33" tires read your speedo ~16% low — going 60 actually = 70. Fix with a TruSpeed / Yellow Box module, GPS speedo (Speedhut, Scangauge), or correct speedometer gear (Renix only).
1987-1995 Renix/HO XJ with mechanical speedo cable: there's a colored plastic speedo gear inside the tail housing of the transfer case. Different colors = different tooth counts. Calculate the right one for your tire/axle ratio combo using a chart (Crown Auto Parts has a calculator). Cost: $15 for the right gear, requires pulling the tail shaft cap and swapping.
1996-2001 XJ with electronic speedo: VSS (vehicle speed sensor) feeds the PCM which feeds the cluster. Solutions:
(1) Hypertech 730125 / TruSpeed Yellow Box / Hayden 530: inline module on the VSS wire that scales the pulse rate. ~$120, plug-and-play, adjustable. Programs for any tire/gear combo. CORRECTS the PCM signal too which means trans shift points are also correct (important!).
(2) Custom PCM tune: a programmer like Superchips or Hypertech can write a tire size into the PCM, correcting the speedo AND the shift points. ~$300.
(3) GPS speedo (use a phone, or Scangauge II): doesn't fix the PCM (so shift points are wrong), but tells you actual speed.
If your 33s+4.56 gears combo has your odometer reading correctly but speedo high, you mismatched something — recheck the math.
| Part | Vendor | Est. price |
|---|---|---|
| Hypertech 730125 Speedometer Calibrator | Hypertech | ~$150 |
| Speedo gear (NV231 / NV242, color varies) | Crown Auto | ~$15 |
| Scangauge II | Linear Logic | ~$170 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.