This page is dedicated to : HPN Motorradtechnik GmbH

	a "monolever" with longer arm (+ 10cm.)
	with two arms (+ 10cm.) and two shocks, as on the official Paris-Dakar GS
	a special version of the R1100GS "Paralever"

Basic: without rear suspension modification
	HPN Basis
Rear suspension with longer arm(s) (+ 10 cm.)
	HPN Baja a very light model with small tank,..
	HPN Adventure with Monolever rear suspension
	HPN Paris-Dakar with two arms rear suspension
The Sport family with HPN special Paralever rear suspension
	HPN Sport also known as Zebra bike a very light enduro bike model with alu sub-frame, small tank,..
	HPN Rallyesport THE rallye-raid bike

A version with a modern dress: the HPN/KRONSEDER

• the HPN official web pages where you can find picts, comments, price list,... (in german and part in english);
• the Possi's page, in German (and some in English, but the pictures are perfect for the quality and the details, like the one on the top of this page. You have to look to the airplane type dash-board of his two arms HPN-GS. Don't forget to visit his travel photo albums.

Company Overview

The name "HPN" is the abbreviation of the initial letters of the company’s founders, Alfred Halbfeld, Klaus Pepperl and Michael Neher, who brought the company into operation in 1979. The company became known for the further development of a road-racing tubular chassis made for BMW-boxers, which company founder Alfred Halbfeld already raced together with Peter Zettelmeyer. The work on the frame was also the basis for Peter Zettelmeyers thesis (diploma). The tubular chassis was sold in a limited series by Krauser, manufacturer of motorcycle-accessories, under the name MKM1000.

The break-through on the rally circuit first occurred in 1981, as Hubert Auriol won the Paris-Dakar Rally on a BMW, specially developed by HPN to BMW’s specifications. Besides winning the Paris- Dakar Rally, other similar races were won during the 80’s. Among the riders were well known names like Gaston Rahier, Eddy Hau and Richard Schalber.
The BMW-factory is still HPN’s main client, assigning development work for both production, and competition motorcycles to the 5-man operation located close to the Austrian border. For example: the first prototypes of the frame for the K-model and Paralever-swingarm were built by HPN. BMW’s decision to outsource such jobs, confirms the Know - How of today's managing directors, dipl. Ing. K. Pepperl and A. Halbfeld.

A second line of business, is the production and selling of accessories for BMW motorcycles, both to customers and retailers. Here, benefits of the fact that, contrary to Japanese manufacturers, BMW- motorcycles are built to a “baukast” (backward compatibility) system are quite evident. For example, an oil cooler-thermostat developed by HPN, can be fitted to any BMW motorcycle manufactured during the last two decades, as engines and frames of the different series varies only slightly. These facts do not apply to the Japanese competition motorcycles.

Third and last line of business, is the refinement of BMW-motorcycles, in particular the older R80 G/S-models and the newer R80 GS or R100 GS’s (“Reise-enduros“) for private customers. These are individually modified depending on customer’s wishes, either towards competition or “reiseenduro extreme“. Earlier HPN rally motorcycles are used as models. The modifications depend fully on customer's request, ranging from above mentioned accessories, to a complete modification of the motorcycle, where, e.g., engine capacity is increased to 1043 cc, dual ignition is fitted, reinforce- ments are welded to the frame, rear swing arm is lengthened by 100 mm’s, etc... The cost for a modification ranges from 25000. to 40000. DM, depending on the customer’s wishes. The overall impression of the operation is one of an attitude of professionalism and absolute accuracy by which they perform their work, not to be compared to some dubious “do-it-yourself” tuners. The basis for this professionalism lies in the enthusiasm of the company’s two managing directors. Quality is given absolute priority--profit comes second. Work is not performed "as exactly as necessary", but primarily "as exact as possible." The sense in this philosophy can be argued. Fact is, however, customers benefit from this and coworkers enjoy their work, no time-pressures develop and good workmanship is first and foremost.

