RKP – TKP: term pertinence

I tried to bring the images to a similar scale (using bushing width as a reference), so that we can see the TKP is clearly smaller.

In this short post I want to explain why I think the terms “TKP” and “RKP” do not really tell us much about how trucks work.

Traditional kingpin trucks (TKPs) appear to originate from the trucks used for “quad” roller skates, before skateboarding was invented (hence, “traditional”) (more on this, here). The pivot axis (PA) of the truck is at an acute ∠ (not right ∟), angle with the kingpin (KP) (more on this, here) and the axle of the truck is offset forward (forward rake). Notice that the pivot pin is not in line with the PA (I’ve written about this cringe-worthy flaw in this article).

Reverse kingpin trucks (RKPs) started in the late 1970’s, probably by Randal. The KP ends on the other side of the axle (hence, “reverse”) (Don’t be overly confused. The principle is basically the same. RKPs are just taller) The KP is at a right angle with the PA and there’s minimal or zero axle offset. This design has, possibly accidentally, gotten the pivot alignment right.

These two designs are so strongly imprinted in the imagination of truck makers, that there are remarkably few variations. However, it is important to note that there is no reason to keep the offset of RKPs close to zero, or the pivots of TKPs misaligned with the PA, nor is there any constraint for the KP/PA angle. An example of an RKP breaking the mold is Carver’s CX front truck, with significant backward offset and an acute KP/PA angle. An example of a TKP finally fixing the pivot pin/PA alignment is Surf-Rodz’s “Traditional” trucks.

Even further, the very idea that trucks are categorized based on where the KP is in relation to the axle is on shaky ground. What would we then make of Tracker’s offset truck (on which I focus in this piece), whose kingpin intentionally intersects the axle? Is it a TKP or an RKP truck (answer: not that it matters, but it’s neither)? More to the point, given that axle offset and KP/PA angle are enough to describe a truck’s basic geometric and physical character (for more, see here), while also its KP position relative to its axle is inconsequential, why use the conventional but hollow TKP/RKP terminology? If anything, the perpetuation of these terms only stifles the imagination of truck makers, who appear constricted by the same old two blueprints and cannot seem to at least correct obvious and easy to fix faults.

I’m not arguing there’s no use in those terms at all. At the very least, they denote the 1970’s blueprints still ubiquitous today. I’m just saying that offset (aka rake) and KP/PA angle is largely independent of whether the axle is in front of or behind the KP and that the former characteristics are more pertinent and have more descriptive content. Consumers must realize that the common designs of TKP and RKP trucks share the same principle, but differ only in offset and KP/PA angle.

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