Thank you so much for conducting your experiments. Your results are interesting and I have a few questions. The 937 having the brass bushings, did you replace the wheelsets with steel wheels or leave the Flyer plastic wheels? I think you results are not very different from mine, however you view of them is a bit more optimistic than mine. I outright dismissed ½ car length more coasting being worth the effort.
I did my tests over 16 years ago and I am sure my memory of them is a bit fuzzy at best. Rather than pushing the cars, I build an adjustable incline which I felt gave every trial the conditions. IIRC, I raised the ramp until a raw (unaltered) Flyer 640 would roll to the bottom. Then converted it to the brass bushings but leaving the Flyer wheelsets and gave it many trails, noting each end point. Next I changed out the Flyer wheels for SHS replacement steel wheels and repeated the trails. As I said before, the steel wheels made more of a difference than the bushings alone. My memory is such that I never bothered converting another car to brass bushings. The steel wheelsets are probably of more value as an aid in keeping the track clean rather than the increase in roll-ability.
Your test with a string of cars is intriguing and it would be interesting to have a pull scale to really measure the difference. A small difference in one car adds up to a big difference in many cars.
I wrote to Doug Peck asking about plastic bushings and stating what I thought about the brass bushings. His response:
The REAL purpose of the brass bushings in the AF KC trucks is to correct the level of the axle in the truck, due to axle wear against the top of the hole in the die cast sideframe, causing the trucks to ride a bit lower.
But at the same time, they do improve rollability.
Because I don’t use knuckle trucks I have never attempted to convert then to the brass bushings. Do you have to ream out the hole in the sideframe for the bushing? How do you ensure the bushings are all the same distance from the rail so the car rides level?
Doug also mentioned he was not aware of any plastic bushing (though I seem to remember someone had them for passenger cars many years ago) other than what Lionel puts in their freight trucks. Can anyone offer more information about the Lionel bushings?
I guess until someone develops (if it is possible) a conical bushing for pointy axles we are stuck with only a little bit of improvement with the brass bushings.