Ursidae69 said:
How much performance is being lost due to incorrect speed being given to the computer? The Superlift site claims that there are noticable performance losses.
From my own experience running the "wrong" tire size for quite a while...there's nothing noticeable other than an increase in fuel required to overcome the increased torque necessary to move a larger tire. If there's anything else, other than maybe reduction in efficiency of the cruise control, it's big news to me. Superlift's ad makes a not-so-veiled, weasel-worded reference to authority in stating that the ECM is all goofed up, therefore causing a "subtle yet real" decrease in efficiency. My guess is you won't be able to tell a difference without the butt-o-meter.
The vehicle speed sensor (probably in the transfer case or somewhere, some vehicles I think have it in the tranny) only seems to feed the ADD computer in my truck (a 2000my Tundra), which limits engagement to below a certain rpm in the tcase (it's about 50mph or so). If you have ADD, just keep using the vehicle speedometer for the shift/no-shift point, it will be correct, but with the calibrator, depending on where it's installed (before or after the tap to the ADD), the new cutoff point would be at a higher
indicated speed than before...original speed plus the correct percentage increase in tire size. Since the guage is currently reading low, I wouldn't worry about it, since the threshold is effectively increased with larger tires, stock gears and a calibration unit. Once you change the differential gearing it'll be back to normal...just always keep in mind the vehicle does its job (or doesn't) based on rpm, not speed, since actual speed can vary based on so many things inside or outside the vehicle--speed is just what the cop measures, to put it bluntly.
My guess is shift points are determined by load, throttle request, current rpm or all three, not vehicle speed. Anybody here familiar with auto trannies?
If you have a manual tranny and tcase, don't even sweat it...get any of them or don't, you're the ECM in that case. I wouldn't trust the Superlift ad any farther than I could throw a Superduty with 12" lift blocks.
As far as the units...it's really difficult to tell. I know some people using the TruSpeed with good results on Tundras. All those units will install "in-line" like the TruSpeed advertises and correct the odo, cruise, etc... The Dakota Digital product actually seems like the most tech-oriented, the TruSpeed is the most "black box"-like, the Yellr is somewhere in the middle, but they'll all do the same thing. I'd call 'em up and see how well each retailer/mfr knows the product, but my gut feeling is I'd get the Yellr since it's small and inexpensive with similar features as the others...
And thanks for the links
. I'm about 13% off right now, been putting off calibration til after the BIG gear and tire swap.
-Sean
