re your drive roller:
I like the FD setup you have, except for one thing: Your 'V' roller does give more roller-to-tire contact by 'wrapping' around the tire surface... but it also has greater losses, roller wear and tire wear between roller and tire than a single diameter roller.
At the larger roller diameter, the speed at a point on the circumference of the roller is moving faster than a point at the smaller diameter. (the linear speed is proportional the diameter times the RPM, and since, at a given RPM, the RPM times the smaller diameter gives you a slower speed than the RPM times the larger diameter.) Something has to slip, which leads to increased tire and roller wear, increased losses at the roller-tire interface, and hotter tires.
If there were a 10% greater diameter (large diameter/small diameter = 1.1) then, for every revolution of the drive roller, a point at the large diameter will 'move' 10 percent further than a point on the smaller diameter. Since the roller can only spin at one RPM, and the tire can only spin at one RPM... there HAS to be 'slip' in the system.
And, since the large diameter of the roller contacts a smaller diameter portion of the tire, the effect is actually a little worse than the 10% I mentioned. (the percentage is much less - a quarter inch when compared to the drive roller is much more than a quarter inch when compared to the wheel diameter.)
Here's an estimate, based on what I can see of your setup : You've got a high RPM motor. I'll go on the assumption that it has a 10000 max RPM. Since you say that it's geared for 50 MPH, this means that the roller diameter is about 1.75 inches; I'll assume that this is the large diameter on the roller. And, it looks like the roller is about a quarter inch thinner in the middle.
So, based on these assumptions, at 10000 RPM, when the large diameter of the roller is moving at a calculated 'ground speed' of 52.06 MPH, the small diameter is moving at a calculated 'ground speed' of only 44.62 MPH. There IS slippage taking place where the rubber meets the roller - about seven-and-a-half MPH worth at top speed.
Note that with a single-diameter roller, the tire deforms to a single roller diameter, so you don't have the same roller 'scrubbing' that you have with a multi-diameter roller. You WILL get a little, but, since it's based on the deformation of a 26 inch tire the amount if scrubbing is proportionally smaller... for a quarter inch deformation in a 26 inch tire, the percentage of slip caused by tire deformation is a little less than 1 percent, instead of apx. 14 percent in your case. (And, the V roller also has approximately the same tire deformation slip as a single-diameter roller.)
