Homebuilt Recumbent Motorcycle Racer Competes in MRA Sanctioned Event

Bob Horn takes the EXperimental500 through a left hander at speed in an MRA sanctioned roadrace

Bob Horn takes the EXperimental500 through a left hander at speed in an MRA sanctioned roadrace. First ever for a recumbent?
Photo by Margaret Oliver

Recumbent motorcycles are nothing new, but most (all?) efforts are focused on street legal machines. Bob Horn, though, is proof there is at least one (feet) forward thinking builder, who has been working for the past half dozen years to design, build and test a recumbent racer. His persistence and dedication finally paid off when he recently lined up against conventional motorcycles in his first MRA sanctioned road races at High Plains Raceway in Colorado. In fact, these may have been the first ever sanctioned roadraces with a recumbent motorcycle in a grid filled with sport bikes.

Have you ever seen a recumbent motorcycle racing with a conventional sport bike? Me neither.

Have you ever seen a recumbent motorcycle racing with a conventional sport bike? Me neither.
Photo by Margaret Oliver

Bob the builder

Bob has been a builder for a long time, he built a unique Sportster powered concept back in the early 1990s, and he later built an electric powered recumbent to test some ideas about two wheel steering, but this recumbent racer project has been the focus of his efforts since 2008.

The secret motivator

Whether by design or by accident, Bob did something at the start of his project that may have contributed to its success, he wrote a post on his blog clearly outlining what he was planning to do. It's all too easy to find an excuse for coming up short if you never publicly commit to anything, but tell everyone up front what you're going to do and there's a simple measure of failure and success. Either you did it or you didn't. Unless you're comfortable with a lifetime of excuses, you might as well get to work and make it happen.

The Workshop

The home of Bob Horn's recumbent racing project

The home of Bob Horn's recumbent racing project

The project build took place in the palatial surroundings of Bob's garden shed. We've seen some amazing builds come from workshops like this and Bob's efforts should provide more than a few yet-to-be builders with the confidence to begin. It's not the space, it's the builder.

The Kawasaki EXperimental500

While registering the racer at the track, Bob had to come up with a name for the bike, and though there were a lot of nicknames bandied about, the name Kawasaki EXperimental500 was chosen, a take off on the EX500 500cc twin Bob is using for power.

The bare bones of the Kawasaki EX500 powered recumbent

The bare bones of the Kawasaki EX500 powered recumbent during the build

Here's Bob's list of answers to the most common questions:

  • The race number has no deep meaning - it was just an available number.
  • The exhaust exits out the side, not to the rear - there are no "flaming butt" issues.
  • The steering axis is not parallel with the front fork - there's a virtual pivot at the hub.
  • The EX500 engine is internally stock.
  • The rear swingarm, vertical link, and drum brake are temporary - a more advanced system will be installed later.
  • NO street conversion or version is planned. Ever.
  • NO movie replica bodwork is planned. Ever.
  • The bodywork could be a lot more aerodynamic, but finished bodywork beats unfinished bodywork every time. 
  • 4 (now 6) years construction time in a garden shed at a budget of under $1.00/day.
  • The donor bike cost $500.00 - the leftovers were sold for $600.00.
  • Having a full time job not even remotely related to the motorsport industry, younger and older children, internet connection, lack of money, etc... didn't stop this from getting built.
  • No, I'm not giving away any design or building advice. Nor am I asking for any.
  • 414 pounds ready to ride except fuel, 50/50 weight distribution with fuel and 150 pound rider. 74 inch wheelbase. Just over 4 inches of trail.
Bodywork, what little there is, in place

Bodywork, what little there is, in place

Track time and hard lessons

Early in 2013, Bob had his first track time with the racer. The first session pointed to a few easy to remedy bugs, fixed with a carb kit and a headrest. The second session, though, was more costly as a lowside in a left turn followed by a roll in the dirt meant rebuilding the racer. Thankfully, no injuries, but there were definitely repairs to do which take time and money and a blown transmission in his van used up the race budget for 2013. Of course, that meant extra time to get things ready for the following year.

