Speedometer Recalibration, by Platform

Programmers, FORScan, dealer flashes and speedo gears — how each platform takes the correction, and what it costs.

Change tire size or axle ratio and your speedometer lies — by exactly the percentage you changed the gearing math, which the speedometer correction calculator spells out. A 10% under-read is 7 mph at 70: speeding-ticket territory, and on modern platforms the lie also corrupts shift scheduling, odometer math and (on some rigs) stability systems. Recalibration isn't cosmetic.

Electronic platforms

Jeep JL/JT: programmer required. A Tazer JL (~$329) or AEV ProCal SNAP (~$225) writes tire size and ratio into the modules; the 850RE automatic then schedules shifts correctly. Dealer flashes cover a limited factory menu only.
Jeep JK: same idea, one generation simpler — ProCal-class programmers run ~$170–$230.
Ford Bronco (2021+): FORScan can adjust tire size within a factory window; larger corrections need an inline calibrator (~$200).
Toyota Tacoma/4Runner: no dash setting exists. An inline calibrator (Hypertech-class, ~$180–$230) intercepts and corrects the signal. Many owners tolerate a one-size-up error (~3–4%); past ~6% the odometer error alone justifies the box.

Mechanical platforms

TJ and XJ Jeeps and classic Ford/GM trucks read speed from a gear in the transfer-case or transmission tail housing. Correction is a driven-gear swap — ~$35 in parts, one bolt, and a tooth-count chart matched to your tire/ratio combination. It's the cheapest recalibration in the business and one of the old trucks' genuine advantages.

Which one do you need?

If your platform is electronic and you're regearing, budget the programmer in the original quote — see the regear cost guide. The Decision System shopping lists include the correct recalibration line for each platform so it can't be forgotten at parts-order time.