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Discussion Starter #1
I just finished a Japanese VCD titled "Best Motoring" and I am amazed by how the Japanese driver maneuvers the Altezza(IS). The driver smoothly and controllably drifted through ALL the corners(It was raining and not on muddy road). The drivers in the VCD commented that the Altezza (IS) is a newer version of the AE86 and is designed for drifting.

Has anyone tried drifting with the IS300?

I have tried drifting but it is hard to control when to stop drifting and the drift angle. In addition, it damages the tires... very badly 'x'

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Impact Yellow
 

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The Altezza's engine is a lot lighter, so less weight on the front wheels means less understeer. The IS300 seems tuned to understeer, which is safer for American drivers. Newer BMWs are the same way, but benefit from better weight balance.

Originally posted by Jumbo Robin:
I just finished a Japanese VCD titled "Best Motoring" and I am amazed by how the Japanese driver maneuvers the Altezza(IS). The driver smoothly and controllably drifted through ALL the corners(It was raining and not on muddy road). The drivers in the VCD commented that the Altezza (IS) is a newer version of the AE86 and is designed for drifting.

Has anyone tried drifting with the IS300?

I have tried drifting but it is hard to control when to stop drifting and the drift angle. In addition, it damages the tires... very badly 'x'
 

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Discussion Starter #4
Originally posted by ckolsen:
The Altezza's engine is a lot lighter, so less weight on the front wheels means less understeer. The IS300 seems tuned to understeer, which is safer for American drivers. Newer BMWs are the same way, but benefit from better weight balance.

I thought more weight on the front wheels means less understeer and more oversteer.

I might be wrong but from a phyical approach, more weight on the front wheels result in more grib. If we are to examine the following equation:

uFn = F

u = coefficent of friction
F = Force of friction
Fn = Normal force = mass x gravity acceleration

According to the above equation, as Fn (weight) increases, F incrases as well.

Example:
Assume u = 0.1
Fn = 100; F = 10
Fn = 100; F = 100

Understeer occurs when the front wheels lose grib. Meaning the applied force to the front wheels exceeds the Force of friction avaliable on the front wheels.

Drifting is sometime called Braking-Drift because when brake is applied (Not locked), a weight shift occurs. This will shift most of the weight to the front of the vechicle, causing the rear wheels to lose grib during cornering, thus inducing oversteer.

Well the above are just paper-talk. I don't know what really happend. But so far I still stick to the stuff I listed above.


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It's true, there's more frictional force, because there's more weight for it to hold in place. Friction/grip is just a force that counterbalances a weight. The more weight on the front wheels, the more grip is NEEDED to keep the wheels from slipping. Therefore, the wheels with more weight on them will slip first. If you brake or accelerate while turning, you can adjust for this.

Originally posted by Jumbo Robin:
I thought more weight on the front wheels means less understeer and more oversteer.

I might be wrong but from a phyical approach, more weight on the front wheels result in more grib. If we are to examine the following equation:

uFn = F

u = coefficent of friction
F = Force of friction
Fn = Normal force = mass x gravity acceleration

According to the above equation, as Fn (weight) increases, F incrases as well.

Example:
Assume u = 0.1
Fn = 100; F = 10
Fn = 100; F = 100

Understeer occurs when the front wheels lose grib. Meaning the applied force to the front wheels exceeds the Force of friction avaliable on the front wheels.

Drifting is sometime called Braking-Drift because when brake is applied (Not locked), a weight shift occurs. This will shift most of the weight to the front of the vechicle, causing the rear wheels to lose grib during cornering, thus inducing oversteer.

Well the above are just paper-talk. I don't know what really happend. But so far I still stick to the stuff I listed above.

 

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Discussion Starter #6
http://members.home.net/rck/phor/02-Tires-Stuck.html

The above link talks about how weight affects grip.

I just checked out some website regarding understeer and oversteer and they all say that putting more weight at the rear will reduce understeer.

Although I don't know the physic behind it, the following is what I have figured out.

More weight in the front means more momentum in the front, thus require a larger impulse to change its direction. Therefore a vehicle with weight distribution front >> rear will tend to understeer.

On the other hand, more weight in the rear means more momentum in the rear. Therefore a vehicle with weight distribution front << rear will tend to oversteer.

