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08-19-2007, 07:14 AM
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#21 (permalink) |
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Senior Member
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I dont know about everyone else but the problem I was concerned with was tire rubbing when deciding what suspension setup to go with.. One thing I found besides offsets of the wheel was tire size in terms of circumfrance Here are some examples:
215/45/17 = 24.3 (stock tire) 205/40/18 = 24.4 225/40/18 = 25.1 215/35/19 = 24.9 225/35/19 = 25.2 Hope this helps... |
  
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08-19-2007, 09:36 AM
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#22 (permalink) | |
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*Northeast Crew*
  
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08-19-2007, 11:35 AM
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#27 (permalink) |
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non-Cilantrist
 
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http://www.tirerack.com/tires/tiretech/tiretech.jsp
Lots of good Tire Information, courtesy of our site sponsor Tirerack. |
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08-19-2007, 11:40 AM
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#28 (permalink) | |
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*Northeast Crew*
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08-19-2007, 02:17 PM
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#29 (permalink) | |
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HR1!!!!!
 
Join Date: Mar 2006
Location: DIRTYJERZ
Age: 28
Posts: 3,492
Greg@Redshiftmotorsports.com
iTrader: 1 / 100%
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JUST some thought/changes
 How does a tire make traction? “Handling is all about maximizing tire traction. Regardless of how much advanced hardware the car has, the bottom line is that the car's entire braking, accelerating, and cornering performance has to be translated through the four small patches of rubber in contact with the road. Think about it. Ignore absolutely everything about a car except for how much rubber is in contact with the road. Maximizing the performance of these four small patches is what "handling" is all about. Maximum traction, of course, is affected by the suspension design, the type of tire, it's rubber compound, its contact patch size, and several other factors. Once a given car and tire is selected, there is still the task getting the absolute most out of that specific tire. Three factors determine the maximum potential grip of a tire: the coefficient of friction provided by its rubber compound (stickier is better), the amount of rubber as determined by the tire size (bigger is better), and the amount of downforce applied to the tire (pushing down adds to the total friction applied). Of course there is a limit to all of these, and a point is reached where more is not better. Slip Angle There are two factors in reaching and sustaining the maximum traction performance from the tire. First, a tire's maximum traction potential is actually reached when there is a small amount of slippage. This "slippage" is translated differently for braking, accelerating, and cornering. Under braking, the peak performance of the tire is reached when the tire is turning slightly less than a one-to-one relationship of the distance traveled. In other words, if the car were at a steady state, and the wheel turned 10 times to cover a certain distance, under braking, the wheel would now turn perhaps only 9-1/2 times to achieve the peak slippage performance. It is possible to learn how to feel the car through the brake pedal, steering wheel, and seat and sense this tiny bit of extra braking force from the tire.(For the Si this is generally right before ABS kicks in) In acceleration, the tire should travel slightly more distance than the distance of the acceleration (spin just a bit faster than normal). The tires will actual slip; not a lot all at once to result in free wheelspin, but ever so slightly during the whole acceleration phase. When you can sense this slip, and control it, this is when you're getting maximum acceleration from the vehicle. (You will feel the car almost wiggle underneath you, don’t go to a fun spin, just a nice wiggle is good.) In cornering, this slippage is present when the wheels are actually turned just slightly more than the actual amount required to go the intended path (this difference is an angle and is where we get the term "slip angle" from). To accomplish this slip angle the car must actually be sliding ever so slightly during cornering. Not a big power slide, just a little extra slip. At first, this can feel very uncomfortable, as though you are starting to lose traction. In fact, this is where the car has its greatest traction. The tricky part is approaching this limit and not crossing it. If the car is not sliding at all, then it isn't going fast enough. If it is sliding enough to actually drift (or have noticeable understeer, or oversteer), the tire is being used beyond its limit. The corner speeds will be slower, and the tire will wear out much more quickly. In each of these cases, we emphasized the "slightly" aspect of this slippage. Too little, and the tire does not reach maximum performance. If the car feels "hooked up on rails," then the car is not being driven fast enough. Until you feel that tiny bit of slip, you can go faster. Knowing how to approach that point without exceeding it takes a great