Dr. Jekyll goes over to the dark side... :-/
12-10-2005, 03:56 PM
#11
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Honestly, the best way to do that is with a GPS...
A LASER gun is only only practical for getting speeds over a short distance. A GPS will allow you to look at speeds over a much longer period of time and compare them to what the car is reporting.
I've used GPS to do this many times. In fact, anytime I ger a new tyre size I will do this to make sure the speedo is accurate.
Stephen
I've used GPS to do this many times. In fact, anytime I ger a new tyre size I will do this to make sure the speedo is accurate.
Stephen
12-10-2005, 06:17 PM
#15
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yep, that was my plan, but I keep forgetting my antenna in the S4 :o) One of these days I'll do it
as I previously noted here:<ul><li><a href="https://forums.audiworld.com/mk4/msgs/143.phtml">https://forums.audiworld.com/mk4/msgs/143.phtml</a</li></ul>
12-10-2005, 07:26 PM
#16
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Porsche speedo "error" is 10% up to 100 km/h and then a flat 10 km/h to redline...
Of course, this is optimistic. :-p
My own checks have been confirmed by many others. Basically, all modern Porsche follow this formula. They are exceedingly accurate in this "error".
So these aren't errors at all. Germany's TUV requires that the speedo never be pessimistic (no matter the conditions of the tyres). So the German manufacturers make all speedos slightly optimistic.
When I saw how optimistic Porsche was making their speedo I considered this deceptive. It makes the cars appear faster than they are. And if the odometer is also optimistic it would be cheating the customer out of some of his warranty coverage and residual value on leases (though now I think the odometer is actually accurate). I found that there was an SAE paper which provided guidelines on what was reasonable. And guess what, PAG had their speedos set to exactly the most optimistic setting allowed by the SAE paper.
So basically, the manufacturers have got together and agreed among themselves that X amount of cheating on the speedo is ok. Because they all agree, that has become an industry standard. And so they in turn are able to cheat their speedos by the standard amount. What is especially galling is that with today's technology they are able to get their speeds accurate within a mile or two per hour yet some manufacturers still take full advantage of this fudge (Porsche takes the speed at each individual wheel, discounts the unreasonable speeds - due to spinning wheels for example - and uses the remaining data to computer the speed).
Some manufacturers use the full fudge factor and some don't. When I checked my Audi I found it accurate within a mile or two per hour. I'll bet your Audi is also accurate but your VW is not. If I'm right, you will find the VW varies by a percentage to 100 km/h and then a flat amount. :-)
Anyway, the moral of the story is that you cannot trust the speedo until you have checked it with a GPS and determined its error rate. Calculating 0-60 MPH on a Porsche speedo will actually yield a 0-54 MPH speed which could take almost half a second off the actual time!
Stephen
My own checks have been confirmed by many others. Basically, all modern Porsche follow this formula. They are exceedingly accurate in this "error".
So these aren't errors at all. Germany's TUV requires that the speedo never be pessimistic (no matter the conditions of the tyres). So the German manufacturers make all speedos slightly optimistic.
When I saw how optimistic Porsche was making their speedo I considered this deceptive. It makes the cars appear faster than they are. And if the odometer is also optimistic it would be cheating the customer out of some of his warranty coverage and residual value on leases (though now I think the odometer is actually accurate). I found that there was an SAE paper which provided guidelines on what was reasonable. And guess what, PAG had their speedos set to exactly the most optimistic setting allowed by the SAE paper.
So basically, the manufacturers have got together and agreed among themselves that X amount of cheating on the speedo is ok. Because they all agree, that has become an industry standard. And so they in turn are able to cheat their speedos by the standard amount. What is especially galling is that with today's technology they are able to get their speeds accurate within a mile or two per hour yet some manufacturers still take full advantage of this fudge (Porsche takes the speed at each individual wheel, discounts the unreasonable speeds - due to spinning wheels for example - and uses the remaining data to computer the speed).
Some manufacturers use the full fudge factor and some don't. When I checked my Audi I found it accurate within a mile or two per hour. I'll bet your Audi is also accurate but your VW is not. If I'm right, you will find the VW varies by a percentage to 100 km/h and then a flat amount. :-)
Anyway, the moral of the story is that you cannot trust the speedo until you have checked it with a GPS and determined its error rate. Calculating 0-60 MPH on a Porsche speedo will actually yield a 0-54 MPH speed which could take almost half a second off the actual time!
Stephen
12-10-2005, 11:34 PM
#18
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Yes, I've found my S4 speedometer to be more or less perfect at any speed with 225/40/18 tires.
<ul><li><a href="https://forums.audiworld.com/s4/msgs/2047004.phtml">Click!</a></li></ul>
