A perfect motorcycle is one with a perfect geometry. A bike could do only two things where ever you go 1) Straight run 2) Turn or corner. Designers initially work on the geometry when they design a bike. High-tech computers with advanced software land a much needed hand in this designing process. After hours and hours mouse clicking and key pressing, a bike is virtually designed.

  Geometry is the overall profile of a bike. It is the cluster of numerical measurements that are considered to create a next to perfect design. Frame along with chassis forms the base of a bike and holds all the parts from cosmetic to mechanical ones. This makes it a building block of the bike and thus it is designed first. Geometry of bike refers much on designing the frame. Everything on a completed bike could be changed except the frame. Just think of the modifications that are carried out on a bike. Technicians would give you an option to upgrade the parts and panels but would never touch the frame. Of course, he could weld some extra mountings on the frame but never replaces the entire frame. Frame is therefore designed precisely as once it is installed in a bike, the bike rolls out of the factory then there is no turning back. Even if the entire line of body panel with engine is changed, the bike would still feel messy if the frame has some issues. For more information on frames, go through my web page on (https://typesofmotorcycleframe.blogspot.com/2020/07/motorcycle-skeleton-by-aman-mishra.html). The reason why I used the line “next to perfect” is because even if a designer spends hell of a time in designing a bike and if he does make a perfect one, developers would find some or the other way to create the next generation a better version of that same bike later on. That is why you would find nearly all the bikes have different generations of a particular model with the latter better in all aspects than the former. No two bikes with different models have the same geometry. Consider the two iconic bikes -- Bajaj Dominar and Mahindra Mojo. Both are close in terms of performances on paper and you might go for any of the two. When you swing your leg over them one by one, only then you would realize that the two even after having nearly the same profile feel distinct from each other. This is because the two have different geometries. But believe me that both have tremendous on road/off road capabilities. Yes, I remember not to derail the article from the topic “geometry”.

Just have a look at the specs of both the bikes before going to the basics.  

Bajaj Dominar 250

Mahindra Mojo UT300

What all things come under geometry?

What is the effect on the bike by adapting different measurements in the geometry? At the end of the article, you would come to know that all terms which make up the geometry are all interlinked to each. This means that by making any change in any one would affect the remaining parameters in some of the other way. I’ll crack it all down for you.

The main parameters considered in geometry are:-

Frame – Usually bikes are purposeful m/cs that are built to fulfil the need of the needy. For e.g., a sportsbike should launch fast, reach higher top speeds, agile and nimble handling, stopping distance should be short and many more. It is quick with negative laziness in the overall performance. Cruiser on the other hand is a slower, lazy m/c compared to a sportsbike but powerful with good handling and cruising abilities. Frames are selected according to the purpose of the bike.

Sportsbike – It is a quick launching, fast going bike capable of reaching speed exceeding 270 km/h. Light weight is a factor that is considered while selecting a frame. Monocoque, trellis or perimeter frame is a choice of one in a sportsbike. These frames are designed in such a way that with speed, it also gives that agility factor which means it could change directions at high speed or in simple words good high speed cornering skill.

Cruiser – It is simply a couch on wheels. The bike is heavy not just due to the heavy body material but also due to the massive power plant(engine). Cradle or tubular frames are more on the heavier side and built to take up heavy loads. These are basically not very flexible and a lot stubborn towards taking turns. It also makes the bike least nimble due to the weight, shape and properties. 

Rake/Camber Angle – It is the angle between steering axis and vertical axis passing through the center wheel nut. Rake is responsible for increased or decreased rake angle. The increase in rake angle would increase stability on unpaved surfaces but surely hassle in steering.

Sportsbike – It is clearly observable in a sportsbike that rake angle is less. Rake angle is set in between 23.5 – 24.5 degrees. This is done to give a more upright ergonomics to sync with the aerodynamics. Rider tends to lean forward when sitting on a sportsbike which makes the overall profile like an egg shell or oval which is considered as the most perfect aerodynamic shape.

Cruiser – A back leaning design of the bike is achieved by increasing the rake angle or shooting the front fork even further ahead. The rake angle is close to 30”- 40” degrees. In this way, the handle gets closer to the rider giving a much relaxed arm position. It is preferred for long rides where the rider just wants to relax and enjoy the ride as if he is sitting on a recliner and enjoying a movie. Increased rake also lowers the overall height of a cruiser making the rider stay close to the ground for better control on the bike.    

