Why Are Rails Shaped Like That?

An overview of the wheel/rail interactions and part of the railway engineering series.
Errata: At 6:52, the graphic should show the dimension of the wheel's diameter (not radius).
In the 19th century, railway engineering was all about how to build railroads. Modern rail engineering focuses on getting the most out of the system. It might not look like much when you see a train passing by, but a huge amount of research, testing, and engineering went into the shape of those rails and wheels.
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Practical Engineering is a KZbin channel about infrastructure and the human-made world around us. It is hosted, written, and produced by Grady Hillhouse. We have new videos posted regularly, so please subscribe for updates. If you enjoyed the video, hit that ‘like’ button, give us a comment, or watch another of our videos!
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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.
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Video by Grady Hillhouse
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[@PracticalEngineeringChannel]

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[@RobThaDestroyer]

More stuff bout trains pls

[@macmurfy2jka]

I actually wish you had gone into the math on this one

[@AngmarCosplay]

Please do a video on our favorite Structural Analysis topic….Wind Loads!

[@d00mf00d]

😊

[@rogink]

I know this is not a 'history' channel, but of course we didn't start with steel or iron rails. We used the most abundant material - wood.

[@tlum4081]

I'm a retired 73 year old mechanical engineer (stress analysis) also with an electrical engineering degree (computer & SW). I enjoy Grady's videos of civil engineering and related subjects and learning yet more engineering I used to ignore or take for granted. Never too late to learn even more. Thanks Grady!

[@sagittariusa2201]

It's good isn't it.

[@icosthop9998]

Nice

[@jamesbudd9900]

Do you remember Budd engineering Inc. Back in the day?

[@krus0094]

I can tell you that railroad engineering is very specialized in civil engineering, they don't even use geometry in the same way as a highway engineer. A person designing roads would not consider designing rail just as a software electrical or controls engineer would not consider doing power distribution.

[@Door_Casts]

The issue about hunting behaviour is really interesting because it comes up in downhill skateboarding as well where they refer to it as "speed wobble" and have some interesting ways of combatting it

[@longiusaescius2537]

Do you skate?

[@DasGanon]

Makes sense! I mean I've always heard of the skateboard axle also called a truck!

[@carterjanssen265]

The secret is putting your weight over the front trucks, and a little prayer

[@pyropulseIXXI]

@@carterjanssen265and crouching down

[@pyropulseIXXI]

Speed wobble also occurs on motorcycles, so I’m not sure it’s from the same phenomena. It isn’t happening because the wheels have different diameters; the oscillation happens because the trucks can ‘pivot,’ and the speed can get you locked in an oscillation, even with flat wheels. Flat wheels should greatly dampen the effect, though. Or, rather, non-flat wheels amplify the effect

[@garou5333]

As a steel worker at a rail mill this was very interesting & cool to get better insight on the workings of the stuff we make.

[@josephgaviota]

4:30 That whole wheel segment was FASCINATING. As a kid, we lived in a house that was three houses from the tracks, so I've heard all the various noises you describe since being a youth, plus the schwing-squeak-schwing sound you mentioned. And just today, 50 years later, I'm learning why. 👏👏👏

[@fredsalter1915]

I love the way Grady builds mock-up models to help explain what he's discussing!

[@matusfekete6503]

Long time fans know this channel is just excuse to make elaborate models.

[@woutervanr]

Agreed. It helps soooo much. Also the models he made for water flow a couple years ago. I greatly accelerates my understanding of the subject.

[@adriancooper78]

As a subway train operator, they give us the basics in the engineering on how the train moves on the rail. These are good reminders. Additionally, the detailed explanation is quite rinformative on the things we do not know about train movement.

[@billkurek5576]

Yes. I sure his models contribute greatly to the success of his channel. Thanks.

[@BS-vx8dg]

@@woutervanr I would love to see a Grady model to explain the water wedge in the Mississippi right now.

[@timmallette1888]

I was just in Japan and rode the bullet train and I noticed how the top of the rails was rusted over except for one tiny strip down the middle where the wheels actually contact it. Impressive precision for them to let the train go 200mph!

[@tomellis4750]

That comes at the cost of huge maintenance every night with an army of workers to keep the track perfect. How was the ride?

[@vanadot]

Thank you for probably make me staring at rails whenever I'm in a train station in the future...

[@BB-uo1qy]

@@tomellis4750 sounds like you're a trackman or know one or two

[@jonathansmith6050]

Hunting, where the wheels oscillate side to side going down the track, is a real problem for high speed rail because it can amplify to the point it causes a derailment. Japan put a lot of work into their high speed train engineering to nearly eliminate hunting -- which must be what lead to the very consistent tiny wear strip you saw. Very cool.

[@tomellis4750]

No, I just watch KZbin videos. Go well.@@BB-uo1qy

[@KalebPeters99]

What a masterclass in detailed and efficient science communication! Your script-writing is off the charts to pack so much into 15 minutes without it feeling overwhelming. The delightful animations and physical models make it so digestible, even for a total newcomer. You're the best, Grady! 🙏✨

[@giangkim8789]

ok

[@KalebPeters99]

@@Forakus well simplification is obviously necessary for this task, but could you give any examples of him being "entirely wrong"?

[@ArchangelExile]

Ok

[@inigo_montoya]

Grady is out here keeping me sane. Engineering is rad

[@The1andOnlyWog]

My grandfather was an Engineer for Santa Fe. He started as a Fireman on the ATSF (Atchison Topeka Santa Fe) 3751, a 4-8-4 steam engine when he was 16. He eventually worked his way up the ranks to Engineer. He also went to college and got a degree in Mechanical Engineering along the way, too. That's why I am obsessed with trains. I miss him. He was an awesome guy.

[@chaomatic5328]

A quote to honor his passing: Don't be sad it stopped, be happy it happened

[@Skylancer727]

Funny I'm a certified mechanical technician and just got a job as a conductor. If all you want is to be an engineer though, some railroads hire straight up for it. That's mainly public rail though, freight cares a lot more about experience since you need to know the yards and the dispatcher instructions. Very few passenger trains are designed to be separated or cut: they usually stay as one piece long term till they go to the shop or wash stations. Obviously the whole point of freight is to pick up and set off cars, it's a lot more you need to know.

