If you want the same gear ratio you're using the wrong calculator. Using the "distance between shafts" calculator just tells you the distance between the shafts with a particular set of gears, it does not tell you the ratio. Your 23/87 combo has a ratio of 3.78:1 while the 12/60 is 5:1 so your top speed is going to be different. A 16/60 combo gets you a ratio of 3.75:1 which is as close as you are going to get to your existing 3.78:1 ratio. Now if you want to make sure this combination will fit you can enter it into the calculator to find the distance between the shafts with 16/60 and make sure you can achieve that distance between the shafts in your vehicle.
Last edited by Maj_Overdrive; 07-07-2014 at 11:42 AM.