It would be great if someone could give me a full and detailed explaination on this issue =)


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Impact Yellow

[This message has been edited by Jumbo Robin (edited January 26, 2001).]
 

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(Not an expert, just $.02)
I think what everyone is talking around is Polar Moment. The force/equipment needed to overcome tendency of one end to rotate faster than the other. Weight contributes but so does suspension settings and tire size/compound.
I was able just this morning to drift quite nicely around a corner, and enduce over steer quite easily too (even without LSD).
 

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1> The IS300 is a bit heavy to be a good "drifting car".
2> The IS300 tires are too grippy to drift easily. You would want to put on harder, less grippy tires if drifting was your goal.
3> Please DO NOT attempt to "drift" on public roads. You could swing the rear end into an apposing lane of traffic or slide right off the road. It is a dangerous thing to do unless you are on a race track.
 

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Jumbo Robin: It goes like this. The more force (weight) that presses an axle to the ground, the more static and dynamic grip that axle will possess. However, that downward force (weight) will not vary between standing still, maintaining a set speed, or taking a turn at set speed. It's a constant in relation to any constant speed and turn radii. Centrifugal "force" of the mass that's responsible for the increase in overall grip however, does vary, and increases at a rate proportional to speed and turn radii that the effect immediately overcomes the increase in grip, causing understeer in the case of the IS300. BTW, the overall effect is completely dependent on the tire/surface friction characteristics. It is theoretically possible that a fantasy tire/surface can be so responsive to added weight that the increase in grip can overcome centrifugal "force" until it reaches an extremely high level.

So the increase in forward mass makes the IS300 an understeerer relative to the Altezza and 3-series. It does mean that it's harder to provoke oversteer, but that doesn't mean it's necessarily less of a drifting machine.

I have something to attend to right now, so I'll expound on that in a bit later today.

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Oversteer Behavior vs. Drifting Behavior

Why is it that in real racing, drifting is only regularly employed on dirt, snow, mud, sand, and surfaces generally categorized as lacking in conventional cornering grip? If drifting can supposedly find more cornering grip where there is very little, shouldn't it stand to reason that you can use it to extract even more cornering grip on good tarmac?

The answer to these questions lies in the behavior of tires. On dry tarmac, the behaviour of tires for the most part follows the static friction/kinetic friction model that all car enthusiasts/science students should be familiar with. The highest friction is only available when the tire surface is not moving relative to the tarmac (read: rolling). Any movement of the tire surface relative to the tarmac (read: spinning or sliding) follows the kinetic friction equation, which means 1) a lower maximum friction and 2) reduction from this maximum with greater relative movement (read: spinning the wheels faster will result in even less grip). This is the basis for the weight-shift/gas oversteer technique, and it also explains why it is necessary to modulate the throttle (read: decrease slowly) to keep the rear from coming all the way around. This is also why road racers generally grip instead of slide.

(FYI, the actual behavior of tires deviates slightly from the strict static friction/kinetic friction model. In many tires, maximum friction is achieved at around 10% of slippage.)

If the static friction/kinetic friction model applies, why do people drift? Spinning the tires only gives you less than what you can achieve gripping, right?

Well, that model doesn't apply on dirt, snow, mud and sand, since beyond the really low threshhold of static friction, there's an effective lubricant between the tire surface and the "road". The kinetic friction model for the most part goes out the window, and a fluid shear model takes over. With this model, the force that the tire surface can impart to the "road" and vice versa is proportional to the speed difference between the two. The faster the wheels spin, the more "grip" they give. Once you throw a car into a drift, you open the throttle to stabilize the car (compare that to the previous where you open the throttle to destabilize the car) and keep it sweeping through the corner. This is why there is an insatiable need for more horsepower in rally racing; unlike other racing where too much horsepower can reduce the driveability of the car, the more horsepower a rally car has, the higher the cornering potential.

The way to differentiate oversteer from true drifting is yaw angle. In an oversteer situation, it's almost impossible to approach large yaw angles without looping the car, and just as hard to sustain any yaw angle, making it unsuitable for anything but quick, tight corners. For anything but the loosest surfaces, true drifting is hard to sustain at small yaw angles. But once you get it completely sideways, it's easy to maintain the yaw angle with just steering corrections alone.