[@Pufferish]

I feel like we take for granted a lot of the engineering and design work done in seemingly simple objects and tasks. Awesome vid btw!

[@Arcexey]

@Pufferish yeah I had that realization seeing someone demonstrate an old metal gas can and how literally every single part of it has a purpose so obvious yet also over our heads.

[@Krahazik]

I have had a similar realization studying ancient architecture. A lot of elements which became decorative in later decades to today, started out as practical engineering solutions to problems architect faced due to limitations in their knowledge and availability of materials and tools. Engineers, be-it ancient to modern are cleaver people.

[@Kawoaa]

Conic wheels would make the track tip on its side and cause derailment. The weight has to push down, not sideways. It only held down by track spikes. (Big nails.)

[@matthewxavier8067]

I always thought the cartoons showing train tracks go up and down like waves were just cartoons until I witnessed it in real life.

[@OutdoorLonghair]

I just realized the other day that wooden barrels are conical shaped to be able to self center while rolling on rails in the warehouses.

[@drzman6901]

One of my most interesting experiences learning about trains was when I was touring England and stopped in at the National Train Museum in York. Wow! Just wow! I was so lucky to find a volunteer that really knew his stuff and was willing to spend an hour with me. We started with a longitudinal section of a real steam engine, and he explained how these trains were powered. When he got into the engineering behind the power transmission to the wheels, my jaw hit the floor. If you think it's appropriate, please consider covering these topics. There is some fantastic engineering involved. Better yet, go to York. Find a great volunteer and give us video tour of the museum. 🙂

[@jurjenbos228]

In the Netherlands, train wheels have "tires" (also made of steel, of course) that are replaced regularly to combat wheel wear without having to take off the wheels. I guess this is true in other places as well. The tires are slightly smaller than the wheel, and are heated before mounting so that the stress will firmly keep them put.

[@JohnADoe-pg1qk]

These "tires" (german: Radreifen) have also led to a number of small and large accidents.

[@johnstudd4245]

That was standard practice on the big driving wheels of North American steam locomotives also.

[@TheHenzen]

​@@JohnADoe-pg1qk As far as I know, because of those incidents, "Radreifen/ Bandages" are not produced to only use shrink fit anymore, instead they are now Shrink fitted and boltet to the "Rims", atleast thats the change we experienced in our newer trainmodels compared to the old models!

[@jmcortade8161]

Some french Metros have actual rubber tires.

[@ratvomit874]

​@@JohnADoe-pg1qkAhem ahem Inter-City Express Eschede crash

[@neildunhamii4069]

I was an electrical engineer on a project at Griffin Wheel where they make some train wheels. There is a lot that goes into each and every wheel. One of the most interesting projects I got to work on.

[@petersennello813]

Can you explain to someone not in the field why an electrical engineer would be involved in the design or manufacture of train wheels? My only guess would be for the design of electronics that control brakes but I really have no idea.

[@Taschenschieber]

@@petersennello813 Presumably because the machinery used in manufacturing basically anything is powered by electricity and a steel press doesn't work off a 230V socket. The comment doesn't read like OP was involved in the design or manufacture of train wheels itself, just a project at the factory. Train wheels do have some intersections with electrical engineering - the wheel is an electrical contact point between the vehicle and the ground, and on electrical engines in particular, a lot of current needs to go through that contact point. But that's not really something that needs a lot of involvement from an electrical engineer, I presume. Also, the brakes do not have any components that are on the wheels, at least not in any brake system I am familiar with.

[@MsCriticalthinker201]

There are three items about the rails that need to be mentioned. First, the rails are not flat on top. The apparent flat surface is actually a gentle radius. Previously it was a 10" radius, new rails are now manufactured with an 8" radius across the head. This, in conjunction with the second item, called cant, keeps the wheel contact patch centered on the rail head. Cant is induced by the tie plates that support the rails. The plates are flat on the bottom where they bear on the crossties, but the seat that supports the rails is slightly tilted to the inside at a 40:1 pitch. This tips the railheads inward about 1/8" each from a true 90 degree angle to the crosstie. Third is superelevation. Raising the outside rail to bank the track slightly in curves. In track designed for really high speed running the difference in elevation between the inner and outer rail is as much as 6". This effect also helps the tapered wheel treads self center at speed and keeps the flanges from dragging on the high rail. Excess superelevation where trains are not running fast enough to use it is a disadvantage. Now the low rail receives excess weight and wear. In fact trains can actually tip over at a stop if they are carrying top heavy loads. Another interesting item is, that despite their huge imposing appearance, the center of mass of a locomotive is actually only about 5' to 6' above the railheads, which are set at standard gauge, 56-1/2" measured 5/8" down the railhead. This gauge dimension puts the webs of the rails at just about 5' even, which varies only slightly depending on which size rail is being used. All the really heavy parts are down low.

[@heathwirt8919]

Very interesting.

[@ImConstantlyDrunk]

I was thinking they may also introduce some slight banking to help equalize the distance the wheels travel as well. Thanks for the detailed comment!

[@Avidav]

How u kno so much train stuff?

[@thomasa5619]

Most I’ve personally seen is 5” of cant/superelevation At that point hydraulic oil started to leak out the breather on the equipment i worked with, and we couldn’t unload spoil because of tilting protection

[@johnsmith1474]

@@Avidav - How are you functionally illiterate?

[@SarahWRah]

Fifty years ago my young son became a rail fan, and I developed an interest alongside of him. I'm still fascinated with the complexity of how railroads work, and the incredible cost-per-ton efficiency of the system. I know there's basic physics involved, but it's still magical to me how an engine set can get a huge freight train in motion from a dead stop. Thanks for this great video.

[@hairyhoudini5565]

There's a couple of inches of play in the coupling that links the cars together, so depending of the length of the train the engine could be several yards down the track before the last car ever moves.