Motorcycle modifications

The modifications executed by HPN are various and complex. Thus, apparently easy modifications, such as the switch to the larger 43 liter fuel tank, even requires modifications, not only to the seat, but on some models, the oil cooler must be re-located and mounted on the frame tubes below the steering head. This in turn requires changing the front fender.

Next I would like to give an overview of the modifications HPN makes to BMW motorcycles. By reading this the reader will gain a clear understanding of the expertise and work connected to the development. The overview cannot cover everything, since each motorcycle leaving the workshop is a unique example following the customer’s requests. The overview begins at the front, passing along the motorcycle to end--the tail light.

1. Front end, suspension, brakes etc:

Here, almost nothing of the original equipment remains: normally an upside-down (USD) front fork manufactured by White Power (WP), with 290 mm travel becomes standard, whereas the original fork has only 220 mm travel. A USD-fork is basically the reverse arrangement of a normal fork: slider tubes and stanchions (inner tubes) are turned “up-side-down,” thus the slider tubes are mounted in the triple clamps. The stanchions acts as sliders, and are now the lower part of the fork, where the brake caliper and wheel are mounted. The result of this modification is that the upper area of the fork becomes more rigid. This is an advantage, as the bending forces are concentrated in this area. Larger tube diameters and sturdier fork triple clamps provide improved strength. The longer fork also increases the wheel-base, adding to straight-line stability.
The single disk brake assembly of the GS and particularly the G/S models leaves much to be desired. There are many possibilities for improvements available—ranging from a larger single disk to a two-disk arrangement, and in all cases a multi-piston brake caliper is used. On all pre-1990 motorcycles, a full-floating disk should replace the original brake disk. The technical designer must take the width of the brake assembly, mounting points for brake calipers along with the fork used, into consideration. Additionally, a steel-braided hose is used in place of the stock rubber hose, resulting in a more accurate pressure point and a decrease in hand-force necessary. Lastly, it may be necessary to change the size of the master brake cylinder.

The quality of the wheels can be improved, by using other spokes and rims. The final touch within the front area is done by using another handlebar, short stroke throttle, modified instruments (e.g. electronic tachometer with digital display, roadbook-holder), brush-guards, modified turn signals and fender, shrouding, and a larger headlight...

2. Frame (excluding rear subframe):

Each frame is blueprinted and straightened if needed. It is sandblasted and strengthened at critical points (steering head, frame main tube, rear swingarm and suspension mounting points), by adding sheet metal. Some of the already present support plates are doubled. Additional mounting brackets for the oil cooler, tank, frame-fixed shrouding etc. are added. Depending upon version (e.g. single or dual swing-arm, modified rear subframe), the mounting struts for the rear shock absorber must be relocated. By using welding jigs, very precise work is made possible. An outside firm manufactures the reinforcement sections, according to HPN-drawings. By using laser technology, a more precise cut is made; more precise than possible to make within the HPN workshop. Welded frames are again blueprinted and straightened, positions of bearings are checked and adjusted etc. The center stand and the sidestand must be lengthened to adapt to the increased ground clearance. Following the customer's request, the frame is finally either painted or powder-coated, by an outside firm, for better protection and durability.
Since the G/S and GS models have steel frames, modifications can be executed relatively easy. These modifications would be more difficult, if the frames, as is often the case with Japanese Superbikes, were made from light alloy, or if, like the new BMW boxer generation, where the engine and drive train are the basis for the motorcycle, onto which the remaining chassis items are added.

3. Tank:

The selection can be made from any of five versions:

• 19 liters tank from the G/S
• 32 liters tank from the G/S Paris - Dakar
• 24 liters tank from the current GS
• 35 liters tank from the current GS Paris - Dakar
• 43 liters HPN tank available in polyethylene or nylon

4. Engine:

The capacity of the two valve boxer-engines used in the G/S and GS models is either 800 cc (50 HP) or 1000 cc (60 HP). In addition to these versions, HPN offers a conversion to 1043 cc.

The performance of the engines can be increased in several ways. The intended use of the motorcycle must be taken into consideration when deciding which modifications to perform. The engine can permanently produce approximately 70 HP without loosing reliability. From many years of experience it has been realized that increasing the engine’s output is only of interest in sporting events because the durability of the engine comes second to performance.

