Robert Q. Riley Enterprises: Product Design & Development

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XR2 Solar powered recumbent bicycle

XR2 solar winner (in category) of Australian World Solar Cycle Challenge

RACE IMAGES XR2 Solar on starting line of race

Solar XR2 drive train

XR2 Solar crossing finish line in Australian World Solar Cycle Challenge

Ground Hugger XR2

Original prototype of XR2 XR2 Recumbent bicycle

Cocpit of XR2 Ground Hugger XR2 cockpit

Closeup of steering connection Closeup of XR2's front end

The Ground Hugger XR2 power train

XR2 suspension system

Foam frame prior to applying carbon fiber XR2's urethane foam core

3D CAD wireframe of Ground Hugger XR2

More photos in
DIY Gallery






Order Online
- or -
by Phone, Fax, or Mail

CD-ROM Includes...

3D models of
  individual parts &

Complete set of 2D
  CAD drawings
  viewable on
  computer & in PDF
  format for full-size

In-depth manual
  with large high-
  resolution photos &
  links to on-line
  services & vendors.

Files for making
  decals & logos.

Links to free 2D &
  3D CAD viewers.
  Race, first-ride & 
  pre-race practice

Mac users, please
see "Important Notice" below and to the right in the body text.

+ Shipping & Handling
(Shipping charge is calculated at the time of purchase & varies according to destination)

Shipping and guarantee info


Frequently Asked Questions about the XR2








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Ground Hugger XR2 HP High-Performance Recumbent Bicycle

  New Release!    

 Build This Advanced Carbon Fiber Solar Assist Recumbent
For Clean, Gasoline-Free Commuting and Cycling Pleasure

Winner in Category of the Australian World Solar Cycle Challenge

Place Your Order Now

Featured in Wired Magazine

Jump to: About the Plans - Championship Solar XR2 & Video - Specifications - Interviews & Reviews

How to order XR2 plansxr2-video.jpg (8132 bytes)There are few times when a designer has the opportunity to pull out the stops and create an advanced, race-winning design like the new Ground Hugger XR2 HP.  This new HP (High Performance) machine leapfrogs ahead of anything available anywhere in the world to raise the bar on recumbent bicycle design and deliver an unparalleled sense of excitement and pleasure to your cycling experience.  Its unique architecture provides for three versions from a single design:

Three Optional Versions

  • Electric/Human hybrid power with on-road or stationary solar charging, or rapid plug-inrecharging. (This is a refined version of the Solar XR2 that won the Australian WorldSolar Cycle Challenge.)XR2 Ground Hugger

  • Conventional e-bike power (wheel motor) and with rapid plug-in recharging, plus optional solar recharging.

  • Dedicated human powered version built on the most advanced technology available.

Break Free of the Gas Pump

          With today's soaring fuel costs, it's about time to break free of the gas pump and enjoy clean and virtually free mobility.  You can slash high commuting costs and smell the roses in the process, and do it without the pedal-pumping work of a conventional bicycle.  With its combination of battery-electric and solar capabilities, the Ground Hugger XR2 HP offers a new way to cut monthly expenses and have fun doing it.  With either of the two electric power systems, you can select  the amount of necessary pedal power.   Or you can stop pedaling altogether and cycle on battery power with assistance from solar power.  On a sunny day, solar power can maintain up to 8 km/hr with little or no drain on the batteries.       

Ground Hugger XR2 HP Based on a Proven Track Record 

Major advances in the first release included a carbon fiber composite seat and frame, a rear suspension system ("soft-tail"), and the latest in cycling components, along with its characteristic steering system.  In terms of esthetic design, the Ground Hugger XR2 broke new ground by making a uniquely independent statement of its own. We call it our Ferrari on two wheels.
          With this new HP release, you receive an upgraded frame with improved strength and ascetics.  You also get improved steering geometry engineered around the ISO 406-28 mm front wheel and 20x1.1 high-pressure tire, a breakthrough in steering system design for superior control, and optional battery-electric and solar power.  The tastefully integrated on-board photovoltaic panels can stretch out range and recharge batteries while you're parked.  Or simply leave off the electric power system to create the most advanced human-powered recumbent on the planet. 