Is this the new future of motorcycle racing?

Could this be the new future of motorcycle racing?
Photo by Jim Browning - Rocky Mtn Photos

Real racing

Well, the purpose of a racer is to race and in early May of 2014, Bob lined up on the grid for the first time. He was confident, but realistic. He wanted to finish, learn a lot and not be in last place at the end. He accomplished all three goals, 24th out of 25 entries. He also found he has lots of straight line speed, but his "biodegradable guidance unit" needs some tuning to master the corners, something more practice should take care of very nicely. When you're riding a recumbent of your own design, there's a lot of learning to do.

The EXperimental500 in action

The EXperimental500 in action
Photo by Margaret Oliver

In race two, a few weeks later, he placed 17th out of 18 while shaving six seconds from his lap time, it appears a little practice goes a long way. He's starting to settle in and identify what needs to be tweaked, on the bike and with his technique. More track time may lead to some interesting battles as the season advances.

Craig Vetter has already offered a Photoshop version of what streamlining might look like on the racer which Bob says has a drag coefficient similar to farm implements, but faster corner technique might be more useful right now and the legality of streamlined bodywork in the racing world could mean it's a moot point, unless of course, there was a separate class where rules haven't yet been written.

This is how you find out if an idea will work, you build it

This is how you find out if an idea will work, you build it
Photo by Jim Browning - Rocky Mtn Photos

The beginning of something big?

Bob got a nice surprise when the Discovery Channel called and asked to make some video of his project, you'll notice a camera mounted in some photos as a result. TV exposure could give Bob and his racer some well deserved notoriety and it could also spark efforts from other builders who, after seeing Bob take the lead, might want to jump in to this form of racing to see what they can do with it, especially if he seems to be having too much fun all by himself. If he's competitive with conventional motorcycles, it could lead to a whole new recumbent racer series or more mixed racing with both recumbents and conventional bikes, maybe someone with an old Gurney Alligator will dust it off and get on the track, too. Who knows?

Manufacturers may be slow to sponsor this sort of racing because there's no obvious street version they can sell, though component companies should be willing to get their name out front in what could be a new venue, but it's tailor made for the DIY home workshop guys. I'm not sure how many hands on builders there are ready to take on a project like this when the end result is for track use only, but we might soon find out and since one of Bob's aims with this project was to keep costs to a minimum, his success is another plus for the home builder.

Isn't it refreshing to see something completely different? I love this whole project. He had an idea, designed it, built it and now he's raced it. It's taken six years so far, but I have a hunch the years going forward will be a lot more fun. Nice work, Bob! Very nice work.

Link: Rohorn.com
Link: Motorcycle Roadracing Association

Bob Horn with his EXperimental500 recumbent racer

Bob Horn with his EXperimental500 recumbent racer

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Comments

  1. Wave says

    What a fantastic story! It looks like it would be great fun to ride.
    There would be so much room for potential future development, I can imagine the project would be fascinating. If tyre sizes aren’t set by the racing class, it would be interesting to experiment with the effects of varying width tyres front and rear. I wonder if it would ride better with equal width tyres, or a wider one on the back?

    • says

      Oh yes, it could use better tires! But the wheels it has were paid for, and the GT501s are relatively cheap and last a long time. The obvious down sides (Hah) are having less traction than the competition and my knowing that they have less traction than the competition. The next racer will have real race tires on it – and hopefully someone who knows how to use them.

  2. Nicolas says

    Excellent !

    There seems to be a lot of frame/structural components on that thing, what material did you use to keep the weight low ?

    • says

      Thanks!

      All of the frame tubing is .083 mild steel from the local steel yard. The frame is actually very heavy (70 lbs). It should weigh at least half that, but it was cheap and easy to weld. Erring on the side of making it heavy and stiff seemed like it would be less hazardous than making it light and floppy.

