Stefano Ganddini

WRIT 340

12/11/13

Skateboarding’s Evolutionary Counterpart: Downhill Longboarding

Abstract

Since its advent in the 1950s, skateboards have drastically evolved in form and function. The

invention of the urethane wheel in the 1970s was the first stepping stone in creating what is now

known as downhill longboarding. Over the years, longboards have been modified to increase speed,

control, and stability. It has been found that longer decks, big wheels, and wide trucks are best

suited for handling these functions. This paper examines the unmistakable correlation between the

design and function of a longboard, as well as the role of some of the underlying physics concepts

behind common longboarding maneuvers.

Introduction

Skateboarding first emerged in the mid-1950s around the same time that the surfing scene

exploded in Southern California. When the surf was too low or too rough, surfers took to the streets

on home-made boards they created by attaching the wheels of roller skates to a wooden plank.

Their attempts to imitate the fluid motion of surfing on concrete pavement led to the birth of

“sidewalk surfing” [1].

However, it wasn’t until the early 1970s that modern longboarding really took off with the

invention of urethane wheels [2]. Urethane wheels created an unprecedented smooth and stable

ride, which—when coupled with adrenaline junkies’ unquenchable thirst to race down bigger, faster

hills—led to the creation of the modern longboard and a discipline referred to as downhill

longboarding. At speeds upwards of 60 mph [1], downhill longboarding involves riding down hills as

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fast as possible, either in organized races or recreationally.

While the main components of a longboard are similar to those found in a typical

skateboard—deck, trucks, and wheels (see Figure 1)—there are clear distinctions to be made

between the two.

Innovators have found that longer decks, soft urethane wheels, and wide trucks are better suited

for handling the high speeds that downhill racers manage to achieve [3]. An understanding of the

correlation between the design, function, and physics of longboarding will shed some light on the

evolution of the longboard and the rise of a longboard market increasingly devoted to developing

well-designed, high-performance downhill longboards.

Characteristics of a Longboard

The Deck

In the most basic terms, a longboard is simply a longer version of a skateboard. Most

longboard decks are between 35-50" long, whereas skateboard decks are usually between 28-32”

long [1]. The increased length gives riders more stability because a larger surface area makes it

easier to balance on. A longer deck also makes the board heavier, which translates into improved

stability as explained by Newton’s First Law of Motion, which states that objects with more mass

are more resistant to change in motion, or inertia [4]. This means that as stability increases with the

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Skateboard Components

Trucks

Deck

Wheels

Figure 1: The components of a skateboard – deck, truck, wheels.Modified from: http://www.skateboardhere.com/skateboard-parts.html

length of the deck, maneuverability decreases. Thus, in order to achieve the right balance between

stability and maneuverability, downhill longboards are typically in the length range of 37-43” [3].

While all skateboards are made of multiple layers of birch or maple glued together and

pressed into shape, some longboards are manufactured with additional materials such as fiberglass

and carbon fiber. These materials decrease the weight of the board while providing extra strength

and stiffness. The stiffness, or “flex,” of a board is its ability to react to pressure from the rider’s

weight [5]. Stiffer boards provide more stability at higher speeds and are easier to control because

they do no react to any pressures caused by the rider’s movements or by bumps in the road.

Many downhill longboards also feature a lowered platform called a “drop-through” or

“drop-deck” (see Figure 2). A drop-through features cut-outs and mounting holes which are used to

mount the truck baseplate on top of the deck, reducing the height of the board [1]. A drop-deck

mounts the truck baseplate below the deck like a normal skateboard, but features a curvature that

dips in the center of the deck. In both cases, the longboard sits lower to the ground, giving the rider

a lower center of gravity for increased stability.

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Drop-through deck Drop-deck

Figure 2: A drop-through deck mounts the truck baseplate on top of the deck. A drop-deck mounts the truck baseplate below the deck but features a curvature that dips in the center of the deck. Modified from: http://www.ehlerslongboards.com/index.php/complete-longboards-skateboards.html (left), http://www.aliexpress.com/cp/compare-9-skateboard-deck.html (right)

Drop-through vs. Drop-deck

Truck baseplate

Lowered platform

The Wheels

Longboards also have bigger and softer wheels than other skateboards, which allows for

higher speeds, improved grip on the pavement, and a smoother and more responsive ride.

