- Purpose of the article
- Who’s who
- What it is for
- The mechanism
- Marketing claims
- Other points on the website
Purpose of the article
The Curfboard truck came to my attention when someone asked me whether it makes geometrical sense in the same way that Major Arc trucks don’t. As soon as I saw it and the principle on which it turns (picture 1), I was intrigued. At first glance, there is no inconsistency about the mechanism: the design is foolproof and flawless. Still, I wanted to dig a bit deeper and model it (picture 2) to understand its geometry and determine what one can expect its ride to be like. In what follows, I present this model while simultaneously looking into a few of the claims the company makes about its truck, but only after a short introduction on the company and its aspirations with this product.
I must note that this text was written in the spring of 2021 and it is based on an earlier version of Curfboard’s website, which has since been revised. I provide links, when available, from web.archive.org.
Curfboard is a young German company that was started less than five years ago by a veteran designer of novelty skateboards, Stephan Augustin and his son, Jonas. With a successful Kickstarter campaign, they raised enough funds for the evidently popular Curfboard design to get off the ground. You may have stumbled upon the Streetcarver. Augustin was behind that. Presumably, with this new venture Augustin realized, and the fundraiser proved him right, that a design can have mass appeal only if it is simpler and cheaper than what his previous efforts were.
What it is for
This doesn’t mean that his new design is uninspired. Curfboard is meant to imitate the feeling of a surfboard and it incorporates significant insights on what a “surf-skate” truck is meant to achieve. Most important of those (as I’ve written here), and successfully executed with this truck, is a pronounced lateral motion of the deck’s nose when turning (I’m explaining this motion here for traditional trucks). Another one is an effortless turn. These two ideas are incorporated in all so-called surf-skate trucks, most prominently Carver’s C7. What the Curfboard truck achieves, as we will see, that the others don’t, is that it avoids dropping too much when turning. It avoids the vertical motion that is inherent in traditional single pivot truck designs with a long backward offset1 (again, check here for an explanation). See in picture 3 how a board with a regular truck with plenty backward offset drops when turning.
The concept is simple and easy to recreate in a model. Essentially, it is a quadrilateral with changing angles (picture 4). One segment, the black one labeled f, is fixed on the baseplate. Its opposite, the orange segment l, is part of the hanger. Segments g’ and k’ link the baseplate and the hanger and rotate freely, constrained only by the length of segments f and l. The quadrilateral lays on a plane at an angle with the deck. This angle determines how much the hanger turns on the ground when the deck is tilted. If it were 0°, the planes would be parallel and the truck wouldn’t work. If it were 90°, tilting the deck wouldn’t yield axle turn. The equivalence with regular trucks is obvious, so let’s call this angle’s complementary angle the pivot axis angle (PAA) of the truck. The balance line of the board, just as with regular skateboards, passes through the center of the axle. That’s it. It is an ingenious design for a skateboard truck, which permits plenty lateral movement of the hanger without too much axle turn or drop of the deck. We’ll see this in more detail while investigating four not entirely unjustified claims the company makes.
“No speed wobbles”
I do see merit in the argument that a long trail (for a definition of trail, see here, or the wikipedia on bike geometry) prevents instability at speed and that in fact the faster a skateboard goes, the more stable a truck with a long trail is. This claim seems even more convincing for this specific truck, which moves its hanger laterally much more than a regular long-offset truck does for a comparable turn (see pictures 4 and 5). However, I am also aware that skateboard stability is a very active research field and speed wobbles in particular attract great scholar attention (see my post on academic literature), without yet having produced conclusive evidence of what causes them. The argument that trailing wheels prevent wobbles has been made again by Neil Carver, but that formulation was sloppy at best (for a critique of his piece, see here). A counterargument that reveals trail as a non-definitive factor of stability, is that inverted rear trucks are obviously more stable than their front counterparts, despite their wheels being ahead of the PA (i.e, trail is actually negative). The point here is that Curfboard’s claims to have eliminated speed wobbles (homepage) ring slightly overenthusiastic, though not entirely unjustified in the context of a market saturated with fibs.
“The board elevates when turning”
Compared with regular long-offset trucks in regard to deck dropping while turning, Curfboard is unquestionably remarkable. That doesn’t mean the deck doesn’t lower at all when turning and it certainly doesn’t mean it actually “elevates” (tech data page video, 1:10) enough for “gravity” to provide a “restoring force” (see archived homepage). Likewise, I find it hard to understand what the website authors imply with the claim that the truck “self-adjusts to […] weight” (see more recent homepage screenshot). I do not have the actual proportions between the segments that constitute the basic Curfboard model described above, nor its exact PAA (I simply guessed these by looking at product photos and videos) and therefore I must assume it is possible there is a certain configuration of these analogies for which the deck rises. I just couldn’t find them! No matter how much I experimented with different values, elevation remained elusive. For the record, I found higher PAAs do offer deck elevation possibilities, but these PAAs would render the truck unusable. At any rate, my approximation yielded minimal deck rise (see picture 6, where the distance to the ground – the blue plane – is measured from the center of the deck). This was possible only with PAA=80°, which seems higher than what we see in photographs of the product.
