I've always kind of noticed this around town, it's seems off by 1 mph. When I go by one of those cop radar "your speed is" signs, I'm always 1 mph slower than my speedo (speedo 35 & radar 34). Well driving to Oregon last weekend, HWY 5 has some of them in a curvie section of the road, through the Lake Shasta area. The signs warn you of a big curve and have a suggested speed and a radared "your speed" also. My truck said 71 mph on the speedo using cruise control and two different radar signs said 69 mph. I've noticed this at the track too, when I finish a run, my speedo says 92 mph and my time slip is always 90.+++. How can I correct this? The 255/70R16 tires are 30" tall, can I use my HPP and put the tire setting on 30". The factory setting should be this also but I'm wondering if I actually set it using the HPP would help. Don't want to go to the dealer ans shell out some $$ for a minor thing like this since I'm out of warrenty. Any thoughts?
Jim

 

well, mine speedo shows is off too.
i have 2" taller tires than stock, so if it says i'm going 40, i'm really going like 43 i think that online calculator says... so i just go slower to compensate, but sometimes you do forget about it. i wonder if the dealership would program it for you? if so, wonder how much they'd charge? i dont want to buy any kind of programmer until after X-MAS

 

Maybe if you had 100% tread, it would be right but I am not sure <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Maybe if you had 100% tread, it would be right but I am not sure
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Hey Stephen! That's the thing, the tires are brand new, only a month old. It's not that big of deal really, just wondering why is all.
Jim

 

the needles on the speedo might be off.
i dont think they are completely accurate, several people have stated that the tach is also off some.

 

yeah, there could be slight faults in calibrations both in the cluster and in the radar things.

also yur speed at the track isn't measured by yur speed directly at the finish line. its an average of the last few feet (the actual distance escapes me). the tracks measurements could also be slightly off in calibration too.