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|17th April 2006, 11:08||#16|
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along with tires ,tire pressure is also improtant ....we have have sticky v-rated rubber ,but the wrong tire pressure can change things drastically ..
also the road condtion is also important
|17th April 2006, 12:15||#17|
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|17th April 2006, 22:32||#19|
Join Date: Mar 2005
Location: pune / Bahrain
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here guys is a view of my strut braces front
what it does as far as my driving is concerned is that the front end does not dip down when sharp cornering and normally where the suspension would be going down faster in this case the struts come in action. and in RWD into sharp cornering there is more kind of unpredictable drift which can be dangerous if u have to maintain lane discipline, with struts "on" the drift part is very controlled and u could make it drift to ur potential and be in control knowing what and when r u doing it.
rwd and struts should go in conjunction i feel.
|18th April 2006, 20:08||#20|
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a few things that came to my mind at first thought;
1) steering ratio (no. of turns lock to lock/ steering g'box ratio)- this would come under point number 13. ah, and yes-all wheel steering.
2) perhaps i'm a little off, but i thought that the optimal weight distribution should be 40:60, i.e, rear biased to overcome understeer; point number 3.
there are so many other points, but all of them come under the above said categories, only in more detail....
|6th November 2009, 17:06||#21|
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Diffusers? Look at what Brawn achieved this year on the double deccar diffuser alone? Also, I have see a lot of the super cars having those.
Paint quality will also help you in achieving that hunderth of the second.
|6th November 2009, 17:25||#22|
Distinguished - BHPian
All of these contribute
2. Lower Center of gravity
3. 50:50 weight distribution
4. Taut and Rigid Chassis
8. Tight Suspension (Multi-Link, Active, Double wishbone...)
9. Traction Control + Electronics
What also contributes in terms of old-fashioned phyics is
21. Spring and damper ratings - how much they deflect with a given amount of force
22. Anti-roll bar ratings
and in terms of pure electronic wizardry, there is significant contribution by
23. ASC - automatic skid control, which kind of compensates for the incompetence of
20. The nut holding the wheel!
One can add
24. Caster and camber angles
to the above list.
Last edited by SS-Traveller : 6th November 2009 at 17:27.
|7th November 2009, 11:20||#23|
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|7th November 2009, 11:39||#24|
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Let's break this down in subcategories. For tyres: height of sidewall, compound used, tread design, width, tyre temperature.
Other external factors affecting handing: road conditions, cross winds, driver familiarity with the road / circuit, familiarity of the driver with the car (amount of time the driver has driven the car and gotten used to it's characteristics)
EDIT: I would also add amount of fuel in the tank as a point
Last edited by Tejas@perioimpl : 7th November 2009 at 11:47. Reason: see edit
|7th November 2009, 12:11||#25|
Join Date: Nov 2009
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Recently I saw a palio 1.9 D which had 17" alloys with very wide and very low profile tyres.(profile being something like just 3 inch, also tyres were jutting way out from the body of car)
How does that effect handling and ride?
|13th November 2009, 22:26||#26|
Join Date: Oct 2009
Location: Pride of Deccan - Hyderabad
CAr Handling : Various factors that affect it..
Center of gravity height
The center of gravity height, relative to the track, determines load transfer, (related to, but not exactly weight transfer), from side to side and causes body lean. Centrifugal force acts at the center of gravity to lean the car toward the outside of the curve, increasing downward force on the outside tires.
Height of the center of gravity relative to the wheelbase determines load transfer between front and rear. The car's momentum acts at its center of gravity to tilt the car forward or backward, respectively during braking and acceleration. Since it is only the downward force that changes and not the location of the center of gravity, the effect on over/under steer is opposite to that of an actual change in the center of gravity. When a car is braking, the downward load on the front tires increases and that on the rear decreases, with corresponding change in their ability to take sideways load, causing oversteer.
Lower center of gravity is the principal performance advantage of sports cars, compared to sedans and (especially) SUVs. Some cars have light materials in their roofs, partly for this reason. It is also part of the reason that traditional sports cars are open or convertible.
Body lean can also be controlled by the springs, anti-roll bars or the roll center heights.
