`MiniTwins` Championship Regulations 2017
‘MiniTwins’ Championship Regulations 2017
Final Version - 04/12/17
All items not mentioned in the following articles must remain as originally produced by the
manufacturer for the homologated machine. Everything that is not authorised and prescribed in
these rules is strictly forbidden.
Each club may appoint Eligibility Officers for the class. They will refer to the organisers of
the series for the definitive interpretation of these regulations. This decision will be final.
a. Any four-stroke twin cylinder motorcycle originally sold for road use with a water-cooled engine
of up to 650cc, or an air cooled engine of up to 820cc, may be used provided it adheres to the 72
SAE hp power limit for the series.
b. Older models may be updated with genuine parts found on a newer version of the same model
and newer models may use parts from older machines. All parts must be used as intended for the
homologated machine and in accordance with the manufacturer’s recommendations.
c. All machines must comply with the machine preparation regulations as set out in the 2016 ACU
handbook for road race meetings.
d. In order to control costs, machine damage may be repaired in a manner agreed with the series
Eligibility Officer and the Chief Technical Steward of the club. No advantage may be gained
from such modifications.
e. All machines must function on normal unleaded fuel available from public service stations with
a maximum 102 octane in adherence with ACU standards. E85 Bio-Fuel from public outlets is
permitted.
1 Frame and Swing Arm
1.1 Frame and swing arm must remain as originally produced by the manufacturer for the
homologated machine. Nothing may be added or removed from the frame body.
1.2 Rear sub frame may be replaced or modified. The sub frame may only be altered if it was
originally designed to be unbolted from the frame body.
1.3 Refinishing of frame or swing arm to a suitable standard is acceptable.
2 Suspension
2.1 Forks must remain as originally produced by the manufacturer for the homologated machine
with the exception of the following:
• 2.1.1 Original internal parts of the fork may be modified or replaced. After market damper kits
or valves may by installed. Fork springs may be replaced.
• 2.1.2 Fork caps may not be modified or replaced beyond the homologated standard to allow
external adjustments.
• 2.1.3 Fork stanchions must retain the original finish. No additional surface treatments are
allowed.
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• 2.1.4 Refinishing of the outer fork tubes to a suitable standard is acceptable.
2.2 Steering damper may be added although it cannot act as a steering lock device.
2.3 Rear suspension unit can be changed or modified. The original attachment to the frame and
swing arm must be as homologated.
2.4 The rear suspension linkage must remain as originally produced by the manufacturer for the
homologated machine.
3 Wheels
3.1 Wheels must remain as originally produced by the manufacturer at the time of sale into the
dealer/distributor network for the homologated machine except for the following:
• 3.1.1 Wheel bearings and spacers may be modified or changed where required.
• 3.1.2 The speedometer drive may be removed and replaced with a spacer.
• 3.1.3 Refinishing of wheel rims to a suitable standard is acceptable.
3.2 Front and rear wheel axles must remain as originally produced by the manufacturer for the
homologated machine. Modifications can be made in order to accept safety retention devices.
4 Brakes
4.1 Front and rear brake discs may be changed but must fit the original calliper and mounting. The
outside diameter must remain as fitted to the homologated machine. Only ferrous materials are
allowed for brake discs.
4.2 Front and rear brake callipers, including mount, carrier and hanger, must remain as originally
produced by the manufacturer for the homologated machine.
4.3 Front and rear master cylinders must remain as originally produced by the manufacturer for the
homologated machine. Front and rear brake fluid reservoirs may be changed with aftermarket
products.
4.4 Front and rear hydraulic brake lines may be changed. The split of the front brake lines for both
front brake callipers must be made above the lower fork bridge (bottom yoke).
4.5 Front and rear brake pads may be changed.
5 Tyres
5.1 All tyres must be road legal unless the race is declared wet where full wet tyres may be used.
Slicks and intermediates are not permitted.
6 Controls
6.1 Footrest and foot controls may be replaced or relocated but brackets must be mounted to the
frame at the original mounting points.
6.2 Handlebars, hand controls and cables may be altered or replaced (does not include brake master
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cylinder) from those fitted to the homologated motorcycle.
6.3 Engine starter switch and electric stop switch must be located on the handlebars and must be
operational at post race technical inspection.
7 Fairing and Seat Unit
7.1 Fairing, mudguards and seat unit may be altered or replaced and need not conform to the
homologated shape as originally produced by the manufacturer.
7.2 Windscreen, if fitted, may be replaced with transparent material only.
7.3 The original instruments and fairing brackets may be removed or replaced.
7.4 The petrol tank must remain as originally produced by the manufacturer for the homologated
machine although it may be refinished if required. The position of the tank mounting points on the
frame must remain as standard.
7.5 Race numbers must be black on a yellow background and displayed on the front of the bike and
on both sides of the seat unit. Background and number sizes as per the ACU handbook.
8 Wiring Harness and Battery
8.1 The wiring harness may be altered or replaced. Additional wiring may be added where required.
8.2 No wiring or electronic equipment may be added or modified to alter the ignition or engine
timing characteristics from those of the homologated machine with the exception of the following:
• 8.2.1 The use of flash memory (flash RAM) for fuel injection mapping is allowed where the
capability exists within the homologated motorcycle. An additional control unit to change the
fuel mixture may be installed and must be fitted to the original connectors. The unit must not be
able to perform any other function.
• 8.2.2 The side stand switch, and related wiring, may be disabled or removed.
• 8.2.3 Any electrical switchgear located on the handlebars or front sub frame may be unplugged
or removed as required. Engine starter switch and electric stop switch must be fitted.