Trail/Caster Angle – It is the angle between steering axis line touching the ground and vertical line passing through the centre wheel nut touching the ground. Trail is basically a dynamic factor of a bike which keeps a rider balanced on the moving bike compelling the front end to travel straight as long as possible. Rake and trail work together which means that if trail is increased then rake will increase and vice versa.

Sportsbike – The ergonomics of the bike is more kind of an upright one to make it aerodynamic. This is achieved by the reduced distance between the wheel and steering axis hence reducing trail angle. Less trail angle would make the bike quick on corners. So, even if a rider figures out late about an approaching turn, he could still lean to his side and the bike would impressively respond to him making a sportsbike fit for fast late cornering. Less trail angle also makes the bike ask for less force to turn the steering handle. Also, a sportsbike would easily climb a slope due to less trail.

Cruiser – Cruiser is not as aggressive as sportsbike due to the weight and geometry. It has more trail angle which is due to the kicked out front fork out making it heavy and lazy. Cruiser is a relaxing m/c and rider just demands it to cruise smoothly with less efforts. More trail angle makes straight run stable and smoother. Also, a cruiser would descend a slope easily due to that extra supporting force given by the extended force resulting in trail.

Fork tube height – The height of the fork tube above the top end of the triple clamp is fork tube height. It is an important factor to be considered in terms of handling and stability. Increased fork length decreases swingarm angle which increases wheel base. It also increases compressing of the rear end under acceleration which is known as squat.

Sportsbike – Front end of a sportsbike is light enough for the rider to gain confidence to nimble the bike. Lowering the fork tube height would make it more stable at high speed but induce instability factor while cornering. Sportsbike have fork tube set at an optimum height to give a best of both factor at the same time which is stability at high speed and better cornering.

Cruiser - Raising the fork tube height would make the bike turn better but also become less stable at high speed due to increased weight on the front wheel. Cruisers do not have to go through aggressive cornering but focus more on high speed stability. Fork tube height setting is high making the bike heavy on the front end. Weight is something that is not considered much in a cruiser as everyone understands that if it is a cruiser then it is going to be heavy.

Swingarm angle – Swingarm or rear fork is a part that connects the rear wheel through the center lock nut to the chassis through the pivot.  It is the angle between swingarm and ground horizontal line. Swingarm takes up torsion at high speed run and cornering which makes it a part of suspension unit. The rear wheel is a live wheel which means that the power cranked out is transmitted to the rear wheel by the chain. The rotation of the chain on the rear wheel sprocket and the vertical forces are all taken up by the sprocket. The chain crawling on the sprocket tries to exert a force in forward direction or the direction of the bike travelling. This forward force often known as thrust keeps the rear end of the bike lifted under hard acceleration. The front fork, rider and the swingarm form a triangle with each other. The rear center wheel nut should be at a lower height with respect to the swingarm pivot point. Swingarm is associated with grip/traction so if the angle is increased then it increases rear traction.

Sportsbike – Considered to be short in length, sportsbike has greater swingarm angle. This improves the traction on rear end. Greater swingarm angle means more degree of oscillation at the wheel end. This is effective when the bike is travelling on a bumpy ride which makes it to absorb more jerks from travelling up to the rider. It should be noted that increasing a swingarm does provide its benefits but too much increase would make the rear wheel go under the bike and rotate with jerks making the ride pretty unstable.

Cruiser – Swingarm angle is less in a cruiser which means the rear wheel feels less effort to rotate. This also snatches away the necessary traction from the rear wheel. But loss of traction due to this is like nothing as the ergonomics of the bike with the riding position deviates whole weight to the rear end. This solves the traction issue caused by less swingarm angle. Low swingarm angle also improves stability under straight run which means that the bike will have less swingarm travel and won’t bounce much ultimately increasing the wheel base.

Swingarm length – Swingarm is a mechanical part that is attached to the body through pivot point on one end and to the tire on the other. It is installed in such a way that it could make a vertical movement with respect to the bike and absorb most of the shocks coming from the surface of the road.