[@fiddley]

Here in London, they've just opened the Elizabeth Line which also has a bunch of brand new rolling stock. I swear every time I'm on the new section of rail in a new train it feels like a flying carpet. Accelerating up to speed with just a whistle, and a ride that is smooth as butter. Just boggles the mind how they can get 1000 tonnes of steel on steel interacting like that.

[@rejames4136]

H 2:48 2:49 2:51 lol this

[@rejames4136]

Mm mmm

[@hannahranga]

Speaking of wheel rail interfaces one of the more unusual faults I've seen was caused by a loco having a slightly different contact patch to the normal EMU that ran on that track. Because it wasn't touching the narrow unrusted part of the rail head the rust was acting as an insulator and preventing activating it the track circuit's consistently.

[@johnopalko5223]

I'll bet _that_ was an adventure to figure out.

[@Landogarner83]

Thats a nasty and potentially dangerous one. (if electric) If the loco has bad electrical contact to the rails then it is going to have some voltage compared to ground. Meaning if someone wants to get on or off the loco he may be in for a shock.

[@Taschenschieber]

A train not reliably activating track circuits isn't "potentially dangerous" if electric, it is definitely dangerous regardless of mode of traction because there is a pretty significant risk of another train entering the occupied section and then a collision. There was a case in Mainz a few years back where a train just dropped off the track circuit because the driver had used sand while breaking, and the train then essentially stood on the sand. Another train was then cleared to enter that section. IIRC there was no collision because the other train was entering at a low speed and the driver could stop in time after seeing the standing train. That's just more evidence that axle counters are superior.

[@jaelwyn]

@@Taschenschieber The best answer is almost certainly "both" - and if they disagree, everything stops until it gets sorted out. Like most proper fail-safe systems.

[@Woodsy3211]

I'm a Signalling Engineer, the problem of poor electrical contact in the wheel-rail interface is at the forefront of our minds for safe Signalling practices. Particular attention is paid when performing re-railling activities where the new rail is potentially rusty. I've even heard of a case where millions of millipedes have caused a train to disappear on a track circuit. Axle Counters certainly are a great way of eliminating this. They have their own challenges though.

[@BloodyMobile]

I think one of the factors why trains are so impressive in general is, where else do you see something with the weight of a house move with speeds up to or even above the speed of cars on highways?

[@bearcatracing007]

Every time I see A380 fly!

[@Soupy_loopy]

Yeah, trains weigh a lot more than a house. It's amazing how efficient they are at moving extremely heavy loads.

[@SlartiMarvinbartfast]

@@bearcatracing007 A380's fly on highways???

[@azrobbins01]

@@SlartiMarvinbartfast The highways of the sky

[@Sonny_McMacsson]

High speed jet ferries. They weigh way more than a house. I don't see it often but others do.

[@xyvernthederg5760]

fun fact, old railway tracks are so compressed down by the weight of all the trains they have carried that they can make good anvils

[@simonm1447]

That's right, they are a cheap replacement for an anvil. I used one before I got a big, old anvil from my grandfather, which may be from the 19th century (the anvil, not the grandfather ;-)

[@jamesdoyle5405]

I am a retired locomotive mechanic. Wheel measurements are so important, if the flange gets too low the car or engine can derail in a curve. Flanges that get too narrow can "pick" a switch and send a wheel set down the wrong track. Locomotive have flange lube sticks that lubricate the flange to slow wear. The other important measurement is diameter which needs to be close side to side. Really enjoyed this video explaining rail loads and design.

[@BarredCoast0]

I'm really looking forward to more in this series. We railfans are always looking for more answers to unknown aspects of railway engineering. Thanks Grady!

[@azrobbins01]

What is the main draw to locomotives? There are so many train fans out there, so surely someone can tell me. Is it just because they are so large and strong? I think they are cool as well, but I am not obsessed with them like a LOT of other people. Are train fans also fans of mining equipment to the same degree? Why or why not?

[@willisverynice]

To be fair, if you are a fan of trains, you probably knew all this already.

[@azrobbins01]

@@willisverynice Thinking trains are cool is not even close to the obsession that some people have with them. Everyone thinks trains are cool, right?

[@martinkominek6712]

@@azrobbins01 Throughout the history it took a lot of development and it is nice piece of machinery. From horse drawn to hundreds of miles per hour.

[@azrobbins01]

@@martinkominek6712 Very true. So you think most of the fascination comes from their history, and not as much from what they have become today?

[@j.electric]

Babe wake up! Practical Engineering posted 🥵

[@Very_Grumpy_Cat]

I can be your babe 😘

[@eruilluvitar]

I'm up, I'm up!!

[@joerionis5902]

well that's fast

[@elcocoreyes]

Exactly my reaction when i see a new post

[@djtruth8425]

Same tho!!

[@ilovetotri23]

I am not really a train enthusiast, however, there is no denying their importance. I love the engineering side of everything! This was probably my favorite episode on this channel. I has no idea how much thought went into rail travel. All we ever hear about are the derailments, and lack of oversight! Thanks for an awesome video!

[@mailleweaver]

The "hunting" phenomenon reminded me of something that would probably make for an interesting episode idea for you: trailer design and loading. In a game called Space Engineers, I've built a lot of trucks and trailers of various types for hauling things, and it's taught me a lot about how trailers behave with different designs and load distributions. One of the things I've had to deal with has been similar to "hunting" where, when going downhill, my lack of ability to implement trailer braking causes the trailer to push on the truck. This tends to try to turn the truck, so I steer to correct. Once that steering turns the truck back to the balance point, the forces suddenly flip and I have to correct my steering the other direction. This tends to lead to a progressively violent lashing side to side and can lead to rolling the entire truck and trailer if I'm going too fast for my load or don't reach the bottom of the hill before the progression gets out of hand. It behaves like balancing a stick on end (with the truck being the stick). It's easy for the system to go out of control. All sorts of different hitch methods, trailer designs, and trailer loading can lead to stable or unstable systems. It's a really interesting topic to explore. That same game has been pushing me towards becoming a railfan, too. I once tried to design a train, and hours and hours of different designs led me to having a truck on each end of each car. I was still having trouble at that point so I started looking up actual trains to get design inspiration. I found it really cool that my own designs so closely resembled reality. My train attempts in the game were eventually stifled by having to admit that the game can't handle the complicated physics when the train gets up to practical speeds, but it's left me with a bit of a craving for trains.

