# How are wheels affixed to railroad cars? **URL:** \ **Category:** Factual Questions\ **Created:** [December 29, 2015, 8:24pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675 "2015-12-29T20:24:37Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [December 29, 2015, 8:24pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/1 "2015-12-29T20:24:37Z")
There have been a number of derailments in the news lately, apparently for weather-related reasons. Aerial footage typically shows the rail cars lying on their side near the track, and as often as not, the axle assemblies have separated from the car. A lot of the time the axle assemblies actually remain on the tracks, as if the rail car had simply been lowered onto them. So what’s the deal? Are these massive axle assemblies just held in place with a couple of M6 bolts? ---
**Author:** ![SirRay](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@SirRay](https://boards.straightdope.com/u/SirRay)\ **Post date:** [December 29, 2015, 9:13pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/2 "2015-12-29T21:13:36Z")
The “axle” assemblies are generally known as “trucks” in North America, and “bogies” in Europe. For most NA freight cars, the freight car is kept on the trucks by gravity, simply seated on the truck bolster (center beam), kept in place with a bolster pin sticking into the carbody bolster. No bolts or welding involved. On the bolster may be mounted “side bearings” which help stabilize the carbody in turns and such. The truck itself consists of several moving parts which are not necessarily bolted or welded to each other, e.g. the bolster is supported by springs in the sideframe, and the sideframes in turn are supported by the axle via bearings. [This image may help a bit](https://app.ntsb.gov/investigations/fulltext/RAB1203/RAB1203_3.jpg), as [may this one](https://app.ntsb.gov/investigations/fulltext/RAB1203/RAB1203_7.jpg). ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [December 29, 2015, 9:51pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/3 "2015-12-29T21:51:43Z")
On modern freight cars at least, the wheel axle assembly has a roller bearing attached on each end. This bearing fits into the side frame on the truck assembly. All held in place by gravity. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [December 29, 2015, 9:54pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/4 "2015-12-29T21:54:40Z")
I guess no one’s going to mention that the cars just sit on the wheel trucks. ---
**Author:** ![SirRay](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@SirRay](https://boards.straightdope.com/u/SirRay)\ **Post date:** [December 30, 2015, 2:00am UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/5 "2015-12-30T02:00:20Z")
> [@TriPolar](#): > > I guess no one’s going to mention that the cars just sit on the wheel trucks. Well, except for the fact that I mentioned that in the second post, I guess not…:dubious: ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [December 30, 2015, 7:43pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/6 "2015-12-30T19:43:56Z")
In Christopher Swan’s book \*Cable Car, \* there is a detailed description of the hardware beneath the wooden superstructure of the cars, which seems to resemble full-scale railroad rolling stock, at least where the metal hardware is concerned. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [December 30, 2015, 7:54pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/7 "2015-12-30T19:54:16Z")
> [@SirRay](#): > > Well, except for the fact that I mentioned that in the second post, I guess not…:dubious: I was being facetious, so far everybody had mentioned it. ---
**Author:** ![SirRay](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@SirRay](https://boards.straightdope.com/u/SirRay)\ **Post date:** [December 30, 2015, 10:45pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/8 "2015-12-30T22:45:27Z")
> [@TriPolar](#): > > I was being facetious, so far everybody had mentioned it. Umm, say what? There were only 2 response posts at the time, mine & Gary M’s - barely enough for a “Hi Opal” list. In addition, when I read Gary M’s post, I figured he was going further than my initial statement (that the car body is simply held on the truck bolster by gravity and aligned with the bolster pin), and was adding the fact that the truck sideframes are, in turn, supported by the wheelset axle roller bearings via gravity; they are not bolted or welded to the sideframe (again, this is modern N.A. freight truck practice). [Here is an stock image of some stored wheelsets](http://cache2.asset-cache.net/gc/181793158-railcar-foreman-james-harper-inspects-new-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=GkZZ8bf5zL1ZiijUmxa7Qf2FjX2Al1%2BYlprTrn7BVw4YqzPCdeHYeHghCSppDVCVvhSAIo8XJTNFgFSGfgttDg%3D%3D); Note the roller bearings already installed. Those bearings fit into the sideframe