EMD's HTCR radial truck is probably the most technologically advanced piece of equipment on locomotives. It's an amazing design. Yes we all know it can steer it's leading and trailing axles into a curve, but it doesn't stop there. Nerd time!
Using the HTC as an example:
Weight is transferred from the frame to the truck center plate (connection 'pin') to the bolster (connects truck to the center plate) then to the truck's outside frames and then to the axles. Since the weight of the locomotive is centered on the center plate, when high tractive effort is applied to the truck, a weight transfer takes place like in a car. The front axle of the truck comes up (not noticeably by eye sight) but it can reduce tractive effort drastically. This can cause the front axle of each truck to slip while the remaining axles do not.
With the HTCR truck, doesn't have a center plate or a truck bolster, but still has a center-pivot pin which only holds the truck to the locomotive's frame. The weight transfer happens through four rubber compression springs located between each outter axle and the center axle stopping this occurrence.
If you put an HTCR truck under your average SD40-2, you could increase tractive effort by roughly 28% (if I remember that article correctly...
GE Tried to compete but only figured out the steering capabilities. Their problem is is that only the center axle moves. For some reason unbeknownst to me, this causes the truck to put a lot of force on the inside edges of the curve (Canadian Pacific reportedly has been noticing this, yet I haven't heard anything of the same from CSX) The only thing I'm not impressed with by EMD is that they only use 2 inverters; one per truck. Whereas GE uses 6; one per axle. The problem? When an EMD A/C traction locomotive starts slipping, it decreases power to all axles on that one truck where the GE decreases power to only the slipping axle(s). I'm also a bit impressed that GE is cranking 4400hp off of 12 cylinders where EMD is still using 16. (Side effects of two-stroke diesel engines ya know
So now my nerd rant is done....