"Wait, I've seen modified Supras, that Veltex Altezza, and narrow-tired AE86's drift on dry tarmac..."

And they are drifting. On the effective lubricant (rubber dust and semi-liquid) that their tires produce as they are ground against the tarmac. This requires either massive power or relatively low-friction tires.

Wow, all this and I haven't even begun to talk about the Is300...

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Some stuff that might help to explain...maybe
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Oversteer is when the rear wheels are carving a larger arc than the front wheels or the intended line of the turn. Rear "slip angles" exceed those of the front tires. This is often described as a "loose" condition, as the car feels like it may swap ends, or be "twitchy."
This condition can be caused by "power oversteer", where you need to reduce power in order to bring the back end back into line.
Understeer is when the front wheels are carving a larger arc than the rear wheels. This is often described as "push" or "pushing" - as the front end feels like it is plowing off of a corner.

Further acceleration only compounds the push, as weight shifts back to the rear drive wheels off of the front turning wheels, leading to a further lessening of the car's ability to turn in.

Understeer can be remedied by slight modulation in throttle to transfer weight forward to the front wheels, aiding their traction and ability to carve the turn.

Many cars are designed to have a tendency to understeer. If the driver gets uncomfortable and "lifts" off the gas, that will cause the front end to tighten the curve - a relatively safer, and more predictable condition.
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UNDERSTEER
In a constant radius turn, when the slip angle of the front tires is greater than the slip angle of the rear tires the car will understeer as speed increases. A race car driver will say the car 'has a push' or 'is tight'. (Most production cars are designed with mild understeer, the rationale being that street cars driven by distracted drivers will move away from on-coming traffic to the outside of the road.)

From behind the wheel, a driver senses understeer when the car is running wider than steering input, and increasing the steering angle does not make the front end turn in. This means the front tires need more download to generate more grip. To transfer weight to the front means giving up the acceleration you just worked so hard to achieve. Reduced cornering speed means reduced corner exit speed, and a loss of rpm's all the way down the next straight, or driving off the road!!!

Determine the problem. Test for understeer
Tape the top of the steering wheel when the wheels are pointing straight. Note how much steering angle is used through a given corner at a moderate speed. If there is more steering input with increased speed, the car is pushing. Determine if what seems like exit oversteer is really the car's reaction to too much steering input through the corner because of tight entry.

OVERSTEER
In a constant radius turn, when the slip angle at the rear tires is greater than the slip angle of the front tires the car will oversteer as speed increases. A race car driver will say the car 'is loose'.

From the drivers seat, when you recognize that the front of the car is turned too far into the apex, you are sensing that the car is going into oversteer. Your first reaction should be to dial in opposite lock, steering into the direction that the rear is moving. Then settle the rear by adding a little throttle. When you lift off the throttle, weight shifts from the rear to the front, reducing rear tire adhesion. This is commonly known as 'trailing throttle oversteer'. With just a slight lift, the driver can help the car rotate into a smooth transition to oversteer; with too abrupt a lift the car will snap into a spin.

DRIVER INFLUENCES
The driver influences tire loading by throttle application. Adding throttle transfers load on to the rear, giving additional grip for acceleration, but reducing grip for cornering. With a gradual application of throttle understeer will result. Remember smoothness. Too abrupt on the throttle will throw the car into oversteer.

THE CAR
What we are looking for in car set-up is balance. If you are doing a lot of steering, something is wrong. Start soft - soft tire pressures, soft springs, soft shock - so you
 

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Discussion Starter #14
Thx for the information guys. Especially HIBBoyScott ^-^

I am just a beginner in mechanics so I don't know the physics behind all these stuff. I am looking forward to learn more on this board =)



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HIBBoyScott-

Whew! That was well written! I'd like to use your piece in my upcoming contributing writers section of www.shinkairacing.com. Let me know if I have your permission.

For all of you that aspire to drift- go karting.
It's a lot of fun and you learn to use throttle and brake while learning to drift. It also saves wear and tear on your car and is a lot cheaper/safer.

Dale
Shin-Kai Racing, Owner www.shinkairacing.com
[email protected]
bus/fax: 360-679-1968
 
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