Center of gravity forward or back
In steady-state cornering, because of the center of gravity, front-heavy cars tend to understeer and rear-heavy cars to oversteer, all other things being equal. The mid-engine design offers the ideal center of gravity.
When all four wheels and tires are of equal size, as is most often the case with passenger cars, a weight distribution close to "50/50" (i.e. the center of mass is mid-way between the front and rear axles) produces the preferred handling compromise.
The rearward weight bias preferred by sports and racing cars results from handling effects during the transition from straight-ahead to cornering. During corner entry the front tires, in addition to generating part of the lateral force required to accelerate the car's center of mass into the turn, also generate a torque about the car's vertical axis that starts the car rotating into the turn. However, the lateral force being generated by the rear tires is acting in the opposite torsional sense, trying to rotate the car out of the turn. For this reason, a car with "50/50" weight distribution will understeer on initial corner entry. To avoid this problem, sports and racing cars often have a more rearward weight distribution. In the case of pure racing cars, this is typically between "40/60" and "35/65." This gives the front tires an advantage in overcoming the car's moment of inertia (yaw angular inertia), thus reducing corner-entry understeer.
Using wheels and tires of different sizes (proportional to the weight carried by each end) is a lever automakers can use to fine tune the resulting over/understeer characteristics.
Roll angular inertia
This increases the time it takes to settle down and follow the steering. It depends on the (square of the) height and width, and (for a uniform mass distribution) can be approximately calculated by the equation: I = M(height2 + width2) / 12.
Greater width, then, though it counteracts center of gravity height, hurts handling by increasing angular inertia. Some high performance cars have light materials in their fenders and roofs partly for this reason.
Yaw and pitch angular inertia (polar moment)
Unless the vehicle is very short, compared to its height or width, these are about equal. Angular inertia determines the rotational inertia of an object for a given rate of rotation. The yaw angular inertia tends to keep the direction the car is pointing changing at a constant rate. This makes it slower to swerve or go into a tight curve, and it also makes it slower to turn straight again. The pitch angular inertia detracts from the ability of the suspension to keep front and back tire loadings constant on uneven surfaces and therefore contributes to bump steer. Angular inertia is an integral over the square of the distance from the center of gravity, so it favors small cars even though the lever arms (wheelbase and track) also increase with scale. (Since cars have reasonable symmetrical shapes, the off-diagonal terms of the angular inertia tensor can usually be ignored.) Mass near the ends of a car can be avoided, without re-designing it to be shorter, by the use of light materials for bumpers and fenders or by deleting them entirely.
Automobile suspensions have many variable characteristics, which are generally different in the front and rear and all of which affect handling. Some of these are: spring rate, damping, straight ahead camber angle, camber change with wheel travel, roll center height and the flexibility and vibration modes of the suspension elements. Suspension also affects unsprung weight.
Many cars have suspension that connects the wheels on the two sides, either by a sway bar and/or by a solid axle. The CitroŽn 2CV has interaction between the front and rear suspension.
The flexing of the frame interacts with the suspension.
The severe handling vice of the TR3 and related cars was caused by running out of suspension travel. Other vehicles will run out of suspension travel with some combination of bumps and turns, with similarly catastrophic effect. Excessively modified cars also may encounter this problem.
Tires and wheels
In general, larger tires, softer rubber, higher hysteresis rubber and stiffer cord configurations increase road holding and improve handling. On most types of poor surfaces, large diameter wheels perform better than lower wider wheels. The fact that larger tires, relative to weight, stick better is the main reason that front heavy cars tend to understeer and rear heavy to oversteer. The depth of tread remaining greatly affects aquaplaning (riding over deep water without reaching the road surface). Increasing tire pressures reduces their slip angle, but (for given road conditions and loading) there is an optimum pressure for road holding.
Track and wheelbase
The track provides the resistance to sideways weight transfer and body lean. The wheelbase provides resistance to front/back weight transfer and to pitch angular inertia, and provides the torque lever arm to rotate the car when swerving. The wheelbase, however, is less important than angular inertia (polar moment) to the vehicle's ability to swerve quickly.