pedestals (in those ‘notches’ in the sideframe), and a wheel bearing adaptor goes between the pedestal top and the roller bearing, such that the sideframe rests on the bearing adaptor, and in turn the bearing adapter rests on the roller bearing (OK, it’s a bit more complex than that). Yes, everything seats and items are keyed, but gravity does the real work. [Here’s a page concerning inspection of roller bearings with some images that may help](http://www.aidtrain.com/products/AIDTANKDemo/inspect/pages/237/content.htm). So that machine elf can feel relieved, there are some bolts involved in keeping things together beyond the roller bearing end cap screws: there are metal pieces at the bottom of the sideframe pedestal called bearing retainer (frame keys), which are designed to keep the sideframe with the axles if the sideframe skews up due to…a derailment. Otherwise, they should play no roll in normal operation. So, sorry TriPolar, old chap, your facetious post was a very bad show indeed. 😛 ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [December 30, 2015, 10:55pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/9 "2015-12-30T22:55:55Z")
There are places in the world where track gauge changes, and the cars have to be lifted off the trucks of one gauge, while trucks of the new gauge are rolled underneath them. This is done overnight on a ferry in Canada, to Newfoundland’s narrower track gauge. The trucks are not permanently attached under the rail cars. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [December 30, 2015, 11:03pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/10 "2015-12-30T23:03:12Z")
> [@SirRay](#): > > So, sorry TriPolar, old chap, your facetious post was a very bad show indeed. 😛 Sorry, I mis-overestimated the number of responses agreeing with you. I’ll try to keep the train on the track next time. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [December 30, 2015, 11:43pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/11 "2015-12-30T23:43:06Z")
There are lots of you tube videos showing both wheel/axle changes and the complete changing of the truck sets mentioned by jtur88. Do a search for “train wheel change”. ---
**Author:** ![SirRay](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@SirRay](https://boards.straightdope.com/u/SirRay)\ **Post date:** [December 31, 2015, 12:58am UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/12 "2015-12-31T00:58:12Z")
> [@jtur88](#): > > There are places in the world where track gauge changes, and the cars have to be lifted off the trucks of one gauge, while trucks of the new gauge are rolled underneath them. This is done overnight on a ferry in Canada, to Newfoundland’s narrower track gauge. The trucks are not permanently attached under the rail cars. Quite so, although the Newfoundland Railway itself was closed in the late 1980s. A good image of [this operation is here](http://webspace.webring.com/people/ab/billmoores/Changingtrucks.jpg) - as you can see, lift up the freight car, roll out one set of trucks, roll in the other gauge truck, lower, and away you go. Following on GaryM’s comment, I know the gauge break from Russian Broad gauge to Central European standard gauge uses similar truck change concepts. I wonder about other nations such as Japan, Spain, India, Australia and so on with multiple gauges, maybe in the past they did this, but is it more common now to just transload freight between rolling stock of different gauges, particularly with shipping containers? ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [December 31, 2015, 1:48am UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/13 "2015-12-31T01:48:52Z")
What gauge is the railroad in Russia? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 31, 2015, 2:12am UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/14 "2015-12-31T02:12:36Z")
Russian guage: [5 ft and 1520 mm gauge railways - Wikipedia](https://en.wikipedia.org/wiki/5_ft_and_1520_mm_gauge_railways) Originally 5 feet and later redefined to be 1.520 meters which is about 1/8" narrower. The actual size didn’t change, just the center of the tolerance band. See [Track gauge - Wikipedia](https://en.wikipedia.org/wiki/Track_gauge) for more on worldwide track gauges than you ever wanted to know. ---
**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\ **Post date:** [December 31, 2015, 7:54am UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/15 "2015-12-31T07:54:02Z")
It’s too bad Sheldon Cooper isn’t a member here. He’d probably know the answers. Although he’d probably be a dick about giving the answers too. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [December 31, 2015, 5:37pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/16 "2015-12-31T17:37:02Z")
