The Truth about Gears and Tires

[Timmy]

i have the superchips flashpaq 3872 and have tried to dial in the tach and speedometer as close as possible

i have done the unscientific verification with my wife following me as well as tried to measure distance. basically, at 70 mph im running rite around 2700 rpms. obviously resistance will change that a bit. wind against me its a little higher, wind behind me its a little less

Durp? You just be-futtled my brain... I'm hoping I'm just reading this wrong, but I wouldn't think you would be able to "dial in the tach," and I can't imagine your RPM's would change based on resistance?

Very curious... Why not just set your cruise control at 70Mph and then use the GPS on your phone to tell you how fast you are going and then use Superchips to adjust your speedo as needed until it is dead-on accurate? This is what I did with my AEV Procal. I programmed for what was suppose to be the correct tire size, went out on the road and verified and then adjusted as needed. Right now I'm running exactly 1 Mph slower than what my speedo says. I could correct that so it is dead accurate but I'm leaving it that way in case anyone else drives my Jeep so they have just a slight buffer should they ever get pulled over.

[dalearyous]

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.

[Timmy]

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 ;-)

[KaiserBill]

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.

GPS systems have a percentage of error like anything else.