      Even with this engine (Close to 130 lbs), I think a properly engineered 4130 frame, modern wheels, and lighter suspension components would easily lighten it by 100 lbs without resorting to CF or Ti.

  3. Barry Glading says

    Good on MRA for making room for this sort of thing. There’s far too much control of design convention with most organisations’ class structures, so allowing Bob to race this against conventional bikes shows some very cool outside the box thinking. And good on you, Bob, for persevering.
    Cheers
    Barry

  4. Decline says

    Shut up and take my money! I want one!
    Fantastic!
    And it looks great, unlike a lot of other attempts.

  5. says

    Love the story. As I always say but cant take credit for the quote ” How do you eat a elephant ? One bite at a time.”

  6. Jim Frost says

    If he finds a way to upgrade his “biodegradable guidance unit” I would love to hear about that. My bike has similar problems and could really use an upgrade too.

  7. Grant says

    This is excellent, and it makes me want to get back into the garage and work on my own far less ambitious projects.

  8. says

    It’s tremendous that he has built his dream and that he is racing it.
    It seems to me that a Hossack front suspension would be perfect
    for this endeavor, rock solid, easily adjustable very predictable.

  9. says

    Great stuff! Good to see someone learning how to do it properly.

    Track time for Feet First motorcycles is nothing new though…..
    (incase you don’t see it, this is the bike in that picture from @1985

    They have even been crashed

    Good stuff though Rob – keep your best foot forward! ;-)

  10. says

    Damn it! For some stupid reason I can’t post links. So that was a waste of effort.

    Search for ‘Bikeweb’ – you’ll find lots of pictures of older (mostly UK based) FF’s some of them on tracks.

  11. says

    Very refreshing to see in this age where prototype racing includes a spec tire manufacturer & soon-to-be spec ecu’s. It is also odd that the support class (to the “prototype” series) includes the same engine for every bike on the grid.

    Congrats Bob. Keep building & racing.

  12. Dave says

    I know Bob mentioned he isn’t taking any building advice & the following is not advice at all, it’s just asking questions from someone who knows zilch about recumbent design & construction & is interested in learning more….

    What if the engine was placed behind the rider & the foot controls were ahead of the front wheel? Would the foot controls be allowed that far out front? These questions came to mind when I noticed the length of the chain & the swing arm.

    • says

      Dave,

      Good question – I’m glad you asked!

      There are benefits and problems with both front and rear engine layouts. I originally tried the rear engine layout on paper with this engine, but getting the weight and balance right, the rider reclined at that angle, keeping the wheelbase somewhat reasonable, keeping the front wheel out of my crotch, and getting my feet relatively close together (Which didn’t work out so well with this one after all, but could be a lot better) resulted in the current layout. I also needed to keep the steering column in the center of the bike for, well, I’ll get into that reason next year. The current chainline is temporary – it was designed around a 2 stage chain system that will make a lot more sense (And make a lot less noise!) than the current one.

      • Dave says

        Thanks Bob. This is fascinating b/c it’s a whole new world to question everything from suspension to engine to chassis. And, that isn’t happening too much on the traditional motorcycle, particularly with suspension.

        While aesthetically these are different, it’s refreshing to start thinking about this situation & the experience it offers… i.e. That top pic must have provided quite the sensation of speed !

        additional questions:
        1. what prohibited you from moving the motor backwards so the trans would fit at the front of your seat? (where the vertical frame spar is located). Is that vertical frame piece structural to the rest of the frame or is it more along the lines of a subframe? If the latter, could this be triangulated around the trans?…or would all of that shortening provide an un-wise, short wheelbase?

        2. the swing arms are fascinating. It’s hard to tell where the rear, bottom one pivots?

        thanks for pursuing this build. It opens the 2-wheeled mind that has been going with the flow for decades

        • says

          Dave,

          You’re right – the sensation of speed is absolutely insane. The different perspective really throws off my braking points, which means I need a lot more track time – a terrible thing, right…

          Answers:

          1. Yes, it could – the Gurney ‘Gator’s architecture is a very good example. BUT – for the new rear suspension, I needed about 3″ of space between me and the engine, so I used it for frame structure as well. Can’t give away the reason, yet – it should be much faster – if it works.