Sportsbike – It is basically a m/c with short length so it is clear that the swingarm length is short. This is done in order to make the bike corner faster, technically to improve nimbility or agility. On a track with more number of corners, this bike could enter and exit turns faster irrespective of the direction of the turn. Shorter swingarm oscillates at greater swingarm angles due to the surface of the road which increases anti-squat.

Cruiser – It being a heavy m/c has longer Swingarm. Whole weight of the bike gets focused on to the swingarm undergoing a corner. Long swingarm is prone to flex more under cornering. This gives stability while taking a turn. The wheel absorbs more movement because the tire is not getting deformed much. So this bike would be much more stable or less shaky while taking a turn. The rider would be more confident on this bike when leaning to any direction. In straight runs, the change in swingarm angle with the movement of suspension is less which means reduced anti-squat.

Wheel sprocket – Wheel sprocket is a toothed wheel that is bolted on the rear wheel and is connected to the transmission output shaft by a chain. Transmission shaft is smaller than the wheel shaft. This is done to increase torque at the wheel end so that the engine could move the load with less effort.

Sportsbike – Mostly a sportsbike is a chain driven bike with sprockets. Chain are absolutely strong in taking enough load not very heavy loads but does the job for a bike that is not designed for carrying heavy loads but to crank out power and performance. Rear sprocket size is smaller compared to a heavy load carrying bike with approx 55-60 teeth. This gives a perfect low end torque at the rear end and pulls the load through the rear wheel.   

Cruiser – Generally a cruiser is a belt driven bike with a pulley instead of a sprocket. Large sized pulley is installed in a cruiser which provides a better torque on the rear wheel and makes the bike easy to pull that massive body weight, accessory load and the two travelers. Cruiser is a perfect bike for long tours which attracts pillion rider also to be a part of that ride. Pulley along with the rotating high strength Kevlar belt on it, keeps the bike going irrespective of the amount of load that is put on the bike. This also makes a cruiser a better puller of the load than a sportsbike.

 

Wheel base – It is the horizontal distance of the rear centre wheel nut from the front center wheel nut. 

Sportsbike – Sportsbike has short wheel base to induce the bike a quick turning characteristic. Sportsbike is not much focused on comfort but performance given at any cost. Shorter wheelbase makes it prone to wheelies and stoppies which is why all best stuntmen use a sportsbike to perform their stunts. Adding to this, short wheelbase reduces turning radius of the bike. Sportsbike is also used as daily commuter for the reason that it could be maneuvered in tight spaces. However, short wheelbase heats up the tyre to greater degrees as the closer the tyre are to each other, the more they have to take up the central load of the bike with the rider on. This also improves the traction and the rider has full confidence on the bike even if he is going through a zigzag or a road with unknown number of sudden turns.  

Cruiser – Cruiser is known for its oversized or stretched ergonomics. The main reason is the long wheelbase. Long wheelbase is adapted to make it stable on straight runs and comfortable overall. Cruisers basically belong to highways which do not have sharp turns or corners instead are smooth and straight. Of course there are turns but they are so lazy that the rider won’t even feel that he took a turn unless he fix his eyes far ahead on the road line. Longer wheelbase also lowers the ground clearance. Cruiser also gets that extra space in between the wheels to add up more features and sitting space. This gives space to extend the seat. Rider with the pillion rider do not pack themselves in between tank and back rest but have enough space to move and change posture easily on the bike.

Ground clearance – It is the height of lowest end of the bike from the ground.

Sportsbike – Sportsbike have high or intermediate ground clearance in order to tackle off road conditions with not getting lower body of the bike damaged. Supermoto(SUMO)/dual sport has high ground clearance for the place where it spends the maximum time i.e. off road region. Sportsbike has intermediate ground clearance which is in between that of a SUMO and a cruiser. Increase in ground clearance increases the leaning angle of the bike while cornering. So, a sportsbike could lean at greater angles which make cornering possible at high speed. High ground clearance also gives room to load more stuffs on the bike which would compress the suspensions but the bike would still be at an optimum height for a safer ride. Intermediate ground clearance also gives a better aerodynamic profile to the bike as less air would pass through the bottom of the bike while moving.   