[@Mirality]

For trailers, that is typically called "fishtailing", which may lead you to some interesting resources.

[@jeffloveless6536]

I have operated locomotives at the power plant I work at. Even after 15 years of driving them, fixing rails and doing inspections I learned more watching your video than I learned in 15 years. I look forward to seeing your next video.

[@itsmebatman]

It is fascinating how much engineering went into something that looks so simple.

[@danhtranquoc3745]

ok

[@itwontcomeout5678]

@@danhtranquoc3745ok

[@josephgaviota]

_It is fascinating how much engineering went into something that looks so simple._ I think that's true of a lot of things. When you watch anyone perform a task that they're really good at, it just looks so easy. I have come to the conclusion that the easier something looks, the more effort went into making/doing it.

[@PeteMcCrea]

Looking forward to the next videos in this series! I spent a couple of years working in Switch and Crossing Renewals in the UK between 2001-2004 and loved the time. The team I was involved in laid some of the first new CEN60 S&C (Switch and Crossing or ‘Points’) in the UK. These are built up from 60kg/m ‘CEN60’ flat bottom rail as opposed to the older 113lb/yard (51kg/yard?) and 110lb rail to give improved resilience and service life. In some parts of the rail network there was older bullhead rail that had been in service for close on 80 years and still had some life left in it…

[@jayski9410]

As a kid who lived near railroad tracks, we "played" with the contact patch between the wheels and rails. The train that went thru our neighborhood had to come to a complete stop before crossing an old bridge over the Hudson River. At that moment we'd place coins and other objects under the wheels to see if would flatten or crush them. It resulted in some cool oval shaped coins but mostly crushed and destroyed everything else. Yes I know this was very dangerous behavior but kids in the 1950's & 60's took a lot more risks than children do today. We didn't have video games, we had to seek our entertainment outside in the real world.

[@kkfoto]

Coins become nice big ovals, and nails become neat little swords. I still play with that from time to time 😅

[@j_taylor]

I was surprised how dang hot a coin is just after the train has passed!

[@FTW23-qq8nb]

@@kkfoto Maybe that inspired the coin to souvineer stamp machines.

[@JacobSmith_emjds]

Never even occurred to me that the wheels must be conical but now that I know it I don't know how I ever thought otherwise. Absolutely ingenious.

[@seymoarsalvage]

More train content? I'm here for it!

[@sorakojootti2725]

Choo Choo!

[@Lilly-Lilac]

Love your pfp btw!

[@PaulFisher]

BART in SF used to run on cylindrical wheels. When I rode it (early to mid 2010s), the wheelslip, the flanges riding the turns, and the corrugated wear patterns on the rail made the ride incredibly loud and significantly less comfortable. On a completely different track, you might want to check out Rio Tinto Australia’s fully automated ore hauling trains, running hundreds of kilometres from the mines to the ports. It’s truly amazing, running these thousands of metres long machines, safely, without an operator in the cab. (It helps that it’s a fully private system with no grade crossings, but still quite the feat.)

[@kaitlyn__L]

I’m baffled by why any modern late-20th century railway would use cylindrical wheels, since all the (basic) engineering on wheel shape was done in the 18th and 19th centuries. I would hope there was some specific reason rather than just negligence

[@bryanbush7139]

Great video! I have been a railroad designer for about 7 years now and am always excited to see great railroad content. It’s an interesting industry that often gets taken for granted. Looking forward to the rest of the series!

[@markmuir7338]

Kudos to the excellent animations in this video - they made wear progression immediately understandable. That's pretty hard to do in textbooks.

[@DMLand]

Love how they hit upon a quite modern profile as early as 1788, then kept evolving the track cross-section to the profile we see today. I wonder how the evolution of wheel profiles drove track profile evolution?

[@LeCharles07]

It's safe to say it had a rather marring effect.

[@LeCharles07]

Get it?

[@nickwallette6201]

Kind of looks like there were two, or maybe three, competing schools of thought, and the predominant shape alternated between them a few times. I wonder if we'll see a resurgence of some other shape, or if we've been able to calculate the ideal shape now, and it's just down to squeezing out the last few percentage points of efficiency and resilience.

[@wzdew]

I've wondered about most of this for a long time and now I finally got an answer. I'm curious how these factors apply in rail switching and crossovers. Thanks for the great videos. :)

[@PaulSteMarie]

Trains aren't just fascinating. They are also the most efficient means of land transportation. We really need, as a country, to buckle down, eliminate long-haul trucking, and move cargo by train if we're going to stop climate change. Also, train dispatching and control operations are a fascinating topic. There's not only control panels, but also huge sheets monitoring train progress and an entire safety protocol with control lock-outs of varying controls. I worked on a contact with SEPTA in the 80's to automate those spreadsheets and touring the facilities was fascinating, although the engineers at the electric plant weren't very happy about getting visitors.

[@Machinist2022]

@Practical Engineering I'm a train driver in the Netherlands, and it's very nice knowing a bit more about why and how rails wear out. Large part of the grinding on wheels and tracks also seems to come from slipping wheels when the track and wheels can't produce enough friction. And when trying to stay on schedule, you sometimes need to let the front wheelsets slip a bit but keep the power on for the rear/middle motors. Slipping season as I like to call it is coming up, autumn always brings leaves and leaves, well, we all know what leaves do to trains and schedules.

[@ppdan]

If you slip a lot with older material that still uses series motors ... the maintenance technicians will hate your guts for burning those motors.

[@everettrailfan]

Are leaves really that much of an issue? Over here in the Pacific Northwest we always get lots of wet leaves on the rails in the fall but it almost never produces any issues. Maybe because our trains are just bigger and heavier in general than European ones?

