Historical background - Ducati ST origins

Towards the middle of the Nineties, the first Ducati Sport Touring model, the ST2, was developed. This bike was an advancement in the modern Sporttouring concept: fast, content on long motorway journeys, agile on windy roads, yet still stable when loaded with luggage (packed in specially-designed panniers) and carrying a passenger. The ST2 Desmodromic L-twin cylinder engine was liquid-cooled, with two valves per cylinder and a total displacement of 944cc, achieved with 94mm bore and 68mm stroke. This engine’s maximum power was 83 HP at 8500 RPM, with a maximum torque of 84 Nm at 6500 RPM.

In further development of the Ducati Sport Touring family of bikes, the ST4 version was added. The engine used was the 916cc Desmoquattro:

a displacement achieved with a 66mm stroke and 94 mm bore

The Desmoquattro had four valves per cylinder, liquid cooling and maximum power increased to 105 HP at 9000 RPM, while maximum torque was 89 Nm at 7500 RPM. The L-twin cylinder engine proved eminently suitable for this new touring application thanks to its small front cross section, high torque delivered over a wide rev range, and considerably high peak performance. The geometry and highly rigid tubular steel trellis frame of the Ducati ST2 and ST4 offered the great handling and stability typical of Ducati motorcycles. A comfortable yet sporting riding position was developed by placing the rider with his body slightly inclined forward, while positioning the handlebars and footrests in a complimentary position. The advanced fairing design provided the necessary aerodynamic protection.

The ST design has always been well balanced, well-proportioned and conservative in its character. In response to the requests of ST owners themselves, the ST family now sports a new front fairing with more aggressive styling and much improved wind protection at high speed. The front turn indicators and instrument panel have also been modified and improved. The remaining bodywork, side panels and tail sections remain the same as previous models. The front fairing nose now extends further out towards the front end of the bike. This enabled the designers to raise the nose fairing and make it wider to achieve better aerodynamic protection, without altering the bike’s overall well-proportioned design. The  windscreen is now larger and has an aerodynamic shape which diverts the air flow over the riders helmet, delivering optimum comfort even

at high speeds.

Enter The Desmotre (ST3)

Desmotre key characteristics: The new, three-valve-per-cylinder engine has the same bore and stroke dimensions as the Desmodue 1000 DS (94 mm bore, 71.5 mm stroke and a total displacement of 992cc). The crankcase, crankshaft, gearbox, camshaft, primary drive with the clutch and accessory parts (alternator, starter motor) are the same as used in the Desmodue. Other parts were specifically designed for this engine: the cylinder (very similar to the  Desmoquattro’s), cylinder head, con-rod and piston. The Desmotre is water cooled with the water pump mounted in the left-hand alternator case to circulate water around the cooling system.

The two intake valves and single exhaust valve are inclined at 20°, and reproduce the same arrangement found in the Desmoquattro engine (included angle between valves = 40°). This “steep” valve angle helped create an efficient and compact combustion chamber surrounded by a considerably large squish band, facilitating flame front propagation. This is all achieved while still having a high compression ratio of 11.3:1, without having to use domed pistons.

The exhaust valve diameter is 40mm, while the two intake valves are 34mm each in diameter. The valve stems are 7mm, which are light weight and enabled the use of clearance adjusters already used in the Desmoquattro, Testastretta and Desmodue 1000 DS. The valves have a dished shaped surface facing the combustion chamber, and consequently weigh 10% less compared with the traditional flat surface design.

The Desmotre has a highly compact camshaft layout because all six lobes are machined on one camshaft only. Their distance and width has therefore been kept to a minimum and, consequently, the rocker arms are also compact.

The camshaft journal on the end opposite to the cam belt pulley has a smaller diameter than the 1000DS.  This special construction has helped to considerably reduce the weight of the cams, which are now supported in plain bearings, vs. the formerly used roller bearings.

The Desmotre heads are created by the chill gravity casting process. During casting, the combustion chamber is turned downwards (chill bottom) and is formed by the first aluminium poured, which cools rapidly creating a better material molecular structure (finer aluminium grain size). The combustion chamber and exhaust ports obtained with this technique require no further machining afterwards (however, the intake ports do receive further machining). Because the intake ports are linear, the air taken into the cylinder enters in a tumbling motion instead of swirling motion as in the the Desmodue engine, which is because of the single intake port’s tangential position with respect

to the cylinder. The Desmotre head has been carefully designed down to the smallest details. For example, the cooling fluid circulates around the two spark plugs’ hollow housings and the exhaust port, two hot spots in the head.

