Railworks America

How do you add realistic traction onto a steam locomotive? A lot of steam locomotive slip when they start to move, but in railworks there is no wheelslip at all. For example you're starting your Just Trains A4 Pacific in the snow and you have to open the throttle to full. One of the problems in the real A4s is that they had a hard time starting in wet weather. Or you're driving your NKP Berkshire on a heavy fast freight in the winter. So how do you add wheelslip on locomotives?

K4 has wheel slip.