          2. The lower rear swingarm (Probably sounds as odd to read as to write that) pivots are the rod ends bolted to the far aft bottom corners of the frame and threaded aft of the swingarm lateral member. The swingarm geometry is opposite of common practice (For more reasons that I’d rather not give away – yet), but it works very well.

      • says

        Yes, exactly like that! That’s a great illustration of how the rider position affects the configuration. And how good bodywork will be more streamlined than a lower rider with no bodywork.

        The development potential for recumbent/FF racers is amazing….

  13. FREEMAN says

    This is a great and inspiring story. I really like your recumbent racer. Keep at it! I look forward to seeing where you go from here.

  14. paolo tiramani says

    fantastic
    certainly mass centralized along a horizontal axis, wonder how it deals with fast transitions
    you may want to try alternate riders as well for feedback

    • says

      If it’s like the road-going ones then the transitions will be quick. Normal riders do a double dip going into their first corner as they don’t expect to roll in so fast and they stand it up again thinking they are falling. The seat-back is a great idea as it forces you to counter-steer and makes you one with the machine.

    • says

      As you guessed, It is a blast through chicanes. It rolls into – and stops rolling into – a turn with a lot less effort, but with lots of feel. The only “problem” is that, as a very responsive yet stable bike, it doesn’t compensate in any way for bad riding.

      But that’s also just my opinion. The opinion of better riders would be very valuable – that should happen this season.

    • says

      Fast transitions Paulo?

      Have a look at the physics….. http://www.oesten-creasey.eu/hightech/feetfirs.htm

      In reality you change direction REALLY FAST even with a 22 year old lardy steel framed road going ‘prototype’.

      Quite seriously, I had to ride a mates Ducati Monster S4 and it felt (compared to my Voyager) to be slow steering! Other comparisons – BMW R1100RS – battleship slow turning and ’06 (rubber mounted) Harley Sportster – felt like it handled like a 1970’s dirt bike on worn knobblies. And once you are used to non-diving forks and you grab the brakes on a motorised bicycle that is still stuck with them it feels like you are going to crash. Which is presumably why so many of them do…….! ;-)

      • paolo says

        I can see the benefits for sure and I loved Royce Creasey? triangular bike in the 70’s.
        you have longer a longer wheelbase and the rider is fixed ballast with a very centralized mass there are pros and cons to that
        a regular bike has shorter wheel base and the rider ballast is movable in a chicane that can have some benefits on transitioning, plus in corners the ballast can move to the inside and keep the tire a little more upright, its the same issue with cruisers and Harley where you can move around much
        I love the whole concept and I’d be curious to see the top speed differential between you’re bike faired and the original doner bike I bet you’d add maybe 15mph
        your half formula 1 and half bike, hope to see more updates
        p

  15. says

    Great to see Rob’s efforts getting the publicity they deserve! FWIW, I’ve been on track with quite a variety of FFs since I raced the Difazio-Creasey at Silverstone back in 1984, and again in 1987. http://www.bikeweb.com/node/1184
    I took part in the first Ecomobile world championships at Most in 1991, (and many subsequent ones)
    and presented a short film about the event which can be seen here:
    https://www.youtube.com/watch?v=GPZmqK5uogA
    Several of us have taken a variety of Quasars around circuits too. And you can take a virtual ride with Roger Riedener around Brno in the first electric Ecomobile, back in 2008, at a goodly lick, as I had the privilege of doing for real: http://www.youtube.com/watch?v=H4J4lBIHuvs

  16. Strong Eagle says

    He needs to shorten the distance between front and rear wheels. Well known that longer bikes need more lean for an equivalent radius… get the feet positioned up near the front wheel.

