Of the above bikes the Honda CBR125 is by far in the majority but there has been a few Yamahas and a sole KTM 125 Duke. In the right hands any bike can be competitive the Honda CBRs are readily available and cheap to prepare and run.

There may be other Asian bikes out there which could be eligible, however for this article we will only concern ourselves with the Honda CBR125.

Sourcing a suitable Commuterlite

Look in the Auctions, Wreckers, Gumtree, Trading post and motorcycle sales sites on the web. Usually the Honda CBR125 can be picked up cheap with superficial crash damage.

Success

So you've managed to get your hands on a donor Honda CBR125. To turn your sporty road going bike into a competitive Commuterlite race bike You will need to do the following:

Race preparation

Race preparation must be done according to the MA's Road racing GCRs (General Competition Rules) which can be found in the  MOMs (Manual Of Motorcycle Sport). The manual is published in it's entirety on the web and can be found HERE... on the MA's website.

Shopping List

Put the following on your shopping list:

• Tires; Up to Year 2010, 100/80 x 17 rear and 90/80 x17 front
• Tires; After 2010, 130/70 x 17 rear and 100/80 x17 front (MITAS seems to be the tyre to have.)
• After market sports exhaust.
• Lock wire
• Roll of pvc tape.
• Race Numbers
• Race number background paint (BlacK)
  

For Recalibrating the Fuel Injection map.

• 1x 5K potentiometer
• a few 1/2 watt resistors
• 50mm clear sleeve or heat shrink to slip over resistor.

Engine

The engine must remain standard, it should be ultra reliable keeping running costs down.
The OEM ECU must be retained and rev limiter must remain in operation.

The starter motor must remain along with the battery and standard alternator, all OEM. The bike must be able to start off of it's installed start motor at all times.

Exhaust

After market sports exhaust.A good aftermarket exhaust has power and weight benefits.  Fuel Injection map will need to be recalibrated when hi-performance exhaust fitted (see below).

(Stock pipe with catalytic converter is a perfomance killer and heavy.)

There are many brands of exhaust systems to choose from. NMF, Danmoto, Yoshimura, DBS, Endurance and homemade systems have enjoyed success.

Fuel Injection

• Fuel Injection must be retained, carbys not allowed if fuel injection is originally fitted.
  
• When a hi-performance exhaust is fitted the fuel map has to be recalibrated.

Recalibrating the fuel map:

• Find the plug (3 wires) for the water temp sensor on the thermostat housing. (Underneath the petrol tank on RHS looking forward) See picture below.
  
  
• Cut the Yellow/Blue wire and place a 0-5K potentiometer (available from Jaycar) in series. More resistance = more fuel. Preferably done on a Dyno with an O2 sensor although it can be sorted at a track day. Once the correct value has been established, replace the potentiometer with a 1w resistor of the closest standard value. 
   
• Resistor size in 1.2Kohm to 1.8Kohm range seems to work. Several bikes run well on aroud a 1.4K resistor but it can vary.

 

Wiring Electrical.

All electrical equipment not required on a race bike should be discarded.

Disconnect the battery before doing any electrical work.:

Discard

• Headlights, tail light, flasher lights and flasher unit.
• Horn, you wont be needing it on the track.
• It's ok with the rules to remove the radiator fan.
  
• sub sections of wiring loom not needed can go but be careful when disconnecting stuff as for instance when you remove the side stand and disconnect it's switch the bike wont start.
• As you progress through disconnecting things, reconnect the battery every other disconnection and check the bike still starts. That way you wont have far to backtrack to troubleshoot the problem.
  

The tilt switch has also caused some grief, if your bike doesn't start check that its in the right orientation. If it's upside down it sends a signal to the CPU that the bike is upside down and shouldn't be running.

Instrument Panel

The standard instrument panel is good to use does the job but its ok to use aftermarket gauges if it's damaged. Replacement cost of standard panel is prohibitive.

Airbox.

Leave the air box in place along with the inlet bellmouth. Remove the airfilter if you like.

Fuel

No point in using exotic fuels, compression ratio too low.

Chassis Mods.

Tyres

Sticky tires. Mitas 110/80 x 17 rear and 90/80 x 17 front are a popular choice and reasonably priced. They must be mounted on standard OEM rims. Get the tyre fitted by your seller and have the wheels balanced.
After 2010 the CBR125 have wider wheels.
Their wheel sizes are front 100/80-17 - rear 130/70-17

Forks

Use 20W fork oil and a 25mm to 35mm spacer to increase spring rate.

Rear Suspension

Rear suspension unit can be modified/changed but it is ok-ish if it's in good condition. The adjustable YSS and Elka shocks made for the CBR125 are a improvement but are expensive. A cheaper alternative is to get the proven Keo Watson modified unit. He does these units on an exchange basis.

Rear set Footpegs

Footpegs can be left as is but they are low and can ground. Two alloy plates as per the picture below can be run up and do the job nicely getting the footrests up and back. Aftermarket footrests are available from Thailand but again bumps the cost up.

Rear sub-frame.

To facilitate the fitting of aftermarket fibreglass seats the rules allow the back section of the rear sub-frame to be cut off as per the picture below.

If you retain the original rear plastic leave sub-frame in place as the rear seat cowl need it for support.

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Bodywork/Fairing.