'98 Instrument Accuracy

From: Joe Dille (joe@dille.montgomery.pa.us)
Date: Mon May 25 1998 - 14:27:48 EDT


Hi,

For what its worth, here is the the data for the accuracy of my speedometer and
the mileage computer in my 1998 2WD sport CC 5-speed with 3.55 SG. The last
mileage reading was with only highway miles at 60-65 mph and the gate down. It
may be a little higher than the actual mileage since I may have filled it a
little extra at the start of the trip.

All in all the computer reports the mileage at about 6% less than the actual
mileage. Not too bad. The last gas purchase was in NY, which explains the high
price!

                        Average MPG Error= -5.98%
                        Average MPG= 14.03
Miles Gals Cost $/Gal Actual MPG Computer MPG MPG Error
205 15.76 $15.75 $0.999 13.01 12.4 -4.9%
463 19.34 $18.75 $0.969 13.34 13 -2.6%
747 19.35 $19.95 $1.031 14.68 14 -4.8%
938 13.64 $15.40 $1.129 14.00 13.2 -6.1%
1124 15.11 $16.00 $1.059 12.31 12.3 -0.1%
1261 6.67 $8.00 $1.199 20.54 17.5 -17.4%

Speedometer checks

Indicated Actual Error
60 61.8* -3.0%
60 61.18 -2.0%
60 60.92 -1.5%
66 67.92 -2.9%
66 66.32 -0.5%
66 67.15 -1.7%
        Average Error= -1.9%

* Performed with GPS all others done with interstate mile markers

I also checked the accuracy of the speedometer over several sections on the
interstate using the mileage markers over a 2-4 mile stretch. I also used my
dad's aviation GPS which computes the speed and direction. The GPS reading is
comperable with the time and distance measurements. On average the speedo reads
2% low. Not too bad either.

The compass in the trip computer was right on.

Drive Safe,

Joe Dille

Telford PA USA
(joe@dille.montgomery.pa.us)



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