    • says

      As the turn radius increases, the effect that wheelbase has on lean angles decreases. In the pits, the racer feels like a barge – on the track, I don’t feel the steering/lean angle effects in the corners at all. In fact, the steeper steering geometry and optimised mass centralization makes it steer a lot better. The lower seat makes small shifts in rider’s weight far more effective.

      The main reason why longer wheelbase motorcycles steer “Slower” is due to upward mass distribution (One’s butt might be lower on, say, choppers, but the torso and head is a lot higher), slower steering geometry, limp front ends, and limp chassis.

  17. Paulinator says

    This guy is cool!!! I love his resourcefulness. I use the same type of five-point steering linkages on a couple of hand-cycles (a three-wheeler and a two-wheeler…both front wheel steer/drive). I guess great minds think alike?

  18. Josh says

    How does the 5 point steering work? I’m having a hard time visualizing the top half. Do the top arms form a sort of wishbone, to which the shock connects? – so that’s 3 points on the frame, but only 1 contact point on the fork..

    And am I right in assuming the trail is a virtual axis from the frame-side shock mont through the center of the wheel?

    • says

      The steering axis runs through the top center of the fork (Connected to the ball joint at the front of the upper A-arm) and down through the virtual pivot point defined by the two lower arms.

      The axis doesn’t run through the frame side of the shock mount. Down by the hub, the axis runs just forward of the axle.

      I hope that helps rather than confuses! I really ought to make a quick video of the steering system in motion. I think it is a very good racing system, but with too little steering range for the street.

      • Josh says

        Thanks for explaining, Bob! Some pictures or a short video would really help. I hope to see more of this machine, I think it’s a fascinating concept. How limited is the steering range?

        • says

          The steering range is 21 degrees on either side of center. Last I read their rules, FIM requires 15 degrees minimum and AHRMA requires 20 degrees minimum.

          I’ll forward Paul a quick video of the bike’s front end in motion soon…

  19. FormerTurbineGuy says

    Bob,

    I stumbled upon your project a couple of weeks ago and it struck a chord with me. Much like some One off Rods ( sometimes it happens in the Rat Rod world ) and in Homebuilt Aircraft arena, every once and a while someone builds something that has an “Ah-Ha” moment associated with it, and you want one, Your Ex-500 has it. This is kinda like Max Balchowsky’s Old Yeller with 2 wheels. Ya gotta love American Ingenuity, doing it @ home and for low bucks and you don’t care what anyone thinks. In a world that is trying to tell us “you didn’t build that” you did build it. Outstanding Sir, you make us all want to get off our Arse’s and build something on the cheap in the garage ( or join a maker workspace ). It is time for America to “build your own stuff” especially vehicles, you never know what a catalyst you and this bike might be for others and their crazy ideas and to finally give it a try, regardless if it is a success or failure.Congrad’s Sir, they are in order!

  20. Robwrt Swift says

    I draw and do a bit of conceptual design work as a hobby and I have always wanted to build a bike just like this one. except with way cooler styling. I’m designing an amphibious bike around the same sort of platform for its low center of gravity. and that suspension system lends itself well to having a rotating control arm attached to the shock to give the bike retractable wheels.my design has 2wheel drive and retractable floats/ landing gear on the sides behind the rider.

    • says

      Funny enough, I know the answer! I do tend to stay with the bike. A combination of points keep the weight of the bike entirely off of me while sliding on my side. Otherwise, the thought of being a human brake pad just sounds like a drag!

      My second (Latest) crash was in the apex of the fastest long corner of the track – the initial impact and slide through the turn was otherwise very uneventful and pain free – it was the landing in the dirt after being “launched” off the edge of the track that resulted in a high enough impact to break the “Safety peg” and crush my foot between the frame and the ground. If it weren’t for that, it would have been a walk-away crash – NO injuries anywhere else!

      My biggest concern is rolling the bike – further developments will protect against that.

      Thanks for asking about that – I’m looking forward to a future where racing will be even more exciting for both the rider and spectator – where increased safety can result in even more intense riding!

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