Thunderbike UK Championship Regulations 2010

(Updated 06/07/10)

Overview :

What sort of bike fits the Thunderbike uk series ?
The series is designed to allow engineers, riders, and anyone with an interest in improving their bike more freedom from the current “production style” rules, prevalent in all forms of current motorsport.
The rules give a wider range of bikes a chance at racing. In some cases riders have used machines from nearly 2 decades ago. Others have used modern technology throughout. Many have taken machines and upgraded them (forks, brakes and suspension etc..)
The power to weight restrictions mean close racing is always achieved and any rider can be competitive. Some competitors believe light weight is better, others that more power is best.
2009 has seen winners on bikes from 600cc - 1000cc including twin and 4 cylinder machines so the argument to which is best continues.

There are no restrictions on manufacturer for any parts other than the Frame/crank cases and cylinder heads.

A basic Thunderbike must confirm to the rules shown, but any Technically interesting machine whose engine and intake conforms to the rules stated may also be considered and approved on an individual basis by the series coordinator(s) and eligibility officer(s). Successful applicants will be notified in writing by the series co ordinator(s) or eligibility officer(s), their decision is final.

A power to weight ratio applies to all machines.

Technically interesting could include but not restricted to : Spondon, Harris, Vyrus, Bimota, Rob North, Self build or prototype or something interestingly modified. If in doubt and you want to build something not obviously listed please ask. We actively encourage different ideas.
Single cylinder machines are exempt from production and street use requirements. Single cylinder 2 stroke GP road race machines are not allowed in this class. All machines must have unaltered VIN numbers.
The organizers will appoint eligibility officers for the series. Their decision on the interpretation of the rules will be final.

All machines must comply with the machine preparation regulations as set out in the current ACU Handbook for road race meetings

The Rules & Technical specifications :
1. Frame, cylinder head(s) and engine cases must be from the same production model and year where applicable.
1.1 Single cylinder motorcycles and accepted “technically interesting” motorcycles may use any frame and engine within the engine (section 3) guidelines.
1.2 Swinging arms may be modified or replaced and rear shocks may be replaced or relocated.
1.3 Front forks or suspension may modified or replaced.
1.4 Seat sub frames where fixed, may be replaced by bolt on replaceable rear sub frames in the interest of economical crash repair.

2. Wheels and tyres
2.1 Wheels may be replaced. Tyres can be treaded or slick. Rain tyres may be used.

3. Engine
3.1 Reducing engine size of machines from stock displacement to meet Thunderbike class
displacement limits is not allowed.
3.2 No larger capacity engine may be fitted into a frame designed to originally take a smaller displacement . Ie a 600cc engine into a 250cc frame.
3.3 You may UPGRADE a carburetor model engine to fuel injection but NOT fit a fuel injected bike with carburetors.
3.4 Engine displacement limits are absolute and are set as follows:
Single cylinder, Unlimited displacement
Twin cylinder, air cooled, Unlimited displacement
Twin cylinder, liquid cooled, 3 or less valves per cylinder, Unlimited displacement
Twin cylinder, liquid cooled, 4 valve per cylinder, up to 750cc (Ducati 749 to 2004 model not S or R)
Three cylinder, non-fuel injected, up to 1200cc
Three cylinder fuel injected 650cc.
Four cylinder air-cooled, 2-valve, unlimited displacement.
Four cylinder, air-cooled, 4 valve up to 1200cc
Four cylinder, liquid cooled, up to and including 1995 model year, up to 650cc
Four cylinder, liquid cooled (oil or water), pre-1990 model year, up to 860cc

(Model year refers to year of manufacture, proof of which lays with the competitor)

4. Power Restrictions (measured at the rear wheel)

4.1 Single cylinder machine 1 SAE horsepower to every 1.56 kilos in weight.
Eg : current super mono 75bhp = 117kg
4.2 Twin cylinder machines up to 75bhp max 1 SAE horsepower to every 1.63 kilos in weight.
4.3 Thunderbike machines producing 76hp or more are required to meet a maximum power to weight limit of 1 SAE horsepower for every 1.81 kilo in weight, i.e. a maximum of 1hp per 1.814kg
4.2 Power to weight ratio will be calculated as the weight of the machine divided by the tested horsepower when inspected. Inspections can occur post race or post qualifying or randomly as required by the organiser or official scrutineer.
4.3 Any machine found to exceed the power to weight ratio on a dyno or weighing device selected by the organizers may be excluded from the results.
4.4 All machines must carry a sticker identifying their power to weight class.
These will be :

Single Cylinder
Under 75 bhp
Open class

5. Controls

5.1 Throttle stops or cable adjustments must be fixed or secured in a manner that will prevent adjustment by the rider or crew without the use of tools prior to dyno testing.