Measured in diameter, longboard wheels usually measure between 64-80mm, compared to the 50-

55mm size wheels of skateboard [1]. Larger wheels translate into a faster rolling speed, as given by

the linear velocity formula v = rω where v = velocity, r = radius, and ω = angular velocity. Velocity

and radius are directly proportional which means that as radius increases, so does velocity.

Therefore, if two wheels of different size are rotating at the same angular velocity, the wheel with

the larger radius will have a greater velocity. Bigger, wider wheels also create more traction for

making turns due to the increased surface area of the wheel that is in contact with the ground,

called the “contact patch” [6]. A wider contact patch provides more grip for making controlled,

hairpin turns at high speeds.

Wheels are also measured by their softness, referred to as its durometer rating. Typical

skateboard wheels have a relatively hard durometer between 90A and 100A, while longboard

wheels have a much softer durometer ranging from 75A to 85A [1]. Made of polyurethane,

longboard wheels are characterized by their ability to “rebound,” or to return to their original shape

quickly after being distorted. When pressure is applied to a board, the wheels compress slightly as

the wheel rolls on the road. Then as the wheel rolls off the ground it rebounds and pushes against

the road, returning the energy that was used to compress the wheel and resulting in forward

momentum [6]. Softer wheels absorb the bumps of rough terrain, creating a smoother and more

controlled ride.

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The Trucks

Longboard trucks, the metal turning mechanism that attaches the wheels to the deck, differ

from skateboard trucks in two ways. First, the truck is usually wider to increase stability. Wider

trucks are more stable because the board has less leverage over the hanger (see Figure 3). It's not

uncommon for people to deliberately choose a wider hanger than normal in order to lower their

board's leverage and increase stability [7]. The tradeoff here is that wider trucks also result in a

decreased turning radius. However, the turning radius can also be adjusted by tightening or

loosening the trucks via the kingpin (see Figure 3). The kingpin is the bolt that holds the truck

together as one unit, and how tight it is affects turning radius. Loosening the trucks increases

turning radius because it reduces bushing compression within the trucks. Tightening the trucks

increases compression and therefore reduces maneuverability (turning radius). In other words,

tightening the trucks makes them “stiffer” and less responsive to board-lean, while loosening them

makes them “softer” and more responsive to board-lean. Because stability and maneuverability are

inversely proportional, downhill longboarders must make their trucks tight enough to be stable at

high speeds but loose enough to make sharp turns.

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Figure 3: Parts of a longboard truck.Source: http://www.warehouseskateboards.com/blog/index.php/2012/07/31/how-to-buy-longboard-trucks/comment-page-1/

Common Maneuvers

Accelerating

The most basic thing you can do on a longboard is accelerate. In downhill longboarding,

longboarders gain speed due to a concept known as gravitational potential energy. This is the

energy than an object possesses due to its location in a gravitational field. When a rider is

positioned at the top of a hill, he has a large amount of potential energy due to his mass, the

height of the hill, and gravitational acceleration. The formula for gravitational potential energy

is w = mgh, where w = potential (in units of energy per unit mass), m = mass, g = acceleration

due to gravity (assumed to be constant at about 9.8 m/s2), and h = vertical height. Potential

energy and height are directly proportional, which means that the bigger the hill, the greater

the potential energy. Potential energy and mass are also directly proportional; therefore,

increasing mass also increases potential energy. As a longboard begins to gain speed down a

hill, the potential energy he had at the top of the hill is converted into kinetic energy, so that by

the time he reaches the bottom of the hill, all of the potential energy will now be in the form of

kinetic energy [8]. Thus, the potential energy at the top of the hill is equal to the kinetic energy

at the bottom of the hill.

Braking

The easiest and most common form of braking on a longboard is known as foot braking. This

entails placing and dragging one foot on the ground while moving. Doing so creates kinetic friction

between the bottom of the rider’s shoe and the ground, decreasing the rider’s speed until coming

to a complete stop. Kinetic friction, the resisting force that occurs when two objects are moving

relative to each other and rub together, is the underlying concept behind braking on a longboard.