Ignoring the flexing of other components, a car can be modeled as the sprung weight, carried by the springs, carried by the unsprung weight, carried by the tires, carried by the road. Unsprung weight is more properly regarded as a mass which has its own inherent inertia separate from the rest of the vehicle. When a wheel is pushed upwards by a bump in the road, the inertia of the wheel will cause it to be carried further upward above the height of the bump. If the force of the push is sufficiently large, the inertia of the wheel will cause the tire to completely lift off the road surface resulting in a loss of traction and control. Similarly when crossing into a sudden ground depression, the inertia of the wheel slows the rate at which it descends. If the wheel inertia is large enough, the wheel may be temporarily separated from the road surface before it has descended back into contact with the road surface.
This unsprung weight is cushioned from uneven road surfaces only by the compressive resilience of the tire (and wire wheels if fitted), and which aids the wheel in remaining in contact with the road surface when the wheel inertia prevents close-following of the ground surface. However, the compressive resilience of the tire results in rolling resistance which requires additional kinetic energy to overcome, and the rolling resistance is expended in the tire as heat due to the flexing of the rubber and steel bands in the sidewalls of the tires. To reduce rolling resistance for improved fuel economy and to avoid overheating and failure of tires at high speed, tires are designed to have limited internal damping.
So the "wheel bounce" due to wheel inertia, or resonant motion of the unsprung weight moving up and down on the springiness of the tire is only poorly damped, mainly by the dampers or Shock absorbers of the suspension. For these reasons, high unsprung weight reduces road holding and increases unpredictable changes in direction on rough surfaces (as well as degrading ride comfort and increasing mechanical loads).
This unsprung weight includes the wheels and tires, usually the brakes, plus some percentage of the suspension, depending on how much of the suspension moves with the body and how much with the wheels; for instance a solid axle is completely unsprung. The main factors that improve unsprung weight are a sprung differential (as opposed to live axle) and inboard brakes. (The De Dion tube suspension operates much as a live axle does, but represents an improvement because the diff is mounted to the body, thereby reducing the unsprung weight.) Aluminum wheels also help. Magnesium alloy wheels are even lighter but corrode easily.
Since only the brakes on the driving wheels can easily be inboard, the CitroŽn 2CV had inertial dampers on its rear wheel hubs to damp only wheel bounce.
Aerodynamic forces are generally proportional to the square of the air speed, therefore car aerodynamics become rapidly more important as speed increases. Like darts, aeroplanes, etc., cars can be stabilised by fins and other rear aerodynamic devices. However, in addition to this cars also use downforce or "negative lift" to improve road holding. This is prominent on many types of racing cars, but is also used on most passenger cars to some degree, if only to counteract the tendency for the car to otherwise produce positive lift.
In addition to providing increased adhesion, car aerodynamics are frequently designed to compensate for the inherent increase in oversteer as cornering speed increases. When a car corners, it must rotate about its vertical axis as well as translate its center of mass in an arc. However, in a tight-radius (lower speed) corner the angular velocity of the car is high, while in a longer-radius (higher speed) corner the angular velocity is much lower. Therefore, the front tires have a more difficult time overcoming the car's moment of inertia during corner entry at low speed, and much less difficulty as the cornering speed increases. So the natural tendency of any car is to understeer on entry to low-speed corners and oversteer on entry to high-speed corners. To compensate for this unavoidable effect, car designers often bias the car's handling toward less corner-entry understeer (such as by lowering the front roll center), and add rearward bias to the aerodynamic downforce to compensate in higher-speed corners. The rearward aerodynamic bias may be achieved by an airfoil or "spoiler" mounted near the rear of the car, but a useful effect can also be achieved by careful shaping of the body as a whole, particularly the aft areas
In recent years, aerodynamics have become an area of increasing focus by racing teams as well as car manufacturers. Advanced tools such as wind tunnels and computational fluid dynamics (CFD) have allowed engineers to optimize the handling charistics of vehicles. Advanced wind tunnels such as Wind Shear's Full Scale, Rolling Road, Automotive Wind Tunnel recently built in Concord, North Carolina have taken the simulation of on-road conditions to the ultimate level of accuracy and repeatability under very controlled conditions. CFD has similarly been used as a tool to simulate aerodynamic conditions but through the use of extremely advanced computers and software to duplicate the car's design digitally then "test" that design on the computer.