[@stephenallman2484]

​@everettrailfan they can be a issue. It can cause wheel spin which damages the rails. I can't say much about the Pacific Northwest but in the UK we have many passenger trains that stop and start fairly frequently due to the amount of stations and the proximity to one another. The leaves increase the stoping distance. We have RHTT (rail head treatment trains) which blast the head of the rail with high pressure water. Also some test being done using lasers. If you knew all that sorry for wasting your time. Also the species of plant the leaves came off can make it worse.

[@everettrailfan]

@@stephenallman2484 I just realized something too, we primarily have evergreen trees, so we don't have quite as many leaves to deal with, and here on the Sounder North line there is a total of 4 stations so really not a lot of stopping and starting. The real issue here is the threat of landslides in certain places and snow/ice up on the summit of Stevens Pass to the east, which dwarfs anything leaves could do.

[@BobDiaz123]

In my train club, where our equipment is 1/8 the size of the real thing, we started using free spinning wheels on passenger cars. Thus the left and right wheels can turn at different speeds. We have less issues with friction and everything seems to last longer.

[@chrisallen2005]

You are comparing apples to oranges when you compare your toys to the reality of shipping product of immense weight and still making a profit.

[@BobDiaz123]

@@chrisallen2005 Actually with the engineering of things, models are a good reflection of the real world and are used to predict how the full sized item will act.

[@ef-tee]

@@BobDiaz123the problem is that you lose the "self-centering" behavior, since the effective diameter of the wheels doesn't matter anymore once the wheels can spin at different speeds

[@BobDiaz123]

@@ef-tee One would expect the flanges to wear out sooner with the free wheeling system. However, this system was tested on a layout in Oregon for several years and they have not reported this issue. I'm not exactly what force is involved here, but there must be something that helps to keep the wheels centered on the track.

[@Skylancer727]

Main issues I see are wear. Like he said in the video, most trains have solid axel because of the forces at hand. One of the big pain points for rail is the bearings failing and to make free wheels we're either talking distributing less force from the bearing making it be the weight taking part like a car, or having two of them. And remember that with a car or a model you can hear when a bearing fails, you can't hear something a mile back and the yards are too slow to hear it there. That's why they need detectors. It could work with passenger which tend to be lighter, but definitely not for freight.

[@timecowx]

My great grandfather had a piece of rail that he used on occasion when he needed something to serve as an anvil, which is a pretty common practice. I held onto that piece, keeping in in the shed or garage for years until I finally had a use for it. It was a rail that had obviously seen a lot of use in its day and since my use was would be better served by a nice flat surface, I took it to a shop to have it machined flat. The machinist said he had done a few before and he would just do it that afternoon and I could pick it up the next day. I was fortunate that he was stubborn (and kind) because when I went to pick it up he only charged me $20. I say stubborn because he said he broke three bits on it, and only managed to slightly improve the top of the rail. According to him he kept trying because he had never had trouble with one before, but he thought it had something to do with the age of my rail and it having seen a lot of use in its time on a track, compressing and hardening it over time. Now I'm wondering if it was one of the harder rail segments you mentioned they use on turns, though I don't know how long they have done that, nor do I know the age of my rail, so hard to know for sure. I just thought it was interesting (if true) that rails might harden as well as wear, over time.

[@Ice-Fall]

I have a 6" rail, 12" long. A friend with a mill flat topped that rail. Great anvil! I also have 40" of 8" rail. If yours is 8", then I believe it is the harder steel, than that of a 6" rail.

[@alastairvize7052]

That was just wonderful; lucid explanation pitched at exactly the right level for the interested layman. Great stuff - thank you.

[@Yojibby]

I’m excited for your next deep dive on the engineering of airports! There’s a ton of interesting engineering that goes on when building airports, even small ones with no commercial service.

[@TheIrishBosnian]

I don't even study engineering of any sort but its fun to watch. Its entertainment. I'm a "How It's Made" TV show guy.

[@naamadossantossilva4736]

Yeah,the special porous concrete they use to prevent crashes is amazing.

[@johnopalko5223]

@@naamadossantossilva4736 You mean EMAS? I remember when they first came up with that. It was revolutionary. It's not used where you have room for a full-sized RSA.

[@hkr667]

EMAS is my favorite feature, but it feels like airport design in some ways is just in its infancy. I love the plane specific taxi route lights too.

[@DryBones111]

I could watch a 20-minute video on the engineering of runway lights.

[@Highraven]

Just wanted you to know my family are so thankful for all your videos. Always highly educational and entertaining! Not easy to do both well!

[@happyslappy5203]

Fun fact: French HST (TGV) broke 3 world speed records on rails without any issues: 380 kph (1981) 515 kph (1990) 574 kph (2007)😀

[@AccAkut1987]

I wouldn't call having to regrit the tracks and replace the overhead power lines "any issues" 😅 It was a stunt, and everything had to be prepared and repaired afterwards.

[@jimrennison1]

I bet that if you were to interview any of the engineers on the amazing TGV project, they would tell you that before they set records there were many, many issues to be resolved, but they did resolve them.

[@happyslappy5203]

@@jimrennison1 I'm talking about the speed record not the preparation of the record. On 3rd April 2007 the TGV train reached 574 kph in 13 minutes without any issue. btw on 29th march it reached 568 kph, and 541 kph under the rain. No issues during the speed tests.

[@tiggy2756]

@@AccAkut1987 It was the 1955 speed record 206 mph that damaged track and overheads , the current world record high speed run 574 kph required very little attention afterwards

[@MattHobbie]

I am one of those guys that doesn't mind waiting at a railroad crossing. I love the vibration of those huge diesel engines! The raw power is mesmerizing to me. Love your focus on the railroad lately!

[@philip_fletcher]

Traditionally coopered barrels (beer, whiskey etc) are a similar profile to rail wheels for the same reason - they were moved on rails within the processing plant. I suspect the barrel profile predates (and was borrowed by) railways - might be worth investigating.

[@Reavenk]

A bunch of rapid-fire, concise, and intuitive examples that build up a story of constant innovation. Love it!

[@RailRider9571]

I’m a railfan, and I found your videos and I learned a lot, thank you for posting. Now I can be MORE of a train nerd

[@66block84]

Great video. I worked as a carman repairing rail cars in 1978. The following summer I worked on a section gang installing ribbon rail, quarter mile long solid piece of rail.

