Rosko 650b MTB

Rosko 650b MTB

It’s ironic that for a city as large as New York, space is such a rare commodity. More often than not, frame builders have to work in shoebox-sized garages or basements. The bikes made by Seth Rosko are created in a four-metre square workshop, therefore it’s also ironic that they are so big in spirit.

Maybe it’s not such a surprise, given that Seth is such a highly respected character. He’s a veritable institution of the NY skate scene and has provided massive support of local racers of both road and cyclocross disciplines, most notably the King Kog CX team and numerous on-and off-road racers.

Rosko 650b MTB

His latest build, a 650b MTB, is for a good mate, Ernesto Rodriguez, who had nothing but good things to say about it: “I first met Seth Rosko in the mid 90s when I was a bike mechanic at Bicycle Habitat here in New York City. He was working at Brooklyn Machine Works at the time and I was good friends with that crew since Joe from BMW had once worked at Habitat as well.

Rosko 650b MTB

“Shortly after meeting Seth he went to the United Bicycle Institute to further his knowledge of frame building. He returned a very competent welder with an even greater passion for building bikes and I was happy for him. Years went by and it was great to watch the birth of Rosko Bikes and when the time was right I asked him to build me the mountain bike I had been wanting.

Rosko 650b MTB

“I’ve lost count of how many bikes I’ve owned over the years, especially the number of mountain bikes. But one bike has always been my favourite. It was an orange 1997 Bontrager Race Lite (pre-Trek acquisition), that I built up with Shimano XT, a Marzocchi Z2 fork, Chris King hubs that I laced to Mavic rims, Thomson stem and post, and Titec bars.

Rosko 650b MTB

“The bike was awesome. It had the right amount of flex and rigidity to handle what I threw at it. It was fast when cranking on hard pack single track and floated over roots and rocks. I rode a lot of latest-and-greatest cross-country duallies at that time but nothing really made feel like my Bontrager did. Of course, head tubes got larger, disc brakes took over and eventually my beloved Race Lite was retired.

Rosko 650b MTB

“Fast forward to 6 years ago when I purchased an aluminium hardtail 29er and got really excited about the larger diameter. I loved the flow that it forced you to have. But I didn’t like how long the bike felt. I have always ridden BMX and love a bike that I can manual easily, and I never got comfortable doing that on the 29er.

“I also couldn’t get used to the feel and sound that an aluminium hardtail has. But when the 650b size became an option I knew it was the perfect size for a good steel frame to capture what my Bontrager once had. Then I saw Seth’s red 650b single speed. It instantly got me excited and I reached out to him. He knew exactly what I was wanting to capture: my 90s Bontrager with 2015 technology.

Rosko 650b MTB

“For me, the 650b diameter is the best of both worlds and the frame was built around that. Steel, naturally, was the most important feature of the bike. I wanted it rigid enough to handle the larger diameter wheels but still be light and flexible enough to soak up the bumps. It also has a short-enough rear triangle to make it easy to bunnyhop and manual like I wanted.  

Rosko 650b MTB

“My old Bontrager had cable routing across the top tube, which was great for keeping the cables relatively mud free, but they were noisy and sometimes painful in a wreck when the flesh would meet the cable guides. Seth suggested internal cable routing, which has always made perfect sense to me for a mountain bike.

“Plus, I’ve always loved the look of it on old roadies. The Paragon dropouts and hanger are a really nice touch as well. For components, I’ve always been a Shimano guy and prefer the XT line. The wheels are Stan’s NoTubes Crests with Continental X King tires. Chris King headset, Easton EC70 bars, ESI grips and Thomson stem keep the X Fusion Sweep HLR in place and in control.

Rosko 650b MTB

“The final feature that I really wanted was a dropper post. No, it’s not an enduro bike but I do like to ride down steep descents with larger drop offs so having the seat out of the way is helpful. The X Fusion Hilo Strate made sense since the bike was going to be internally routed. The post increases the bike’s functionality while maintaining its clean lines. Plus the Ergon seat feels amazing.

Rosko 650b MTB

“Overall, the bike is everything my old Bontrager was with everything I love now. It handles better than my previous 29er, rolls fast, and is maneuverable and nimble. The X Fusion fork, once I got it dialled in, floated over little stuff and handles the bigger drops with ease. The bike flies on straight single track, carves low berms and winds through twisting switchback beautifully.

“The bike is perfect. It’s even more perfect that it was built in Brooklyn by one of the nicest guys I’ve ever known, a true friend that has poured his life into his craft. That is such a rare and precious thing these days.” Special thanks to Ernesto Rodriguez for the words and pictures.

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Rosko 650b MTB