It is worth noting that the wheels are solidly mounted to the axles, and this is key to keeping the train on the tracks. It is the bi-conic geometry of the wheel/axle assembly that keeps the wheels centered in the tracks, the flanges are only a secondary safety device, and by design rarely touch the rails. This is also part of the reason that weather can cause derailments. The centering depends on the wheels having reasonably decent traction on the rails. If ice reduces the friction enough, then the wheels won’t center in the rails. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [December 31, 2015, 5:50pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/17 "2015-12-31T17:50:10Z")
> [@LSLGuy](#): > > Russian guage: [5 ft and 1520 mm gauge railways - Wikipedia](https://en.wikipedia.org/wiki/5_ft_and_1520_mm_gauge_railways) > > Originally 5 feet and later redefined to be 1.520 meters which is about 1/8" narrower. The actual size didn’t change, just the center of the tolerance band. > > See [Track gauge - Wikipedia](https://en.wikipedia.org/wiki/Track_gauge) for more on worldwide track gauges than you ever wanted to know. I wonder if this interfered with Hitler’s invasion plans in World War II–he might have wanted to use German rolling stock on Russian track as part of his invasion. ---
**Author:** ![Sangahyando](https://avatars.discourse-cdn.com/v4/letter/s/f14d63/32.png) [@Sangahyando](https://boards.straightdope.com/u/Sangahyando)\ **Post date:** [December 31, 2015, 7:18pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/18 "2015-12-31T19:18:10Z")
> [@dougie\_monty](#): > > I wonder if this interfered with Hitler’s invasion plans in World War II–he might have wanted to use German rolling stock on Russian track as part of his invasion. A large part of Russia’s reason for originally choosing 1520mm gauge for the country’s railways – rather than 1435mm, standard for most of Europe (and North America) – was to make things more difficult for prospective wartime invaders. It wasn’t a very successful ploy: basically it’s not difficult or very time-consuming to convert rail lines to a gauge which is different not by a great order of magnitude. In World War II, and World War I as well, Germany when advancing into Russia, just narrowed lines’ gauge to 1435mm: they had plenty of locos and rolling stock of their own 1435mm gauge, to operate the lines. ---
**Author:** ![SirRay](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@SirRay](https://boards.straightdope.com/u/SirRay)\ **Post date:** [December 31, 2015, 8:56pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/19 "2015-12-31T20:56:48Z")
> [@Sangahyando](#): > > A large part of Russia’s reason for originally choosing 1520mm gauge for the country’s railways – rather than 1435mm, standard for most of Europe (and North America) – was to make things more difficult for prospective wartime invaders. I’ve long ago heard that hinder invasions was not really a reason for the choice of Russian broad gauge, and the [wiki entry on Russian gauge agrees](https://en.wikipedia.org/wiki/5_ft_and_1520_mm_gauge_railways#Russian_Empire.2C_1842): > [@](#): > > It is widely and incorrectly believed that Imperial Russia chose a gauge broader than standard gauge for military reasons, namely to prevent potential invaders from using the rail system. In 1841 a Russian army engineer wrote a paper stating that such a danger did not exist since railways could be made dysfunctional by retreating forces.[citation needed] Also the construction of the Warsaw–Vienna railway in 1,435 mm (4 ft 8 1⁄2 in) was precisely so it could be connected to the Western European network, in that case to reduce Poland’s dependence on Prussia for transport. Finally for the Moscow - Saint Petersburg Railway, which became the benchmark, the choice of track gauge was between 5 ft (1,524 mm) and the wider 6 ft (1,829 mm), not standard gauge 1,435 mm (4 ft 8 1⁄2 in). Politics and corporate decisions played much more of a role in choosing a gauge during the early period of railroading - why did Ireland choose (or had chosen for them) broad gauge? Why such a mix of gauges in Australia. Why Broad gauge for the Indian Subcontinent? Lots of historic reasons, many of them kind of silly in retrospect, but as many articles on track gauge mention is that in the beginning of railroad development it didn’t much matter what gauge you choose for lines which went from the hinterlands to the coastal port cities, but when you started to connect cities which already had established, differing gauge local rail networks is when you run into trouble. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [December 31, 2015, 9:17pm UTC](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675/20 "2015-12-31T21:17:37Z")
Can anyone explain why they can’t just build the trucks with two wheels on each end of each axle, so they can just roll from one track gauge onto the other? [Next page](https://boards.straightdope.com/t/how-are-wheels-affixed-to-railroad-cars/741675.md?page=2)