Why Locomotives Don't Have Tires

Friction is the final frontier of vehicle/rail interaction!

A single modern diesel freight locomotive can deliver upwards of 50 tons of forward force (called tractive effort) into the rails, but it’s somehow able to do that through the tiny contact patches between two smooth and rigid surfaces. It’s just slick on slick.

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DISCLAIMER
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This is not engineering advice. Everything here is for informational and entertainment purposes only. Contact an engineer licensed to practice in your area if you need professional advice or services. All non-licensed clips used for fair use commentary, criticism, and educational purposes.

SPECIAL THANKS
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This video is sponsored by Nebula.
Stock video and imagery provided by Getty Images, Shutterstock, Pond5, and Videoblocks.
Tonic and Energy by Elexive is licensed under a Creative Commons Attribution License
Video by Grady Hillhouse
Edited by Wesley Crump
Produced by Ralph Crewe
Graphics by Nebula Studios

[PracticalEngineeringChannel]

Sorry for the lack of actual F1 cars in the intro! Turns out, very hard to license footage 😄

[DavidCaddock]

I'm sure Brady knew the cars at the beginning were not Formula 1 cars, because F1 is very protective of copyright, and he didn't want to deal with the headaches.

[davidphillips]

I was a location manager and had a retired train engineer working for me. When I was having a "challenging" day, Brad would see this and say, "David - How do you start a train?" and walk off. One day, I stopped him and asked him what he meant by that statement.
"There is no locomotive set that can possibly pull a mile long train from a stand still. The locomotive pulls the first car, which pulls the next car, which pulls the next." The slack in the coupling is crucial to allow this 'chain reaction' to occur.
He shared that sometimes, with a green engineer, they'd pull into a stop to change crew while under power, taking all of the slack out of the couplers. No go. The solution was to back the train a distance to re-create the coupler slack.
So, the life lesson was, if you have a big challenge you're dealing with, find the solution in a series of small fixes rather than viewing it as one big problem ... one car at a time.

[AaronShenghao]

0:04 It's also the pinnacle of Copyright Strikes. Therefore, have some Indy Cars instead.

[Swindy]

I work for Wabtec (former GE Transportation), we build freight locomotives. The sheer weight and power is unbelievable.. they are truly an engineering marvel.

[Hyce]

Excellent video, Grady! The "Creep" demonstration was wonderful. This effect actually leads to one of the biggest wheel defects we experience in the railroad - shelling. The creep and deformation actually causes slip dislocation motion in the grain structure of the steel, and atoms start getting peeled out of the wheel, and thrown off - resulting in shelling, which is essentially a "missing chunk" of wheel.

Also, Steam Locomotives actually *do* have tires! Different hardnesses as well, depending on the size and weight of the locomotive. They're really neat. The wheel on a diesel locomotive is a much simpler, and standardized part that can just be replaced; so the whole wheel just gets changed out; but with a steam locomotive and their various wheel sizes, castings, etc. - it made sense to have a dedicated tire to replace, instead of a complicated casting.

[DaHitch]

starting with "Formula One is..." while showing Indycar is a really good way to get a lot of people up in arms. 😄


But clearly not as many people who seem to read this comment as some sort of insult, indictment or judgement. Ya'll must be fun at parties.
Lighten up 🙄

[smeagolplaysgames]

6:51 "For longer, heavier trains, you can't just use a single, massive locomotive -"

Union Pacific during the transition era: "Wanna bet?"

[alexconmy]

If Grady ever wanted to lure me in to kidnap me for some reason, all he'd have to say is "Come take a look at these demonstrations in my garage" and I'd follow without a second thought

[mitchelldurward]

Grady is just so wholesome. Listening to him talking about engineering is like receiving a big informative hug.

[DomyTheMad]

i swear about 9/10 videos you make could just be called
"check out this cool thing i built in my garage"
and i'm here for it.

[EngineeringMindset]

Me: About to eat lunch, YouTube: Hey Practical Engineering just published a new video about trains. Perfect timing. 👍

[kiefershanks]

Hard to imagine a solid steel wheel stretching and effectively increasing the size of its contact patch to obtain maximum tractive effort. Its actually genius. Once the tractive effort reduces, the contact patch shrinks to its normal size and rolling resistance becomes minimal at cruise. The more I learn about trains, the more respect I have and the cooler I think they are.

[trooper]

Was a tanker in the Army and this principal reminds me of how tank track moves. You'd think that the tank track, rotating but laid down stationary, under the tank wouldn't move until the rear end of it gets lifted and starts moving up then forward only to get laid down again, in a cycle. The fact is, when a tank is really hustling, all 60+ tons, the track thats in contact with the ground, which may appear not to be moving, is in fact sliding forward with the tank, slightly but evidently. If you watch closely and see video of a tank moving quickly, especially over a hard surface like pavement, you'll notice that the track on the ground is sliding, "creeping", forward as the tank moves. Pretty cool physics going on there too.

[johnopalko]

"I've set up a demonstration in my garage."

Of _course_ you did. That's what we love about you, Grady.

[schniemand]

4:10 Rolling friction (or rather, rolling resistance) isn't the same as adhesive friction. Adhesive friction is GOOD for rolling, it's what defines it. Rolling resistance is bad, unless you want to brake.
This is the distinction people often forget to point out, which usually leads to confusion. Weaker adhesion doesn't help you roll better.

[Keiranful]

The German high speed rail trains ICE (inter city express) actually started out with rubberized steel wheels to reduce vibrations and thus increase passenger comfort. That stopped when we had a horrible accident at Eschede. What happened was that the rubber sleeve of one wheel started tearing off roughly a few kilometers before a switch and a piece of rubber jammed itself into the switch, forcibly changing the tracks for the rear part of the train. This derailed the entire train that had been going around 200 km/h (~125 mph), which would have been bad enough, but only led to broken bones in most cases. The problem was that a few hundred meters after the switch came an overpass and the sliding train took out the pillars of the bridge, causing the bridge with cars on it to collapse onto the train. All in all, more than 100 people died.

[justandy]

As soon as I saw the title I was thinking..."But many locomotive Do have tyres though"
Especially Steam Locomotives! I don't know of a single design that doesn't.
Back then, they were well aware of the lack of friction between the driving wheels and the rails, So these hard wearing "tyres" were installed to help increase the friction without affecting the rolling resistance too much. Also alot of steam locomotives were very prone to wheelslip. Some were better than others, but generally, the larger the wheel the more likely it was to slip. Hence why alot of freight locos had relatively small driving wheels.
So the reason for tyres on Steam engines was purely cost saving. The Driving wheels are very expensive to mold and machine (Some can be in excess of 6 or 7 foot in diameter), So they put tyres on, these ware out and you just put on a new set. Saving the steel part of the wheel and a truck load of money in the process.

[zfotoguy]

Several decades ago I was lucky to go on a ride a long in the cab of a diesel electric through the Appalachian mountains on a short line. It started raining lightly as we were going up a mountain and the wheels were slipping. The sander was not functioning. They had me stand at the front of the locomotive sprinkling sand on the track in front of the train so we could ascend. Such a cool experience.

[L_Cyphr]

The ad for Nebula at the end was so good. No this isn’t sarcasm. I’ve heard about Nebula since a few years ago, but your way of presenting the platform, and how it compares to other platforms (loved the How it’s made reference) was just so watchable.
You might’ve actually convinced me to give it a go, so hats off to you sure for producing such great content!