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Transmission Calibration Question

Discussion in '1st Gen. Tacomas (1995-2004)' started by beefcake, Mar 7, 2011.

  1. Mar 7, 2011 at 9:05 PM

    beefcake [OP] J-rob

    May 25, 2010
    First Name:
    Central California
    98 4WD V6
    Debadged,Deck Plate mod, Helix throttle body spacer, magnaflow two chamber, smoked corner marker lamps, cb radio, smoked headlights, grillcraft mesh grill, URD short throw shifter, ultagauge, billstein 5100 front struts, spidertrax 1.25 spacers on all four
    I'm not sure what it's called, but it's the sticker that is in the door jam of the driver side door. It says that stock my truck was equipped with 225/75/15 size wheels/tires. But the window sticker from when it was purchased off the lot says 265/75/15 were on the truck as part as the package included. My question is: If tires size is a factor in correct speed, then what tire size was my transmission calibrated at in the factory? I know i can use the tire size calculator to figure out what my speed would be with different tire sizes, but where to i start? at 225/75/15 or 265/75/15?
  2. Mar 8, 2011 at 3:40 AM

    EnolaGaia Well-Known Member

    Sep 9, 2006
    Midwest USA
    '01 & '04 S-Runners
    01 SR: Double Cab conversion, S/C, lowered.
    265/75/15 tires were available in 1998 as part of either a factory alloy wheels upgrade package or the Sport Value Package. So I believe your larger tires were a factory option.

    There's no 'calibration' of the transmission at all - it has the same gearing for all equivalent models regardless of options or equipment. Same basically goes for the differential / final gear ratios, though these do vary depending on exact model / configuration.

    Any speed-related calibration would have involved your speedometer (which became electronic with the 1998 model year).

    If your speedometer / ECM had been calibrated for 225/75/15 tires, the larger ones would have the speedo reading 8.4% too slow. Toyota calibrates speedometers to read up to 5% fast.

    Based on these facts (plus a known incident where reverting to 'standard size' tires caused a big miscalibration of the speedo on a similarly-optioned 1st gen Taco) I'm pretty confident your truck's speedometer was calibrated for the larger optional tires.
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