Re: Tire Change Question

John Cole Wrote:
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> Kelly, how do you center the tire on the wheel, is
> there a notch in the wheel that you push the tire
> up to? I used to change starter ring gears on
> manual transmission truck flywheels which is a
> miniature scale to locomotive wheels and tires.

There are as many methods as there are shops. Here is one of the traditionally more popular. The main idea is to get the tires accurately centered between the ends of the axle.


A page from the US Army steam locomotive manual

The wheel centers themselves are usually too irregular to trust with how the tires are spaced, being often as not out of round, wobbly, eccentric, and or with rims set back different distances from the ends of the axles. Where I worked, if possible, we would take a skim cut off the o.d. of the wheel centers to make them round and concentric. Then, if possible, we would face the outside edge of the rims to an equal distance in from the axle ends, then order tires with lips on the i.d. to engage with that face.

Barring that, we would drill and tap three holes around the inside face of each rim, then fit custom stepped blocks for the back face of the tire to butt against at the proper back-to-back and centered between the axle ends.

It's impressive how flexible larger diameter wheel centers are. For example, if you take an inside micrometer and measure the back-to-back at three places around the circumference of a set of mounted tires while the wheel set is still sitting on the horses with the tires off the ground, then crane the wheel set onto the floor, and measure those three spots again, they will have changed, i.e. the wheel set will sag and distort under its own weight before it is even supporting the locomotive. If you rotate the wheel set one half turn and measure again, the back-to-back will have changed again. If you are turning tires in the wheel lathe, the wheel set is driven by dogs that grip the outside face of the tires by jacking out from the lathe faceplate. If the tire is wobbly by say 1/16", which would make for an uneven width flange, you can crank on the dog jack where the tire has wobbled out, to flex the wheel center and bring the tire truer before cutting metal.