Cruiser – Low ground clearance is one of the signature features on a cruiser which gives a recliner feel while riding. Low ground clearance also gives an opportunity for short riders where they could land their feet easily on the ground for a proper control and feel about what it’s like to ride a bike. Centre of gravity is an important aspect of any object which is affected by the height at which it placed above the ground. Cruiser staying close to the ground has low center of gravity which adds up to stability. One downside of low ground clearance is that if a cruiser is getting ridden in a city with tight traffic then the rider is in the layer of pollution. When you get boxed around vehicles in a traffic jam then you might have observed that the exhaust located below the big vehicle like bus, truck etc. emit emissions at the height a rider who is sitting on a cruiser. It is quite dangerous for the health and could lead to severe lung problems if unknowing done for longer period of time.  

Seat height – The distance of the lowest end of the seat from the ground is called seat height. Seat height assists riding position.

Sportsbike – Due to the high profile of a sportsbike, it has higher seat height when compared to a cruiser. Of course, the ground clearance is one factor which plays an important role in the height of the seat. High setting gives the rider enough room to stretch and move his legs or temporarily change his position. This also assists to achieve quick and greater leaning angles on cornering as higher seat height means enough space to shift his body by shifting his body and also open up his knee in the direction of the turn to finally lean. High seat height means the rider sits in a much greater forward leaning position to achieve better aerodynamics.

Cruiser – Cruiser come with low seat height to give a low ground profile to the bike. Rider is in much comfortable posture with such a setup which is necessary on long continuous rides. Distance of the seat from the foot peg is reduced which determines how much the rider’s legs would be bend. Lower seat height makes a rider feel as if he is resting his hips in the seat rather than on the seat. This increases the contact patch of his hips on the seat hence increasing the area of hip getting supported which would ultimately relax his body better(maximum pressure is taken up rider’s hips). Short rider could easily land both his feet on the ground for better control on the bike.

Triple clamp offset – Triple clamp is connected to the front portion of the bike to the chassis/frame. It has three mounting nuts. Two end lock nuts fix the two front forks. The remaining third lock nut is fixed to the steering stem.

Sportsbike – It generally has more triple clamp offset which decreases trail angle so that the bike could enjoy the advantages of less trail angle making the steering light. Steering response becomes better which would turn the fork with less effort and within less time.

Cruiser – A cruiser due to comfort factor has less triple clamp offset to increase trail angle. More triple clamp offset induces more force on the fork making it heavier. This is one another reason why cruiser is less responsive to steering and never used for racing or stunting. In return, the bike gets that straight run stability which makes the steering stable when the bike is travelling on a straight road usually highways.

Wheel geometry – The distance of one side of the wheel to the other taking the center point as reference. Tyre is the only part of any automobile that has a physical contact with the tarmac(road). The material of tyre and grip helps it to gain the necessary traction which ultimately moves the bike forward (Newton’s III law of motion). The geometry of the wheel depends on the engine capacity of the bike. 

Sportsbike – A purposeful bike build for race and performance should go fast, launch fast, turn fast and it should be light in weight at the same time to achieve all of these. The traction or friction force developed at the contact patch should be enough but minimum. Less friction force would cause the rear wheel to spin(wheel spin) under hard acceleration and more friction would try to stop the wheel from rotating and so some amount of power would be wasted in moving the wheel. A sportsbike has both the wheels of same size which have medium size diameter. Small wheels compared to a cruiser have greater maneuver which gives the rider an easy and quick turnings. The wheels are made of alloy which is a light weight with good strength. There are several alloy arms instead of spokes which reduce weight of the wheel and gives a sportier look. Alloy wheels could handle higher speed also it does not bend like spokes. Medium sized wheel have less aerodynamic drag which improves aerodynamics of the bike.     

Cruiser – The ergonomics of the bike is such that the front end or the nose of the bike is set at a higher height and the rear is made as low as possible. This gives a back leaning sitting position. It is achieved by mounting a larger diameter front wheel and smaller diameter rear wheel. Also, the size of rear wheel is broader than the front wheel. Rear end of the bike has to bear greater load than the front. Thinner rear wheel would not give enough traction and also it might burst in case of heavy loading. Broader rear wheel has greater area of contact which means the force is distributed on large surface area. The downward force due to the heavy loading on a greater area releases pressure on a particular point which happens in a thinner tyre. In order to make the front end lighter, thinner sized wheels are mounted which has to bear less force on itself. The other reason is to make the front end little light and easy to steer. This type of setting compromises acceleration and speed as it experiences a greater traction/friction trying to stop the bike. This is one another reason why cruisers have high capacity engine. But yes, it does add up comfort which is the only purpose of a cruiser. The wheels are made of heavy and strong material like stainless steel. They are either spoked or full aluminium solid disc. Broad wheel is also hard to turn it quick. Heavy tyre is resistant to turning which means that the wheel would force itself to move in a straight line again adding stability on straight run. One last advantage of broad wheel is that there would not be any wheel spin even if the bike is accelerated hard due to the increased traction.   

