The Evil Twin: 1200 Sportster Street Tracker

Bill Brosius shares a Harley street tracker build with his father… 

Bill Brosius grew up on the back of his father’s Harley-Davidson, as father and son followed the flat track races all around California and the neighboring states, even cross-country. One of the mechanics from Modesto Harley-Davidson, Bob White, even taught young Bill how to help in the pits, which allowed him to rub shoulders with legends of the sport.

“I was about 13 years old, and he taught me to groove the tires and change the sprockets at the local races. One of those races at the Sacramento Mile I got to push the bike by myself out to the starting line in front of the crowd. We were front row — I had Springsteen, Morehead to my left and Parker, Carr to my right!”

While Bill never had quite the pocketbook to support a flat track campaign, he raced AFM (American Federation of Motorcyclists) for several years, rides hare scrambles with his buddies, and is an instructor for Z2 Track Days.

In 2021, we featured the 2001 Harley-Davidson 1200 Sportster street tracker that Bill built to celebrate his father and their shared love of flat track racing. It was an especially moving tribute, as Bill’s father was diagnosed with dementia and Parkinson’s, and their times together at the races were some of the memories he retained. His father especially loved to sit and watch his son wrench on the machine whenever he was in town.

Flat Track Tribute: Harley-Davidson 1200 Street Tracker

Fast forward a little, and Bill’s mother had tasked him with selling off his father’s motorcycles in the final year of his life. One was a 2003 100th Anniversary Edition 1200 Sportster, which gave Bill an idea for another street tracker build — and a new way to connect with his father.

“I thought it would be cool to make 15-to-20-minute videos on YouTube so that he could follow along with the build. My mother would stream it to the TV and he could feel like he was right there with me as I was piecing it together! I sent the first video and it worked! My mother told me that his eyes lit up seeing me and the build happening.”

It would be difficult to think of a better reason to build another street tracker, and Bill went all out, ordering an arsenal of parts to keep the build going week after week. Highlights include 19-inch wheels, Öhlins Black Series forks and rear piggyback shocks, Brembo brakes, and parts gleaned from various Aprilia, Buell, Ducati, and Kawasaki models.

Bill is no stranger to the racetrack, and he builds his bikes to perform as well as they look. This “Evil Twin” street tracker is no exception:

“It has a smooth transfer from left to right-hand turns and it doesn’t mind at all to be sideways coming into a corner…Passing liter bikes at Sonoma Raceway in the corners is one of the best things this bike can do!”

Even more special is the fact that Bill finished the build in the final months of his father’s life — and his old man was able to follow his son through every step of the process.

“For the very last video I was able to fly down to Arizona where he lived and watch it side by side with him. The video was a recap of the entire build and a few laps around the track at Thunderhill Raceway, CA. He couldn’t say very much but I got to see the enjoyment of the American thunder in his eyes. He had an ear to ear smile the entire time.”

What an incredible tribute. Thank you, Bill, for sharing your story with us. You’ve done your old man proud — very damn proud — and we’re honored to call you a friend.

Sportster Street Tracker: Builder Interview

• What’s the make, model, and year of the donor bike?

This is a 2003 Harley-Davidson 1200cc Sportster 100th Anniversary.

• Why was this bike built?

My father was diagnosed with dementia and Parkinson’s, and in the final year of my father’s life, my mother had tasked me with selling off his bikes and cars. This was a very hard task knowing the future we were headed towards. The Sportster that was back east in Indiana needed a new home, so I rode it back to California and I had this great idea to build another tracker, but this time I would do more!

His dementia was really kicking in and he could not hold a conversation anymore over the phone. I had gotten a pretty big bonus at work, and I thought it would be cool to make 15-to-20-minute videos on YouTube so that he could follow along with the build.

My mother would stream it to the TV and he could feel like he was right there with me as I was piecing it together! I sent the first video and it worked! My mother told me that his eyes lit up seeing me and the build happening.

She continued to say that this was the only thing that he would pay any mind to on TV. I made some pretty poor financial decisions by ordering part after part so the videos could continue and did a new video almost every week until it was done. I was able to complete the bike within the last couple months of his life. He got to see and be a part of this from start to finish.

For the very last video I was able to fly down to Arizona where he lived and watch it side by side with him. The video was a recap of the entire build and a few laps around the track at Thunderhill Raceway, CA. He couldn’t say very much but I got to see the enjoyment of the American thunder in his eyes. He had an ear to ear smile the entire time.

• What was the design concept and what influenced the build?

Throughout the years my father and I would follow the flat track circuit across the US, and I would be traveling with him on the back of his motorcycle to watch the races. We would spend a lot of time in the pits looking at the different bikes and my father had a passion for Harley-Davidson motorcycles. Flat track was the sport that Harley-Davidson dominated. This build would resemble the first tracker that I built from a bunch of spare parts, but it would be better because it would be all new parts across the board.

• What custom work was done to the bike?

This bike has the black series Öhlins front end with matching rear piggyback shocks. It has pieces from a bunch of different manufacturers such as Aprilia RS250, Kawasaki ZX10, Ducati Diavel, Aprilia RSV4, Buell Lightning, and other custom-made parts.

Every part took some fabrication to adapt. Custom triples, rear Brembo caliper mount, cables / lines, wiring for relocations, 19-inch wheel conversion, and brake system modifications.

• Does the bike have a nickname?

“The Evil Twin.”

• Any idea of horsepower, weight, and/or performance numbers?

Sitting at just over 400lbs. This Sportster has 67 horsepower at 70 ft-lb at 4000 rpm.

• Can you tell us what it’s like to ride this bike?

This bike rides amazing! I am the guy who will ride a motorcycle and really understand every part that was chosen to add to a build. It is an art piece with horsepower! With the 13.5-inch shocks in the rear, it really stabilizes the front end. It has a smooth transfer from left to right-hand turns and it doesn’t mind at all to be sideways coming into a corner.

The Brembo brakes in combination with the Öhlins make this machine a real demon. You can ride this bike with a ton of confidence until the cases hit! Passing liter bikes at Sonoma Raceway in the corners is one of the best things this bike can do!

• Was there anything done during this build that you are particularly proud of?

I am proud of the color set up along with the 2:2 S&S pipes. This bike was built to be the “Evil Twin” of the first tracker, and I think I nailed it.

• Is there anyone you’d like to thank?

I would like to thank my mother for helping share the joy to my father ever week. The video calls to see my father watching made every project worthwhile.

• Parts, Brands, and Mentions:

Öhlins Racing, Saddlemen, Brembo, S&S Cycle, Progrip, Protaper, Supertrapp Industries, Motion Pro, Z2 Trackdays, Harley-Davidson

Follow the Builder @cleanedwithqtips