8.3 All original electrical equipment not directly related to road use must be fully incorporated in to
any modified wiring loom, including generator, CDI, regulator and starter motor.
8.4 All original connections to the CDI must be retained and maintain their normal use.
8.5 The size and type of battery may be changed and / or relocated.
9 Radiator and Oil Cooler
9.1 The original radiator and oil cooler, if fitted, must remain as homologated.
9.2 Radiator hoses may be replaced with those of a similar internal diameter.
9.3 Oil lines may be modified or replaced. Oil lines containing positive pressure, if replaced, must
be of metal reinforced construction with swaged or threaded connectors.
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10 Air Box / Carburation / Fuel Injection
10.1 The air box may not be altered or replaced from that fitted to the homologated motorcycle.
10.2 The air filter element must be fitted but may be replaced with an after market item.
10.3 The air box inlet rubbers may not be removed or altered.
10.4 Carburettors must be the standard units as on the homologated model. Throttle bodies for fuelinjected machines must be as on the homologated model.
10.5 Carburettor jets and needles may be replaced. Resizing of the air metering holes in CV
carburettors slide control is permitted. No other alterations are permitted to the air intake or
carburation system.
10.6 Bell mouths may not be added, altered or replaced from those fitted to the homologated
motorcycle.
10.7 The fuel injection management system may not be altered or replaced other than the
remapping of internally stored fuelling maps.
11 Engine
11.1 Cylinder head, camshafts, cam sprockets, crankshaft, rods, pistons, valves, cylinders and all
other engine components must be as homologated. No internal engine, gearbox and clutch parts
may be altered or replaced with the exception of the gearshift detent spring, the clutch friction and
drive plates and the clutch springs.
11.2 Polishing and lightening of engine parts is not permitted. Balancing or gas flow modifications
normally associated with individual tuning are not permitted.
11.3 Compression ratio of the engine must remain as homologated.
11.4 Camshaft timing must remain as homologated.
11.5 No other engine tuning or alteration from the homologated standard is permitted.
11.6 The crankcase/gearbox casing, clutch and generator covers may be protected by additional
means, e.g. protective covers made of stainless steel or carbon/Kevlar composites.
11.7 The thermostat may be removed from the housing to aid cooling, if required.
11.8 The maximum horsepower limit for the series is 72 hp SAE measured at the rear wheel. Any
machine found to exceed this figure on a dyno selected by the club may be excluded from the
results.
12 Transmission
12.1 Additions to gearbox or selector mechanism, such as quick shift systems, are not allowed.
12.2 Clutch springs, friction and drive plates may be replaced.
12.3 Clutch baskets must remain as homologated. The use of slipper clutches is prohibited unless
fitted as standard.
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12.4 Gear shift detent spring may be replaced with a heavy duty item.
12.5 Front and rear external drive sprockets, chain pitch and chain length can be changed.
13 Ignition and Engine Control System
13.1 Ignition and engine control system (CDI) may not be modified or changed. All units must
remain fully interchangeable with available control units.
13.2 No modifications or alterations, whether electronic or mechanical, may be made to the
motorcycle to alter the engine ignition timing.
13.3 The use of flash memory (flash RAM) for fuel injection mapping is allowed where the
capability exists within the homologated motorcycle. An additional control unit to change the fuel
mixture may be installed and must be fitted to the original connectors. The unit must not be able to
perform any other function.
13.4 Fuel injection mapping may be reprogrammed. Alterations must remain within the capability
of the standard fuel injection system as fitted to the homologated machine unless overridden with a
permitted control unit.
14 Generator
14.1 The generator, starting system, starter crank gear and starter shaft may not be altered, replaced
or removed from those fitted to the homologated motorcycle.
15 Exhaust System
15.1 Exhaust pipe and silencers may be altered or replaced from those fitted to the homologated
motorcycle. This must adhere to the maximum noise regulations as set out in the ACU handbook.
15.2 The number of final exit(s) to the exhaust may be altered from that of the homologated
machine.
15.3 Wrapping of exhaust systems is not allowed except in the area of the rider’s foot or an area in
contact with the fairing for protection from heat.
16 Fasteners
16.1 Standard fasteners may be replaced with fasteners of any material and design. The strength and
design must be equal to or exceed the strength of the standard fastener it is replacing for structural
applications.
16.2 The use of titanium in the swing arm spindles and the wheels spindles is forbidden. For wheel
spindles the use of light alloys is also forbidden. The use of titanium alloy nuts and bolts is allowed.
16.3 Aluminium fasteners may only be used in non-structural locations.
17 Miscellaneous
17.1 The following items MAY BE removed:
17.1.1 Instruments, instrument bracket and associated cables, horn, license plate brackets, tool kit,
tachometer, speedometer and wheel spacers, radiator fan and wiring, passenger foot rests, passenger
grab rails and upper chain guard.
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17.2 Emission control items (anti-pollution) in or around the air box and engine (O2 sensors, air
injection devices). Please note that any valves or other devices bolted directly to the engine may be
blocked off but must remain in place.
17.3 The following items MUST BE adhered to:
17.3.1 Motorcycle must be equipped with a functional ignition kill switch or button mounted on the
handlebar that is capable of stopping a running engine.
17.3.2 Side stand must be removed.
17.3.3 All drain plugs must be safety wired. External oil filter screws and bolts that enter the oil or
water cavities must be safety wired.
17.3.4 Headlamp, rear lamp and turn indicators must be removed. A suitable material must cover
the openings. Mirrors must also be removed.
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