Quote Originally Posted by dalearyous View Post
should have clarified: ok yeah obviously you can't adjust the tach, i meant the ratio of RPMs to speed. anyway, to clarify the resistance: i was referring to the amount of RPMs need to sustain a speed with the cruise on. your vehicle is obviously going to work harder if you are driving straight into a strong wind and so you get that slight fluctuation (in speed and RPMs). all i was referring to.

i don't like trusting a GPS for my speed. my OBCD dongle has an app that allowed me to basically drive one mile at a constant speed (again as best i could) with a timer and then i did the math. i always found GPS to be 1-2 MPH slower than actual speed.
Ahh, got it.

I agree with you, some GPS can be a little off. Of course, if the GPS is consistent, that's what matters most as that is something you can work with (either consistently above or below.) I have found when I calibrate to GPS and then I cruise past one of those stationary pole mounted radar guns that displays your MPH, that my MPH displayed in the dash matches pretty close to what the radar gun shows on the pole, so I think the GPS is close enough. Also, it's usually good to be a little high on the speedo as it helps save you a ticket. That's why most German cars have a built in 3% margin to the high side ;-)