[@beboboymann3823]

Awesome report. I’ve been a rail fan all my life but your report shows that I am a locomotive fan with practically no knowledge of the rails themselves. Good job!

[@bc-guy852]

Well said! There's a lot more to it, (apparently) than the big noisy part at the front!

[@justinblin]

Waking up to Practical Engineering is pretty cool 🔥

[@nick_riviera]

Even as a Railroad engineer I learned something today! Great video Grady!

[@jovanweismiller7114]

Fascinating! I'm looking forward to the rest of the series. I grew up in a Division Point on the UP. My Granddad, my Dad, my three Uncles, & several cousins worked on the UP. I rebelled and went to work for the Santa Fe. I know lots about the working of the railroads, but very little about the engineering behind it all.

[@MikeV8652]

As a transportation historian, I've always been amazed that the railway (locomotive-hauled trains offering scheduled transportation of passengers and freight on flanged wheels and iron rails) existed about 50 years before the "safety bicycle" (two wheels of similar size with a chain drive and so arranged that the rider's feet could touch the ground).

[@daveash9572]

You might be interested to learn that there was a now abandoned type of rail called Barlow Rail which was used for the West Cornwall railway, and much of the railway lines in south wales. It was different to pretty much any other type of rail system, as the rail was flared in such a way that it was designed to be laid directly onto ballast stone, without the need for sleepers.

[@Skylancer727]

I think we can see why they went away then. Even today one thing you want to avoid is hitting something between the rails and it snagging a hose.

[@busman2000]

Thanks again Grady, yet again you have made the complex look relatively simple and straight forward, for those of us that find things like this hard to understand. Keep up the good work.

[@goodoldcarburetors5592]

He has such a comfortable voice to listen to. I love winding down with his videos at the end of the day

[@EwingTaiwan]

6:52 You said the "Out side diameter is 6mm less than the inside diameter" but the graphics actually shows a 6mm less for its RADIUS, that is **12 mm** difference between outside and inside diameter. Great video still!

[@MalloonTarka]

I've always noticed the sinusoidal movement when riding trains. I always assumed it was from sideways momentum acquired when going round bends that was sustained through the suspension. The fact it's actually from the wheel profile is so cool!

[@balaam_7087]

You have an excellent manner of conveying information. I grew up in a rural area with a substandard school. Most teachers were lousy. You remind me of the few who went above and beyond and excelled at reaching the students, the only ones I really learned anything from and the only ones I even remember. Thank you for taking the time to produce these fantastically informative videos!

[@seb2721]

So happy you’re doing all these series! I love learning about stuff I usually don’t think about.

[@zachpw]

The bit about the wheel going different speeds throughout the contact patch was really interesting. I suppose that probably applies to wheels on every vehicle, since they deform under weight and won't be perfectly parallel to the riding surface.

[@Ornithopter470]

At least with pneumatic wheels, they're "effectively parallel", as the tires deform to the road surface. So if the road surface is flat, the wheels should be parallel.

[@zachpw]

@@Ornithopter470 Hmm that's a good point. On the other hand, since a tire deforms so much, the contact area is going to be quite large, so I wonder if the edges of the contact patch might experience differences in speed beyond what the rubber stretch is able to account for. Doesn't the tire wear down purely because each point of surface doesn't perfectly match the speed of the road?

[@nickdumas2495]

@@Ornithopter470 The contact patch zachpw is talking about is within a single wheel, and the differences across the axle are handled by the differential. When your wheels are rubber instead of steel, they're going to deform for a relatively huge contact area. The different speeds across the contact patch don't need to cause slip, because the tire can compress so there's a different density instead. Rather than slipping faster to get the wheel around, it can simply pass more rubber at once through the slow zone as it compresses before contact.

[@bc-guy852]

@@stevexracer4309 NOT TRUE. As a Caterpillar guy I can assure you that ALL roads do NOT have a crown in the middle. Yes - roads have profiles, largely to deal with the elimination of water but the high point - the crown as you describe it - is NOT always in the middle. It changes as roads curve and if one direction is higher than the other.

[@Timoohz]

@@zachpw On car tyres, the contact patch is relatively flat tyre touching a relatively flat road, so there is not much grinding. The rubber has to deform to grip the asphalt but as it is flexible it bounces back. On rail wheel, it's not flat. In an exaggerated example, both 1 foot diameter and a 2 foot diameter part of the train wheel touch the rail at the same time.

[@user-dn4iv2ne6r]

There also is the "tilt" of the rail added by the tie plates so the cone face of the wheel and the face of the rail are approximately parallel. At least on older wheels, with which I am most familiar, the wheels are of a double conical design. Also, the radius of the flange is somewhat progressive so the flange seldom actually contacts the side of the rail. While seemingly small, the rail and wheel each compress somewhat while in contact producing a "wave" in the rail. This has been a limiting factor in the maximum weights of railcars. Another interesting factor historically is that the common steam locomotive with rods jump up and down on the rails imparting a pounding motion that requires more material in the rail head.

[@naamadossantossilva4736]

So that is why diesel locomotives were a big deal.

[@hedgehog3180]

@@naamadossantossilva4736 That wasn't actually the big advantage of diesel locomotives. Their big advantage was that instead of having big driving wheels, where their size was essentially your final gear, they could power all of their wheels through a gear train. This gave them much better tractive effort, ie. the ability to actually impart energy from the motor onto the track to move the train, this gave them an easier time getting heavy cargo trains moving and accelerating in general. This was actually a big enough problem on steam locomotives that they were often fitted with iron "tires", basically a big iron band around the wheel, to increase friction with the rails. Beyond that there were also all the regular advantages of internal combustion over steam, not having to carry around heavy coal and water and not having to regularly stock up on water, and being somewhat easier to fit an electric generator to. Though initially diesel locomotives did have a somewhat harder time breaking because they didn't weigh as much and weren't as good at compressing air.

