I am working on my Esci Demag D7 and I want to turn the front wheels.

What is the best way to do this so that the wheels are exactly turned?

Here's an idea. Build yourself a little jig. Put the Demag on a flat surface with the wheels pointing directly ahead. Take either plastic or wooden strips and lay them against both sides of the tires, effectively to lock them into position. You could secure them to the surface with double sided tape. Then, rotate the rear of the vehicle to whatever side you want to put the tires at a different angle. Then you could cement them in place.

Again, this theory only as I have not actually tried it, but it sounds logical.

I will have to be a boring old fart and point out that because of Ackermann effect the inner wheel (that is the wheel on the inside of the turn) should be turned to a sharper angle than the outer.

Regards Dave :-)