Fork length – The total length of the fork measured from lower end of the frame neck and front centre wheel nut. Fork length affects rake and trail angle to a great extent.

Sportsbike – Sportsbike is a short bike with less trail and rake angle. This is done by reducing the fork length. The bike is fitted with a short fork. It brings down the nose of the bike to the front fender. This gives better aerodynamic position to the bike by providing the air a smoother path to flow. Less fork length makes the bike less stable at high speed. Lower fork length means the bike has less suspension travel and so the bike won’t save your butt on going through a deep pit or bigger breaker.  

Cruiser – A bike intentionally made longer by increasing the wheelbase for greater comfort and stability is achieved by increasing the fork length. The signature mark of the look that distinguishes it from the rest is the kicked out fork or the extended forward fork of a cruiser. This of course reduces the force on front wheel which costs in terms of traction. Long fork gives a better suspension travel to better absorb jerks. It would still feel stable and comfortable going through harsh terrain.

Fork offset – It is the distance between wheel lock nut and fork. Fork offset is inversely proportional to trail. With each millimeter decrease in fork offset, there would be an increase in the trail. It is the distance between the front axle and the steering axis. It is inversely proportional to trail. This means that with every mm increase in offset, there would be a decrease in the trail. By rigorous experiments, it is observed that changing trail at axle gives better results than changing trail at triple clamp. Fork offset would not make the front end heavier as observed in the case of triple clamp offset. Fork offset has no effect on wheelbase because the center wheel nut remains at its place before and after offset. Only some bikes have fork offset as the other parameters make the bike achieve the results.  

Sportsbike – Sportsbike has more fork offset in order to reduce trail. Fork offset on a sportsbike is less and pulls the wheel closer to reduce trail. This makes the bike nimble with handlebar feeling lighter and more responsive.

Cruiser – Cruiser has less fork offset to enjoy increased trail for stable straight runs. The steering response is low which means the bike is better at straight run.

Centre of Gravity (CG) – Often denoted by a circle comprising a plus sign. CG is a point where the combined mass of the bike with rider are at equilibrium in all direction. It is quite obvious that the point lies in between the two wheels. The intersection point of the horizontal and vertical CG is the point of the actual CG. This point keeps on shifting according to the road conditions.

Horizontal CG is could be calculated with the formula –

Where,

                                          x=horizontal position of cg from front axle

Wf=front weight

Wr=rear weight

WB=wheelbase

Weight on front and rear wheels keep on changing when the bike is ridden. Ascending and descending a slope, speed breaker, luggage, rider position and many more are some factors that keep shifting which result in the shift of horizontal CG. Horizontal CG comes into picture at the time of acceleration and braking.  

Vertical CG is calculated by simply dividing the value of ground clearance by 2 or it is the half of wheelbase.

Wheelbase also keeps on changing by some mm all the time the bike is ridden. Initially, the wheelbase of the bike without the rider is less than the wheelbase after the rider is on the bike due to change in swingarm angle. Vertical CG is responsible for handling of the bike. Different road conditions make the swingarm angle to change all the time that result in vertical CG to change. By these reasons, the total CG keeps on changing in a bike. Suspension travel and swingarm pivot is also taken into consideration to find the accurate position of CG.

Sportsbike – CG shift on a sportsbike is more as the bike goes through torturing hard acceleration, braking and cornering. This is also accommodated by the rider who keeps changing his position under the above mentioned conditions. The point of CG in an ideal state is little high and at the mid portion (compared to a low cruiser) making the rider to apply more force to turn the bike. Low and narrow handlebar also establish the centre of gravity. CG shifts as the rider sits and holds the handlebar which makes him lean forward. Given this, this bike would also change the direction quick on a zigzag road. At a given speed, it would require less lean angle to exit a corner safely(compared to cruiser).   

