Motorcycles used to be simple. You had an engine, a frame, a couple of wheels, seat, something to hang onto, brakes, suspension and that was about it. And then marketing got involved and now we have all manner of different segments and bike types to choose from. What follows is a simple guide to the sectors.
The simple motorbike that most children would draw on a piece of paper. No wind-cheating bodywork, no special performance parts, flat-set handlebars, low-set footrests Your grandad/grandma would have ridden one to work in all weathers, while smoking a pipe and wearing a flat cap backwards.
These are usually based on a sports bike but with higher handlebars, slightly less performance and minimal bodywork that leaves the engine on display. They grew out of what used to be called Streetfighters – a sub-set of biking that turned sports bikes into stripped-down customs. Currently popular because they offer much of the performance of a sports bike but with a more comfortable riding position.
Usually have fully-enclosed bodywork for aerodynamic slipperiness. High performance engines, suspension and brakes plus the latest electronic rider aids (traction control, anti-wheelie systems and electronic suspension control). The riding position is designed for speed and control in corners, not comfort, with low handlebars and high footrests. Passenger comfort (if provided) or ability to carry luggage isn’t a priority.
Tourers are usually bigger, heavier and designed for long-range comfort. That means a huge fairing to deflect wind and rain around the rider and passenger, a tall screen and comfy seats, loaded with built-in luggage and accessories such as cruise control, stereos and sat-nav.
As the name suggests these are comfier than a sports bike, sportier than a tourer. At the top of the pile are the ‘hyper-sports bikes which are fast enough to be sports bikes, but a bit too heavy and long to be sporty enough, making them sports tourers by default.
Trail bikes are traditionally lightweight, simple machines designed to be used on and off road. In the last 20 years these have grown into much bigger, heavier, more complex adventure bikes that are as much meant for touring as they are for off-roading.
Long, low, heavy and usually styled like a mobile American Diner. Cruisers are for life in the slow lane; looking good, being noticed, it’s a journey, not a destination etc. Think Harley Davidson and you’re there although most other manufacturers have their take on the style too. Much of the influence is retro and recently, mainstream custom bikes have evolved into a variety of different looks including café racers (custom meets sports bike) and bobbers (stripped back, minimal customs).
The technical definition would be ‘engine, final drive and rear wheel are one unit under the seat with step-through bodywork’ but try putting that on a poster and making it sexy. Modern scooters are usually automatic with smaller wheels than a motorcycle and mostly a smaller engine too. The emphasis is on practicality with some weather protection built-in, storage room under the seat and the simplicity of automatic transmission. Maxi-scooters are the same but with bigger engines, more weight and a price tag that looks expensive until you compare it to a season ticket on Southern Rail. Three wheel scooters are harder to fall off and can be ridden on a car licence, but are also top heavy, a bit clumsy till you get used to them and expensive.
A 50cc scooter or bike restricted to 30mph top speed that can be ridden aged 16.
The bodywork that deflects air around a rider including the windscreen. Fully faired bikes include lower bodywork that covers the engine too, half faired machines leave the engine exposed.
Add on crash protectors that take the impact when a bike falls over and protect the bike’s bodywork from expensive damage.
Something for the passenger to hold onto
Plastic cover that prevents water and mud being thrown from the spinning rear wheel onto the rear suspension.
Almost all modern engines are four strokes because this technology produces cleaner emissions. A few smaller engine bikes, mopeds and scooters are still two stroke powered. Two stroke engines have few moving parts and a power stroke every two turns of the crankshaft. Four strokes have lots more moving parts and a power stroke every four turns. So you’d think the two-stroke would be better. Sadly, it’s not that simple.
Imagine a piston moving up and down inside the engine. All a two stroke needs is one turn of the cycle to fill the cylinder with fuel and air and another to combust it. One power stroke every two turns of the engine. A four stroke engine uses valves and camshafts (see below) to meter fuel and air into the engine for combustion. Four stroke engines are complex, heavy and usually less powerful for a given capacity because they need four cycles for each power stroke; one to suck the fuel in, another to squeeze it, one more for combustion and a final one to get rid of the exhaust gasses. But they have much cleaner exhaust emissions and waste less fuel. Two stroke engines lubricate themselves with oil that is burnt in the cylinder during the combustion stroke. This oil needs regular topping up via a tank. Four stroke engines recirculate their oil through the engine and only need periodic top ups.
Camshafts control the opening and closing of the four stroke engine’s valves to meter the fuel and air going in and exhaust gasses going out. Most modern engines have double overhead camshafts (dohc) which means two cams mounted above the engine - one controls inlet and the other controls exhaust.
