Some thoughts on suspension trucks

There has been talk about suspension trucks for mountainboards for as long as I can remember, probably for as long as there have been mountainboard trucks. It’s not a huge mental leap from riding non-suspension mountainboard trucks, to seeing bikes, cars, etc. with suspension, to thinking maybe mountainboards should have suspension trucks.

Now, some people will say, ‘No need, your legs are your suspension.’ And in a way they’re right. The riders legs do a lot of the work suspension would do and they have a really fast organic computer controlling them. However, that doesn’t mean there might be benefits from also having some kind of suspension or dampening built into the trucks. It’s certainly worth considering, even if just to get our heads around the fundamental concepts involved in suspension trucks, think about the advantages and disadvantages, and decide whether it’s worth pursuing or not.

Firstly, a quick nod the closest thing to suspension trucks currently on the market; the noSno flexi axle.

Goofy’s noSno Flexi Axles

Now, we have to be clear that these haven’t ever been claimed by noSno to be suspension trucks, and although they do a lot for dampening rough terrain (and have other advantages too) the problem with noSno flexi axles is that they suffer from ‘bump-steer’. This is important because it’s one of the big challenges in designing mountainboard suspension trucks. Bump-steer occurs when one wheel hits a rock and gets pushed up. Since the wheels are connected by an axle which is mounted at an angle to effect steering, one wheel hitting a rock can cause the board to steer. Riding over lots of rocks causes lots of bump-steer and can make the board difficult to control at speed.

So, now we understand the need for suspension a bit more and have a reason to explore it, let’s get the basics right. First some quick definitions of the differences between ‘suspension’ and ‘dampening’. Flexi axles (noSno or otherwise) are designed to provide dampening. They reduce the effects of rough terrain on the board and the rider, but they are not suspension. To be a true suspension truck the wheels would have to actually be suspended in the same way bike and car wheels are. That means that when they are being ridden they are held in equilibrium between the spring effect pushing the board up (or the wheel down) and the weight of the rider pushing the board down. Now that we know the difference, we can throw the differences aside as the aim is still the same; to reduce bump-steer and give a smoother, more controllable ride.

The most important fundamental concept to get your head around when it comes to suspension and dampening trucks is that each wheel needs to be able to move vertically to effect suspension/dampening completely independently of the truck moving diagonally to effect steering. Time for a quick sketch…

Steering and Suspension Angles

It’s this keeping the suspension independent from the steering that is the biggest challenge in designing suspension and/or dampening trucks, partly because there isn’t much room to work with, and partly because of how complex suspension design actual is.

Here are a few examples of some of the designs people much smarter than me have come up with:

Beiran’s Flexi Axle Trucks
ODB’s suspension truck idea
Eric Brinner’s suspension trucks
Josh Tulberg’s Suspension Trucks
Brennig’s Suspension Trucks

All sorts of designs, idea, models and prototypes out there. Some have lots of promise, some are overly complex, and some just won’t work as they miss the point about steering moving on one plane while suspension moves on another plane. Let’s try to get down to the simplest reduction of what would be required to build a flexi axle that doesn’t suffer from bump steer. Another quick sketch and it might look something like this.

Twisted flexi axles

This seems to me to be the simplest version of a flexi-axle truck that can (hopefully) keep steering separate from dampening. The diagonal base bolts on to a noSno baseplate (or Nompa deck) while the horizontal axles can flex for each wheel individually. I can’t think of a simpler way of doing it so this seems to be the starting point to begin designing better dampening trucks. Maybe it’s time for the ideas people to step aside and the engineers to step in. Either way, there’s lots of work that can be done with suspension and dampening trucks, but is it worth it?

Josh did a survey on SurfingDirt Forum, and found that of the sixty responses, 24  were not interested, 31 were some what interested and 5 were very interested in the idea of ‘suspension trucks’, and 33 of those 60 were interested in specifically seeing suspension on mountainboard trucks. Since mountainboard suspension trucks would only ever really be for riding very rough terrain they will always be a high-end specialty feature, but then again, we used to say the same about brakes