Putting a brake on friction theory

FFrom Mr Timothy Birrell

Sir: My understanding of wheelslip protection as fitted to modern trains is that its principal purpose is not, as with anti-lock braking on cars, to improve the rate of slowing, but largely to protect the steel tyres on train wheels from developing flats: that is, worn flat surfaces caused by locked sliding contact with the railhead.

In other words, it is concerned with avoiding the considerable expense of having stock out of traffic from premature tyre-turning. I recall not long ago reading in the railway press that there is some research evidence that a train, unlike a car, stops more quickly in a locked wheelslide than with the repeated application and release of the brakes caused by automatic wheelslip protection.

Yours faithfully,

TIMOTHY BIRRELL

Lockerbie,

Dumfriesshire

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