Delivery of power to the wheels and brakes
The coefficient of friction of rubber on the road limits the magnitude of the vector sum of the transverse and longitudinal force. So the driven wheels or those supplying the most braking tend to slip sideways. This phenomenon is often explained by use of the circle of forces model.
One reason that sports cars are usually rear wheel drive is that power induced oversteer is useful, to a skilled driver, for tight curves. The weight transfer under acceleration has the opposite effect and either may dominate, depending on the conditions. Inducing understeer by applying power in a front wheel drive car is useful via proper use of "Left-foot braking." In any case, this is not an important safety issue, because power is not normally used in emergency situations. Using low gears down steep hills may cause some oversteer.
The effect of braking on handling is complicated by load transfer, which is proportional to the (negative) acceleration times the ratio of the center of gravity height to the wheelbase. The difficulty is that the acceleration at the limit of adhesion depends on the road surface, so with the same ratio of front to back braking force, a car will understeer under braking on slick surfaces and oversteer under hard braking on solid surfaces. Most modern cars combat this by varying the distribution of braking in some way. This is important with a high center of gravity, but it is also done on low center of gravity cars, from which a higher level of performance is expected.
Depending on the driver, steering force and transmission of road forces back to the steering wheel and the steering ratio of turns of the steering wheel to turns of the road wheels affect control and awareness. Play ó free rotation of the steering wheel before the wheels rotate ó is a common problem, especially in older model and worn cars. Another is friction. Rack and pinion steering is generally considered the best type of mechanism for control effectiveness. The linkage also contributes play and friction. Caster ó offset of the steering axis from the contact patch ó provides some of the self-centering tendency.
Precision of the steering is particularly important on ice or hard packed snow where the slip angle at the limit of adhesion is smaller than on dry roads.
The steering effort depends on the downward force on the steering tires and on the radius of the contact patch. So for constant tire pressure, it goes like the 1.5 power of the vehicle's weight. The driver's ability to exert torque on the wheel scales similarly with his size. The wheels must be rotated farther on a longer car to turn with a given radius. Power steering reduces the required force at the expense of feel. It is useful, mostly in parking, when the weight of a front-heavy vehicle exceeds about ten or fifteen times the driver's weight, for physically impaired drivers and when there is much friction in the steering mechanism.
Four-wheel steering has begun to be used on road cars (Some WW II reconnaissance vehicles had it). It relieves the effect of angular inertia by starting the whole car moving before it rotates toward the desired direction. It can also be used, in the other direction, to reduce the turning radius. Some cars will do one or the other, depending on the speed.
Steering geometry changes due to bumps in the road may cause the front wheels to steer in different directions together or independent of each other. The steering linkage should be designed to minimize this effect.
Electronic stability control
Electronic stability control (ESC) is a computerized technology that improves the safety of a vehicle's stability by attempting to detect and prevent skids. When ESC detects loss of steering control, the system applies individual brakes to help "steer" the vehicle where the driver wants to go. Braking is automatically applied to individual wheels, such as the outer front wheel to counter oversteer, or the inner rear wheel to counter understeer.
The stability control of some cars may not be compatible with some driving techniques, such as power induced over-steer. It is therefore, at least from a sporting point of view, preferable that it can be disabled.
 Static alignment of the wheels
Of course things should be the same, left and right, for road cars. Camber affects steering because a tire generates a force towards the side that the top is leaning towards. This is called camber thrust. Additional front negative camber is used to improve the cornering ability of cars with insufficient camber gain.
Rigidity of the frame
The frame may flex with load, especially twisting on bumps. Rigidity is considered to help handling. At least it simplifies the suspension engineers work. Some cars, such as the Mercedes-Benz 300SL have had high doors to allow a stiffer frame.
Driver handling the car
Handling is a property of the car, but different characteristics will work well with different drivers.
