Directscan question/help

[Turbonut]

I have dumb question, I installed 28" slicks on my car, i set the prefrences on tire height to 28", Going down the rd, ds data is 5mph higher than the speedo but at the track the top speed is always 3 mph slow? Normal or my error? Thanks, Rob

 

[BoostKillsStres]

speedo

Congrats on your new hardware and et/mpg gain. What are you comparing the DS mph too, not the speedo I hope because its going to be wrong now also because of the taller tires effecting the vss reading and DS should be giving you an almost exact mph reading your actually going. If you put a taller tire on a car the stk speedo is going to read slow(think larger circunfrence tire = less vss pulses) so if DS is showing higher then that should be the correct mph. The track mph is always going to be off since the mph reading is measured over I think the last 250 ft( the last 2 sets of cones you pass before the finish) and DS is reporting mph at the finish line so you don't want it to match the timeslip.
HTH, and hope I got all that right,
Mark
87GN

 

[J. C. Plemons]

The speed trap used to be from 60' in front to 60' after the 1/4 mile light. If you let off as soon as you cross the light your DS reading will be higher than the speed trap since you quit accelerating 1/2 way through the trap. It will not be practical with slicks, but the best way I have found is to use a GPS and set the tire dia. to make DS match the GPS. You can get dead on with this method. On a straight and level road, the GPS is accurate to 0.1 MPH. my .02