For quite a while I've had the suspicion that the dinosaur burning Blackfly (Pontiac Firefly) is a better roller/coaster than the wind & hydro powered ForkenSwift (electric Geo Metro).
But! I don't put much faith in Butt-o-Meter readings in general, even my own.
So today I ran a simple, controlled-as-possible comparison to gauge the cars' relative rolling performance to see if one was really better than the other.
The winner? In a way, both cars are winners!
But in another a more accurate way, the Blackfly was the winner.
And in an even more accurate way, the Blackfly's
tires were the winners.
Preparation:
- I made sure both cars had the same tire pressure.
- I equalized the weight between the two cars, which meant adding 240lbs to the Firefly (~1830 lbs stock) to equal the heavier electric Metro (~2070 lbs post-conversion). (I actually ended up adding 260 lbs, since at 65 lbs each, 4 flooded golf cart batteries were a quick way to do it.)
- I washed, waxed and Armor Alled each car (OK, no.)
Methodology:
The distance of the "course" between the ForkenSwift (blue) at the start, and Blackfly (black) where it rolled to a stop.
- I drove each car the same distance (from a cold soak start - overnight) to a quiet dead end road with a small downhill followed by an almost level "run-out" (very slightly uphill).
- Start: at a marked position on the hill, engine/motor was shut off, transmission placed in neutral and the brakes were released (from a stop).
- Finish: after rolling down the hill (maxing out at approximately 21-22 km/h) and coasting to a stop, the "end" position was marked on the road with chalk for each run.
- 3 runs were done for each car
- Then the wheels/tires were swapped between the two cars
- 3 more runs for each car were measured
- There was also waving at and/or talking to several neighbours who were either curious about or suspicious of the repeated slow driving up and down the hill on their quiet street.
Conditions:24 C / 75 F - clear & dry
wind west 6 km/h (~4 mph)
humidity 34%
pressure 101.4 kpa / ? in. hg
Results:First set of runs (tires in their "proper" places)
219.9 m / 721.5 ft - Average Blackfly distance
201.6 m / 661.4 ft - Average ForkenSwift distance
18.3 m / 60.1 ft - difference in coasting distance
Second set of runs (wheels/tires swapped between cars)
205.3 m / 673.4 ft - Average Blackfly distance
221.1 m / 725.5 ft - Average ForkenSwift distance
15.9 m / 52.1 ft - difference in coasting distance
That's not insignificant.
The tires: Firefly:
Goodyear Invicta GL M+S (79S)
155/80/13
Max Load 436 kg / 969 lbs @ 44 PSI
Treadwear 260
Traction A
Temperature B
Tread: 3 plies (1 polyester cord + 2 steel cord)
Sidewall: 1 ply polyester cord
Made in Canada
ForkenSwift:
Magna Grip Radial HT M+S (82S) (Walmart winter tires)
175/70/13
Max Load 470 kg / 1036 lbs @ 240 kpa / 35 PSI
Tread: 3 plies (1 polyester cord + 2 steel cord)
Sidewall: 1 ply polyester cord
Made in Canada
Experiment, part two!
The next part isn't at all scientific, but after doing the controlled comparison, I took the ForkenSwift for a drive - still wearing the Blackfly's Goodyear Invictas (and borrowing its smooth wheel covers) - to see if there was a measurable difference in energy consumption compared to recent driving.
I won't argue that this is in any way a valid comparison. All I can say is I tried to do similar driving to previous cycles - ie. all sub/urban use, in light traffic, while trying to maximize efficiency.
The car is on the charger now - should be done in about an hour. So while waiting for the numbers, here are some (subjective) differences I noticed:
1) the Goodyear tires seemed quieter (makes sense when you look at the blocky tread pattern of the snow tires)
2) even at the same inflation pressure, they seemed to absorb bumps better (which makes sense, since the narrower tires should deform more on impacts)
3) not surprisingly, I found myself coming in "hot" when coasting up to several familiar stops & turns. I had to adjust my driving as the "test" went on.
Power consumption results to come!