Torque is the work that an engine does. That shove in the back you get when you open the throttle. Power is a measure of how fast the torque can be delivered and is calculated by multiplying torque times revs per minute. So, a low-revving cruiser engine can make a lot of torque, which you feel as a surge of acceleration, but because it only revs to 5000rpm, it doesn’t make a lot of power. Where a 600cc sports bike engine makes a small amount of torque, but revs to 15,000rpm and so makes a lot of power. And because those smaller pistons in a four-cylinder 600cc engine rev a lot quicker than the big ones in a 1500cc v-twin, the smaller bike makes its torque quicker and so accelerates more quickly too.
Engines burn fuel and air in exactly the right ratio to give the most power. It’s easy to get more petrol in - use a bigger fuel pump - but getting more air in is harder without a turbocharger or supercharger. One alternative is to force air into the bike’s airbox at high speed using air intakes mounted in the front of the fairing. High-speed air rushes into the airbox which actively pushes air into the engine rather than the passive method drawing air in by vacuum created as the engine’s pistons move up and down. The faster you go the more pressure you get and therefore the more power you add.
A system pioneered by Yamaha to add midrange power to a tuned race bike engine by altering the volume of the exhaust pipe at different engine revs. Exhaust gas travels in waves and controlling the flow of exhaust gasses allows an engine’s cylinders to fill more efficiently and so, make more power. But because the waves are different at low and high revs, you’d need a variable length exhaust pipe to make the most of it. Butterfly valves in the pipe varies the volume of the exhaust pipe depending on the revs and makes the engine more efficient over the full rev range. The added benefit is that the exhaust is quieter at low revs when the valve is closed and so needs less silencing.
The forks are the front suspension on a motorcycle. The thinner parts (stanchions) used to be at the top and the thicker parts (the sliders) at the bottom. In the late 1980s manufacturers swapped this around because the moving part of the forks is unsprung weight and the less unsprung weight you can have, the quicker and easier it is to change direction on a motorcycle. So fork legs, wheels and brakes all needed to become as light as possible. Turning the forks upside down made an enormous difference. It also makes them much more resistant to bending in a crash
Bikes that were never officially imported to the UK but came in via an independent importer. Grey imports were very popular in the mid-1990s. Many were 250-400cc sports bikes which were perfect for new riders. Fast enough and cool enough to be credible, but easy to ride too. Most popular were bikes like Honda’s VFR400, CBR400 and Bros 400/650.
Radially mounted brakes are located further around the brake disc than traditionally mounted calipers. This reduces the flex and vibration caused by using upside down forks and larger wheel spindles (which brace the fork legs) and in racing it allows teams to use different sized brake discs on a set of forks by simply adding spacers to the caliper mounts.
Most modern bikes have just one rear shock absorber mounted in front of the back wheel. To fit in this small space the shock needs to be short and so has a limited amount of travel. Attaching a shock to the frame via an eccentric linkage mean you can get softer springing for more comfort at low speed which becomes exponentially firmer over big bumps to control the bike because the linkage alters the amount of effort required to compress the shock. It’s like having many different strength springs all in one unit. The first part of the travel is linear to the force from the road, but as the shock compresses it takes more and force to make it compress further. Shocks without a linkage are known as ‘cantilever’ mounted and tend to be firmer to start with.
Most bikes have oil and spring filled telescopic forks at the front and an oil/gas filled shock absorber at the rear. Even the most basic bikes also let you adjust the spring preload on the rear shock(s) which sets the suspension for your weight, preloading the spring so that when you sit on the bike the suspension barely sags, leaving all available movement for soaking up the bumps. Many bikes also have preload adjustment at the front on the fork springs.
Some bikes have rebound (also called tension) damping adjustment. Rebound controls the rate which the spring bounces back after hitting a bump. No rebound damping would mean your spring bounced back too quickly like a pogo stick. Too much rebound damping and it won’t return quickly enough meaing if you hit another bump, there’s less travel to soak it up.
Rebound on the front forks determines how quickly the forks spring back up when you release the brake. Too little and the front bounces up too quickly which extends the forks, making your bike run wide in corners. Too much rebound and the front wheel will feel unstable on acceleration because the forks are still compressed.
Sports bikes add compression damping adjustment also. This controls the rate at which the spring compresses and can be split into high and low speed compression damping. High speed damping is about the size of the bump and the amount of travel, not the speed of the bike. A big bump makes the suspension react quicker than a small one so the damping adjustments can be made separately.
Motorcycle clutches can be fragile and one too many traffic light races or fluffed wheelie attempts will damage the clutch of many bikes. 1990s Yamahas are especially bad as are Ducatis and some Triumphs. Clutch slip is where the clutch plates have overheated and lost some of their friction. As you rev the bike the clutch can’t hold the drive between the engine and gearbox. So the revs rise quickly but the bike goes no faster
This is a device that allows you to go aggressively into a corner while changing down the gearbox and release the clutch, without locking the rear wheel. It works by controlling a limited amount of slip in the clutch unit and has become essential in racing but of limited use on the road where smoothness is the key to speed.