Cruiser – It is a bike with long wheelbase and has the point of CG more forward and low in ideal conditions. This makes the steering easy to steer and stable at the time of cornering. However, the bike would require more leaning to its side in order to safely exit a sharp turn at a high speed. But that is not possible due to low ground clearance of the bike which makes foot pegs and exhaust pipe to rub against the road if the bike is tried to tilt at a high angle. High leaning angle is not a good idea on a cruiser because when the bike is tilted on a particular side, the whole weight shifts to that side making enormous weight of the fully loaded bike shift in that direction to be controlled by the rider. This is why it is safe to slow down a little bit and takes the turn. It would avoid the bike from asking the rider to take the turn with greater leaning angle.  

Riding Position – Riding position is a key factor which determines how the rider sits on the bike while riding. Riding position is the amalgamation of handle bar height, seat height and foot peg location.

Sportsbike – Sportsbike is an aggressive looking bike and to make it reach its potential, the rider also has to synchronize with this aggression. Handlebar height is low and far from the riders reach. He has to lean forward and down to get his hands on the handle bar. This is possible when the seat height is high and tilted forward a little bit. Foot pegs are either just below the rider hips or shifted little rear to the rider hips. Rider’s Chin, elbow and knee are in vertical line with the hips and feet in a line. This makes the spine to lean forward. This is often a sharp leaning posture where most of the rider’s weight gets concentrated on his wrists. The rider seems as if the bike is carrying him on its back. This could be made even sharper if the rider rests his chin on the fuel tank area making a perfect aerodynamic shape. This is to make the rider bring his chin close to the tank and make an aerodynamic shape or the famous eggshell/oval shape in order to allow a smooth surface for the air flowing over the overall system. This type of posture is also suitable for quick change of his body from the center to either left or right when a corners approaches. The direction of shift obviously depends on the direction of the corner. Forward leaning position also puts weight on the front end which is very helpful in cornering as the front end is the first thing that enters the corner.

Cruiser – The profile of the bike is that handlebar is wide and long which is stretched back closer to the rider. Seat setting is low with foot pegs way ahead of the rider approximately in the line of radiator.  Riding position on cruiser is a back leaning one or in simple words, a lazy or relaxed one. Wrist and knee align in a straight vertical line with hip and elbow in one line. The front extended leg position where rider’s feet are placed forward basically away from the body makes his spine to lean backward and feel as if he is on a recliner. Legs do not bend but are much straighter to avoid pain due to folded legs. By such riding position, the rider requires fewer stops to stretch his body or relieve a temporary pain due to long hours of cruising. This type of position focuses his weight exactly on his hips. Cruisers have backrest both for rider and pillion rider to give that extra support to the back. This is the reason why cruiser is the most comfortable segment of bike for long tours like continental tours or world tours. Rider cannot stand on the foot pegs in off road conditions and so cruiser should not be taken for off road rides (Anyways it is not make for that purpose). The rider sits much inside the seat to support his hip better and keep the rider relaxed while riding.

 

Weight bias – It indicates how much weight of the bike is on the front wheel compared to the rear wheel.

Sportsbike – Weight bias in sportsbike is more to improve front tyre traction. It purely helps in steering at high speeds. The front end of a sportsbike is heavy due to the presence of fairing, forward tank and rider position. The ergonomics is such that the nose of the bike is situated close to the front wheel whereas the rear is raised high. So the resultant forces of all loads on the bike tend to the front wheel. This is the reason why a sportsbike pops a stoppie under hard frontal braking.

Cruiser – Weight bias in a cruiser is less due to the lazy and back leaning ergonomics. Due to the kicked out front fork that increases rake and trail angle, whole weight of the bike shifts to the rear wheel. This is another reason why a cruiser has broader rear wheel than the front. It is a touring bike and should have good language carrying capacity which it actually has. Panniers and pure metal parts used up to build this bike make them concentrate on the rear wheel. The resultant of all the forces and loads on the bike tend towards the rear wheel giving enough rear traction for better cruising feel.

Handlebar setup – It is actually the arc between the left and right bar ends.