Unique Steering System

            Link to animation of steeringThe XR2's characteristic steering system has to be experienced in order to be fully appreciated.  It's part of the matrix that gives the XR2 its graceful appearance and superior control.  Improvements on this HP release add a new dimension to the system's feel of the road and stable performance.   And it solves a problem that has plagued recumbent bicycle designers since the beginning - the long reach to the front wheel. 
            Showing reduced frontal areaLong wheelbase (LWB) recumbent bicycles allow designers to take full advantage of the small frontal area made possible with a low, sleek layout.  But it introduces the problem of how to steer the front wheel when it's located out in front of the rider's feet.  Short wheelbase (SWB) recumbent layouts locate the front wheel approximately underneath the rider's knees, which shortens the reach to the front wheel but it does not fully solve the problem.  Tiller, under-seat, and laid-back-handlebar steering often result in compromised steering geometry or an awkward steering layout, or both.  The XR2's steering system produces a comfortable and intuitive system with a rock-solid feel of the road that is unmatched by previous designs.  

Winner in Category of Australian World Solar Cycle Challenge 

A team at Prince Alfred College in Australia, under the leadership of Professor Paul At Prince Alfred College during pre-race testsBalestrin, built a solar assist version of the first Ground Hugger XR2 and entered the 2001 Australian World Solar Cycle Challenge.  The Solar XR2 took first place in "B-Class" and third place overall.  B-Class is a category for unfaired recumbents; machines having no aerodynamic body to reduce drag.  Average speed over the 1553 km course was 41.1 km/h.  Top speed was 65km/h on a level run. This new release includes plans for an upgraded and refined version of the race-winning Solar XR2. Click here for more information on the winning machine built at Prince Alfred College.  Plans show an upgraded electrical system with greater collection area and Lithium-Ion batteries.

Carbon Fiber Construction

         The frame and seat are built of hand-laid carbon fiber over a urethane foam core. The molds and vacuum bagging typical of conventional carbon fiber construction are unnecessary.  We've used vinylester resin, which is about half the price and nearly as strong as conventional epoxy. The main advantage of vinylester is that it's catalyzed and applied just like polyester resin, which makes it much easier to use for the do-it-yourselfer. 
         Lay-ups are applied to the urethane foam core, and the foam remains as an integral part of the frame. So the foam serves as a mold and it adds significantly to the strength of the frame. Imagine bending a hollow metal tube to the point where it kinks and collapses. The same failure point occurs with any hollow structure, regardless of the material. But with a foam core, the walls of the structure (the carbon fiber skin) are held in place so they cannot kink and collapse. Even though the foam has little strength of its own, it plays an important role in the overall strength of the composite structure. 
        Metal fixtures are laminated in place at attachment points, such as the head, bottom brackets (there are two), steering tube, and rear suspension hardpoints.  The bottom bracket shells are purchased ready-made, and the other items are simply cut from lengths of aluminum tubing.  The photo of the foam core (in the left margin) shows the aluminum steering housing cemented in place.  Plans provide instructions for eliminating the electrolysis that sometimes happens between carbon fiber and bonded-in metal parts.  
         Table T1 provides a listing of materials and the cost to build the seat and frame (exclusive of finishing materials).   Due to the abundant choice of components, the three optional power systems, and builder preferences in components, a complete cost to build has not been estimated.  Consider that building the XR2 HP is mainly a frame building and assembly project, and equipment choices are mostly within the control of the builder. 

Table T1

Frame and Seat Materials

Carbon Fiber Cloth 3.5 yrd $122.50
Vinylester Resin 1 gal $  35.00
Urethane Foam* 4 x 8 ft x 2.5 inch $  65.00
Steering Housing 25 inch of 1.5 OD x 0.035 T6 alum. $  25.00
Tandem BB Shells (2) $  50.00


*Enough foam for three bicycles.  Normally sold only in 4 x 8 ft sheets.


         Table T2 provides the weight of a few of the XR2's primary components. Specifications are provided in the Table T3.   

Table T2

Weight of Primary Components  
(One ounce = 28.3 grams)

Frame* 6 lb 6 oz
Steering Tube** 1 lb 8 oz
Fork Assembly 1 lb 0.02 oz
Chain Stay Assembly 1 lb 14 oz
Seat 1 lb 10 oz
Front Wheel 3 lb 7 oz (Aerospoke carbon fiber wheel with tire)
Rear Wheel*** 5 lb 8 oz (Aerospoke carbon fiber wheel with tire and 9-spd. cassette)
Bottom Bracket 8.8 oz  ea. (two required)

*Includes 1-3/4 lbs of filler/surfacer and paint.   Frame may be natural-finished for weight savings. 
**Cab be reduced to approximately 10 - 14 oz by drilling lightening holes shown in the plans. 
An alternative 36-spoke rear wheel equipped with an identical tire, an aluminum rim, the Sachs 3 x 7 internal hub, and a 7-spd cassette weighted precisely the same.

Table T3


Front Wheel:
Rear Wheel:
Rear Sus.
Seat Adj.

