Young, Wild, & Sporty: ’77 Ironhead Sportster from the Thunderbike Customs trainees…
Last month we featured Snow Race Willingen 2026, where more than 130 competitors — mainly amateurs — tried to ride to the top of a snow-covered ski slope in the heart of Germany’s Sauerland region. It was a true “run what ya brung” event, with riders “sending it” on everything from specialized hillclimb bikes to modern motocrossers, classic enduros, baggers, choppers, and more.
One bike caught our eye more than most, a 1977 Harley-Davidson XLH1000 Ironhead Sportster from the good folks at Thunderbike Customs based in Hamminkeln, Germany.
Founder Andreas Bergerforth originally established this shop as Motorradschuppen (Motorcycle Shed) in 1985. From the late 1980s to the early 2000s, the shop focused on Japanese sportbikes and racing, earning many overall and class victories in the German endurance championship.
After hanging up his racing suit, Andreas became more interested in building custom bikes, especially Harleys. In 2006, he acquired the H-D license to the Lower Rhine.
“When the doors to Harley-Davidson Thunderbike opened for the first time, the former one-man show had long since become a stately company with over 30 employees. In the meantime, the base area alone had increased more than tenfold compared to the initial scale.”
Today, Thunderbike combines an official Harley-Davidson dealership, a parts production facility, and a custom workshop — quite the growth from that original shed! Passing down a passion for individuality, design, and craftsmanship to the next generation has remained an important part of the company philosophy. The bike you see here — the “Iron Rookie” — is a direct upshot of that practice.
“The bike is a very special project marking the company’s 40th anniversary in 2025. Three trainee mechanics from our shop were tasked with transforming a pretty beat-up 1970s-style Ironhead chopper into a cool custom bike in just five months — with complete creative freedom.”
The team consisted of Moritz in his first year of apprenticeship, Ronan in his second, and Justin in his third. Together with their instructor, Otti, and the support of other team members, they set out to transform the old Ironhead chopper into something truly special.
“Since we’ve already built so many choppers, that route wouldn’t have been very exciting. The guys wanted to create something unique — young, wild, and sporty. That’s how a concept emerged that goes far beyond classic cruising and works off-road as well.”
The double-loop central-tube frame has been fitted with Evo Sportster forks and a custom-fabricated swingarm whose triple-adjustable mounts allow for various setups.
The rear shocks are for the Mupo ST1 units, and the bike is running TTS spoked wheels in 21″ front / 19″ rear sizes with Bates Baja tires. The front brake comes from a Honda XR600, and the rear drum was retained.
Many of the parts were custom-made in-house, including the fenders, engine guard, license plate holder, footpegs, and the signature aspect of the build, a custom under-seat dual exhaust system.
“The highlight for all three of us was definitely the under-seat exhaust. We designed and built it ourselves together with our coworkers. It was a huge challenge, but that’s exactly why it’s the part we’re most proud of.”
The tank is an XR replica, and the cockpit consists of Renthal Twinwall 996 handlebars, Thunderbike risers, and a Motogadget speedometer with a streamlined wiring harness. Meanwhile, Chiko’s Pinstriping handled the paint.
The engine itself was completely rebuilt with Wiseco pistons, S&S conrods, Andrews cam, Manley valves, Dyntek Dualfire ignition, and a classic S&S Super E carb. Displacement is 998cc, and the bike makes 55.8 hp at 5,736 rpm and 59.5 pound-feet of torque at 3,976 rpm — stout!
The Iron Rookie looks looks amazing, like a wicked crossbreed between an old-school flat track TT racer and an overgrown motocrosser, and it more than proved itself more than capable in the harsh condition of the Snowrace in Willingen.
Congrats to builders / trainees Justin Skiba, Moritz Schulze Böckenhoff, and Ronan Lenk on this build, as well as their instructor, Otti, and the rest of the Thunderbike team.
We absolutely love the story behind this build, and we can’t wait to see what’s next for this long-legged V-twin brute…and those who built it!
Below is our full interview with the team, along with more photos from Michael Rauscher (@glatzzo). A special thanks goes to Thunderbike’s Kim Lara Bergerforth for wrangling up all of the photos and information for us. Danke schön!
Ironhead Scrambler: Builder Interview
• Please tell us a bit about yourself, your history with motorcycles, and your workshop.
Thunderbike was founded in 1985 by Andreas Bergerforth in Hamminkeln — originally as a small motorcycle shop under the name “Motorradschuppen.”
What began as a deep passion for motorcycles evolved over the years into one of Europe’s best-known custom motorcycle manufacturers.
In the early years, the focus was on Japanese sport motorcycles and racing, where Thunderbike celebrated numerous successes in the endurance championship between the late 1980s and early 2000s.
Starting in the early 2000s, the focus shifted increasingly toward Harley-Davidson and the custom bike sector. Since then, Thunderbike has not only created custom builds but also developed and produced many of its own parts and components in-house.
Today, Thunderbike combines several divisions under one roof: an official Harley-Davidson dealership, its own parts production facility, and a custom workshop. This combination allows the company to develop bikes entirely in-house — from the initial concept to the finished vehicle.