In order to facilitate assembly and maintenance operations, the same size of screws are used everywhere and the O-ring seals have a special protruding tab to allow quick visual inspection to ensure their presence and position.

The Ducati Desmotre engine features double ignition-just like the 1000 DS Desmodue. The two spark plugs ignite a twin flame front and for this reason, CO and unburned HC levels are reduced significantly and the cylinder head temperature is also reduced thanks to higher combustion propagation speed. Additionally, reduced spark advance and lean mixtures can be used without generating misfire risks. All these advantages are especially evident at low RPM.

The ST3 exhaust system dimensions have been specially engineered to improve the engine’s power delivery and top performance. Like in many other Ducati models, the exhaust manifolds are connected to a collector located below the engine sump, near the swingarm. From this collector, pipes exit turning at 90° to reach the area below the silencers. These pipes are inserted in the collector in such a way that they can rotate. The effect is that the silencers (like in earlier ST models) can be raised if the rider wishes greater ground clearance as is required by aggressive sport riding. A catalytic converter is provided at the inlet of each silencer (one on each side).

The highly rigid tubular steel trellis frame, rear suspension lay-out and the characteristic chassis dimensions of the new ST models have not changed compared with the previous series. However, the fork and top fork yoke have been modified. The handlebar clamps that grip the fork stanchion have 20mm

of adjustment up or down. The handlebar lower adjustment is governed by the stepped diameter of the fork stanchion, while the upper adjustment is governed by the bottom surface of the top yoke. Consequently, the rider can modify his riding position to suit their riding style or road conditions. When making handlebar adjustments, the handlebar has height reference marks notched on their outer surface to ensure equal height. They may not, however, be turned fore or aft, because they are retained in position by special locating pegs fixed under the steering head. This is done to prevent misplacement and consequential contact with the tank or fairing when the handlebars are at full lock in either direction.

The ST3 has been equipped with upside-down Showa forks adjustable for pre-load and a Sachs rear shock adjustable for pre-load, plus compression and rebound damping.

The rear suspension uses an öhlins shock, also fully adjustable for compression and rebound damping, plus pre-load is adjusted via a remote control and can be regulated without the use of tools.

Evolution in master cylinders: The front discs, rear disc and the corresponding callipers are the same as used in the earlier ST series. The newly fitted front brake master cylinder and clutch master cylinder are the same types introduced on the Multistrada 1000.

The fluid reservoir is therefore integral with the hydraulic pump. The lever distance from the handlebars is adjustable.

A CAN bus to simplify the electric system

Using a CAN (Controller Area Network) avoids bike sensor duplication and thus simplifies the electric system dramatically and considerably reduces the bike’s overall weight. The two nodal points connected to the Controller Area Network are the Magneti Marelli engine control unit and the instrument panel. The signals generated by the sensors are therefore shared between the two electronic processing units connected to the network. The CAN line is a network consisting of only two cables, conveying trains of digital signals, each one delivering clear, perfectly identifiable information. The nodal points connected to this line (the engine control unit and the instrument panel) have special hardware able to tell whether a certain train of pulses contains relavant information, which then has to be processed by the computing unit. This special electronic technology has helped to considerably simplify the bike’s electric system, which in certain sections only includes one pair of cables for the CAN line.

The Multistrada instrument panel (suitably modified in its control software) has been used for the new ST series. It has an analogue engine rev counter with blue back-lighting. To the left of the rev counter is a back-lit liquid crystal display, which shows, in addition to the bike’s speed, the fuel level, engine oil pressure, time, total/trip mileage and the cooling fluid temperature. It can also display the instant fuel consumption, the average consumption, miles that the bike is able to travel with the current amount of fuel in the tank (range), and the average speed. All this information is  useful during long trips, and in areas where frequent refuelling is not possible. Additionally, like in the 999 instrument panel, a warning light illuminates at fixed intervals to inform the rider that the time has come for a scheduled service. The instrument panel is very compact and light (thickness: 48.1mm, weight: 340g). High-integration electronics have been applied to directly control the step-by-step motor operation of the rev-counter and the headlight height adjuster. The headlight height can be adjusted up or down by using two buttons located on the top edge of the instrument panel. The rider can easily modify the light beam height, according to varying loads such as rider only, rider and passenger, rider and passenger plus saddlebags.

This ensures optimum night-time visibility and increases safety. The front headlight is of a new complex surface design. The double curved, multi-refector headlight produces class leading performance for both intensity and spread.

A new control has been added to activate all four indicators as hazard lights.

The instrument panel also includes a status lamp for the anti-theft Immobilizer system.