A person learns to control a car much as he learns to control his body, so the more he has driven a car or type of car the better it will handle for them. One needs to take extra care for the first few months after buying a car, especially if it differs in design from those they are used to. Other things that a driver must adjust to include changes in tires, tire pressures and load. That is, handling is not just good or bad; it is also the same or different.
Position and support for the driver
Having to take up "g forces" in his/her arms interferes with a driver's precise steering. In a similar manner, a lack of support for the seating position of the driver may cause them to move around as the car undergoes rapid acceleration (through cornering, taking off or braking). This interferes with precise control inputs, making the car more difficult to control.
Being able to reach the controls easily is also an important consideration, especially if a car is being driven hard.
In some circumstances, good support may allow a driver to retain some control, even after a minor accident or after the first stage of an accident.
External conditions that affect handling
Weather affects handling by making the road slippery. Different tires do best in different weather. Deep water is an exception to the rule that wider tires improve road holding.
Cars with relatively soft suspension and with low unsprung weight are least affected by uneven surfaces, while on flat smooth surfaces the stiffer the better. Unexpected water, ice, oil, etc. are hazards.
Common handling problems
When any wheel leaves contact with the road there is a change in handling, so the suspension should keep all four (or three) wheels on the road in spite of hard cornering, swerving and bumps in the road. It is very important for handling, as well as other reasons, not to run out of suspension travel and "bottom" or "top".
It is usually most desirable to have the car adjusted for a small amount of understeer, so that it responds predictably to a turn of the steering wheel and the rear wheels have a smaller slip angle than the front wheels. However this may not be achievable for all loading, road and weather conditions, speed ranges, or while turning under acceleration or braking. Ideally, a car should carry passengers and baggage near its center of gravity and have similar tire loading, camber angle and roll stiffness in front and back to minimise the variation in handling characteristics. A driver can learn to deal with excessive oversteer or understeer, but not if it varies greatly in a short period of time.
The most important common handling failings are;
* Understeer - the front wheels tend to crawl slightly or even slip and drift towards the outside of the turn. The driver can compensate by turning a little more tightly, but road-holding is reduced, the car's behaviour is less predictable and the tires are liable to wear more quickly.
* Oversteer - the rear wheels tend to crawl or slip towards the outside of the turn more than the front. The driver must correct by steering away from the corner, otherwise the car is liable to spin, if pushed to its limit. Oversteer is sometimes useful, to assist in steering, especially if it occurs only when the driver chooses it by applying power.
* Bump steer Ė the effect of irregularity of a road surface on the angle or motion of a car. It may be the result of the kinematic motion of the suspension rising or falling, causing toe-in or toe-out at the loaded wheel, ultimately affecting the yaw angle (heading) of the car. It may also be caused by defective or worn out suspension components. This will always happen under some conditions but depends on suspension, steering linkage, unsprung weight, angular inertia, differential type, frame rigidity, tires and tire pressures. If suspension travel is exhausted the wheel either bottoms or loses contact with the road. As with hard turning on flat roads, it is better if the wheel picks up by the spring reaching its neutral shape, rather than by suddenly contacting a limiting structure of the suspension.
* Body roll - the car leans towards the outside of the curve. This interferes with the driver's control, because he must wait for the car to finish leaning before he can fully judge the effect of his steering change. It also adds to the delay before the car moves in the desired direction.
* Weight transfer - the wheels on the outside of a curve are more heavily loaded than those on the inside. This tends to overload the tires on the outside and therefore reduce road holding. Weight transfer (sum of front and back), in steady cornering, is determined by the ratio of the height of a car's center of gravity to its track. Differences between the weight transfer in front and back are determined by the relative roll stiffness and contribute to the over or under-steer characteristics.
When the weight transfer equals half the vehicle's loaded weight, it will start to roll over. This can be avoided by manually or automatically reducing the turn rate, but this causes further reduction in road-holding.
* Slow response - sideways acceleration does not start immediately when the steering is turned and may not stop immediately when it is returned to center. This is partly caused by body roll. Other causes include tires with high slip angle, and yaw and roll angular inertia. Roll angular inertia aggravates body roll by delaying it. Soft tires aggravate yaw angular inertia by waiting for the car to reach their slip angle before turning the car.