deal of practice. Too much slippage and you'll exceed the tire's limits and the tires slide excessively resulting in locked-up braking, wheel spin in accelerating, excessive sliding during cornering. Driving Smoothness & Traction One more principle to learn. A tire's maximum traction potential will not be realized unless it is brought to that point gradually. This is true of just about everything dealing with frictional traction, and you experience it regularly in everyday occurrences. Imagine this experiment. Place a piece of paper on a table, and an ordinary breakfast bowl on the paper. Start pulling on the paper slowly, then gradually faster. The bowl remains on the paper and is dragged along with it. Next, yank the paper immediately. It will come out from under the bowl leaving the bowl unmoved, or barely moved. Same bowl, same paper, same table. What was different? The acceleration of the forces applied. In your car, the tires are the paper. Ease the car smoothly into a corner, and the tire will have a high level of traction. Jerk the steering wheel too quickly, and the tire will not maintain grip with the road. Same car, same tires, same road. The difference is the acceleration of the forces, or the smoothness with which cornering, acceleration, and braking forces are applied. Smoother is grippier. The principle of driving smoothly is paramount to every factor of improving a car's handling performance. All the hardware in the world will not fix a car with a driver using "jerk and stab" braking, accelerating, and turning control behavior. Inexperienced drivers frequently blame the lack of the greatest hardware in their car for performance problems which are actually caused by their driving style. There's enough stories to suggest even a few pros have this habit. Be honest and analyse your driving, or get an experienced instructor to analyse it for you. Smooth driving maximizes tire traction. Maximized tire traction is what leads to fast driving. We repeat -- smoother is grippier. Mechanical and Aerodynamic Downforce (Not somthing we really have to worry about now) Another factor which affects tire traction, but one that is not likely to be factor in the weekend racing of your street car is vertical loading -- the combination of mechanical and aerodynamic downforce. Whether applied by mechanical forces (which is essentially gravity), or aerodynamic forces, the total amount of downward push on the tire affects the available traction. To demonstrate, lightly drag a pencil eraser across a table. It slides easily. Now push down on it and drag it. There is much higher friction. Same goes for tires. Summary All handling modifications and adjustments come down to improving the traction of the four tire patches on the road. Tires are actually their grippiest when there is about 5% slippage involved. Driver smoothness is a major factor in the car's overall grip. All the fancy hardware in the world won't cure the loss of grip created by a jerky driver (and we don't mean personality).” ALIGNMENT TERMS Toe  Toe settings affect three major areas of performance: tire wear, straight-line stability and corner entry handling characteristics. To minimize tire wear and power loss, toe will be zero. Meaning both tires on the one end of the vechile are pointed ahead when the vechile is going straight. Too much toe in/out causes the tire to scrub, becuase the tire is always clocked away from the direction the car is going.Too much Toe out = Excessive wear on the inside shoulders Too much Toe In = Excessive wear on the out side shoulders “So if minimum tire wear and power loss are achieved with zero toe, why have any toe angles at all? The answer is that toe settings have a major impact on directional stability. The illustrations at right show the mechanisms involved. With the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect each other. Under this condition, the wheels are at odds with each other, and no turn results. When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If it's a minor disturbance, the disturbed wheel will steer only a small amount, perhaps so that it's rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still don't describe a turn. The wheels have absorbed the irregularity without significantly changing the direction of the vehicle. In this way, toe-in enhances straight-line stability. Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This is another reason why many front-drivers are set up with toe-out in the front If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.” Camber  “Camber is the angle of the wheel relative to vertical, as viewed from the front or the rear of the car. If the wheel leans in towards the chassis, it has negative camber; if it leans away from the car, it has positive camber. The cornering force that a tire can develop is highly dependent on its angle relative to the road surface, and so wheel camber has a major effect on the road holding of a car. It's interesting to note that a tire develops its maximum cornering force at a small negative camber angle, typically around neg. 1/2 degree. To optimize a tire's performance in a corner, it's the job of the suspension designer to assume that the tire is always operating at a slightly negative camber angle. This can be a very difficult task, since, as the chassis rolls in a corner, the suspension must deflect vertically some distance. Since the wheel is connected to the chassis by several links which must rotate to allow for the wheel deflection, the wheel can be subject to large camber changes as the suspension moves up and down. For this reason, the