How do train wheels not skid or lose traction?

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Basically the title. Considering that train wheels are made of metals and run on metal tracks, how do they prevent wheelslip or loss of traction especially when starting with heavy loads or when going uphill? I’ve heard of sandboxes which can be used to provide more grip by spraying sand onto the track but I’m not sure if they’re still prevalent.

Thanks!

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12 Answers

Anonymous 0 Comments

Weight, plain and simple.

Trains weigh hundreds of tons and the wight alone will overcome the lack of friction. Similar in principal to putting sand bags in the back of a 2 wheel drive truck during winter, more weight=more down force=better traction.

On a side note: overhead cranes in factories also run steel wheels on steel rail

Anonymous 0 Comments

They can slip. The engines are powerful enough to spin the wheels in place. But that would damage the wheels and the rails, so they start in a low gear. There are engineering tables with friction coefficients for steel on steel, they know the calculations and new people are always mentored. They are called engineers for a reason

Anonymous 0 Comments

Wheelslip on trains can occur in heavy rain, oil on rails, and especially leaves – all these factors add to increased stopping distances and reduced traction.

Anonymous 0 Comments

There’s two kinds of friction: traction/grip (good) and rolling resistance (bad). Steel wheels on steel tracks won’t provide as much traction as rubber on asphalt, but they’re still good enough to gradually accelerate/decelerate trains. The rolling resistance is far, far less, which is why trains are so energy efficient.

Anonymous 0 Comments

Open your dominant hand, place it palm-down on a table or countertop, and run your hand back and forth along the surface. Slides relatively easily, right?

Now, take your other hand and put pressure on your dominant hand. Try to run your hand back and forth on the surface again. Much harder, right?

This is how grip with trains works. Relatively slippery surfaces with little friction build a lot of friction when there’s pressure.

Anonymous 0 Comments

**short answer:** weight

**more details:** wheels are round, so only the very very bottom of the wheel touches the rail. also, [train wheels are angled](https://www.raildamage.com/wp-content/uploads/Wheel-rail-contact.jpg) so only a tiny part of the wheel actually touches. I read that it’s less than a square inch per wheel actually touches the rail. and trains are really heavy

* train car weight: roughly 200,000 to 300,000 pounds
* a car with 8 wheels would mean each wheel has to carry 20,000 to 40,000 pounds of weight
* less than one square inch touching the rail, means you have 10 to 20 tons of weight on the area about the size of a quarter (the coin) pushing that wheel into the rail

a practical example: a hockey puck would slide easily across a wood floor, right? but if your friend stood on the puck with their heel and had their whole body weight on it, it would be nearly impossible for you to move the puck, right? even though it normally slides on the wood floor easily?

same thing with the train wheels. your hockey puck is now metal and the size of a quarter sitting on the rail, and your friend weighs 15 tons. it’ll take a lot of force to make it slip lol. hope that helps

Anonymous 0 Comments

Trains are very heavy and that does create a lot of friction but sometimes the weight of the train and the friction it creates isn’t enough. The drive wheels sometimes need help going up steep hill L/mountains or even sometimes getting started out. In these cases the locomotives have a sand mix they can put on the track that increases the friction. If you’re ever stopped by a train you can see the sandbox if they are going slow enough.

https://en.wikipedia.org/wiki/Sandbox_(locomotive)

Anonymous 0 Comments

They do. Any British computer can tell you that “leaves on the line” Is a common reason for trains being late. The leaves get crushed into a paste, which reduces friction and the wheels slip (on acceleration, braking, or climbing)

Anonymous 0 Comments

You’re correct that the friction between the wheel and the rail is much less than that of a rubber tire on a road. Because of that, the acceleration of trains is usually much slower than that of a passenger car. Many modern passenger trains are what’s called electric multiple units, where many of the axles along the train are powered. This gives the train a higher portion of the total mass that rests on powered axles, usually allowing them to accelerate faster than locomotive-hauled trains.

Sometimes the wheels do slip and sand is still used to mitigate this during certain less favorible conditions. When the wheels slip during braking it can cause flat spots on the wheels which you can hear as a train passes. These have to be removed by machining a layer of metal from the wheels.

Leaves are particularly bad for traction on railways, so much so that some passenger railways even adjust their timetables to add extra time during the fall to account for the slower acceleration and braking.

Anonymous 0 Comments

The friction coefficient of steel on steel is quite good.

https://www.engineersedge.com/coeffients_of_friction.htm

I suppose the idea that metal on metal is slippery comes from having seen some lubricated linkage. Remove the lube and it grinds bad.

Or maybe from ball bearings. Which are lubricated too. But regardless. Ball bearings have no friction. All contacts are rolling contacts.