2019 Stats - Solar
The downward trend continues, though it is not more than expected. And if I scale the chart from zero, the trend doesn't look nearly so precipitous. Also, I found a website where I can upload my solar data and it will add weather info. 2019 is the first year I've had this active, but I'm excited to be able to see how much the number of sunny days factors into my solar performance. Being above or below my average for a particular month was strongly correlated with the prevalence of sunny days. Overall, 78% of days were "fine" in Fernley Nevada in 2019.
Comments
Having thinner wheels does appear to cause the car to slow down more quickly (deceleration between 4% and 8% greater depending on how much mass I estimated you could take off the wheels). About half of this difference is due to the smaller rotational inertia of the thinned wheels, but the other half is due to increased weight of the non-wheel portion of the car (assuming you add the weight to the car that you remove from the wheels) which increases the friction between the axles and the wheels.
But that still wasn't enough to negate the effects of the greater speed you achieve at the bottom of the ramp by having the thinner wheels. You start the flat part of the track at 1% to 2% greater speed with the thin wheels and end up with a finishing time that is 0.8% to 1.6% less than the fat wheeled vehicle.
There is one more factor that might tip the balance in favor of the fat wheels though, and that is rolling friction. This is the force between the track and the outer part of the wheel that slows the wheel through microscopic deformations in the materials leading to forces that act off-center of the wheel and result in a torque in the opposite direction of the rotation of the tire. This is not something that is easily modeled so I wouldn't trust any sort of ball-park estimate I could come up with, other than to say that the fatter tire would certainly spread the weight of the car over a larger area, thus decreasing material deformation and reducing rolling friction. Whether it's enough to make fat wheels the better strategy, I have no idea. Sorry I couldn't give you something more conclusive.