1. What performance improvements are typically found when upgrading to BST Prepreg Composite Carbon Fibre (PPCFC) wheels?
UK sports bike magazine, SuperBike, performed an independent two-day test at Spain’s Almeria circuit using a Honda FireBlade - which already had particularly light wheels compared to earlier versions.
The bike was representative of a typical lightly modified road/street/track day sports bike by having; race exhaust, Dynojet Power Commander, double-bubble screen, steering damper, a two teeth larger rear sprocket and upgraded brake pads.
The rider, Jamie Wilkins, was already familiar with the circuit after having ridden there twice before. The first day’s testing took place with standard wheels and the only change for the second day was the substitution of BST wheels. Weather conditions were unchanged and the following was observed:
- Acceleration was noticeably stronger with the rider reporting “it felt as though it had gained ten horsepower”
- The bike could be braked later
- The bike could be turned more easily
- Top speed at the end of the main straight was increased by 5mph
- Lap times fell by a full 3 seconds – although the rider did report “pulling the pin out” as he felt very confident on the bike during the second day
These results are consistent with performance gains normally found by virtue of the combination of reduced gyroscopic inertia, rotational inertia and unsprung weight provided by BST wheels and, even if a bike is not being used on a circuit, the same benefits of increased performance and rideability and - probably more importantly - reduced rider fatigue, also apply to road/street riding.
The above is simply one example of the numerous independent back-to-back tests of BST Prepreg Carbon Fibre wheels version metal wheels which have been performed and documented - many of which can be found here. After aggregating all of the data the typical on circuit lap time saving can be seen to be 0.8 sec/mile, which equates to something like a two second lap time reduction at a typical length flowing circuit (like, for example, Donington park), but for some riders the performance gains are more significant.
One of the most startling lap time reductions reported came at the very twisty Lincolnshire track, Cadwell Park circuit (you would expect to make better proportionate lap time savings the more twisty the circuit), where the experienced owner of a highly modified BMW S 1000 RR found that changing to BST wheels reduced his lap time by 5.91 seconds; further details here.
Another example came from an experienced track rider who notified us of his lap time improvements of 4.5 and 6.5 seconds respectively at Portimao and Spa Francorchamps - both circuits where he had ridden several times previously. Other than installing his BST Prepreg Carbon Fibre wheels, this rider had made no other changes to his CBR1000RR track bike since his previous lap times had been recorded; further details here.
2. Why is Prepreg Carbon Fibre Composite more suitable for wheel manufacture compared with traditional materials such as Aluminium or Magnesium metal alloys?
Wheels manufactured from metals are either cast, forged, machined, or manufactured as a combination of the three processes. Being relatively easy to manufacture and also relatively cheap, Aluminium alloy wheels have been around for many years and are common. Their drawback is they are not particularly light because of the density to strength ratio of Aluminium (how much strength provided per kilogram of material). To improve/reduce wheel weight it would be necessary to choose a material that is lighter - such as a Magnesium alloy, but this may be at the expense of strength for a relatively modest weight reduction.
The problems with magnesium are twofold: firstly its fatigue properties are poor and, secondly, so are its corrosion properties. Very often micro-porosity (in effect "holes" in the metal) occurs during the casting process, which has a negative impact on both fatigue life and potential corrosion degradation - meaning a cast Magnesium alloy wheel may not have a very long life expectancy.
Forged magnesium suffers less from porosity but still may not last very long; i.e., sometimes less than a racing season. Several recent high profile failures of forged Magnesium alloy wheels have contributed to them being progressively banned from some high level racing classes - most notably the World Superbike Championship (WSBK) - where 17" Aluminium wheels are now the only permitted type.
If the very significant benefits of having lighter wheels are being sought - but without compromising lifespan and safety - the only entirely effective solution is to use Prepreg Carbon Fibre Composite which is not only both a lighter AND a stronger material, but also a fatigue free and corrosion free material meaning that as an engineering solution for safety critical components such as wheels it is vastly superior to Magnesium or Aluminium alloys (see subsequent Q&A’s for its technical properties to confirm this).