more the wheel must deflect from its static position, the more difficult it is to maintain an ideal camber angle. Thus, the relatively large wheel travel and soft roll stiffness needed to provide a smooth ride in passenger cars presents a difficult design challenge, while the small wheel travel and high roll stiffness inherent in racing cars reduces the engineer's headaches. It's important to draw the distinction between camber relative to the road, and camber relative to the chassis. To maintain the ideal camber relative to the road, the suspension must be designed so that wheel camber relative to the chassis becomes increasingly negative as the suspension deflects upward. (If you go tooo low with the si this is the opposite and you can lose camber as you compress the suspension) If the suspension were designed so as to maintain no camber change relative to the chassis, then body roll would induce positive camber of the wheel relative to the road. Thus, to negate the effect of body roll, the suspension must be designed so that it pulls in the top of the wheel (i.e., gains negative camber) as it is deflected upwards. Since most suspensions are designed so that the camber varies as the wheel moves up and down relative to the chassis, the camber angle that we set when we align the car is not typically what is seen when the car is in a corner. Nevertheless, it's really the only reference we have to make camber adjustments. For competition, it's necessary to set the camber under the static condition, test the car, then alter the static setting in the direction that is indicated by the test results. The best way to determine the proper camber for competition is to measure the temperature profile across the tire tread immediately after completing some hot laps. In general, it's desirable to have the inboard edge of the tire slightly hotter than the outboard edge. However, it's far more important to ensure that the tire is up to its proper operating temperature than it is to have an "ideal" temperature profile. Thus, it may be advantageous to run extra negative camber to work the tires up to temperature. Caster  “Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.  Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The mechanism that causes this tendency is clearly illustrated by the castering front wheels of a shopping cart (above). The steering axis of a shopping cart wheel is set forward of where the wheel contacts the ground. As the cart is pushed forward, the steering axis pulls the wheel along, and since the wheel drags along the ground, it falls directly in line behind the steering axis. The force that causes the wheel to follow the steering axis is proportional to the distance between the steering axis and the wheel-to-ground contact patch-the greater the distance, the greater the force. This distance is referred to as "trail." Due to many design considerations, it is desirable to have the steering axis of a car's wheel right at the wheel hub. If the steering axis were to be set vertical with this layout, the axis would be coincident with the tire contact patch. The trail would be zero, and no castering would be generated. The wheel would be essentially free to spin about the patch (actually, the tire itself generates a bit of a castering effect due to a phenomenon known as "pneumatic trail," but this effect is much smaller than that created by mechanical castering, so we'll ignore it here). Fortunately, it is possible to create castering by tilting the steering axis in the positive direction. With such an arrangement, the steering axis intersects the ground at a point in front of the tire contact patch, and thus the same effect as seen in the shopping cart casters is achieved. The tilted steering axis has another important effect on suspension geometry. Since the wheel rotates about a tilted axis, the wheel gains camber as it is turned. This effect is best visualized by imagining the unrealistically extreme case where the steering axis would be horizontal-as the steering wheel is turned, the road wheel would simply change camber rather than direction. This effect causes the outside wheel in a turn to gain negative camber, while the inside wheel gains positive camber. These camber changes are generally favorable for cornering, although it is possible to overdo it. Most cars are not particularly sensitive to caster settings. Nevertheless, it is important to ensure that the caster is the same on both sides of the car to avoid the tendency to pull to one side. While greater caster angles serve to improve straight-line stability, they also cause an increase in steering effort. Three to five degrees of positive caster is the typical range of settings, with lower angles being used on heavier vehicles to keep the steering effort reasonable.”
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01-28-2008, 10:15 PM
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#35 (permalink) | |
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Senior Member
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01-29-2008, 07:07 AM
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#38 (permalink) |
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*Northeast Crew*
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^ they can just take the entire wheel/tire off of the vehicle and just balance it like that
..........alot of times though if you have a nasty wheel hop and while on the balancer you find its taking alot of weight. Alot of times spinning the tire 180 degrees solves that
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