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The more advanced and most effective way to brake on a longboard is by sliding. Sliding, or drifting,

is also an example of kinetic friction at work, but this time between the wheels and the ground. This

phenomenon requires all four wheels to lose traction during a turn and the board to be turned

perpendicular to its direction of motion (see Figure 4). In downhill racing, sliding is often used to

shave off speed when entering sharp turns at high speeds [4].

Another form of braking is called air braking, which uses the idea of wind resistance, or

drag, to slow down at high speeds. Riders have the choice to either embrace this concept or resist

it. Downhill racers, for example, will usually try to eliminate the force completely by wearing

streamlined uniforms and helmets and engaging in an aerodynamic speed “tuck” (see Figure 5) to

reduce their surface area [8]. Other times you will see riders use air resistance to slow down at high

speeds by standing upright with arms stretched out to increase their surface area.

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Figure 4: A stand-up slide demonstrating that the board is perpendicular to its direction of motionModified from: http://londonlongboards.tumblr.com/post/10960141781/slide-jam

Conclusion

In recent years, downhill longboarding has been increasing in popularity and has created a

new market for high-quality longboards that can handle steep slopes, high speeds, and dangerous

curves. According to ActionWatch, a survey of surf and skate shops across the United States, overall

skateboard sales dropped 2 percent in 2010 while sales of longboards rose 43 percent [9]. There’s

something about the smooth, responsive ride of a longboard that goes unmatched by traditional

forms of skateboarding. Whether you’re looking for a relaxing cruise around the neighborhood or a

heart-pounding adrenaline rush as you race down a hill at 30+ mph, longboarding seems to have

something for everyone.

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Figure 5: A downhill racer performing a speed “tuck” to reduce surface areaSource: http://stokedskateboards.com/blog/staying-speedy-perfecting-your-tuck/

Author Biography

Stefano Ganddini is a Junior studying Industrial and Systems Engineering with an emphasis in

Information Systems & Operations Management at the University of Southern California. He started

skateboarding when he was six years old and rides his longboard around campus every day to get

from class to class.

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References

[1] "Longboarding." Tactics. Internet: http://www.tactics.com/info/longboarding. [Sep 30, 2013].

[2] L. Tadlock. “The History of Longboarding.” LIVESTRONG.COM. Internet: http://www.livestrong. com/article/351382-the-history-of-longboarding/. Jan. 6, 2011. [Sep 30, 2013].

[3] “Longboard Buying Guide: Downhill.” Muir Longboard Shop. Internet: http://www.muirskate. com/longboard-guide/downhill/deck. [Nov 18, 2013].

[4] C. Jones. “How Longboarding Works.” HowStuffWorks. Internet: http://adventure.howstuffworks. com/outdoor-activities/urban-sports/longboarding.htm. [Sep 30, 2013]

[5] M. Rich. “A Guide to Longboard Skateboards.” Life123. Internet: http://www.life123.com/sports/ inline-skateboards/longboarding/a-guide-to-longboard-skateboards.shtml. [Nov 18, 2013].

[6] “Longboard Wheel Guide.” Lush Longboards. Internet: http://www.lushlongboards.com/workshop/all-about-wheels-c-199_249.html. [Oct 7, 2013].

[7] “Anatomy of a Randal Truck.” Randal Truck Co. Internet: http://www.randal.com/guides_faq.html. [Dec 12, 2013].

[8] “The higher you go the more potential you possess.” The Physics Behind Longboarding. Internet: http://physicsoflongboarding.blogspot.com/2012/05/higher-you-go-more-potential-you-posses.html [Dec. 10, 2013].

[8] “To Resist or Embrace Air Resistance? That is the Question.” The Physics Behind Longboarding. Internet: http://physicsoflongboarding.blogspot.com/2012/05/to-resist-or-embrace-air-resistance.html. May 2, 2012. [Sep 30, 2013].

[9] M. Higgins. “Skateboarding Glides Into New Phase.” The New York Times. Internet: http://www.nytimes.com/2010/07/21/sports/21longboard.html?pagewanted=all. Jul. 20, 2010. [Sep 30, 2013].

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Other multimedia suggestions:

Video of Mischo Erban performing a speed tuck and setting a new world record speed of 80.83 mph: http://www.youtube.com/watch?v=EahajVER2mo

Video of a longboarder performing a stand-up slide to shave off some speed before entering a sharp turn (2:05 – 2:16):http://www.youtube.com/watch?v=kkviQ41u0eQ

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