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Old 05-09-2017, 05:47 PM   #16
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My simplest explanation- a non spooled front end on a tc has too much steering and can start hooking. With a spool the front end can be driving harder in and out of the turn.
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Old 05-10-2017, 02:11 AM   #17
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Diff's allow a greater difference in rotation between the two sides of the car. The issue is that comparing full scale cars with ours isn't so easy. The rules of physics don't scale.

If you remove the front belt/shaft on a 4WD car and drive it the car will pull pretty hard in a straight line, but as soon as you start to corner etc using power the inside rear wheel will start to 'diff out' etc.
A spool will cause both sides at the front to pull equally, so even if traction is reduced on one side, it isn't given the opportunity to diff out and waste power.
I've always found a spool to make the car more stable. This is at the slight expense of initial steering into the corner, but typically the extra traction out of the corner more than makes up for it.
This is based on medium grip etc. I notice that in much higher grip carpet etc sometimes team drivers will run a diff, but with something around 2.5million cSt.

You'll notice that if you run too much droop with a spool it is harder to turn as you haven't biased the grip enough to the outside wheel. As you reduce the droop, you reduce grip on the inside wheel more, transferring more to the outside.

Rear oil has always seemed a little harder to understand to me, thicker rear all giving more on power steering whilst reducing turn in, thinner oil doing the opposite.

P.S. Negative ackerman is called anti Ackermann
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Old 05-10-2017, 06:00 AM   #18
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Diff's allow a greater difference in rotation between the two sides of the car. The issue is that comparing full scale cars with ours isn't so easy. The rules of physics don't scale.

If you remove the front belt/shaft on a 4WD car and drive it the car will pull pretty hard in a straight line, but as soon as you start to corner etc using power the inside rear wheel will start to 'diff out' etc.
A spool will cause both sides at the front to pull equally, so even if traction is reduced on one side, it isn't given the opportunity to diff out and waste power.
I've always found a spool to make the car more stable. This is at the slight expense of initial steering into the corner, but typically the extra traction out of the corner more than makes up for it.
This is based on medium grip etc. I notice that in much higher grip carpet etc sometimes team drivers will run a diff, but with something around 2.5million cSt.

You'll notice that if you run too much droop with a spool it is harder to turn as you haven't biased the grip enough to the outside wheel. As you reduce the droop, you reduce grip on the inside wheel more, transferring more to the outside.

Rear oil has always seemed a little harder to understand to me, thicker rear all giving more on power steering whilst reducing turn in, thinner oil doing the opposite.

P.S. Negative ackerman is called anti Ackermann
Interesting information about the droop, something I did not think about but it makes total sense.

"P.S. Negative ackerman is called anti Ackermann"....maybe for you Brits.....LOL.

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Old 05-10-2017, 06:47 AM   #19
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"P.S. Negative ackerman is called anti Ackermann"
I read it described as such in engineering papers, and it was how it was described by the Engineers that I talked to at the 24hrs of Daytona. So that's how I used it.
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Old 05-10-2017, 06:58 AM   #20
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I read it described as such in engineering papers, and it was how it was described by the Engineers that I talked to at the 24hrs of Daytona. So that's how I used it.
Were they Brits?



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Old 05-10-2017, 08:06 AM   #21
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One was British and one was Japanese. They called it Negative Ackermann for in theory it's still Ackerman, it just accounts for the vertical loads on the tires. The numbers they put on the fancy Digital Sheet up sheets they had were just Negative numbers. Maybe I misunderstood for I am an electrical Engineer not a Race Car Chassis (Mechanical) Engineer.
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Old 05-10-2017, 03:13 PM   #22
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Originally Posted by LJH View Post
Interesting information about the droop, something I did not think about but it makes total sense.

"P.S. Negative ackerman is called anti Ackermann"....maybe for you Brits.....LOL.

Cheers,
Jim
I just want to say that a lot of what he said makes sense but some of it I'm not too convinced of. I do agree that too much droop in the front causes your car to push on acceleration. However the reasoning given doesn't make sense to me. The idea that droop would reduce traction on the outside wheel during a turn while on power because you "haven't biased the grip enough to the outside wheel", simply doesn't compute for me. Droop allows weight to be transferred. During a turn, more droop on the inside of the car would cause more weight to be distributed to the outside of the car creating more traction on the outside. But more importantly (and the primary contributor to the push), having droop in the front increases the amount of weight being transferred to the back of the car, meaning significantly less traction in the front. In other words, the reason that you have push is not because the grip hasn't been biased to the outside... it's because the grip hasn't been biased to the front of the car.
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Old 05-10-2017, 04:08 PM   #23
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I just want to say that a lot of what he said makes sense but some of it I'm not too convinced of. I do agree that too much droop in the front causes your car to push on acceleration. However the reasoning given doesn't make sense to me. The idea that droop would reduce traction on the outside wheel during a turn while on power because you "haven't biased the grip enough to the outside wheel", simply doesn't compute for me. Droop allows weight to be transferred. During a turn, more droop on the inside of the car would cause more weight to be distributed to the outside of the car creating more traction on the outside. But more importantly (and the primary contributor to the push), having droop in the front increases the amount of weight being transferred to the back of the car, meaning significantly less traction in the front. In other words, the reason that you have push is not because the grip hasn't been biased to the outside... it's because the grip hasn't been biased to the front of the car.
I think you're exactly right about the droop.
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Old 05-10-2017, 04:49 PM   #24
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I just want to say that a lot of what he said makes sense but some of it I'm not too convinced of. I do agree that too much droop in the front causes your car to push on acceleration. However the reasoning given doesn't make sense to me. The idea that droop would reduce traction on the outside wheel during a turn while on power because you "haven't biased the grip enough to the outside wheel", simply doesn't compute for me. Droop allows weight to be transferred. During a turn, more droop on the inside of the car would cause more weight to be distributed to the outside of the car creating more traction on the outside. But more importantly (and the primary contributor to the push), having droop in the front increases the amount of weight being transferred to the back of the car, meaning significantly less traction in the front. In other words, the reason that you have push is not because the grip hasn't been biased to the outside... it's because the grip hasn't been biased to the front of the car.
I think more droop allows the front inside wheel to be on the ground which in turn makes understeer with a spool(think like a go—kart).

