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Old 06-03-2011, 07:18 PM   #1
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Default Can someone explain anti-squat a bit to me

Can someone explain anti-squat to me and how it is applied. My understanding was it angled the rear hinge pin up in the front and caused the car to transfer less weight to the rear on acceleration and also transfer more weight to the front on deceleration. I assumed this would give LESS on power rear traction as it cannot squat as much and also MORE off power steering as the weight transfer forward more. Apparently this thinking is wrong, can someone explain WHY it is wrong?

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Old 06-03-2011, 08:15 PM   #2
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The amount of suspension rear anti-squat changes the amount of load going through the springs and it also affects the front-to-rear pitch of the buggy. Anti-squat reduces the bump travel during forward acceleration. Anti-squat can only be developed during acceleration. If your buggy is only maintaining a constant speed, there will be no anti-squat. However, a good racer will always maintain the highest amount of acceleration and g-forces possible at all times, whether the g-forces are highest from front-to-rear or side-to-side.

Engine torque reactions change the rear ride height if there is anti-squat. If the buggy is accelerating forward, the rear ride height is raised, and if the buggy is braking, vice/versa.

Raising the rear ride height because of anti-squat on acceleration promotes rearward weight transfer. The wheels will actually push into the ground on acceleration. This can be beneficial under straight line acceleration.

The effect of anti-squat on steady sweeping cornering can be detrimental on rough tracks because of the reduction in bump-travel.
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Old 06-03-2011, 09:16 PM   #3
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mattnin is mostly correct. I thought I would just add that anti-squat helps add lift in jumps aiding take-off. Also, anti-squat is directly proportional to the traction available. The more traction you have, the less anti-squat necessary to get the same lift effect. Less anti-squat gives more rear traction because the chassis dips in the rear more and allows more weight transfer. Because of motor placement and rotation, rear motor vehicles require more anti-squat than mid-motor vehicles. Off-road requires more than on-road...

Anyway, you get the idea. Oh, and anti-squat can reduce side bite.
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Old 06-04-2011, 06:45 AM   #4
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Quote:
Originally Posted by Banshee8530 View Post
mattnin is mostly correct. I thought I would just add that anti-squat helps add lift in jumps aiding take-off. Also, anti-squat is directly proportional to the traction available. The more traction you have, the less anti-squat necessary to get the same lift effect. Less anti-squat gives more rear traction because the chassis dips in the rear more and allows more weight transfer. Because of motor placement and rotation, rear motor vehicles require more anti-squat than mid-motor vehicles. Off-road requires more than on-road...

Anyway, you get the idea. Oh, and anti-squat can reduce side bite.

HMMMM i thought that less anti-squat creates less rear traction due to the weight transfer??? if your weight transfers to the rear you may get an initial traction gain but as soon as the springs return, traction goes away. with more anti squat the "transfer" digs the rear tires into the ground allowing more traction. you said exactly opposite of what Matt says. it has been my experience that more anti squat yields more rear traction. coming from 1:1
drag racing i took me a while to get a grasp on the concept!
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Old 06-04-2011, 08:42 AM   #5
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per Charlie Perez a AE factory driver, you can read more on

http://www.rc10b4.com/forum/showthread.php?t=32

===

Zero degrees of antisquat "Frees Up" the rear end On Power and it also gives you a little more side bite. I like to start with the minimum amount of Antisquat because it gives the rear end the most balanced amount of traction as you enter and exit the corner. It also minimizes wheelies, which are cool to watch, but waste time. The only time that I increase the Antisquat is if I am on a smooth surface track that has limited traction. If I am on a ruff track I always run 0 as it makes it easier for the suspension to soak up the bumps and ruts.

The amount of Antisquat you use depends on the track conditions. If the track is very smooth, more antisquat will give you more forward traction. If the track is bumpy or rutty more antisquat will give you less forward traction
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Old 06-04-2011, 11:17 AM   #6
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On a 1:1 car the weight of the vehicle is a huge advantage in generating leverage for more traction on a very abrasive surface. Also, a 1:1 car usually runs a solid rear axle with a three or four link rear suspension. The forward linkage points generate the "anti-squat" effect and allow you to control how close to the CG you acquire leverage. On an RC car, you have an independent rear suspension and the power to weight is completely different. There is a very limited amount of weight to generate grip which is easily overpowered by an aggressive anti-squat setting, and the force generated is at the hubs, not the chassis. You want to find that sweet spot that makes the car try to wheelie but not quite, which usually isn't possible except on carpet. Go too far and you jack too quickly and simply unweight the rear. Don't go far enough and you are sacrificing forward bite. Track conditions dictate your setting, and not just bite. The roughness and frequency of jumps all play a part. Anti-squat is trying to lift the rear of your car by extending the rear suspension, it's up to you to decide how much is enough.

Quote from AE RC Cheat Sheets:

less anti-squat:
• more side traction in corners
• more rear traction for slick or bumpy
surfaces
more anti-squat:
• less side traction in corners
• more rear lift in jumps


The limiting factor is the traction available which is directly proportional to the net downward force at the rear of the car. You have to find a balance between the anti-squat and the available traction to avoid rear jacking. If traction goes up, so does the force generated by your anti-squat setting. If it goes high enough you simply lift the rear-end and lose all benefit.