This move toward composite materials is not only relevant to motorcycle wheels but it is now also widely known that in other engineering areas where, for safety-critical reasons, having the strongest and longest lasting but still light materials is a necessity (such as in aircraft fuselages and wings, helicopter rotor blades, high performance road car and racecar chassis, as just a few examples) the reliance on light metal alloys is diminishing rapidly. Further information can be founds here from Cytec - the worldwide leader in composites and technology supply partner to not only BST, but also other notable and forward thinking companies such as Boeing, McLaren automotive and Airbus Industrie, to name but three.
3. Are BST wheels supplied by HPS complete and ready to install?
BST wheels from HPS are supplied with:
- All internal bearings, spacers and seals pre-installed
- External spacers, where required
- Air/tyre valves
- Cush drive (rear double-sided wheels)
- Sprocket (rear double-sided wheels) where required - except certain KTM applications
- Sprocket carrier (rear double-sided wheels) where required – additional wheels can be purchased without a sprocket carrier for race teams or track day users
BST wheels are ordinarily designed make use of your bike's original brake discs meaning that after fitting tyres and discs your wheels will go straight in. Please note that disc bolts may need to be replaced with new items as some bike makers specify that their originals are "one use only" stretch bolts. HPS can advise and quote you, if required, for replacements in Stainless Steel or Titanium.
4: How much safer
are Carbon Fibre wheels than standard
wheels?
A: Carbon Fibre wheels have been in
existence for some considerable time
and have been proven to be safe when
designed and manufactured properly
and, as with any wheel, used within
their design parameters. One of the
parameters is the maximum static weight
of the motorcycle for which the wheels
are designed (Black Stone Tek wheels
are designed for motorcycles that
weigh up to 280kg dry) and have more
than adequate strength and damage
tolerance for any usage within a road/street,
sport or race environment. Safety
is dependant on more than just strength,
though, and whenever a bike becomes
more easily controllable because of
better dynamic characteristics, active
safety is enhanced too.
5: What are
the physical properties of Prepreg
Carbon Fibre that make it particularly
suitable for wheels?
A: Some of the properties of Carbon
Fibre composites as used in BST wheels.
Material used - Carbon Fibre Prepreg
in a woven and unidirectional format,
embedded in a resin matrix, made from
toughened epoxy.
- Max structural temperature: 120
degrees C
- Min structural temperature: -40
degrees C
- Corrosion resistance: Totally corrosion
free
- Chemical resistance: Resistant to
most dilutants such as acetone, benzene,
thinners,
- Automotive fluid resistance: Limited
resistance to brake fluids and acids
- Density: Approximately 1.7 kg/qdm
(Aluminium 2.7, Titanium 4.5, Steel
7.9)
- Damage Tolerance: Similar to 2024
Aluminium
- Strength: Better than 2024 Aluminium
- Stiffness: Similar to 2024 Aluminium
Variable wall thicknesses can be created
anywhere as needed in order to increase
strength where required. Fibres are
oriented in the direction of stress
in order to increase strength.
6: How much
stronger are BST Carbon Fibre Wheels
than conventional wheels?
A: BST Carbon Fibre wheels are comfortably
over-engineered for street/road use
and have undergone an intensive programme
of very stringent testing to verify
their design and to confirm their
strength and durability.
A designated test body in the UK performed
the following tests and all tests
were conducted on a single wheel.
It is important to note that performing
a ‘single wheel test’
is not usual when checking metal wheels,
since due to metal fatigue behaviour,
a single wheel could not withstand
all the tests. To allow for this weakness
in metal wheels, the test regulations
actually specify that using one new
wheel for EACH AND EVERY test is permissible
during which it is destroyed, whereas
in this case a single BST wheel withstood
ALL tests and was still completely
serviceable afterwards.
- Cornering fatigue: 100,000 cycles
at 530Nm
- Radial fatigue: 500,000 cycles at
5200Nm
- Torsional fatigue: 100,000 cycles
at 400Nm
- Impact test: 337.5kg from 150mm
(JWL)
The front wheel was designed for a
135kg static load and the rear wheel
for a 145kg static load (this translates
into a bike with a total dry weight
of 280kg). Modern sports bikes normally
weigh between 160-220kg and race bikes
rarely exceed 170kg, so these static
load design parameters comfortably
exceed normal conditions.
