[urq] Speedo Accuracy

Thu Jun 16 12:29:51 EDT 2005

It may not be that they want you to slow down, as it's a law (not sure it's
German or Euro) that a speedometer can absolutely not show a speed lower
than actual.  Thus, the automakers build in buffers on the up-side.  Trip
computers, however, are not subject to these regulations ;-)

-----Original Message-----
From: Louis_Alain_Richard at computerhorizons.com
[mailto:Louis_Alain_Richard at computerhorizons.com] 
Sent: Thursday, June 16, 2005 12:22 PM
To: Pasqualoni, James E
Cc: 'Brandon Rogers'; urq at audifans.com
Subject: RE: [urq] Speedo Accuracy

Two comments about this:

The easy way to verify speedo accuracy is time divided by distance (yeah,
right !). Here in Quebec, on the highway, there is a km marker at each 1/2
kilometer. So I use the cruise control to keep the car at 120 km/h, and
measure the time to cover 2 kilometers. Then, the number of seconds I am off
from 1 minute is the speedo accuracy. Last time, just before the TSD rally,
I was off about 150 meters (over) for each 5 kilometers, that is 3%. Car was
riding 185/65R15 winter rubber.

WRT to speed accuracy, Car and Driver had a paper about this a couple years
ago and the conclusion was : car manufacturers are always optimistic (for
liability/legal reasons) and German cars were the worst, BMW being
constantly 10% high. However, distance from the odometer was dead right. So
they _know_ how to be accurate, they just want you to slow down...

Louis-Alain in rainy Montreal

             "Pasqualoni,                                                  
             James E"                                                      
             <james.pasqualoni                                          To 
             @gs.com>                  'Brandon Rogers'                    
             Sent by:                  <brogers at terrix.com>, Urq List      
             urq-bounces at audif         <urq at audifans.com>                  
             ans.com                                                    cc 

                                                                   Subject 
             2005-06-16 12:02          RE: [urq] Speedo Accuracy           

Funny you bring this up now, as I have been playing with this same issue on
our 3 VAG cars.  Here's what I've found:

83 UrQ-15x8 R-8's - usually around 3 mph over actual, up to a max of approx
5 mph off 03 Passat 4M Stock 16x7 rims - about the same difference as the
UrQ 05 S4 Stock 18x8 AVUS rims - Always runs 10% high.

For the UrQ, I had my wife follow me in her Passat, using her trip computer
to determine actual speed.  While testing both the Passat and the S4, it is
easy to look between the trip computer speed and the speedometer speed to
see the diff.  What a PITA-too much math...

Why do two stay a relatively static amount above actual and one a constant
percentage above?  Good question...

HTH,
Jim

-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf
Of Brandon Rogers
Sent: Thursday, June 16, 2005 12:04 PM
To: Urq List
Subject: [urq] Speedo Accuracy

Guys-
Data point here - I had the chance recently to drive by ( a couple times)
one of those neighborhood radar signs - you know - that tell you how fast
you are going - an appeal to your conscience..)  anyway I kept the speedo
right at 30 and got a readout of 27 on the radar sign - a couple times. This
is with new (3000 miles?) Dunlop SP 8000 225/50 15 on 8 x 15's.  Now if I
can just remember to keep the speedo at about 82 when I want to go 75. I'm
assuming it won't always be 3 off - but it will be about 6 off at 60 and so
on...anyone know different?

FWIW my A4 was right on.

Brandon

_______________________________________________
Audifans urq mailing list
Send posts to: mailto:urq at audifans.com
Manage your list connection: http://www.audifans.com/mailman/listinfo/urq
Have an urq question?  Check the Audifans Knowledgebase!
http://www.audi-quattro.org/cgi-bin/twiki/view/Audi/UrQuattro
Have an urq answer? ... Please help others by adding to the KB ... all
contributions welcome! _______________________________________________
Audifans urq mailing list
Send posts to: mailto:urq at audifans.com
Manage your list connection: http://www.audifans.com/mailman/listinfo/urq
Have an urq question?  Check the Audifans Knowledgebase!
http://www.audi-quattro.org/cgi-bin/twiki/view/Audi/UrQuattro
Have an urq answer? ... Please help others by adding to the KB ... all
contributions welcome!