Novice question: Why is there more resistance when I am pushing a group of cars than pulling? I am guessing it has to do with pressure on the coupler, but have no idea why.
As someone familiar with physics, I think I may be able to help a bit. When you are pulling a string of cars, all of the force from your pulling of the cars is transferred through the couplers, and the trucks follow the car (assuming you are working with truck mounted couplers, as if I remember correctly, you have said previously that you model in N scale). When you push a consist, the force is still transferred through the couplers, but seeing as the cars ahead of the one you are pushing are lighter, the trucks are given much more opportunity to move, and most likely turn as you push them, as physics makes the trucks want to “buckle” together to reduce the distance between them. With the trucks turned, the axles scrape against the railheads, and become harder to move with the increased friction. I am not sure exactly how accurate my explanation is, but from my understanding of physics, this is the most likely scenario for a noticeable difference between pushing and pulling a string of cars (in my own opinion).
When you pull on a coupler, the force is all transmitted along the center shaft and then to the pivot in the center of the car. When you push, the coupler rotates to the side, towards the outside of the curve, and some of the force goes sideways. On a curve, this puts sideways pressure on the wheel flanges, causing greater friction than if you’re pulling.
Going straight, pushing or pulling should make no difference. But, if you have weak coupler springs and the couplers rotate to the side, then you will see the same effect that you do on a curve.
With truck-mounted couplers, a push force that is even microns off-center will cock the trucks, causing flange friction. With body-mounted couplers (or very long wheelbase trucks) the forces that cause the individual trucks to take up skewed positions simply aren’t there. So body-mounted coupler trains take about equal force in either direction, while truck-mounted couplers will require additional push force.
My 4-wheel wagons have moderately long wheelbases and high quality metal wheels with proper RP25 contours, so they don’t exhibit any flange friction problems even though they are equivalent to truck-mounted couplers. Or maybe it’s because they have couplers at both ends.
Chuck (Modeling Central Japan in September, 1964 - in twice-N scale)
My Athearn GP7 can pull or shove 27 cars(on the flat) with no issues…I never seen any KD coupler push to one side on the shove.There wasn’t any issues uncoupling by magnet after a shove.
Thanks guys! It makes perfect sense now.