Have you ever driven a go—kart really slow? It is very hard to turn, because all four wheels are on the ground and there is no diff—out happening.
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Old 05-10-2017, 07:56 PM   #25
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I think more droop allows the front inside wheel to be on the ground which in turn makes understeer with a spool(think like a go—kart).

Have you ever driven a go—kart really slow? It is very hard to turn, because all four wheels are on the ground and there is no diff—out happening.
Sorry man but I am pretty sure you are wrong. Read some set up books. They all explain this situation.
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Old 05-10-2017, 10:34 PM   #26
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Sorry man but I am pretty sure you are wrong. Read some set up books. They all explain this situation.
I think I see it. If the inside front droop screw is touching the chassis under max lateral roll, it takes some weight off the inside front wheel reducing its grip and the understeer caused by the spool.
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Old 05-11-2017, 04:16 AM   #27
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If you go further, say 7 front and 6 rear with the droop, then corner hard (particularly faster flowing corners, you'll actually see the inside front lift during the corner.

Though I agree exactly about weight transfer when on brakes or on power, but I'm talking about mid corner.
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Old 05-11-2017, 06:16 AM   #28
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I think I see it. If the inside front droop screw is touching the chassis under max lateral roll, it takes some weight off the inside front wheel reducing its grip and the understeer caused by the spool.
This is how I was envisioning it, at least for the exit of the turn when applying power. The inside front wheel is un-weighted causing most/all the power to be transmitted to the ground through the outside wheel. Being that the outside wheel is the driving force and the drive is asymmetric the car is pulled by the outside wheel which introduces a bit of yaw and helps turning. I have to put more thought into what happens on entry and mid turn.

Something else I was wondering about, do AWD touring cars suffer from torque steer? If they do I would think it would be pretty minimal because the half shafts are equal length. Why I ask is that back when I was racing one of my best friends campaigned a MK1 GTI in DSP (D Street Prepaired). We installed a Quaife differential (limited slip). Even in this low power application it was a huge help in putting the power to the ground but boy you had to hang onto the wheel as each tire grabbed for traction....the first time I drove that car with the Quaife it was a bit scary as the wheel tried to go every which way depending on what tire had more traction.

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Old 05-11-2017, 04:30 PM   #29
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I think I see it. If the inside front droop screw is touching the chassis under max lateral roll, it takes some weight off the inside front wheel reducing its grip and the understeer caused by the spool.
First things first, a lot of people get confused between downstop and droop. Think of them as opposites. If you want more droop, you have to reduce your downstop. If you want less droop you have to increase your downstop. Virtually every droop guage actually measures downstop.

That being said...

Even in the case where the screw is not touching the chassis, the weight is still distributed to the outside. In fact, the farther the inside arm and the rear arms can lay down, the more weight can be transferred to the front outside tire. Try this exercise:

Sit down on the edge of your couch or a chair. Put both feet down and apply equal pressure to both sides. The amount of effort you have to use to move both feet is equal. Now apply more pressure to the left foot than the right foot but still leave both feet on the ground. Now try to move your left foot. Compare that to how easy it is to move your right foot. The amount of pressure exerted on each foot determines the grip your feet have on the ground.

In this analogy, think of droop as the ability to raise your inside foot up, transferring even more weight to the outside foot. The greater your droop, the higher you can raise your inside foot. Except in a car, less downstop (more droop) allows the arm to lay flatter, allowing the chassis to roll, transferring more weight.
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Old 05-11-2017, 06:45 PM   #30
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Sorry man but I am pretty sure you are wrong. Read some set up books. They all explain this situation.
The problem is the set up guides are very general and often not written to specific situations. For example with a spool more droop = understeer due to the inside wheel not diffing out — like a go—kart going slow. However with a ball diff more droop = more grip at that end due to more tyre contact. Its not really a one size fits all situation. Also people get this idea that less droop means less roll. Look closely and you will often see wheels in the air due to little droop, but the car still rolls. If you want less roll then raise your roll centre or change springs/anti roll bars.

The other factor that goes against this theory, is the suspension that becomes maxed out due lack of droop goes from being sprung weight, to being unsprung. This would affect the balance somewhat.

Lastly, you will only see changes in handling when the droop limit is reached. For example if all four wheels never leave the ground, then it makes no difference what your droop setting is.

Last edited by ixlr8nz; 05-11-2017 at 07:02 PM.
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