The Eurotype Test Centre has tested
the rear wheels where both conventional
and offset versions have been subjected
to cornering fatigue testing in excess
of 1,000,000 (one million) cycles
at 590Nm.
The graph below shows a range of tensile
strength figures to indicate the spread
of properties associated with different
alloys. More information can be found
on the Net
Composites web site. (an independent
research firm).
7: Do BST wheels have
TUV certification?
A: Yes, BST have TUV certification
for both their ISO 9001:2000standard manufacturing processes and facility
and for the wheels. TUV requires
testing on a wheel type per-model basis, so to verify strength and compliance of the predominant wheel designs, the Suzuki GSX-R1000 and Ducati 748/916/998 series were chosen for certification.
8: How much
lighter are BST wheels than standard
wheels?
A: Standard wheels are have become
lighter in recent years anyway as
bike manufacturers fight for magazine
headlines and performance gains. However,
it is still possible to make very
significant weight savings. GSX-R1000
wheels have been used here as a typical
example of a modern sports bike as
it has wheels that are among the lightest.
On older bikes, the weight savings
with BST can even greater.
Weight Examples quoted here include
bearings, spacers, seals, sprocket,
cush drive, valves, but exclude. discs
& tyres
Standard GSX-R1000 wheel weights
Front 4.360Kg
Rear 7.529Kg
BST with Aluminium Alloy hubs
wheel weights
Front 2.380Kg – weight saving
1.980Kg / 45% lighter than standard)
Rear 4.638Kg – weight saving
2.891Kg / 38% lighter than standard)
Total weight saving 4.871Kg
9: How long
have BST wheels been in development?
A: One of BlackStone Tek’s aeronautically qualified design
engineers, Chris Adrian, started developing Carbon Fibre wheels in the early 1990s, some of which have been
used on GP bikes since then. This current BlackStone Tek
range of wheels has been on sale
for around 12 years and, during that time (due to the continuous improvements being made to the prepreg carbon fibre materials provided by BST's supplier - British company ACG/Umeco) the already immensely strong wheels have become 30% tougher.
10: What is
the difference between wet lay-up
and the Prepreg construction, as used
in BST wheels?
A: In a wet lay-up manufacturing process,
the fibres are positioned in the mould
dry and the resin is applied with
a brush. The resin is mixed by hand
and inconsistencies can be found after
mixing. This is a relatively inexpensive
process, but the resulting part is
normally heavier and the Fibres can
distort during the lamination process
meaning the process is less controlled.
This method does not lend itself to
the Autoclave process which cures
the part under controlled heat and
pressure.
In the Prepreg process used to manufacture
BST wheels, the resin is applied by
machine onto the Fibres in a thin
film. Therefore, the resin is very
even and controlled. The layers are
laminated by hand but can be positioned
much more accurately. The parts are
then cured under a high pressure and
temperature environment (Autoclaved).
This results in a well-compacted laminate
with better properties than with wet
lay-up. Laminate properties in Prepreg
Carbon Fibre can be 10%- 20% better
than wet lay-up at a lower weight
(because less resin is used to do
the same job). This Prepreg and Autoclave
process is perhaps more commonly known
as the process used to manufacture
the exceeding strong, but light, chassis
centres (often known as ‘tubs’)
for Formula 1 race cars.
11: How long
do Carbon Fibre wheels last?
A: As Prepreg Composite Carbon Fibre is a fatigue-free
material, their lifespan will always exceed
that for wheels manufactured from
alternative materials and wheels originally
made decades years ago by BlackStone
Tek’s design engineer, using
earlier and less sophisticated technology,
are still running today with any defects.
12:
How much horsepower are BST rims rated
for?
A: BST wheels are safe up to 1900Nm
torque. BlackStone Tek uses the torque
measurement rather than horsepower,
as it is torque that is driving the
wheel. If your bike generates more
than 1900Nm of torque we would like
to see it, as a standard 2002 GSX-R1000
normally tests at around 99Nm…
13:
Are their any special tyre fitting requirements?
A: As Carbon Fibre wheels are much stronger and more durable than metal wheels, there are no special requirements when fitting tyres, and the correct standard tyre fitting procedures should simply be followed as with any motorcycle wheel, see video below...
