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Thunderbike Rules - Base Rules

 Below for review by everyone ahead of the Brands GP meeting on rules, the base Thunderbike Sport rules are below


BMCRC Thunderbike UK Championship Regulations 2013

Introduction :

This series is for motorcycles manufactured which comply with class engine limits, plus later hybrids and "specials" admitted at the BMCRC Eligibility Officer's discretion.


All machines in these classes are restricted to a power-to-weight limit, and an overall maximum power limit, in order to promote close and fair competition. The power restrictions are measured at the rear wheel using BMCRC's scales and dyno, and are as follows :


Single Cylinder Thunderbikes (Tb.)..........1 SAE bhp 1.56 kg weight.
Light Weight Thunderbikes (Tb.).............1 SAE bhp 1.63 kg weight up to a maximum of 75 bhp.
Sports Thunderbikes (Tb.).......................1 SAE bhp 1.81 kg weight up to a maximum of 105 bhp.

Please note the power to weight ratio applies to all machines.

All machines must have unaltered VIN Frame and Engine numbers.

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.    Race numbers and background colours:


1.1.  Race numbers for this class must be Black on White background for Thunderbike


1.2.  All machines must carry a sticker identifying their power to weight class.
These will be :
........................Single Cylinder
........................Light weight
Stickers will be available from the race office at race weekends.


2.    Chassis :


2.1.  Frame, engine cases, and cylinder heads must be from the same
production model and year where applicable.
(Year legacy rules will apply whereby a model extends past cut-off date but remains unchanged)

2.2.  Single cylinder motorcycles and accepted “technically interesting” motorcycles may use
any frame but the engine must conform within the engine (section 4) guidelines.

2.3.   Anything other than frame, crankcases, and cylinder heads may be modified or changed subject to:


2.3.1.                Seat sub frames where fixed may be replaced by bolt on replaceable rear sub frames.


2.4.  Hybrid bikes (Big engine, small frame) whose engine conforms to the rules stated may also be considered and approved on an individual basis by the series coordinator(s) and/or eligibility officer(s). In the case of hybrid bikes, 4 stroke engines must be mounted in a 4 stroke chassis. 2 Stroke engines mounted in a 2 Stroke chassis.


3.    Wheels and tyres


3.1.  Wheels may be replaced. Tyres can be treaded or slick. Rain tyres may be used.


4.    Engine


4.1.  Reducing engine size of machines from stock displacement to meet BMCRC Thunderbike class displacement limits is not allowed.

4.2.  Crankcases may be strengthened.

4.3.  Cylinder heads may be modified but must retain the original number of valves.

4.4.  Engine displacement limits are absolute and are set as follows:


Supermono/lightweight/sport classes
Single cylinder, Unlimited displacement. 2 stroke GP road race machines are not allowed in BMCRC Thunderbike.
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 2006)
Three cylinder, non-fuel injected only up to 1200cc
Four cylinder air-cooled, 2 or 4 valve up to 1200cc.
Four cylinder, liquid cooled, up to and including 1996 model year, up to 650cc
Four cylinder, liquid cooled, up to and including 1994 model year, up to 850cc
(Model year refers to year of manufacture, proof of which lays with the competitor. Year legacy rules will apply whereby a model extends past cut-off date but remains unchanged)

5.    Electronic control systems


5.1.  The use of electronic control systems to aid launch or traction are strictly forbidden.

5.2.  Bikes are only permitted to have one loaded fuel map at any one time, and any bike found with multiple maps loaded in the software will be excluded. Any ‘On-the-fly’ switch-able map is strictly forbidden.


6.    Controls


6.1.  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.

6.2.  Switches or other methods designed to affect horsepower readings during dyno testing are strictly prohibited.

6.3.  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.


7.    Technical Inspection


7.1.  The dyno operator, Technical Official 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.

7.2.  Any machine not capable of post race dyno testing will be deemed to have failed the dyno

7.3.  Machines will be run on the dyno until, in the opinion of the dyno operator the maximum
output is achieved. If 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.

7.4.  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 directly to the dyno when requested to do so after the end of a race will result in automatic disqualification.

7.5.  All machines must have at least 1 spark plug lead or coil 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.

7.6.  All machines will be weighed on the BMCRC Technical Officials 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 BMCRC scales are unavailable).

7.7.  Machine test procedure will be as follows.


7.7.1.               Machine(s) will be selected.

7.7.2.               The machine will be weighed with fuel but without rider.

7.7.3.               The machine will be Dyno tested and a Pass or fail given. No other information will be supplied.


7.8.   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.



Extreme Championship - Age eligibility rule clarification

All Extreme Championship riders - please take note


Currently the rules outlined on the detailed rules page state:

This series is for motorcycles manufactured more than 10 years ago as at the 1st. of March of the racing season or which comply with class engine limits, plus later hybrids and "specials" admitted at the BMCRC Eligibility Officer's discretion.

This is incorrect as the series was not aimed to have a rolling age cut off for homologated motorcycles


To be eligible the bike must be no newer than 2002 unless it is a model that was homologated before 2002 but continued past 2002 as a model for sale


That is to say that should a post 2002 model share its common components with the 2002 model it will be eligible under the legacy rule, i.e. no changes to the engine or chassis but may have a bodywork outline or colour change


The proof of eligibility lays with the competitor and approval should be sought from the Class Technical Officer that a post 2002 bike meets legacy rules before competing in the championship, as with all such matters the Class Technical Officers decision on eligibility will be final


There will be a corresponding update to the rules page shortly


2015 Race Dates Added

The countdown has begun, see the top banner for how little time you have to get ready


Please check the Races button to the left for all the dates




Changes for 2015 - Rain Lights

As you may or may not be aware the 2015 season sees the introduction of compulsory rain lights for use in WET races


The following advice was posted on the Bemsee site:



All motorcycles must have a functioning red light mounted at the rear of the machine to be used in rain or low visibility conditions as instructed by Race Control. The team must ensure that the light is switched on whenever a rain tyre is fitted on the motorcycle and/or when any practice or race is declared “wet” by Race Control.