Curfboard‘s designers can legitimately claim that when compared with regular trucks, the ride feels as if the deck rises; but objectively this is hardly the case. It is even harder to swallow that gravity (rather than forward momentum, as discussed in the previous section) is a restoring force. “Board elevation” and “restoring gravity” is marketing poetry. The skateboarding industry is particularly prone to play fast and loose with the truth and Curfboard is almost justified in this context. However, given the inventiveness their design exhibits, which represents a clean break from the industry in question, a more measured approach to marketing would have sufficed. It’s a bad look.
“No wheel bite”
“No wheel bites [sic] at even the most radical turns,” claims the homepage. This is the most convincing of the claims I examined here and arguably a great feat of the company and good news for top-mount fans. As explained above, I expect that the center of the hanger of the Curfboard truck remains largely at the same height from the ground when turning – or even slightly and briefly lifting, if indeed I missed a configuration of segment proportions and PAA (any reader with evidence to the contrary please submit it to me). During turns, the deck tilts and the half that is tilted lower does approach the wheels (picture 7; look also picture 2), but I estimate that this tilt-drop is never greater than 2-3cm, depending of course on tilt angle and deck width. I assume tilting of no more than 35° of a 10cm deck. That said, “the most radical turns” might prove to be problematic, though it does seem unrealistic that a rider would ever tilt the deck more than 35°. In any case, I lack experimental data. In my view, the poetic license of the “most radical turns” claim is permissible.
Since I addressed this issue with Major Arc, it’s fair to talk about Curfboard‘s bearings as well. I’m inclined, as a lay person, to accept that the hinges between the parts are fit for purpose, while keeping in mind what this truck is meant for. I grant that these bearings probably do not present any drawback in the turning action of the truck and that they are strong enough for skateboarding (however, the details of the warranty would interest me, as this is a relatively new product). I’m assuming they have done their homework on this and the bearing maker seems also trustworthy. At the same time, I understand that simplicity and low weight were key design goals, whereas multiple ball-bearings, or some other elaborate solution, would go against that. Since Curfboard is not marketed as a competition truck, or some fancy (re)invention of multi-link steering for the gullible, but as a lightweight, bushing-less, maintenance-free “surf” truck, it makes sense that a plastic bearing, one that requires no lubrication no less, was the choice of its makers. In sum, Curfboard’s convincing presentation is a welcome departure from the dodginess other brands have us suffice with.
Other points on the website
The rest of the text on the website is more accessible, so I will not comment on anything else, except that I find the website’s design and content appropriate: neither superfluous, nor sparse, but tastefully minimalist. One point I want to make (which I also made to the company directly via email months ago, when I started working on this article, without having received a reply yet) is that their “Q & A page” (picture 9) has a glaring mistake. The second pair of illustrations describes an “all-around” combination of maneuverability and speed. I understand this to mean that the intended turning radius is larger than the first suggested setup and smaller than the third. The configuration of the rear truck for this setup appears to be: regular (not inverted) mount on a wedged (not dewedged) riser. The wheelbase difference alone cannot account for such a difference in ride characteristics (i.e., radius) from the first setup and as a matter of fact, if the riser were 5°, the rear truck 30° and the front 60° (typical numbers and probably about what we see in the photos), then changing the riser’s orientation would result in decreasing the turning radius between these two setups. Then again, the text probably implies that the truck is meant to be reversed, but then that pair of photos is wrong. By the way, it’s commendable that the authors suggest reversing the rear truck for faster riding. An obvious setup suggestion (more, here), which, nevertheless, mystifies the skate community at large. Is the industry entering its enlightenment era?
Curfboard is a simple but ingenious design, which shows that innovation can still happen in an oligopolistic, stale market. New ideas need to be given space to help evolve skateboarding as a distance sport and mode of transportation. A sport that will remain obscure, as long as creativity is outcrowded by mediocrity in unmeritocratic conditions. It would be better though if Curfboard’s marketing steered clear of speciousness and didn’t thus compromise its own integrity. The truck has a lot going for it. Most notably, it doesn’t lower the deck when it turns, with all the advantages this comes2; note also that it does not elevate it either, despite what the company claims. The point on which I would focus for future efforts is the return-to-center force, which is probably not adequate for long distance skating or, why not, racing.
1. The C7 is a double pivot truck, but it can be very well approximated as a single pivot truck; indeed, its second pivot is almost useless and Carver might want to reconsider keeping it for newer iterations, instead of lazily equipping it with stiff bushings.
2. In the linked video, the reviewer of Curfboard asserts that the fact that the board doesn’t lower when turned is a disadvantage. I do not see why though. He juxtaposes it with other backward-offset trucks, which indeed, as I also showed above, lower significantly when turned. But there’s no basis to claim that this is an advantage either.
In any case, it is a fact that trucks with forward offset, e.g., all TKP trucks, do not lower when turned (check here for visual proof), at least not as much as long-backward-offset trucks like all those so-called surf-skate trucks. I never saw anyone complain how Bennett Vector not lowering is bad. I wouldn’t say that either.