Speedo problem

[TDUBNRAE@xxxxxxx]

So I'm cruising back from a great superfast (85+ mph) autocross last Sunday at
Firebird Raceway in Phoenix and I notice I'm going about 110 mph.  I back off
just a tad when I approach some cars and instantly the speedo drops off to
about 80.  I push it up a few hundred rpms and it shows over 100 again.  I
reset the average speed on the OBC and it sows about 85.  I know from the
indicated revs that I wasn't going 110 earlier so I must be some speedometer
problem.  Any ideas?

PS This great autocross course has finally got me step up on do a real drivers
school.  Four years of "playing with the cones" is enough.

Thanks
Tony W
89 M3 - ten year old shocks and struts

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