Sportsbike – A sportsbike is set to a low handlebar setup. A more up right handlebar is used with bar ends set at smaller arc and also at a low height to exert more force on the handlebar to improve traction on front wheel. It also helps in reducing air drag caused by the hanging bar ends out the bike profile. This also accommodated in reducing wheelies on hard acceleration. However, this is not much effective on wheelies as sportsbike are known for wheelies as it sometimes helps the rider to accelerate faster. This reduces rear wheel traction and often affects braking. This is the reason why the rear end slides to a particular side under hard braking as the rear end tries to come forward due to its own inertia. This is clearly due to less traction on rear wheel. 

Cruiser – Cruiser has wide and tall handlebar increasing the arc between the bar ends. Rather than away from the rider, the handlebar is such that it is placed closer to the rider. In simple words, the handlebar is bent towards the rider. When the rider holds the handle, he could feel that the handle has actually made him lean a little backward. This gives a much relaxed arm position and the backward leaning of the rider makes his spine straight and in a much relaxed position. But this type of setting increases air drag with more and more air hitting his wrist which obstructs the performance of the bike. Also, the rider has to stretch his hands more in order to take a full turn as the inner bar end is pulled closer makes the outer bar end to push away from the rider.

Wheel flop – It is the physics involved in the rotating front wheel which compels it to accelerate under cornering. It is similar to what over steering means where the front wheel if turned more would feel as if it would just flip itself towards the epicentre of the turn. This is a very important parameter to be considered in terms of safety as it is concerned with the rider likely to fall off the bike. Increase in the trail angle increases wheel flop. Of course, flopping depends on the way the bike is ridden by the rider. Even a bike with less wheel flop would encounter flop if the rider oversteers the bike.

Sportsbike – Lower trail angle is set on a sportsbike which makes it easy to understand that wheel flopping is less. This is also a result of quick steering response in a bike with short wheel base because the front end of a sports bike is lighter that means less inertia.   

Cruiser – The fork is kicked out in a cruiser and the heavy material used in the parts increase the area of vertical forces acting on the fork making the front end heavier. This increases inertia making the wheel stubborn to be in its present position. If the handle is in turned in a particular direction then it would remain and won’t return to its original position even if a certain amount of force is applied by the rider. Rider has to apply high amount of force to bring it back to its original position. Hence wheel flopping in cruiser is less. This results in the bike to become stable on turns as well as on straight runs. 

Engine position geometry – Engine weight, position and type determine how the bike would respond when ridden. The biggest and the heaviest part on a bike is the engine. The position of engine establishes CG which is an important parameter that affects stability whether the bike is going straight or taking a turn which is also called as gyroscopic effect. The overall performance of the bike is not only defined by how much power the engine cranks out but also by the engine geometry. The rotating parts inside the engine affect the gyroscopic effect which would resist the bike from turning. Engine working at high rpms has greater force exerted on the frame and affect handling. Bikes have longitudinal and lateral type of engine mounting position. Longitudinal engine is one which has the axis of crankshaft parallel to the line of the bike axis. Lateral engine is one which has the axis of crankshaft perpendicular to the axis of the bike. Rotating mass inside the engine resists turning just like a “top” toy. Gyroscopic effect is one most unique parameter that determines handling. Most of the bikes have transverse type of engine arrangement.

Sportsbike – Sportsbike is a quick accelerating bike with an engine capable of reaching a top speed of 300km/h or more. Engine on it is somewhere around 1000cc or less depending on the model. Engine is assembled little high towards mid section of the bike. This helps to enhance CG position and weight distribution. The position is such that if the bike is taken off road, even then the body and the engine would behave like a single body resulting in better handling while ridden in sitting or standing position depending on the terrain. It is also called mid-engine and provides a better traction on both front and rear wheel and assists anti-lock braking system much better. A mid engine bike is much safer due to its balanced characteristic. The characteristic of being balanced gives an improved grade of acceleration, braking and cornering. Mid engine position also benefits the bike by equally sharing the forces on rear and front suspensions which are transmitted by a bumpy road to the bike. This means CG shift would not affect its handling while accelerating and braking.

 The engine is light in weight with parts made of aluminum alloys, platinum or magnesium. Of course, this is done in order to reduce overall weight of the bike. Fast and quick launching characteristics could be achieved only when the bike is light.  

