck with changes there.
The size of the wheel has zero to do with speedometer.
The size aspect of the TIRE with that wheel is what matters... usually one can find the 'revs per mile (here in USA at Tire Rack site) and match revs per mile to get the same speedo calibration as the stock tire.

The general rule for change in wheel size is 5% in aspect ratio change per inch up in wheel size.

So for example: stock wheel: 16" with 205/55/16
go to a 17" wheel and then the tire you need is 205/50/17
and to a 18" wheel then a 205/45/18
If the tire gets wider too, then the aspect also adjusts (as it is a measured ratio of the tire width.)
So a 235/40/18 would be about the same total circumference as that 205/45/18

Tire rack USA site has all sorts of information on calculating the right tire size.. And you may even be able to find the difference from correct for YOUR setup so you can figure out the variance.
 

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OK But once I have all this information where do I put it to correct the speedo??
I don't believe the speedometer can be recalibrated; any adjustment will have to be in your head.

It would be nice if instruments like the speedometer, fuel economy, outside temperature, etc. could be adjusted by the owner, but I don't believe it's allowed by any manufacturer.
 
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