[@user-dn4iv2ne6r]

@@naamadossantossilva4736It was one part of the equation. Geared steam locomotives, principally the Lima Shay, the Heisler, and the Climax were an answer to the pounding while also adding pulling power and flexibility for rough and light track. Steam engines can be balanced for one specific RPM while locomotives operate at a large range of speeds.

[@1978lburick]

Regarding wear on wheels and rails, on some curves you'll find grease pots to lube the wheels going into a curve. But some if not all locomotives dispense flange lube oil when needed (so no need to maintain the pots anymore). And for traction after a dead stop, they spray sand into the V where the wheel meets the rail. There are large sand boxes on locomotives front and rear. You'll see the sand nozzles at the leading and trailing wheels on each "truck". There is a Wabtec (previously General Electric)locomotive manufacturing plant in Texas, I would love you to take a tour (DFW area I think).

[@HandpickedTruth]

Pure fascinating stuff and I never thought about it till now.

[@AdamTaylor-RDL]

I'm unsure if true or not, but i went on a tour of a rail depot here in the UK, and they had a large wheel lathe to help keep the wheels the right shape, whilst touring that machine, they gave us the less contact per carriage than a (British) 50p coin, which was really amazing to me. Also explains why they can't brake all that delicately either in an emergency, with longer high speeds train having vast distances between applying brake and full stop.

[@hedgehog3180]

Trains are optimized for low friction and also enormous so as per Newtons second law it requires a lot of energy to stop them, which with the low friction is hard to apply. The Shinkansen maglev even has airbrakes because it literally has no friction with its track. I think high speed trains take about a km to come to a full stop at top speed, which is both a lot and then not a lot when you consider that they can be traveling at speeds of 350 km/h and carry over a thousand passengers, container ships need several km and planes need more. An effect of this is that the faster a train is the more spaced out the stations should be because otherwise it can't spend a lot of time at top speed, which is usually the most energy efficient.

[@AdamTaylor-RDL]

@@hedgehog3180In the UK except for HS1 (300kmh, or 185mph), mainline trains in the UK are limited to just 125MPH (201km/h), with a lot of the older stock, mostly EMU & DMU being 75 to 90 MPH (120 to 145 kmh). Thankfully I live on one of the 125mph mainline routes 200 mile up from London. I've been on one of them at near max speed before it was forced to do an emergency stop after a report of a vehicle stuck at an upcoming rail/road crossing after the barrier was delayed and hit the vehicle mid crossing the road. That was a very... unpleasant amount of force, but it did surprise me just how quick and forceful it came to a stop. I suspect that train was taken to a depot to have wheel flats removed, it definitely screeched a lot!

[@TerminusVox]

Finally a video about trains that explains why what we are seeing is important and why so many find them interesting!

[@Chronixx11]

Honestly love your channel! The insanely positive and curious attitude is contagious and always makes me look out to the world around me with more and more amazement! Thanks so much

[@carlthor91]

Grady, you showed all of the pictures of wheels on rails, ON tie plates (angled tie plates), but no mention of the importance of the tie plates in reducing wheel wear, or it's assistance in helping the wheels on corners. I worked on the railway, in the 70's, before working as a diesel mechanic then surveying. I am a retired mine planner/surveyor, originally trained, in the late 80's, by a retired railway surveyor. Best wishes from the far North.

[@dracrichards5785]

I was literally thinking about the shape of the wheels on a train like 4 or 5 days ago. This is hilarious. You just confirmed my suspicion that the wheels are connical to compensate for the curves in the track. Thanks for this video Grady!!

[@agbarugo]

the fact that there is a convention specifically for the interaction of wheels and rails is absolutely delightful

[@mmi16]

51 year railroader that has been retired for 7 years. There are more 'tricks of the trade' in railroad right of way engineering and the operating environment than most non-railroaders can even comprehend. Engineering hidden in plain sight.

[@fridaycaliforniaa236]

The most amazing thing to me is that you can make *any* subject become really interesting. This channel is gold

[@HesterClapp]

5:21 This is especially severe on the DLR in London. The trains have to go around some very tight bends, and so they have wheels that are even more conical than normal trains. This causes them to over-correct on straight tracks, wobbling violently from side to side as they try to steer towards the middle. Interestingly, 新幹線 bullet trains do the opposite - they have especially flat wheels to ensure a smooth ride, since they travel on mostly straight tracks anyway

[@BostonClipper]

The Web does more than elevate the rail. Like an I-beam, the height has a strength function to distribute the moment load across more ties reducing the need for a larger foot. Increasing the web height would reduce the required foot size.

[@johnsmith1474]

Ah, no. There is no "strength function to distribute the moment load across more ties" ie the height has no effect on the load below it. And why would it?

[@BostonClipper]

The cross-section of the railroad rail is two dimensions. The rail exists in three dimensions. The load of a moving train in the third dimension creates a dynamic uniform load along the tracks. The best way I can explain it is a hypothetical example. If instead the normal wood tie spacing {19"} consider if that spacing was multiplied by ten times or more {190" or more}. The foot of the rail would be increased proportionately to carry the new load but if the height stays the same...the rail would fail.

[@davidkantor7978]

It seems to me, that the web supports the load between ties. Between ties, there is no support; the rail just has empty space below it. The web provides the strength needed to resist collapse over that span. Between the ties, the rail is a bridge. The web assumes strength in that bridge.

[@davidkantor7978]

… assures strength…

[@stevefirst9521]

Having just taken a cross country trip by rail, I find this all facinating. What amazes me is how all the switches are set correctly to route trains to the correct places safely. Please consider a video series on train controlling and switching.

[@Jopey_Meow]

Not even a train guy, but I'm absolutely here for this series. Love seeing your stuff in my feed! Great video as usual. 🎉

[@TRAVISGOLDIE]

I thought I’d find this boring but as always Grady elevates and expresses so well it’s taught me something new😊

[@PreservationEnthusiast]

*Brady

[@siobhangraham7280]

That's the thing that I love about trains - they're a perfect example of human engineering, including the constant strive to optimize. Fascinating machines that have changed so much since their inception.

