We all know that wheel/tire size, engine swaps, and gearing changes result in a real problem...you're heading down the road at 60mph and your speedo is reading 20-40% off, and you have a vehicle with an ECU that cannot easily be "flashed" to correct speedometer error or if it CAN be flashed it won't correct a large enough range for your needs. So you have learned to just do the math in your head (Or for Jeep owners, maybe you're thinking about spending $45-90 in parts every time you want to put in a new gear. Check out this article on JeepsUnlimited.com about what they found.)
Maybe you've come across a speedometer correction device that sounds like it will fix your problem. But it has daunting installation instructions, makes you flip switches or turn screws and count turns to be sure you're doing it right, or requires you to reprogram it every time you switch from winter to summer tires and back, or re-flash your ECU every time you're going to have your car in to the dealer for servicing (which includes them using the diagnostics function).
The SpeedoHealer® by HealTech Electronics (exclusively imported by Blue Monkey Motorsports, Inc) is a clear and simple solution. For Jeep TJ (98-06), LJ ('04-'06), and XJ (98-01) installation is plug-and-play with FACTORY OEM CONNECTORS (for highest water protection rating). For all other vehicles with 3-wire speed sensors (signal, power, ground) the Universal kit is simple and easy to install for average guys with basic skills, and takes about 45 minutes. And for behind-the-dash direct installations, the Controller-Only kit is the simplest solution. Locate the speed signal and then run power and ground to this unit, and you're done! (Install time varies)
Easy to install...easy to program...durable...reliable...and backed by outstanding support and warranty!