An important part of the company’s philosophy has always been a passion for individuality, design, and craftsmanship — as well as passing this know-how on to the next generation. This is precisely what gives rise to projects like the current bike built by our apprentices.
• What’s the make, model, and year of the donor bike?
Harley-Davidson XLH 1000 1977 – Ironhead Sportster.
• Why was this bike built?
The bike is a very special project marking the company’s 40th anniversary in 2025. Three trainee mechanics from our shop were tasked with transforming a pretty beat-up 1970s-style Ironhead chopper into a cool custom bike in just five months — with complete creative freedom. The goal was to finish it in time for Jokerfest, our big annual summer party in June.
The team consisted of Moritz in his first year of apprenticeship, Ronan in his second, and Justin in his third. Together with their instructor, Otti, and the support of other colleagues, they build this special bike.
• What was the design concept and what influenced the build?
Since we’ve already built so many choppers, that route wouldn’t have been very exciting. The guys wanted to create something unique — young, wild, and sporty. That’s how a concept emerged that goes far beyond classic cruising and works off-road as well.
At the Snowrace in Willingen, the bike already showed what it’s capable of. And that’s likely not all — we can’t wait to see what’s next.
• What custom work was done to the bike?
Chassis:
Double-loop central-tube frame
Fork: Evo Sportster, inner steering stop
Swingarm: Double-sided, triple-adjustable shock mount
Shock absorbers: Mupo ST1
Front wheel: TTS spoked rim, 2.15×21
Rear wheel: TTS spoke rim 4.00×19
Tires: Bates Baja 3.00-21 rear: 4.00-19
Brakes: Front disc brake Honda XR 600
Rear drum brake Original
Custom-Made Accessories:
Exhaust: Underseat Custom-made TB
Fender: Custom-made TB
License plate holder: Custom-made TB
Engine guard: Custom-made TB
Footpegs: Custom-made TB
Other Parts:
Tank: XR Replica
Oil tank: Lowbrow Street XL
Handlebar: Renthal Twinwall 996
Riser: Thunderbike Flat Riser
Seat: Spirit Leather
Instruments: Motogadget Tiny
Dashboard: Yamaha XT/ 350/ 600
Levers: Classic Brake Master
Grips: Pro Grip
Headlight: LED, Highside Dual Stream
Taillight/Turn signals: LED, Kellermann Atto
Electrical: Internal frame routing
Mirrors: MoView
Paint job: Chiko’s Pinstriping
• Does the bike have a nickname?
Iron Rookie.
• Any idea of horsepower, weight, and/or performance numbers?
Displacement: 998
Bore x Stroke: 81.48 x 96.9 mm
Power: 55.8 hp at 5,736 rpm
Torque: 80.7 Nm at 3,976 rpm
Pistons: Wiseco
Connecting rods: S&S
Valves: Manley
Tappet rods: Andrews
Camshaft: Andrews Y Grind
Ignition: Dynatek Dualfire
Fuel system: Carburetor, S&S Super E
Air filter: TwinAir TRS Trail
Kickstarter: W&W
Starter: Tech Cycle
Primary drive: Chain
Clutch: Multi-disc clutch in oil bath
Transmission: Four-speed
Secondary drive: Chain
• Can you tell us what it’s like to ride this bike?
It’s definitely a special feeling to ride this bike. Of course, you can’t compare it to a motocross bike, since it’s much heavier and handles differently. Still, it’s a lot of fun, especially because you know how much work and time went into the project. That’s exactly what makes the riding experience even more intense for me.
• Was there anything done during this build that you are particularly proud of?
There are many modifications to the bike that we’re proud of. For example, we thought the handlebars — which are actually more commonly used on motocross bikes — were especially cool, as well as the relocation of the battery and the underbody protection.
But the highlight for all three of us was definitely the under-seat exhaust. We designed and built it ourselves together with our coworkers. It was a huge challenge, but that’s exactly why it’s the part we’re most proud of.
• Is there anyone you’d like to thank?
Yes, definitely. We’d like to thank everyone who supported us during the project — especially our coworkers. They not only helped us with their expertise but also invested a lot of time and, in some cases, worked on the project with us late into the night. Without this support, it wouldn’t have been possible in this form.
More Photos
Follow the Builder
Website: www.thunderbike.com
Iron Rookie Blog: www.thunderbike.com/custombikes/iron-rookie/
Instagram: @thunderbikecustoms
Facebook: www.facebook.com/ThunderbikeCustoms
Photographer: Michael Rauscher (@glatzzo)
Bike Builder/Trainees: Justin Skiba, Moritz Schulze Böckenhoff, Ronan Lenk
Nice !!
The exhaust system is not dual. It is a single, cobbled together mess with a dual tip. Awful !
Do a better job and show us!
The thunder bike I remember was from early 2000s before they became a Harley dealer, they built some outrageously cool Japanese cruisers, and had the hottest models ever when they became my heart that kind of died out
When they became a Harley dealer that died out.
There are so many ads in my face I can barely read/post .
Does it seem like there are more ads, Hack? We haven’t changed anything! But we can notify our the company that manages the ads.