Tech Talk: Wheels
Every bike’s got them, but how important are the type of wheels your bike uses and is there anything you can do with them to make your bike handle differently? MCM caught up with wheel expert Giles Harwood to find out more. An engineer by trade, he’s work
How do motorcycle wheels work?
Wheels have several different functions. Fundamentally, they’re there to hold the bike’s weight, but they also help to steer the bike and transmit power to the wheel, while conversely they are responsible for transmitting torque through the wheel in the opposite direction when the brakes are applied.
What is the hub?
The hub is the centre part of the wheel. It has two functions, typically. Firstly, it’s the part of the wheel which houses the bearings, upon which the wheel rotates. It also mounts the bike’s brake discs and, on the rear wheel, the sprocket carrier too. The hub is probably the most complex part of a wheel in terms of manufacturing.
What difference do lightweight wheels make to a bike?
Less weight on a bike’s wheels affects a motorcycle quite drastically. Wheels are components, which means they have a certain amount of weight to them, just like any other part of the bike. If a wheel is light, it means the bike can utilise more of its power transmitting it forward, rather than just trying to move the wheels.
Not only do wheels have static weight, they also have rotational weight, which is often measured in inertia. So by reducing the weight of the wheels, you’ll experience less inertia. The same applies in reverse when braking on a bike, so lightweight wheels will allow the bike to slow down faster. In terms of handling, by reducing the weight of wheels, the gyroscopic affect is lessened, so the motorcycle will turn much faster and easier than if it had heavy wheels. This is probably the most recognisable gain to be experienced by using lighter wheels.
What are the main components for the wheel other than the hub and what do they do?
The spokes are the braces responsible for joining the rim to the hub. They normally consist of three or more per wheel and need to be extremely strong to ensure the integrity of the wheel.
The rim is the outer most part of the wheel, onto which the tyre mounts.
Because most contemporary tyres are tubeless, the rim’s profiling is extremely important, to ensure a good seat between the tyre and the wheel. Rims are often marked with a DOT stamp approval, which is a universally recognised standard, denoting rim depth consistency.
What materials can wheels be made from?
Wheels can be made from a number of different products. The most common production wheels are cast or forged aluminium wheels, while carbon fibre and magnesium wheels are more favourable lightweight options.
Is wheel stiffness important?
Stiffness is important because the wheel is the component on the bike responsible for steering the machine. If the wheels weren’t stiff, the energy you put into turning the bike’s handlebars would go to waste, because the wheels would just flex under the pressure applied. In turn, you can go too stiff and the end result of that would be chatter experienced at extreme lean angles.
When cornering at big angles, the tyres and the wheels take over suspending the bike, so a certain amount of flex is necessary. Designers try to produce wheels which work in harmony with the suspension to get the best absorption and correlation between the two components.
How can wheels fail or get damaged?
As long as wheels are used within their design tolerances, they should never fail. Most carbon fibre wheels are capable of withstanding half a ton in pressure, so the likelihood of exceeding those design limits are highly unlikely.
However, just like metal wheels, they are susceptible to damage. If you were to hit a pothole or a kerb on the road, the integrity of the wheel could be compromised. Whereas metal wheels are likely to dint or warp, carbon fibre wheels often highlight their damage through colour.
Metal or carbon then, which is easiest to repair?
When it comes to repairs, metal wheels are probably easier to work with. There are companies out there who specialise in removing dents and making warped wheels true again. Anything that’s made out of metal can be straightened or welded if necessary. Carbon fibre wheels offer a great safety feature by highlighting their damage through discolouration.
Most carbon wheels are unpainted, so when an area of the wheel is damaged, you can usually see the damage because that part of the wheel will show white; just like a piece of plastic if you were to bend it backwards and forwards several times.
In terms of repairs, carbon wheels can be broken down into the hub, spokes and rims, meaning you can replace the individually damaged section of the wheel. Carbon fibre can’t be fabricated because it’s a moulded product.