90 inch (2285.7 mm)
36 inch
(914.4 mm to top of handlebars)
67.9 inch (1725 mm)
27 - 45 lbs
(depending on frame finish and components)
20 x 1.1 (406-28mm rim with 20.1 tire)

26 - 27 inch (optional cross-section)
(R derailleur or Sachs 3 x 7 internal hub)
Optional disc
Trailing arm with air/spring shock
4-inch (101.6mm) longitudinal seat & 6-inch (152.4mm) handlebar adjustment 
(Fits 64 - 72 inch/1625.6 - 1828.8mm rider height as shown.  Frame may be shortened or lengthened for taller or shorter riders.)

About the Plans

Plans are written with the assumption that you have no previous experience with bicycles or composite construction.  We call it "information overkill."  And you will be pleasantly surprised to see how DIY instructions and modern CAD system technologies have been integrated in such a user friendly way.  This type of presentation was developed especially for the DIY field. If you can browse a Website, you'll be at home with the advanced three-dimensional presentations on the CD-ROM.  And it's an ideal way to spark interest in students for professional-level 3D design and engineering technologies.  Modern 3D CAD systems are a little like video games, except they deal with the real world and produce real results.  This DIY presentation provides a sense of what modern design technologies are all about.
         The disc includes 3D electronic models that let you zoom, pan, and rotate CAD-accurate electronic models.  You can even take dimensions in three-dimensional space.  Conventional 2D CAD drawings are also included, but the most enjoyable and enlightening experience will be with the 3D models.  Within an assembly, you can export individual parts into separate documents, make cutaway views by simply dragging a plane across a part or an assembly, and change transparency with the click of a mouse so you can see what's inside. 
        An in-depth manual, which runs in a web browser, provides detailed instructions and click-to-enlarge images of parts and assemblies at various stages of construction.  You can enjoy still images and video clips of the Ground Hugger XR2 HP in action.  The CD-ROM contains a professionally produced video of the 2001 Australian World Solar Cycle Challenge.  You'll see the Solar XR2 cross the finish line and enjoy interviews with other participants. And you'll have direct links to vendors on the Internet.
         The CD-ROM is designed for an ordinary Windows PC, but it will also run on Macintosh OS-X machines (see "Important Notice" below). Links for downloading free CAD viewers are included on the disc.  You do not need a CAD system to view the electronic CAD drawings and 3D models. 
         The presentation on disc contains complete information, including printable drawings and a printable copy of the manual.  If desired, you can order printed drawings and a printed and bound manual from us.  Or a local printer can make full-size prints from the PDF copies on the disc.  The electronic manual on disc is identical to the printed version, with one exception.  A printed manual cannot provide high-resolution images that are larger than the printed page, nor animations, videos, and Internet inactivity.  Both, however, include complete construction and assembly details, technical and design information, a list of vendors, and a materials list.

Important Notice

         The CD-ROM is designed for Windows, but it will also run on Macintosh OS-X systems.  The CD-ROM is written in HTML and designed to run in a web browser.  A link to a free viewer in both Macintosh and PC formats is provided on the CD-ROM.  The 3D programs work best, however, when running on a PC in a Windows environment.  Native CAD files were created in SolidWorks.

Interviews and Reviews

  • BikeRod&Kustom  During an interview with Jim Wilson, Webzine Editor of BikeRod&Kustom, Robert Q. Riley talks about the development and design details of the XR2.  In a separate article, Jim Wilson reviews the XR2 plans.



To Order Plans

  • Mail: Use the online Order Form to automatically calculate shipping charges and provides a total amount. Click on the "Order Ground Hugger XR2 Plans" or any of the red "Order Now" icons above, then press "Add Item to Cart." Fill in your shipping information. You cannot proceed to the Confirmation Page (for freight calculations) without making entries in the credit card fields. If you prefer to enter your credit card information later, simply enter a series of spaces in the Credit card fields then press "Proceed to Confirmation." Print the Confirmation Page and enter any missing information.  Mail your confirmation page to us, along with your check, money order, or credit card information. (Outside the U.S., please make payment in U.S. funds using a credit card or International Money Order.)

  • Order by Phone: Weekdays 8:00 am to 6:00 pm MST:   480-685-3225.

                   -   Shipments to U.S. destinations go by First Class or Priority Mail (depending on weight).
                   -   Shipments to destinations outside the U.S. go by mail: "Airmail, Letter-Post."
                   -   Arizona residents, add 10.2% sales tax.

Robert Q. Riley Enterprises, LLC.
P.O. Box 14465
Phoenix, AZ 85063-4465
Phone: 480-685-3225


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Robert Q. Riley Enterprises: Product Design & Development
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P.O. Box 14465, Phoenix, AZ 85063-4465
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