correcting my Spedo with my SCT
 

hey all, I got my SCT tuner and my custom tune installed in my stang, but for the life of me cant get my spedo right. I set it for 4.10 gears, and changed my tire revs per mile to what the calculators I have used call it. My spedo at 65 reads about 7 mils per hour faster then my actual speed. Should I adjust my gears or revs per mile, and if so, what way? Thanks for any help.

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thanks... though none of that is what I asked. lol. A better way to check my speed is to use my GPS on a straight road and compare. I just need to know if my spedo is reeding slow do I need to add or subtract revs per mile on the tuner.

Just go to the rear axel sections for gears and scroll done to 410 and reset tune. Speedo should be correct.

omg......

I appreciate some people trying to help but dam, the only 2 responses were what I already had done, and said in very first post.

Well fixed it. Going off what I had on my Predator was 721 to work, was like 7mph faster then actual speed. Changed to what a online calculator said, and went to 748. Was 5mph fast. Used the formula Bruce said, got 760 amd was 3mph fast. Following that path, added a arbitrary 20 to bring me up to 780 revs/mile and now I am within 1mph at 70. Thats good enough for me.

I've read several posts saying to use a GPS to check your spedo. Is the GPS that accurate? How accurate is it? Thanks...

well the gps are accurate to within feet, in comparison a MPH is not that perscise a measurement, so I would think it would give you a very accurate reprsentation. My big concern aside from knowing if I am speeding or not is that with my spedo being off, especialy reading higher then I am actualy going, It would appear as I am putting way more miles on my car then I actualy am. Being that I have less then 4,000 miles on my car, I dont want to do that at all.