Gear Ratios
Well, if ya want something done...DIY.
Using Staton's data on his NV/chain drive, Dave starts with a gearbox having 18.75:1 gearing. Mounted outside his gearbox are his drive sprockets, ranging from 16-tooth to 22-tooth cogs. There's a 27-tooth driven sprocket mount on his NV hub. Gear ratio varies from 23:1 to 31.64:1 before entering the hub. The NuVinci ratios vary infinitely from 350%(3.5:1) to 50%(.50:1). Therefore, final drive ratios can vary from a super low of 110.74:1 for a 16t/27t combination and 3.5:1, to an 11.51:1 with a 22t/27t and the highest .50:1 NV ratio.
I'm using this NuVinci hub without the Staton 18.75:1 gearbox. Instead, I'm running a frame-mounted Tanaka engine thru a Scooterguy mount and shift kit, then to the NV hub. I'll be using an 11-tooth drive sprocket linked to a 63-tooth chainring, for primary gearing of 5.727:1. With a 5:1 pocketbike gearbox, ratio increases to 28.64:1. The secondary chainring has 22 teeth, which connects to the 16-tooth NuVinci hub sprocket(I chose this 16t gear for ease of pedalling without the engine). This 22t/16t ratio is .73:1; multiply that by 28.64:1 and you have 20.83:1 gearing before entering the hub. Close enough, because of the NV's gearing.
With the NuVinci's gears of 3.5:1, low gear is 72.9:1 for my 11t/63t and 22t/16t gearing. Highest .5 NV gear decreases to 10.4:1. Unuseable, which is good; according to NV specs, the hub normally rotates counter-clockwise, but kicks CLOCKWISE at .5:1 ratio.(probably momentarily, which wreaks havoc on the hub's torsion bars and the NV axle). This high ratio guarantees that the lowest .5:1 gear ratio will never be utilized in my application.
Looking at Staton's NuVinci web page, Dave uses 18.75:1 gearbox, 6000rpm engine checkpoint at the hub's 1.75:1 and .5:1 ratio for each gear selection. For instance, with a:
16t/27t combination, at 6,000rpm, speeds of 8.5mph @ 1.75:1(total 55.37:1) and 29.6mph at the .5:1(15.82:1).
17t/27t " " " 9mph @ 52.11:1 and 31.4mph (14.89:1) " "
18t/27t " " " 9.5mph @ 49.22 and 33.2mph(14.06:1)
20t/27t " " " 10.9mph @ 44.3:1 and 38mph(12.66:1)
22t/27t " " " 11.6mph @ 40.27:1 and 40.7mph(11.5:1)
http://www.staton-inc.com/Details.asp?ProductID=3274
In comparison, my combination of gears amount to 72.9:1, including the NV's 3.5 gear. Instead of matching Staton's gearbox, I'm comparing this with my present combination with 8-speed cassette of 32t/26t/21t/18t/16t/14t/12t/11t gears.
32t = 28.64 X 32t/22t = 41.65:1. Since 72.9 = 28.64 X (16t/22t) X 3.5(NV's top gear), then at NV's 2:1(200%), it's a gearing equivalent to a 32-tooth cassette first gear.
26t = 33.84:1, or NV's 162%
21t = 27.33:1, or NV's 131%
18t = 23.43:1, or NV's 112%
16t = 20.83:1, or NV's 100%
14t = 18.22:1, or NV's 87%
12t = 15.62:1, or NV's 75%
11t = 14.32:1, or NV's 69%
With a range of 69% to 200%, that's all I need. The NuVinci has a range of 50% to 350%.
I'm in the same ballpark as using my present 8-speed cassette, if I use my existing gearing, the NuVinci hub and its 16-tooth sprocket!