Last edited by Banshee8530; 06-04-2011 at 11:55 AM.
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Old 06-04-2011, 01:53 PM   #7
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Weight transfer or load transfer is a function of only three things, the wheelbase, the CG height, and the braking or forward acceleration force.

So, because anti-squat raises the rear ride height on acceleration and thus raising the CG height, load transfer to the rear wheels is increased with anti-squat.

However, load transfer doesn't always mean an increase in traction at the tire patch especially if there is a reduction in bump travel on a rough road.

Traction force is based on the tires slip at the patch, and there is a max amount of slip which if exceeded will cause a reduction in traction force. Excessive wheel loading past the peak tire slip ratio will effect a spinout and a loss of traction.
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Old 06-04-2011, 07:49 PM   #8
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Quote:
Originally Posted by mattnin View Post
Weight transfer or load transfer is a function of only three things, the wheelbase, the CG height, and the braking or forward acceleration force.

So, because anti-squat raises the rear ride height on acceleration and thus raising the CG height, load transfer to the rear wheels is increased with anti-squat.
Allow me to respectfully disagree. The purpose of the suspension is to control weight transfer. That is why we have so many spring and oil choices. Every adjustment on an RC car is to make the weight transfer in a way that is optimum for best performance.

Everything you said in your earlier post was correct except this statement:

"Raising the rear ride height because of anti-squat on acceleration promotes rearward weight transfer"


Not trying to pick a fight, just pointing out the error in your thinking. Raising the rear ride height effectively transfers weight from the rear axle to the front axle. Anytime you use anti-squat you are limiting the amount of weight transferred rearward through the springs thus improving on power steering. Anti-squat promotes weight transfer through the hinge pins instead of the springs. Associated electronics Cheat Sheets support what I'm saying. So does tmail55. There is some initial traction to be gained with anti-squat, but it can easily upset your set-up if there is enough traction present or you have too much A.S. It does this by resisting compression of the rear suspension on rough tracks. Sure, it does push down on the track, but that downward push turns into jacking if the A.S. Force exceeds the net downward force of the chassis, and it always pushes up on the chassis as hard as it pushes down on the tires. See Newton's Laws. This is the balance I was talking about. If you have so much anti-squat that your car's chassis is lifting above normal ride height, you are transferring unnecessary weight to the front and losing rear grip.

The force generated by a 3-degree anti-squat setting is less that 5% of the total forward driving force generated on acceleration. Thus when traction is low, the benefit of anti-squat is only 5% of a very low number and quite limited. The weight transfer from the chassis squatting is far more beneficial in this instance. This is supported by AE's statement:

less anti-squat:
• more side traction in corners
• more rear traction for slick or bumpy surfaces


To simplify my answer, and to more correctly address your question, TT; yes, anti-squat is the angle of the rear inner hinge pins. This is always used to describe an angle upward toward the front of the car. It is used to generate lift on jumps and improve on-power steering out of the turn. You can have too little and too much. Too little would mean no steering out of corners(pushing). Too much would result in loose rear-end late out of corners and poor performance on rough acceleration zones.

Last edited by Banshee8530; 06-04-2011 at 08:48 PM.
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Old 06-04-2011, 09:29 PM   #9
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For the layman, we are getting into an area of abstract concept. The reality of how the buggy feels for you could be much different than what I, or anyone here is trying to explain. That being said, I will explain wheel loads further...

Raising the rear ride height in a steady-state situation, meaning when the buggy is not moving, will shift the weight forward to the front wheels like Banshee said. However, we must consider everything, especially acceleration.

Longitudinal weight transfer (weight transfer front-to-rear) is a result of Newtons law, F=M(mass) x A (acceleration), F=MA. Because we are dealing with a center of gravity, we must take a fraction of the mass into the equation using h (height) and l (wheelbase). The equation then becomes F = (h/l)M x A

First, the weight of the vehicle must be determined. This value becomes M.

Second, the height of the CG must be determined. This value becomes h, however in this particular case, the CG height is dynamic (changing), therefore that must be considered. We do know that the CG height will increase with antisquat.

Third, the acceleration value must be determined.

By looking at this equation, we can see that an increase in CG height will increase wheel loading in the rear axle because of the multiplier h/l (CG height divided by wheelbase).

Anti-squat increases the vehicles CG height, therefore, there is increased wheel loading on the rear tire patch compared to a vehicle with a lower CG height and the same acceleration.
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Old 06-04-2011, 09:55 PM   #10
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I follow you Matt, except that I believe an IRS system does not have a dynamic CG due to the fact that the chassis is doing the loading and not linkages on a sprung axle. Am I correct in this?
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Old 06-04-2011, 10:00 PM   #11
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Sorry, just answered my own question... the axle output still moves in relation to the CG.
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Old 06-06-2011, 05:32 PM   #12
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Here is a great link to one of the best free RC tuning articles ever written

http://users.telenet.be/elvo/
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Old 06-08-2011, 06:58 AM   #13
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wow, thanks guys..

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