The Yellow Box speedo recalibrator arrived the other day. I read the instructions on how to calibrate it after a bottle of wine and it made no sense at all. The next day i re-read it and it all came together. You can get one of these from
http://yellr.com/ . I got the plug n play version so i dont have to worry about splicing wires. Their customer service is great and the product looks high quality. The reason i need one of these is because according to Go-Jeep, with my 4.88 diffs and 29 inch tyres, i would need a 47 or 48 tooth speedo gear... which they dont make. So this calibrator solves the problem and i can change tyre sizes any time and simply recalibrate.
I will fit the yellow box up next week and do a write up, but i thought i would write up on how the yellow box v5 is calibrated. Firstly you need to work out how much your current set up throws the speedo out. Do this by [new diff ratio/old ratio]x[old tyre diameter/new diameter]. My calculator said 1.3460 which is 134.60% which is 34.60% fast.
You then hold down the two buttons on the yellow box (pic below), for 5 seconds to go into adjustment mode. There is a + and - button. For each second you hold down the + button, you adjust forward 1%. So i needed to hold down the + button for 34 seconds. You tap the + button to get thet smaller 0.6 increments. So i tap the + button six times. Then you wait a few seconds for it to go into memory and then turn it off to store the data.
After that, use a gps, road markers, etc.. to check it and make small corrections as necessary.