Why does putting a carriage on rails make it much easier to pull? As in, how were the first trams such an improvement from omnibuses when the same weight was still being pulled?
In: 520
Three reasons.
There’s very little deformation in the wheels. If you’ve every tried to ride a bike with a flat tire or pumped the tire up hard to roll better, you know that the harder the wheel, the easier it rolls.
The track is very smooth and flat compared to a road surface. The train doesn’t have to waste energy climbing over bumps and out of potholes, even at the microscopic level.
The track is very well supported. Under very heavy loads, relatively soft road surfaces deform so that the truck is always going “uphill” to get out of the dent it creates when it presses down on the road. The design of the train and rails distributes the load over a wide area preventing most of the deformation.
The first railways were made before omnibuses existed. At that time most roads were terrible by modern standards. Steel wheel on steel rail interface was *much* better than the alternative at the time.
ground wheels = fat
Rail wheels = skinny and more controlled ‘ground’ environment
= way less rolling resistance.
Compare what it takes to roll a pool ball (hard ball) on a pool table (hard surface) versus rolling a beach tires(squishy) on a beach (soft).
For the least amount of rolling resistance, you want the hardest possible wheel on the hardest possible surface.
Steel on Steel is the way to go.
This is especially true as early wagons had hard wheels with very little surface area. Great on hard surfaces, but in dirt, mud or grass it would sink and take much more effort to pull.
Great question.
Part of it is materials: metal rimmed wheels roll better. And metal tracks are better to roll on.
But part of it is also infrastructural: building a rail track involves carefully laying down a guide system that covers every meter from point A to point B, and has to be smoothly aligned and joined and so on. *Anything* you do with that degree of precision is going to offer a considerable improvement in terms of energy efficiency.
On the second point, consider the example of an inflated rubber tired automobile on an asphalt surface. Kind of the opposite of a steel wheel on a steel track, in a lot of ways, right? But pushing that automobile is surprisingly easy, at least as long as the grade is close to level.
Try pushing that same automobile across an open meadow. Sure, you’ll probably get a certain amount of distance. If you’re dedicated, and maybe have some friends to help, you might be able to keep it going for a while. But it’s a huge effort to go anywhere — you are constantly struggling against irregular terrain. And sooner or later you are going to hit some dip or shallow depression that you will really struggle to get out of.
By contrast, if you start pushing a car along a decent paved road, a single fit person can keep it up literally for miles.
So, historically, I think to some extent the advantage of rail-guided vehicles was simply that for the first time someone had really laid out a road with a very high degree of care and engineering.
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