[@crackedemerald4930]

Trains rights

[@hedgehog3180]

They're basically the result of trying to build a transportation system optimized for energy efficiency, which makes the physics, maths, and engineering parts of my brain really happy.

[@davidbishop4015]

Thanks for sharing another practical video Grady. You make it very easy to understand the content in your videos. I enjoy and look forward to the next video that you will produce. It was nice to see the family. Stay safe.

[@fleendarthemagnificent7372]

Absolutely delightful and educational video! I have enjoyed trains since I was a kid, but my liking of trains started from finding my first glass telegraph insulator in the ditch of the track that was behind my house. That was 1979 and I was 8. I have been collecting insulators ever since. My first insulator was a clear CD 155 Whitall Tatum No1 and I still have it to this day. However, in my hunts for more insulators, I found trains just as fascinating and I still remember the last train with a caboose rolling down that track about 1981 just before they decommissioned that track and took it out. Great memories! Good education! I had no idea that so much math and calculations went into wheel and rail design!

[@sadgeman4589]

Engineering and the math behind is so freaking cool. Grady does a great job explaining it, as usual

[@pkonneker]

Woah. Seeing the features of train wheels and knowing all the reasons behind it is like two different worlds. This was really fun

[@minnesotaboy]

I had never thought of the solid axle and how that needed to be dealt with for curves on trains. Very nice video. Thanks!

[@chrissim4386]

I just started as an commisioning engineer for plants that produce rails, it´s nice to get some more knowledge about how they are used.

[@thegriffadillo9762]

I'm an industrial engineer who has recently started in the rail industry so this series is perfect! (even if I only work on the simulation side)

[@HammondOfTexas0]

I'm hoping one of the videos mentions rail grinding, which is how they restore the shape of the rails. The train they use to do it is quite impressive, but I've never seen anything explaining how they work.

[@samuelnelson140]

I operated rail grinders for over 10 years, then became a supervisor. Every railroad has a specific 'profile' for their tracks that matches their wheel profile. You basically remove a small amount of rail so the profiles match. Rail grinding can extend the life of a rail by removing minor defects and detecting internal rail problems. Was a good job. But a lot of stress

[@Dreyno]

@@samuelnelson140The same as polishing the frets on a guitar. You remove as little metal as possible to re-profile the top surface and extend the usable life of it despite removing metal to do so.

[@tjtobin86]

I had no idea the wheel shape was conical. That' a genius solution involving no additional moving parts to wear out!

[@lonnieschreiner5879]

Fascinating. Definitely looking forward to the next segment. Had no idea about the complexity of RR rails. Thanks.

[@CreepSoldier]

Having in mind your videos about soil compacting, would be cool to see one related to rail, how they prep it for tracks and trains, and the differences between ones for high speed rail, cargo, metro, etc

[@MsCriticalthinker201]

There's basically three types of rail in use today. The rail section you see in Grady's video is called Tee rail, the regular classic shaped rails in almost all railroad track. Next is Girder rail. Used by streetcars, it is very similar to Tee rail in how the wheel rides on the rail, but has a 'U' shaped flange projecting to the inside to provide a pocket for the flanges to run in and keep the asphalt or other road surface materials away from the gauge face of the rail. Last is Crane rail. Very heavy duty with a very broad head and a short fat web. It is designed , obviously, for gantry cranes and other similar applications. Wheels used by the cranes to roll on this type of rail are typically double flanged, one flange on the gauge side (inner) , one on the field side (outer). These rails are almost always laid dead straight and often quite far apart from each other, 20 or 30' or better vs regular railroading standard gauge of 56-1/2"

[@landscapingspecialist]

A geometric differential! Wow I never knew any of this! So interesting

[@dylangreen6075]

Dude, this video was incredible! You just revolutionized my perspective on vehicular travel, for life. This was a crazy level-up for me. Major epiphanies. Thank you!

[@edwardblair4096]

Another interesting part of the physical rails is how they are used as part if the sensing and signaling system to keep track of where trains are located in the system and when it is safe to move a train from one section to the next. Train location is vital for automatic crossing signals etc.

[@LillianCrawfishDE]

I always enjoy Grady's videos, but this one was really intriguing. I found myself saying, "Wow! I had no idea it was so complicated, but it totally makes sense!" More, please!

[@revjohnlee]

I was an avid model railroader so I knew some of this as a kid. I learned most, but not all, of the rest as an undergrad in C.E. You provided a bit more knowledge but, more importantly, you did an EXCELLENT job illustrating the principles. I remember a prof glossing over them and having to read about them in the textbook. On the rare occasions in the decades since, explaining what you explained in the video made people's eyes glaze over like they were listening to one of my Ash Wednesday sermons. (After a few years of practice, I went to seminary) You illustrated the concepts visually, simply and interestingly. Great job!

[@Tum_Tum_]

OMG! There is so much engineering behind this simple rail and wheel of a train.

[@MileyonDisney]

Conical train wheels is a cool concept. When I was a kid, my dad drove a truck. Whenever there was a badly wrecked truck in the yard, he'd take us down there to see it (kinda like the Drivers Ed highway scare movies). One time, there was a guy hauling train wheels and axles. He made a sudden stop, and they all rolled forward. squishing the cab in the process. That was over 50 years ago, but I remember it well.

[@Santibag]

From what I learned, trains are one of the most common autistic interests. I was a train fan since 1-2yo, myself. I believe I had no idea on the capabilities of trains, at that time. So, it's something more than understanding them that makes them interesting. Of course, learning more about train only adds to the amazement. I personally have - rotating object interest - alignment interest - smooth movement interest etc. that make trains very interesting. For example, a train entering a passenger platform feels extremely satisfying. That smooth approach of that huge object, the alignment of doors and the platform, the contact of catanery and pantograph... So many things. I can count so many...

[@pootispiker2866]

This is the most Twitter thing I've read lmao

[@user-uz1yv2oc9v]

I'm happy to see a video about railways from your channel, you have a great way of explaining things and I've had an interest in trains for a long time so it's nice to get an easy to understand video on the topic.

[@The11devans]

Love the topic. Looking forward to the rest of the series