How do you fix a speedometer that's off? It' seems like it's 1 mph off at 60, really doing 59 and 2 mph off at 90, really doing 88. It's been off for a while but never realized how bad until my last time at the track. When I'm at the track, my speedo says 92.xxx when I cross the finish and my time slip says 90.xxx. When I went to the track last time, I could do a 0-90 run on my stop watch in like 13.5 seconds, I thought I would shatter my best time. I go to the track and do a 15.002 at 90.213 mph. It's disappointing to say the least when I thought I would do a 14.5 or 14.6 at 93.xxx and I do a 15.002 at 90.213. It's not the stop watch, I've got two and they both read the same times pretty much. I guess I'll start doing 0-61 and 0-92 runs to compersate. My tires are the same height as the stock tires, any ideas?
Jim

 

Your tuner should be able to take care of it!

 

If I'm not mistaken the speed on your time slip is calculated from point to point in the last part of the 1/4 so its an average of the last 60'.( That's from a track official at M.M.S.,he may be FOS though) . To accuratly calculate your speed use the mile markers on the freeway and your watch.Divide the no. of seconds it takes you to travel 1 mile into 3600. Mile markers may vary slightly so do this a few times,maintaining a constant speed is important so it may be tough at higher speeds. Example: 60 mph is 1 mile in 60 sec.'s, 80 mph will take 45 sec. and is an easy speed to average on the expressway. If you watch is off by a second it would gain or lose 24 min. a day. Not a knowitall, Just a trucker that's decent at math an seen a lot of milemarkers. Jim
3600 is the number of seconds in an hour.