Racers
Curt’s TCsport feature bike is latest of a series of production prototypes he’s been re-working and re-engineering until the tiniest-detail-obsessed builder gets it right according to his own exacting standards. “The three versions of this bike I’ve already built had some small handling issues like finding the right motor placement, fork angle, wheelbase, seat height, and so on. There’s nothing in a book that tells you how to install a Big Twin motor in a sport-style chassis, so the only way to accomplish this was through trial and error,” said Curt. “I think this bike is very good for what it is. The biggest obstacle in using these Big Twin engines is the transmission and primary assembly, which is an area we at BTR have already started to address.” Yup, as good as this TCsport is, he’s already working on a new one with a radical transmission/primary redesign that will allow him the freedom to package the whole shebang in a frame and swingarm design without having to work around the cumbersome size of the stock tranny/primary.
Meanwhile, the TCsport’s frame design is nothing to lament as Curt’s latest design made from 1.25” .095-wall DOM tubing provides not only a compact-for-a-Big-Twin 59.5” wheelbase (same as a Sportster with its compact unit-construction engine/tranny) with a quick-steering 24.5-degree rake, but has the Twin Cam 88A rubber mounted so you can actually access the engine’s power without eye-ball-rattling vibration. The BTRmoto-fabricated aluminum boxed swingarm works a CBR 600 shock mounted directly to the swingarm (see UP Close). As far as the rest of the stuff hanging off this frame, Curt casually recites a who’s-who of high-end components, “The front end is Ohlins, the brakes are Brembos, and the wheels are BST carbon fibers.” Those ridiculously-light BST wheels are partially responsible for the bike’s overall weight of “high-420s/low-430s” according to Curt, and definitely have a positive affect on handling, acceleration, and braking in a carbon-fiber nutshell.
Even though Curt is a serious horsepower junkie who competes on his nitro-burning Harley hill climber, he used a stock 88” Twin Cam for power. “I got it real cheap on eBay and the only thing I did to it was put a carburetor on it and be done with it. He may have been done with that, but he’s gone through a few exhaust designs ending up with a set of swirling BTRmoto headers culminating in a Thunderheader tip. His previous underseat exhaust heated up the rear shock and didn’t make as much power. “When you’re doing the 30-50mph twisty road stuff and you come out of the turn in the motor’s sweet spot you can actually get it stepping sideways under acceleration,” said Curt. “But yeah, it would always be fun to have more power.”
Clothing his bike in his own tailor-made suit, Curt fabbed up a fabulous aluminum tank with overtones of a TZ 750 and matter-of-frankly said, “That was just kind of hammers, dollies, and English wheels.” Yeah, right. The tail section is fiberglass constructed over an aluminum buck that he pulled a mold off. The overall affect is race-bike simplicity and handsome good looks. Curt’s choice of a headlight is pulled directly off a V-Rod and one of the two things I admire about Harley’s liquid twin, the engine and the headlight. The headlight shell compliments his bodywork and tucks tightly into the Ohlins front end that has an abbreviated carbon fiber fender stuffed between its legs. Curt shot the bodywork in a simple black paintjob and called it a day.
Asking Curt what the final result of this continuing series of bikes was like to ride, he said, “Compared to my previous models, I didn’t want any twitching or have to run a steering damper. It ended up being a real neutral bike that stays in a turn whether you’re on the gas or off. The bike is capable of using all of the tire, the suspension works great, the brakes will bring you to a stop with one finger, and the acceleration is good considering the motor is stock.”
As for the public’s reaction, Curt said, “The bike has been a crowd pleaser everywhere we take it. I’m really happy with the way it turned out. I’m in the process of building another one [No big surprise there, Curt], but this one is going to stay untouched.” Unlike Hollywood movies, I look forward to Curt’s forthcoming sequel. BM
Up Close: TCsport Swingarm
The aluminum swingarm Curt Winter designed and fabricated for the TCsportis a strong and gorgeous design. Under normal circumstances the topic here would be what a lovely piece of work it is, and it is. But there’s a lot more to this swingarm’s story than the lovely bit of work it is, but rather what the limitations of its design led to.
“On something like this bike, you want the longest swingarm possible. On this one, the longest swingarm possible was the shortest one I could make. My goal in this case was backwards,” said Curt. “For instance, it’s not the right application for the CBR 600 shock I used as that requires a linkage setup which I did not have room for. For me, touring around on the street, it suffices, but it’s not right.”
Curt’s solution to this problem is not something simple or quick-fix ingenious, but a whole new innovative, possibly revolutionary take on what the limitations of working around a physically big V-twin entail. “My goal has always been to try and go into production with something like this bike, a sport tourer like a VFR,” said Curt.
“I’m actually in the process of designing my own transmission case that will bolt up to a Twin Cam. It will take 6.5” off the total length of the motor/transmission assembly and it takes 4” off the width of the left-hand side,” he said. “It’s really compact.”
The length of the engine/tranny setup and the width of the engine have been design limitations that have determined what builders have to work around whether they want to or not. With all the room Curt envisions getting from his revised transmission design, everything you might know now about building a sporty Big Twin from the ground up is wrong and in this case, that’s a designer’s dream. Bring it on Curt.
Builder: BTRmoto’s Curt Winter
If you’re looking for a high-performance bike capable of attacking back roads, cruising the highway comfortably with neither bike- nor human- fatiguing vibration, and you want racy sportbike looks, BTRmoto’s Curt Winter has all your bases covered.
“BTRmoto is a shop that is focused on performance. Most of what we do is build custom competition bikes for many types of racing. For the past three years we’ve been heavily involved in the sport of hill climbing, basically building high-horsepower dirt bikes using all types of engines. Some we set up to run on nitro methane, two- to three-hundred horsepower is not uncommon,” said Curt.
Another facet to the business is street bikes. Not your run- of-the-mill street bikes, but custom-built sportbikes using big-inch Harley motors. We’ve been building these sport-style Big Twins for many years and have done just about all we can do with these big power plants. The latest concept is one we call the TCsport. We have built a bike that gives the rider excellent feedback and the ability to aggressively attack their favorite back roads. A production model is in the works and will be using BTRmoto’s new innovative transmission design. Using this transmission will allow us to produce a bike that will have an even shorter wheelbase and better suspension geometry.”
For the past few years most of the BTRmoto’s work has been focused on bikes for hill climbing. What started out as a part-time hobby has turned into a full-time business of building parts and bikes for racers from coast to coast and even Europe as well. But as you can see by Curt’s TCsport, BTRmoto is more than just a one-trick race pony and is a fullservice shop located in Hayward, California, that does service on all makes and models as well as custom fabrication and restorations
For more information about BTRmoto go to www.btrmoto.com or call Curt at 510-612- 1103.
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