An ode to the Shimano PD-M520, the world’s most reliable pedal

The decades-long story of one of cycling's most enduring designs, what is perhaps the world's biggest-selling clipless pedal, and a personal quest to find its inventor.

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Last week, I was washing my bike after a muddy gravel ride. As the hose’s jet of water struck the pedals, they spun in a flurry, shooting droplets of water off in graceful parabolas. As I watched, head a bit numb from exertion and still caked in filth, I remember thinking that there was a quiet, pragmatic beauty to the pedals as they whirred around.

The Shimano PD-M520s on my bike at the moment are at least a decade old, with the black anodising on the pedal body buffed to smooth silver by the rub of shoe tread on the axle and the ends scarred and scratched by falls. They came to me via a well-loved old Cannondale I bought from an old guy on a Norwegian classifieds website for 2,500 kroner (about AU$400), and have since travelled to the other side of the world, where they’ve been installed on three other bikes and clocked up thousands of kilometres – happy rides and sad rides, long rides and short. I’ve never really paid them much attention, because I never had cause to.

That day last week, though, I thought of the places those pedals have been and the memories they’ve been a small, relatively inactive part of. All the clicks and all the twists. I found the patent number etched on the pedal spindle, looked it up, and learnt that Shimano SPD pedals had a single designer, and that designer’s name is Toshiyuki Tanaka. After some Googling, I discovered that there’s an equestrian rider of the same name, and a prolific physics academic, but that neither of those are the inventor of the modern SPD pedal.

So here’s what we know.

Inventing the SPD

Twenty-ish years ago, working in a factory in Sakai City just to the north of Osaka, Japan, Toshiyuki Tanaka had an idea for a better bicycle pedal. In the dying days of the year 2000 – on December 29 – the company he works for, Shimano, filed the documentation for US Patent 6,446,529 B1. In the uniquely dry language of patents, Tanaka had come up with “a bicycle pedal includ[ing] a pedal shaft, a pedal body, first and second clamping members and a first biasing member”. Or, to put that into terms that you’re perhaps more familiar with, Toshiyuki Tanaka had just invented what we know as the modern SPD pedal.

Not every product in the cycling industry is a hit, even for a company with an enduring reputation like Shimano’s. The Japanese company has an impressive strike rate, though. Over the last 99 years, Shimano has evolved from the manufacturer of a single freewheel to the dominant force in the cycling industry, and along the way produced countless items that have become part of the sport’s DNA.

It’s a credit to Shimano’s relentless functionality and ubiquity that some of those products and innovations have entered the cycling lexicon, even without sexy Italian names or slick marketing. Instead, imprinted in the minds of countless cyclists worldwide like a secret robotic code are Shimano’s acronyms and numbers: STI, 6800, Di2, and SPD.

Of Shimano’s many innovations, it’s that last one – an acronym standing for ‘Shimano Pedalling Dynamics’ – that’s arguably the closest thing to a household term.

The cleat interface.

SPD pedals are now ubiquitous, but that wasn’t always the case, with Shimano’s first dual-sided clipless MTB pedal landing in 1990. The PD-M737 was a dense, dark nugget of a thing that bore some familial resemblance to what we know today. As with Tanaka’s design from 2000, the M737 was dual-sided and spring-loaded, and the two use the same cleat recessed into the sole.

But while the M737 and its offspring – with modest refinements like the design used on the M515, pictured below right – were impressive in function, they had a flaw. In muddy conditions, the platform where the cleat sat had little room for the mud to go, with the clamping hardware and the spindle clustered tightly together, like metallic scaffolding on an oblong core.

The original SPD clamping design (top) is both less open and more mechanically complex than Tanaka’s design…
…and bulkier as well.

Tanaka’s design is visibly an evolution of Shimano’s first design, but it was also a significant leap forward. With the design built around the spindle rather than on top of it, there are dual benefits: a lower stack height and a more open binding design. It’s also lighter, smaller, reduces the risk of pedal strike, and is aesthetically cleaner.

Perhaps the most striking demonstration of the merits of the design lies in the fact that Shimano still hasn’t found a need to improve on it. The SPD pedal that Tanaka designed remains fundamentally unchanged two decades later.

Bureaucracy moves slowly, but by September 2002, US Patent 6,446,529 B1 had been granted, debuting at the top end with the PD-M959. By 2004, the new design had filtered down through Shimano’s range, ushering in another soon-to-be-famous product: Shimano’s iconic entry-level PD-M520 pedal.

A workhorse pedal

Cyclists can be a fickle bunch, preoccupied with the latest flashy advances. But while marquee products get all the attention and column inches, that’s not what most people are riding. It’s the workhorses of a brand’s product line-up that are out there in multitudes, not because they’re the best and the most expensive but because they’re perfectly fine and the right price.

The M520 is one such unflashy hero of Shimano’s range. Compared to its fancier brethren it’s a bit heavier – although not by much, with XT-level pedals weighing just 38 grams less. Its platform is not quite as stable, and its bearings and spindles not quite so fancy, but functionally it’s more or less identical.

PD-M520’s form is iconic – a squared-off end with all-caps SHIMANO written across it, a round pedal spindle running to the crank, and Tanaka’s simple, ingenious steel arcs waiting to receive the toe of a cleat. Most of the pedal body is inert, but tucked away at the back is the mechanism: two tiny springs coiled five times on each side, around which the pedal body hinges. To get in, it’s a click down. To get out, it’s a twist to the side.

Every day in virtually every country around the world for the better part of two decades, these actions have been performed millions of times on SPD pedals of Toshiyuki Tanaka’s design.

While Shimano declined to provide any sales data for the purposes of this article, it’s a fair bet that millions of pairs of these pedals are in existence around the world, and I’d have to imagine it’s the biggest selling clipless pedal of all time.

For a long run last decade, the M520 was specced in countless thousands on mountain bikes as an OEM (Original Equipment Manufacturer) model. Today, it remains the cheapest SPD pedal offered by Shimano, a role in which it has ushered countless riders through the rite of passage that is using clipless pedals. Bizarrely, there was even a stint where, via mail order loopholes, it was cheaper in Australia to buy a pair of M520 pedals (with cleats in the box) than to buy the replacement cleats alone.

Like the basic design it carries, the M520’s longevity is its legacy: over a 17-year run in Shimano’s range, it has not changed. And because they’re almost impossible to break, most pairs of PD-M520s have long and fulfilling lives – my pedals among them.

Which, in a roundabout way, takes us back to last week.

Closing the loop

In an ideal world, this is the part where I’d tell you that I emailed Tanaka and after a bit of back and forth, with the help of a translator, he answered my questions about what personal satisfaction he draws from inventing a product as enduring as the Shimano PD-M520; how many iterations he went through before arriving at this design, this single perfect meeting of form and function that remains unchanged all these years later. Perhaps over Zoom we’d smile and forge some sort of human connection, and then Tanaka would go back to his desk in Sakai and quietly invent something else that approaches perfection.

I can’t tell you that part, because Shimano and Tanaka-san declined comment for this story. And while at first I found that thwarted narrative arc a little jarring, I’ve since come to a different understanding.

The SPD pedal and its lowliest representative, the PD-M520, is a quiet achiever – a product that just gets on with its job, without desiring the limelight or adulation. Perhaps in the product rather than the person you can learn something important about its creator after all.

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