Lights must comply with the following:

 a) Lighting direction must be parallel to the machine centre line (motorcycle running direction), and clearly visible from the rear at least 15 degrees to both left and right sides of the machine centre line.

 b) Mounted on the seat/rear bodywork approximately on the machine centre line, in a position approved by the Chief Technical Officer. In case of dispute over the mounting position or visibility, the decision of the Chief Technical Officer will be final.

 c) Power output/luminosity equivalent to approximately: 10 – 15W (incandescent) 0.6 – 1.8 W (LED).

 d) The switch must be accessible.

 e) Rain light power supply may be separated from the motorcycle main wiring and battery.


If you have any questions please contact one of our Technical Reps




Neil Harris Motorcycles - ACU Discount

One of our former Extreme racers 'Neil Harris' is taking a year out of racing to focus on his business, although we will miss him on track he is currently offering clothing dicounts for ACU racers


If you go to his face book group:

Neil Harris Racers Clothing Discounts

You can apply to join the group and gain access to the discounted products- YOU MUST HOLD A VALID ACU LICENCE


Thanks for your support Neil and hope to see you out there next year :)




Tech Inspection - What they are inspecting on your Thunderbike!

HI All,


Mark has kindly let me lift this from his motoforum post and publish here as a useful guide on what is checked when the tech officials scrutineer your bike, it makes for a useful read whether your new to the class or not, enjoy!


As there are so many rookies starting racing this season it can be a bit strange at your first meeting going to Tech Inspection, what to expect, what are we checking for? Well this is looking through my eyes at what i'm doing when looking at your bike, hopefully it gives a bit of insight to what we do.


Technical Inspection ……………what the hell am I doing?

Current Road Race Technical specs can be downloaded from the current ACU handbook on the ACU website.

A little insight into what we, the technical officials are doing and looking at when we inspect your bike, this is a typical set of checks but not exhaustive.

Most officials have their own routine but basically all will check for the same items
First up you will be asked to support your bike from the rear and asked for your scrutineering card (which you will have signed) From this I will check your race numbers, Frame/engine numbers and transponder number
PLEASE NOTE: Anyone found in possession of a machine with tampered or defaced engine or frame numbers will not be allowed to race, even if you have receipts for the bike.
Details can be found here

I will start at the front of the bike checking handlebar clip-ons are securely fixed and the handlebars and levers do not foul the fairing on full lock. Levers have rounded ends. The steering lock is checked such that full lock is only limited by the lock-stops, not by steering damper or brake fluid reservoir smashing the clocks!
Tug on the front fairing to ensure secure fixing.
The throttle will be twisted to ensure it freely returns to its fully closed position (i.e. it snaps shut)
The front brake operation will be checked and if your front brake hoses have a split (1 into 2 join) this must be above the bottom yoke, linked callipers are not allowed. Most race bikes run 2 separate lines from the front master cylinder. While doing this I will also check that there is no play in the head bearings.
Check that clocks are mounted secure and there is a manual engine kill switch accessible.
Coolant, plain or distilled water only, no additives in the cooling system what so ever. There is no requirement for a separate catch bottle for coolant overflow but is advisable to direct into the belly pan if no catch bottle is used.

From here I will check the front wheel, Calliper bolts tight? No visible signs of brake fluid leaking?
Disk bolts all present and tight? Front tyre fitted the correct rotation, valve cap fitted and any wheel weights fitted must be taped up with gaffa tape.
While I’m kneeling down I will also check for any signs of leaking around the fork seals.

I will now check that the oil filter, sump bolt and filler cap has been lock wired (some bikes also have dip sticks this also has to be wired) any engine breathers must vent into a collection bottle.

I will run my hand along the bottom of the fairing catch tray, this must be solid with no holes in it and constructed to hold at least half of the total oil and coolant capacity of the engine (generally all race fairings are designed to this spec) as well as the fact that any openings in the fairing are at least 50mm above the bottom of the fairing. If drain plugs have been fitted these must be taped in place from both sides.

Check left hand side foot peg has rounded ends, if standard ‘flip up type’ pegs are used hero blobs have to be removed. Make sure no excessive play or loose joints on gear shift mechanism. Side stand removed? (Yes it does happen!)

I will check the rear shock visually as well as the upper and lower mounting bolts, I will ensure there is no play in the wheel bearings or swing arm by forcing the wheel from side to side. Shark fin fitted?
Check all sprocket nuts are present and tight, chain adjustment correct?

From here I move to the right hand side of the bike, rear brake working? Calliper is checked for movement and all disk bolts are present and tight.

Exhaust end can securely fitted and exit does not project beyond any part of the vehicle or its bodywork.

Check right hand side foot peg has rounded ends,  if standard ‘flip up type’ pegs are used hero blobs have to be removed, rear brake lever securely fitted and not fouling on any part of machine.

From here I will move to the top of the bike and check fuel tank/filler cap is securely fastened, give the rear seat unit a tug and make sure mounting is solid.

Assuming the bike passes inspection your card will be signed and a ‘Day Sticker’ affixed to your bike.
If for any reason your bike fails you will be asked to fix the problem and bring the bike back to recheck


NOTE: Technical officials are here to get you on track, not to try and stop you. We will endeavour to be as polite and helpful as we can be to get you on track and to enjoy your racing.