Harley-Davidson Gravel Gorilla Was Once a Stock Fat Bob, Looks Great as a Custom Tracker

Harley-Davidson Gravel Gorilla 17 photos
Photo: Purpose Built Moto
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Purpose Built Moto (PBM) has long been seen as one of Australia’s top dogs in the custom motorcycle scene, constantly pushing boundaries and building remarkable one-offs at an astonishing pace. What you see below is one of the latest projects put together by Tom Gilroy and his squad – a ravishing Harley-Davidson Fat Bob revealed about a month ago.
Dubbed Gravel Gorilla, this bad boy went from cruiser to street tracker in stunning fashion, gaining a good bit of off-roading capability along the way. The story began with Phil, an experienced rider who’d been in a constant search for the ideal machine to match his riding habits. After test riding and owning several motorcycles, his interest was finally piqued by a Harley Fat Bob from the model-year 2021.

Captivated by the sheer torque and thunderous growl of its Milwaukee-Eight powerplant, Phil knew he was onto something. However, the bike didn’t just have to sound good and excel at long-distance riding, but it also needed the ability to take its owner off the beaten path for several days at a time. When commissioning the build to PBM, he entrusted Tom’s specialists with a few simple requests.

His vision for what would become the Gravel Gorilla involved making the Harley a lot nimbler while retaining a comfortable upright riding posture. The addition of removable luggage racks for his weekend getaways was also a must, and so was a significant power boost for the 144-cubic-inch (1,868cc) V-twin engine. With the donor on their workbench and completely dismantled, the Purpose Built crew kicked things off in the footwear department.

They reached out to Canyon Wheels to order a set of lightweight custom hoops, measuring 17 inches in diameter at both ends. A gloss-black finish adorns the rims and hubs, accompanied by a contrasting bronze finish on the spokes. In terms of rubber, the guys went with dual-purpose MT 60 RS tires from Pirelli, which ought to provide plenty of grip on dirt or gravel without compromising on-road handling.

Harley\-Davidson Gravel Gorilla
Photo: Purpose Built Moto
Enhanced stopping power is made possible by a mixture of Brembo and Lyndall Brakes componentry, including radial calipers and premium rotors. With the unsprung sector taken care of, the following step saw the Fat Bob’s forward-mounted foot controls replaced with mid-set substitutes from Performance Machine. These offer a much more suitable riding position for Phil’s off-road outings.

PBM revised the motorcycle’s subframe, subsequently topping it off with a custom, tracker-style tail section made of aluminum. There’s some sneaky storage space for tools and camping gear beneath the saddle, but the main luggage is kept in removable saddlebags (not pictured) employing bespoke mounting hardware. Whereas the stock Fat Bob fuel tank has been retained, Sir Gilroy’s artisans did away with the chunky tachometer housing once found up top.

In the cockpit, their work involved adding a tiny digital dial and aftermarket grips, repositioning the handlebar, and removing the standard mirrors for a cleaner look. The Harley’s distinctive factory headlight is still present a bit further ahead, now sitting underneath a tubular chromoly rack manufactured in-house. Peek lower down, and you’ll notice handmade fork guards and a custom fender just large enough to do the job.

Harley\-Davidson Gravel Gorilla
Photo: Purpose Built Moto
A swingarm-mounted license plate holder can be spotted at the opposite end, featuring multi-functional LED lighting from Purpose Built Moto’s proprietary aftermarket catalog. The main taillight is neatly recessed into the tail unit and joined in close proximity by a tailor-made studded saddle. As we've mentioned earlier on, the Gravel Gorilla was destined for some serious performance upgrades, too.

Gone is the original exhaust system, making room for custom ceramic-coated headers that terminate in Competition Werkes silencers. Even though the new pipes look completely separate at first, they actually run a two-one-two configuration by discreetly linking up beneath the foot peg. A top-shelf aftermarket air cleaner was fitted on the intake side of things, but the Aussies were determined to take the affair a step further.

To do so, they gave the Milwaukee-Eight mill a Stage 3 Screamin’ Eagle kit, putting it back together with a mixture of Rough Crafts and Arlen Ness covers. These new cases are all anodized black for a clean and stealthy appearance, while Nathan of Livin’ Loco Garage lent a helping hand for the rest of this creature’s paint job. As you can probably tell, his involvement really worked wonders.

A glossy black base covers the Gravel Gorilla’s bodywork components, along with stylish copper leaf detailing on its gas tank and tail unit. Silver pinstripes also make an appearance on the tank, as do minimalistic graphics depicting Purpose Built Moto’s logo. Last but definitely not least, the Fat Bob tracker was sent to Dynomite Moto for a session of engine tuning, which resulted in a whopping 116 hp and 92 pound-feet (125 Nm) of torque at the rear wheel.
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About the author: Silvian Secara
Silvian Secara profile photo

A bit of an artist himself, Silvian sees two- and four-wheeled machines as a form of art, especially restomods and custom rides. Oh, and if you come across a cafe racer article on our website, it’s most likely his doing.
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