# Straight Axles



## KmH (Apr 12, 2015)

I race go karts.

Go karts use a straight rear axle.

To turn the kart, the inside rear tire lifts off the track and we go through the turn on 3 wheels.

The steering geometry, flex in the chassis, and how much the rear axle flexes accomplish that in turns.

We have a selection of rear axles of different stiffness as one way we can adjust the kart for different race tracks.

Street cars have a differential that lets the outside wheel go faster than the inside wheel in a turn.

Train trucks (bogies) have straight axles too.

Granted railroad track turns are not very sharp, the inside wheel is still going to have a path that is shorter than the outside wheel, and the inside wheel will have to go slower than the outside wheel.

How do trains turn?


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## neroden (Apr 12, 2015)

With a lot of screeching as the wheels turn faster (or slower) than the path along the track. Yes, trains spin their wheels and scrape the track going around turns.

On extremely shallow curves, this is alleviated by the conical wheels, where the outside wheel moves to the larger-diameter part of the wheel and the inside wheel moves to the smaller-diameter part of the wheel (work out the geometry for yourself).

But on serious curves, the answer is loud metal-on-metal screeching.


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## railiner (Apr 12, 2015)

Don't they use some sort of track lubrication system in some places on very tight turns, to ease the friction?

Found this example..... http://www.railsco.com/~automatic_track_lubrication.htm


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## KmH (Apr 12, 2015)

I find it amazing they just let the wheels slip.


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## Ryan (Apr 12, 2015)

The wheels are cone shaped. As you go around the corner, the train shifts laterally, essentially making one wheel bigger than the other.

Link with pictures: http://charming.awardspace.com/trainwheel/trainwheel.html


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## railiner (Apr 12, 2015)

RyanS said:


> The wheels are cone shaped. As you go around the corner, the train shifts laterally, essentially making one wheel bigger than the other.
> 
> Link with pictures: http://charming.awardspace.com/trainwheel/trainwheel.html


Great illustration, thanks for posting!

Also, to help compensate for centrifugal force, railway curves are 'superelevated', (banked), to allow higher speeds. The degree depends on the curvature, and the optimum speed planned for that curve....


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## neroden (Apr 13, 2015)

This is one of several reasons sharp turns are discouraged on railway lines. On shallow curves, the conical wheels will make up all the difference. On sharp curves such as streetcars often go through, they don't, and the wheels do slip, and that's just tolerated, and the track is in fact lubricated to reduce squeal.


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