The trucks on a Luge are both a mounting for the wheels and its means of steering. As a result they are integral to the performance and handling of your board. As a Luger you have three main choices, the Luge Truck and RII 180 made by Randal, and the Z-Roller.

Randal Luge Truck
The Randal Luge Truck is the only Streetluge specific truck that is commercially available. It's 300mm wide floating axle and steep Kingpin angle makes it stable, fast and controlled. Randals require a bit more pressure to turn than the Z-Rollers, this means that you have more control over them and where they are pointing. Steering is not an "all or nothing, hold onto your nuts, here we go" experience. They are great on straights, high speeds and longer, sweeping corners. Of course you can still set them up loose to get through tight hairpins (at the expense of some high-speed performance), they may not be able to turn in quite as quickly as a Z-Roller, but you will probably have more control on the exit. All this comes at a price though, up to £80 per truck!

Z-Rollers
Z-Rollers are considered to be more "turney" than either of the Randal products. Many find that this means that the can throw their board into a corner faster and harder than on Randals. However, I also find that you are prone to over-steer and end up correcting yourself on the way out of the corner. At speed and on the straights the Z-Rollers sensitivity makes the board twitchy, prone to speed wobble and harder to keep control of. These trucks are quite wide (235mm), also have the floating axle and were available long before the Luge Truck, which lead to their popularity. They are also about half the price. However, at the end of the day these were originally a longboard truck, and weren't very good at that.

Randal RII 180
Randal also makes the RII 180, truck of choice for the Buttboard (Classic Luge). These are much cheaper than both of the above, a set of three will cost about the same as a single Randal Luge Truck. They are a compromise in terms of quality and performance, and like the Z-Rollers were not designed for Luge. They do not have the floating axle and they are not as wide (at 180mm) or tall as the Z-Rollers or Luge Truck meaning that they are less stable and may need a lot of risers to stop your board grounding. Importantly though, apart from the price, is the fact that the Kingpin design is the same as the Luge Truck. This means that it has similar turning characteristics, making them predictable and easy to set up. As stock they come with yellow (soft) bushings, for Buttboard and Streetluge these will need replacing with hard or hard/medium rubbers depending on your weight/riding style.

Randal 180s traditionally have quality issues, with drill holes often being several mm out of line. This has resulted in a new breed of copies and alternatives for companies such as Urban Blue and Holey. These trucks are quickly taking over the market due to their performance, low cost and quality manufacture.

These key differences in performance between the Randal and Z-Roller trucks can probably be explained by the way the hanger attaches to the base plate (see pictures). The Z-Roller is similar in design to a "Street/Trick" skateboard truck, with the Kingpin behind the axle. On the Randal the Kingpin is above the axle at 90 degrees to the steering angle. This means that on the Randal the hanger, when pivoting, is not fighting against angle of the Kingpin. It also means that they are easier to adjust and in the long run there will be less stress, ware and damage to the bushings.

To be honest this really isn't an argument any more, fewer and fewer riders are using Z-Rollers. When it comes down to it they are twitchy, hard to adjust and simply weren't designed for Luge. If you have the money, buy Randal Luge Trucks, if not get the RII 180s or a similar, wide axle, longboard truck and upgrade when you can.

Joel

Further Reading:
UKGSA Forum Topic: Streetluge Truck
UKGSA Forum Topic: Z-Rollers