Cruiser – Engine of a cruiser is big and heavy. The rider is positioned little to the rear section of the bike. Maximum amount of force acts on the rear wheel. This weight is balanced by the weight of the engine. Engine is located little in the front section of the bike which means the rider sitting on a cruiser lags the engine by few inches rather than positioned exactly on the engine normally seen in a sportsbike. This helps the weight to concentrate on the mid section of the bike but on a greater area. Engine due to its massive size, has some area hung out of the bike increasing air drag which affects speed and acceleration. However, this helps in cooling the engine faster due the air getting dragged on to the engine. Heavy engine means more resistance to turning. This helps the front wheel to gain enough traction and balance the bike. The engine is placed low and forward which shifts the CG low and forward giving straight line stability. Maximum weight of the bike is due to this heavy engine. It is advised not to lean the bike much as it not only would drag the exhaust and foot pegs but also would shift the CG in that direction. Higher counter force would be then needed to make the bike going without a fall which is very difficult.

          

Exhaust position – Exhaust system consists of header pipe, catalytic converter and muffler. The system is connected to the front end of the engine and guided back to the rear wheel. The header pipe travels either from the side or from the bottom of the engine depending on the ground clearance of the bike. So basically the system is located at the bottom periphery of the bike and influences the overall handling. The placement of the exhaust pipe affects CG as well.

Sportsbike – A sportsbike is an upright bike where stability is something that is taken very seriously. Sportsbike have different location of muffler.

Some bikes have dual header pipes or two into two which runs down the body and later separate to either side of the bike. The two mufflers are angled to some degree which avoids them to get submerged in wet sand or water if the bike is taken off road. This gives an even amount of force that it would bear making it stable with balanced CG. This also makes the rear end a bit heavier to gain more traction on the rear wheel. A rider would feel balanced while cornering it on any of the two sides in terms of handling.

Some sportsbike have header pipes that run down the engine and have the mufflers fixed under the pillion. It is also known as undertail exhaust. The exhaust gives the bike a much aggressive look. But this system adds up weight on the rear end of the bike that makes the rear end heavy and reduces traction on front wheel. This type of setting troubles the rider at the time of cornering. Also, it makes the bike pop unnecessary wheelies due to that extra weight on the rear end. The mufflers are not only far behind the back but also high on the bike making the exhaust gases to take a much longer and curvy path resulting in wastage of some power.

Some high performance bikes have header pipes travelling below the engine and limit the muffler right over there that is below the engine. This type of arrangement is called underbelly exhaust. Underbelly is one of the best arrangements because it keeps the weight in that mid section making the bike better at cornering. It also feels as if there is no exhaust on the bike at all and the weight that the rider is feeling is just due to the engine. The exhaust also does not affect the CG much and makes the bike share equal amount of forces on both wheels making the overall bike balanced. Also, there are less power losses and it is also cheap because of less amount of raw material used in building one. Of course, if a costlier material is used to build it then the rise in the price is quite obvious. But yes, this arrangement does reduce the ground clearance due to the presence of the muffler down below the engine region. However, the bike could be leaned to greater angles dues to the absence of any muffler to the side of the bike.

 The last type of arrangement is the most common one is the side mounted muffler in which the header pipes starting from the engine travel below the bike and then limits the muffler to the side of the bike. This gives an optimum ground clearance. The weight of the muffler on one side of the bike is countered by the pannier fixed to the other side. Daily commuter bikes have such an arrangement.       

Cruiser – A cruiser has header pipes travelling from the engine leading to one side of the engine and end(muffler) at the same side of the rear wheel. The system is places very low and straight. There is no angle of inclination observed at the muffler end. This is obvious as the bike is not made to be ridden off road of in watery regions. The system is often on the heavier side due to the material used to build it. This makes the bike little heavy on the muffler side and also restricts high degree leaning on corners. The reason of such an arrangement is the ergonomics of the bike which is low making the rider and the pillion rider sit close to the ground. Adding to this, there are panniers or saddle bags that fixed to the rear side of the bike. So the only place left is below the pannier bags and that is where the mufflers are located. The bike is obviously not as balanced as a sportsbike but that is not a big concern to a rider as all he needs from his bike is comfort and mid range power.

The other arrangement is similar to the above one with one of the two mufflers diverted to the either side of the bike. The header pipes guide them to either side of the bike. This makes the bike more balanced on both the side(Heavy as already known). The system is a best example of space management on such a fully loaded bike like a cruiser.

by AutoVogue