It is now four years plus
since this article on preparing a Honda CBR125 for competing in the
Bucket Racings associations Commuterlite class was first written.
Since then the class has grown dramatically with young and old trying their hand in
this ultra competitive economical class. There are now two grades of
riders Amateur and Pro. giving a progression path for riders to improve
to Pro status and Pro riders to move up to Superlites, Motolites or the historic classes,
P6 125s being the popular choice there. Last year (2014) saw a lot of
young riders come to the fore.
Ron Pulido 2014 Commuterlite Pro Champion
on the ubiquitous Honda CBR125
This is a slight revamp
of the original article as there is much more information available on getting
the most out of these machines.
The Commuterlite class allows any ADR compliant 125cc 4
stroke motorcycle, of any age to race. The
have been kept very simple only allowing changes to exhaust,
suspension gearing and bodywork. These simple rules keep the costs down to the very minimum
and have been creating close and
exciting racing where beginner and accomplished riders alike can hone
their race craft and have a lot of fun in the process.
Currently the choices are:
- Honda CBR125
- Yamaha YZF R125
- KTM 125 Duke
- Aprilia RS4
- Kymco 125 Quannon
Of the above bikes the Honda CBR125 are 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 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
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.
So you've managed to get your hands on a
donor Honda CBR125.
First of all you will need to do.
First off remove all the unnecessary stuff like:
- Rear mudguard and Rego plate bracket. (You will have to cut these
off of the underside plastic toolbox tray and battery box container).
- Passenger footrests and hangers. (You may need to keep the Right
side one to hang the exhaust on).
- Any unnecessary bolt on brackets on frame.
- Standard exhaust and bin it.
- Sidestand (beware see further on)
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 now published
in it's entirety on the web and
can be found
HERE... on the MA's website.
To turn your rather tame CBR125 commuter bike into
a competitive Commuterlite racer put the following on your
- Tires; 110/80 x17 rear and 90/80 x17 front (Sava seems to be
the tyre to have)
- After market sports exhaust.
- 2 x 6mm alloy plates to raise and move
foot pegs to rear. (this is not essential but it does give more
ground clearance and makes it easier to get into the racing crouch)
- 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.
And that's it, it certainly won't break the bank
The engine must remain standard except for the
modifications allowed in the rules, the
CBR125 engine should be ultra reliable in this totally unmodified
guise, hence keeping running costs down. The OEM ECU must be
retained and rev limiter must remain as supplied.
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
at all times.
After market sports exhaust. a NMF pipe
gave excellent results in the test bike prepared by Garry Briggs of
Big Bang Engines and ridden by Stephen Kairl at Eastern Creek. Fuel
Injection map will need to be recalibrated see below.
(Do not consider using the stock pipe with
catalytic converter.) A good aftermarket exhaust has
power and weight benefits.
Since this article was originally written other
brand exhaust pipes such as Yoshimura, DBS,
Endurance and homemade systems have enjoyed success.
- 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.
To recalibrate 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. Should be done on a Dyno with an O2 sensor. Once
the correct value has been established, replace the potentiometer
with a 10c resistor of the closest standard value. When adjusting
the potentiometer, the engine has to be off when changing the value
from low to high, but you can change from high to low with it
- Resistor sizes in 1.2Kohm to 1.8Kohm range
seems to work but it really needs to be put on a dyno to
finalise the correct value. However anything around those values
should get you started. Several bikes run well on a 1.4K
All electrical equipment not required on a race bike should be discarded.
battery before doing any electrical work.:
- 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 tilt switch has also caused some grief,
if your bike doesn't start check that its in the
right orientation. If it's been fitted incorrectly it sends a
signal to the CPU that the bike is lying on it's side or upside down and
cuts the motor.
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.
Originally it was recommended to remove the air filter and box completely
and leave the plastic air intake bellmouth on Fuel Injector body. Now
it seems its better to leave the bottom half of air box in place along with
the inlet bellmouth. Remove silencer box from plastic bellmouth and
No point in using exotic fuels, compression ratio too low.
Sticky tires. Sava 110/80 x17 rear and 90/80 x 17 front
seem to be a popular choice. They must be mounted on standard OEM
rims. Get the tyre fitted by your seller and have the wheels
balanced. Dunlop's, Pirellis and Bridgestone's have been used with
Cut 100mm off of tighter wound end of fork spring and fit with a
100mm packing piece cut from suitable sized tubing (22mm Outside Diameter, aluminium or steel)
Use a suitable size washer between spring and tube.
Rear suspension unit can be modified/changed but
is fine if it's in good condition. The adjustable YSS and Elka shocks made for the CBR125 may offer some improvement but are expensive.
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.
To facilitate the fitting of aftermarket
fibreglass seats it is permissible for the back section of
the rear sub-frame to be cut off as per the picture
If you retain the original seat plastic tail
piece (rear seat cowl) leave
sub-frame in place as the rear seat cowl need it
Click on pictures for larger view
Replica Fibreglass of original production style silhouette can be used (#74 Red bike above) but standard bodywork plastic can be used to keep costs down.
Lights and all road paraphernalia will have to be removed and headlamp openings to be covered for racing. (#59 White/Black bike above)
Otherwise race the bike naked with normal number plates (as 44 Mark Strong's bike above)
Not pretty though.
Putting it all together
When you have obtained the items given in the shopping list above
it's just a matter of assembling your racer. Just follow the info given
- If you have bought an aftermarket exhaust it should
go straight on without any dramas.
- The original plastic can be used but the headlight
holes will have to be neatly covered. This is the cheapest option.
Racing fiberglass fairing and seat styled on the originals are
available but they bump the cost up a bit.
- The front fork spring mods. are straightforward.
- Recalibrate the fuel mapping as above.
Lock wire the following:
- Front brake caliper bolts.
- Oil filler cap.
- Oil Sump plug
- Radiator water cap
Drilling small holes for the lockwire in bolt heads and nuts require
a little patience.
Choose your colour scheme, stick some numbers on and go
If the donor bike you
bought is low mileage and the engine runs ok then don't go looking
for trouble just run it. These things are dead reliable and dirt
cheap to run.
Time to complete the above shouldn't take more
than a day or two, certainly not more then a week, however if you are
the meticulous type take as long as you like.
As always when
modifications are required especially around
parts that may affect safety like brakes and
controls the work must be done properly. If
you are not sure of what you are doing get
some expert advice or have a qualified
person do the work .
All the modifications
listed here are tried and tested for the
race track but a
certain amount of skill is required to do
some of them. Scrutineering is getting
stricter all the time so all the basics need
to be covered otherwise you wont get to
Some of the
modifications will make the bike illegal for
To contact any of the
Committee members or bike class
CLICK HERE to go to the Committee Page.
They are a friendly bunch and are only too
eager to help.
Many thanks to Garry
Briggs of Big Bang Engines for the above
For the Cheapest Entry
into Motorcycle Tarmac Racing get on a Commuterlite
WAY TO GO