5.2 Switches or other methods designed to affect horsepower readings during dyno testing are strictly prohibited.
5.3 Machines are restricted to the mounting and use of one ignition or engine management module during all competition. Modules with more than one setting must be mounted in such a way that the settings cannot be altered by the rider or crew while on course or prior to dyno testing.

6. Technical Inspection
6.1 The dyno operator, scrutineer or person appointed by the race or series organisers to ensure eligibility, may request removal of bodywork before, during or after dyno testing, and may request removal of other components for inspection.
6.2 Any machine not capable of post race dyno testing will be deemed to have failed the dyno test.
6.3 Machines will be run on the dyno until, in the opinion of the dyno operator, the maximum output is achieved, in the opinion of the dyno operator or race official, an unsafe condition exists while performing the dyno testing, the test will be stopped and the Clerk of the course in conjunction with the Technical officer will make the final decision on the dyno test results.
6.4 Machines will be selected at random by race officials to run on the dyno as soon as possible following the end of the race. Failure to report to the dyno when requested may result in disqualification.
6.5 All machines must have at least 1 spark plug lead accessible to the Dyno operator to allow the pick up clip from the dyno to be attached. This ensures the quality of the test and is in the competitors own interests. Machines where the lead is unavailable may be disqualified.
(This rule will apply from 22nd July 2010).
6.6 All machines will be weighed on the BRMCC Scrutineer’s own scales. They will be calibrated in house before each round and yearly as deemed necessary. They are definitive. Circuit scales will only be used if the BRMCC scales are unavailable.
6.7 Machine test procedure will be as follows.
Machine(s) will be selected.
The machine will be weighed with fuel but without rider.
The machine will be Dyno tested and a Pass or fail given. No other information will be supplied.
6.8 Bikes which have been deemed to have failed the power to weight or technical rules may be excluded from the race results. This exclusion may be for the entire meeting at the discretion of the clerk of the course.
6.9 Machines that have been rectified and presented by the rider as fit to race will start from the rear of the grid. This will apply to the next race in the current meeting only.
From then on the rider will take their place on the grid as usual and score points normally.

Motorcycles approved to race in Thunderbike UK series providing they meet the power to weight regulations. Please note this is not a definitive list but a guideline. Please ask if you are unsure about the model you wish to race. There are some “exceptions” included which are specific bikes thought to be in the sprit of Thunderbike. They must still meet the Power to weight regulations.

Aprilia
Shiver 750cc
550cc twins

British
Any British manufactured bike meeting the engine regulations.

BMW
All air cooled Horizontally opposed twins.
All water cooled twins to 750cc.
K series 750cc triples.

Cagiva
Raptor 650

Ducati
All air cooled SS range. 600cc - 1100cc
multistrada
all air cooled Monster range
All 748 models

Ducati 749 up to and including 2004 model (not S or R model)
ST2 and ST3
ST4 model 1999 and 2000 model only. (special inclusion).
916 upto and including 1997 year model only. (special inclusion).

Egli
All Egli framed bikes meeting the engine regulations or of special interest.

Harris
All Harris framed motorcycles meeting the engine regulations or of special interest.

Honda
All air cooled machines.
All pre 1990 liquid cooled machines up to 860cc
All pre 1996 liquid cooled machines up to 650cc.
CBR600 to 1996
CB500
NC30 - 400cc
Deauville
Firestorm up to and including 1998 year model only (not S model) (special inclusion).

Kawasaki
All air cooled machines.
All pre 1990 liquid cooled machines up to 860cc
All pre 1996 liquid cooled machines up to 650cc.

KTM
All 2 stroke and 4 stroke singles.

Motod
Any motod chassis complying to the engine specifications.

MotoGuzzi
All air cooled 2 valve machines.
All air cooled 4 valve machines

Nevel
Any model.

Suzuki
All air cooled machines.
All pre 1990 liquid cooled machines up to 860cc
All pre 1996 liquid cooled machines up to 650cc.

Triumph
All early air cooled triple models.
Tiger models up to and including1998 with 885cc engine. (special inclusion).
600 water cooled model upto 1999 only.(special inclusion).

Yamaha
All air cooled machines.
All pre 1990 liquid cooled machines up to 860cc
All pre 1996 liquid cooled machines up to 650cc.
TRX 850cc (special inclusion).