IC, antsiquat %, and axle torque / vrs chassis seperation

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3pedals
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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by 3pedals » Sun Feb 28, 2016 5:20 pm

Ok. The Math is where I get lost.
I will try work through it. Thanks for your input

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by 3pedals » Sun Feb 28, 2016 7:01 pm

I cannot grasp where the force comes from to equal and oppose the vertical force at the IC?

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by peejay » Sun Feb 28, 2016 7:43 pm

That would be the weight of the car. Which doesn't need to be part of the math, because the weight of the car is also on the other side of the equation.

Look it it real simple, no math, just changing things around with a drawing. Take a ladder bar suspension because it's easy to work with (roll center is fixed and defined) and everything is known. When you draw out the antisquat, you run a line through the rear contact patch and the roll center and see where it crosses the front axle. If it's lower than the car's center of gravity, you have less than 100% anti squat, if it's higher than the car's center of gravity you have over 100% anti squat.

If you raise the car's center of gravity, anti squat goes less. You will know this is true because a top heavy car will lean back more on acceleration.

If you make the ladder bars shorter, the angle of your drawn line goes steeper and meets the front axle higher up, so antisquat is higher. This also makes sense.

Now what happens if you increase the torque on the axle. The axle will want to twist more under the car pushing it up, BUT the car is also going to accelerate harder which is going to push the car back down. (If it wasn't accelerating harder, it wouldn't have more torque at the axle, that torque is where acceleration is coming from) Whether or not the back end rises or falls will depend on if you have more or less than 100% antisquat, not how much torque is at the drive wheels.

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by 3pedals » Sun Feb 28, 2016 8:12 pm

How does an increase in acceleration push down more on the car?
I thaught gravity was the only force acting downwards on the car?
I appreciate your input, don't think I'm being argumentative, I truly want to understand what's going on
Last edited by 3pedals on Sun Feb 28, 2016 8:14 pm, edited 1 time in total.

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by Brian P » Sun Feb 28, 2016 8:12 pm

In the simple ladder-bar case, the weight of the car acts down and there are three things acting up in balance: the upward force at the ladder-bar attachment point, the upward force at the rear springs, and the upward force at the front springs.

These three things will re-distribute themselves as you vary the applied torque at the rear axle - depending upon, among other things, the amount of antisquat in the geometry.

Acceleration will reach a limiting case when the upward force at the front springs reaches zero: a wheelie.

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by 3pedals » Sun Feb 28, 2016 8:17 pm

Ok. So you are basically saying that if the IC is at the neutral line and an increase in tq happens, the added tq input to the chassis, will lift the front of the car instead of causing rear suspension separation?

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by Brian P » Sun Feb 28, 2016 9:51 pm

The front of the car is going to be unloaded no matter what the rear does. Since the vertical forces on the car as a whole must balance, whatever weight comes off the front tire contact patches goes onto the rear tire contact patches. The only thing antisquat changes is how much of that weight transfer goes through the suspension linkage (via antisquat geometry) or through the springs.

Bear in mind that the springs introduce the concept of "time" into all this. It takes time for springs to extend or collapse and that is associated with a mass moving up or down. There is acceleration vertically as well as horizontally here.

If you have no antisquat geometry at all then all of the weight transfer has to happen via the suspension springs ... which take a moment to react and in that moment, if you are doing a hard launch from a stop, your wheels are spinning.

If you have 100% antisquat then the rear springs stay with exactly the same load on them, which means they don't have to collapse to transfer the load, which means the moment the torque is applied to the axle the linkage plants the additional force down on the tires.

In my motorcycle roadracing world, it's done for a different reason - preserving grip and controlling wheelspin when accelerating out of a corner - but the physics of antisquat are the same.

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by Brian P » Sun Feb 28, 2016 10:02 pm

I should add that if you have MORE than 100% antisquat, then the whole body of the car will lift up during acceleration. This might be what you are calling "separation".

The front is going up because the inherent rearward weight transfer is unloading the front suspension and the springs are making it extend.

Since the forces (and accelerations ...) must balance, that weight is transferred to the rear.

With more than 100% antisquat, the force applied upward by the suspension linkage is MORE than the amount of weight transfer and this REDUCES the amount of force that the springs have to transmit ... which causes the springs to extend and raise up the rear of the car.

And now the concept of "time" and "acceleration" raises its ugly head. For a moment, this more-than-its-share amount of antisquat forces plants the tires harder into the ground and all is well. Then, as the springs extend, the car body accelerates upward. The problem is that it can't do so forever. A moment later, after the springs have extended, the car body STOPS accelerating upward ... which UNloads the tires (Force = mass x acceleration and that acceleration is now a negative number) and THEN they start spinning.

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Re: IC, antsiquat %, and axle torque / vrs chassis seperatio

Post by 3pedals » Sun Feb 28, 2016 10:05 pm

Thank you for all the insight. It is starting to make sense.

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