Ride quality and handling have always been a compromise - technology has over time allowed automakers to combine more of both features in the same vehicle. High levels of comfort are difficult to reconcile with a low center of gravity, body roll resistance, low angular inertia, support for the driver, steering feel and other characteristics that make a car handle well.
For ordinary production cars, manufactures err towards deliberate understeer as this is safer for inexperienced or inattentive drivers than is oversteer. Other compromises involve comfort and utility, such as preference for a softer smoother ride or more seating capacity.
Inboard brakes improve both handling and comfort but take up space and are harder to cool. Large engines tend to make cars front or rear heavy. In tires, fuel economy, staying cool at high speeds, ride comfort and long wear all tend to conflict with road holding, while wet, dry, deep water and snow road holding are not exactly compatible. A-arm or wishbone front suspension tends to give better handling, because it provides the engineers more freedom to choose the geometry, and more road holding, because the camber is better suited to radial tires, than MacPherson strut, but it takes more space.
The older Live axle rear suspension technology, familiar from the Ford Model T, is still widely used in most sport utility vehicles and trucks. The live axle suspension is still used in some sports cars, like the Ford Mustang, and is better for drag racing, but generally has problems with grip on bumpy corners, and stability at high speeds on bumpy straights. Having said that a good live axle can be superior to a poor independent rear suspension system, in most circumstances.
Source : Wikipedia
|13th November 2009, 22:44||#27|
Distinguished - BHPian
Electronic stability control - Wikipedia, the free encyclopedia. This is as opposed to TCS (traction control system) (Traction control system - Wikipedia, the free encyclopedia) where the electronics manage to prevent wheelspin and resultant skid/spin under hard acceleration.
Last edited by SS-Traveller : 13th November 2009 at 22:48.
|13th November 2009, 23:05||#28|
Distinguished - BHPian
The higher the profile of the tyre (i.e. the greater the wall height), the more the outside tyre will "roll" onto its sidewall on a fast turn. Conversely, with a lower wall height (say a 30 profile), this does not happen, and leaves more of the tread (where the grip is) in contact with the road. The tradeoff for lower profile is loss of shock absorption by the tyre itself, leading to poorer ride quality.
Some interesting reading here: Advanced vehicle technology - Google Books.
|14th November 2009, 00:59||#29|
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Aah, A thread on the darkest of the dark arts of automotive design and engineering! Thanks GTO for starting this thread which promises to be informative as well as a 'pot boiler'.
From my scant knowledge, I would say that all of the factors mentioned play a role in the handling of a car. The two most important being rigidity of the chassis (this is the simple one) and Suspension geometry.
Suspension geometry is more than mere toe-in/toe-out, camber, caster etc. These are merely the angles of the wheel, which is only part of the suspension of the car. Suspension geometry is the relative position of the various components of a cars suspension in relation to each other.
Imagine this - the same camber, caster and toe-in/out on the same vehicle - can be achieved by mounting the struts and springs in different places. A strut mounted further in-board on the chassis will behave differently from a strut mounted more to the outside, likewise with springs. Now add the fact that struts mounted exactly above the axle act differently from struts moved a little forward which in turn behave very differently from struts mounted a little behind. Now each of these numerous components can be mounted in infinitely different ways, their total length of travel and rates of travel can again be varied to a large extent. Just to complicate things, the length of each of the components can be varied to some small extent.
Every different placement of the various components changes its angle in relation to every other component. If one notices carefully, on the rear wheel, one angle i.e. the camber of the wheel changes when the body rolls i.e. moves to either side - the aim being to maintain negative camber at all times. On the front wheels, the angles change more dramatically first when the steering is turned and also when the body 'rolls'. Inducing and controlling this change of the angles so as to maintain stability, grip and traction is what designers and engineers hope to achieve through getting the suspension geometry right.
I only wish and hope that someone here can explain all this to me in a manner that I can understand I need to enrol for 101 - Suspension geometry for dummies!
|14th November 2009, 11:30||#30|
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