The most substantial points, in which the engine can be modified:

• Raising the compression by machining the cylinder heads--making them shorter.
• Installation of a dual ignition (i.e. two spark plugs per cylinder, requires many modifications of the ignition system, recommended with high compression and/or low fuel quality).
• Installation of another kind of ignition system (Nippon Denso, eliminates the necessity of a battery).
• Installation of a "sharper" camshaft (modified opening/closing times).
• Lighter crankshaft.
• Installation of a modified exhaust system.
• Addition of an oil sump extension ring in conjunction with a durable-aluminum sump-guard (greater oil capacity, higher stability while supporting bike on its sump-guard).
• Saving weight by use of carbon fiber alternator cover, and perforation of cylinder cooling fins.
• Oil cooler thermostat, developed by HPN, results in a shorter warm up period and a constant oil temperature.
• Modifications to valve covers, securing the covers by use of a screw mounted from the outside, thus making valve-maintenance easier.

5. Seat and rear subframe:

The rear subframe is attached to the mainframe via four bolts, and acts simultaneously as rear support for the seat, luggage carrier, support for luggage racks (panniers) and rear fender, and partially as mounting points for the exhaust system. Particularly, when carrying a passenger and luggage under high stress, the original rear subframe has proven to be rather weak. To improve strength and stability struts and braces are welded to the subframe. Additionally, a complete subframe made of high-quality steel can be fitted. Depending upon the customer's request, the standard seat is shortened and padded differently. The possibilities are varied, and an outside company does seat-upholstering work.

6. Rear swingarm:

The one-piece swingarm is still state-of-the-art at HPN. This solution has the disadvantage of "shaft- effect" or “elevator-effect”, well known to old BMW motorcycles, i.e., while accelerating the rear suspension stiffens and the machine lifts itself, when decelerating the rear suspension is compressed giving the opposite effect. For this reason BMW now uses the Paralever rear suspension, which prevents these side effects. The skill full rider can use the "shaft-effect " to their advantage by blipping the throttle, thus temporarily increasing ground-clearance of the bike while passing over large objects.
HPN treats this in another fashion: an extended version of the old, one-piece G/S - swingarm is used. The old swingarm is cut in two pieces, lengthened by adding a 100-mm long tube, and re-welded. The drive shaft must of course be lengthened in the same manner. The result is a longer wheel- base, resulting in clearly better straight line stability in conjunction with longer suspension travel. The benefits of these modifications become quite evident in tough off-road conditions. If so desired the standard monolever swingarm can be converted into a double for a substantial increase in stability. An advantage of the HPN-swingarm, actually an outdated construction, is its high-durability when compared to the modern Paralever. White Power delivers state-of-the-art suspension components the high quality.

7. The future:

The next project to benefit from HPN-knowledge is the Paralever-swingarm. At present, the rear swingarm of the new BMW-generation (1100 cc four-valve boxer featuring the Telelever front fork) is modified and adapted to the frame of the older boxer models. This modified swingarm is stronger compared to the original Paralever-swingarm, and is controlled by a single, centrally mounted shock absorber.

As the production of air-cooled boxer models eventually comes to an end, HPN will most certainly develop and improve the newer oil-cooled models. However, this is more difficult as the crankcase/gearbox also serves as a stressed member of the chassis. The concept of the new boxer is more complicated and sophisticated than previous models: simple modifications are made impossible by using different and new materials (forged steering head, use of aluminum alloys, plastic materials); the engine uses SOHC four-valve cylinder heads and Motronic fuel injection; Telelever front fork, where the A-formed suspension link makes longer suspension travel distances impossible due to interference with cylinders and/or crankcase.

As the old versions of BMW works rally-motorcycles, developed by HPN, become non-competitive, one can only hope that, upon BMW’s orders, HPN is given the task to develop and build new, competitive rally-motorcycles based of the new boxer-models.

• The special G/S and GS page
• The G/S and GS adresses page