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Advanced Suspension Geometry and Design

Posted by Cosworth 
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Re: Advanced Suspension Geometry and Design
February 04, 2014 04:21PM
Quote
aj_johnson
No in bed on pain pills was pointing out the obvious just hoping to prevent what has been interesting reading, however unusable in application, from being something I don't want to read anymore....

Like an argument.

Here is how left foot braking works: it's a bandaid for something the car does or doesn't do the way you want it too.

Well now, using that point of view, we could argue that the accellerator is a bandaid too since the car isn't going fast enough sometimes. I think, used properly, the brake and the accellerator is as important as the steering wheel in getting around a corner.

But please, let's keep this thread going - it's technically fascinating.



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Re: Advanced Suspension Geometry and Design
February 04, 2014 04:59PM
As far as the rear suspension goes, my gut feeling is that it's not as critical. If the front are gripping, it will clamp the rears down. In a corner, the rears are mostly there to follow the fronts, and when braking, hell those suspensions do the opposite of what you'd expect if you wanted to make grip back there.



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Re: Advanced Suspension Geometry and Design
February 04, 2014 05:23PM
pets



Edited 1 time(s). Last edit at 02/05/2014 08:28AM by Iowa999.
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Re: Advanced Suspension Geometry and Design
February 04, 2014 05:41PM
In oval track cars the #1 thing every team adjust to help the car turn is done in the rear of the car. I say this meaning quick adjustments to dile in a ill handling car. I know you dont all watch Nascar but for you closet guys you always see teams on pit road doing 90% of there work in the rear of the car.

It may just follow? If that were the case then they wouldnt adjust and turn bolts or raise lower the panhard bar in EVERY single pit stop. It maybe #2?Air pressure is probably #1 adjustment.

The point is at least the rear roll center of the car is crucial on making a car do what the driver wants. Getting the front and the rear to work together would be the ultimate goal.

I think this maybe why the gc,gd work well. The strut tops are close to the same hieght. Where as the 08 up the rear spring susp mounts are at least a foot lower. This is so you can get your lugage in the trunk with out those pesky strut towers.



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Re: Advanced Suspension Geometry and Design
February 04, 2014 05:43PM
How do you get prodive in the lca and anti dive in the front strut geometry. Is this the reasoning for the strut mounting in front of the axle?



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Re: Advanced Suspension Geometry and Design
February 04, 2014 05:50PM
or



Edited 2 time(s). Last edit at 02/05/2014 08:28AM by Iowa999.
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Re: Advanced Suspension Geometry and Design
February 04, 2014 06:07PM
Hmm seems plosible. I just thought it was to have more travel in a tiny hole. I figure it still mounts at the ball joint. Didnt think how it got there made any differance. The rotational force makes sense . Smart guys those wrc engineers are!



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Re: Advanced Suspension Geometry and Design
February 04, 2014 07:42PM
Quote
Iowa999
Quote
Reamer
How do you get prodive in the lca and anti dive in the front strut geometry. Is this the reasoning for the strut mounting in front of the axle?

This is what I meant when I said that the two should be thought of separately, because I believe that you can have both.

You get pro-dive (and more compliance) in the lower LCAs by having the rear inboard pivot lower than the front. Thus, when the wheels are push back (by braking), they also push the LCA up.

You get anti-dive in the shock by using the rotational force (aka torque) on the hub end up trying to extend the shock, pushing the hub and wheel down. This is what is greatly increased (maybe even dependent on; I'm not sure) having the axis of the shock pass in front of the front axle. That way, when the hub tries to rotate forward (at the top), it pulls the shock out. edit: i.e., the answer to your question is "yes"

you can't have prodive and antidive on the same wheel. % anti/pro dive is based on the SVSA. the attaced image (not mine, found on google but good example) is for a double a-arm suspension.
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Re: Advanced Suspension Geometry and Design
February 04, 2014 07:50PM
Quote
Reamer
Hmm seems plosible. I just thought it was to have more travel in a tiny hole.

Why not both?



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Re: Advanced Suspension Geometry and Design
February 04, 2014 07:54PM
Quote
samcaron

you can't have prodive and antidive on the same wheel. % anti/pro dive is based on the SVSA. the attaced image (not mine, found on google but good example) is for a double a-arm suspension.

Sure you can, if you are feeding brake loads and thrust loads in separately. Wheel thrust only really feeds into the control arm and brake torque works on the upright as well.

If it were RWD solid axle, it'd be like putting the brake caliper on a pivot with its own instant center, so you can get any amount of acceleration anti-squat you want without compromising traction under braking.



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Re: Advanced Suspension Geometry and Design
February 04, 2014 08:11PM
Quote
samcaron
Quote
Iowa999
Quote
Reamer
How do you get prodive in the lca and anti dive in the front strut geometry. Is this the reasoning for the strut mounting in front of the axle?

This is what I meant when I said that the two should be thought of separately, because I believe that you can have both.

You get pro-dive (and more compliance) in the lower LCAs by having the rear inboard pivot lower than the front. Thus, when the wheels are push back (by braking), they also push the LCA up.

You get anti-dive in the shock by using the rotational force (aka torque) on the hub end up trying to extend the shock, pushing the hub and wheel down. This is what is greatly increased (maybe even dependent on; I'm not sure) having the axis of the shock pass in front of the front axle. That way, when the hub tries to rotate forward (at the top), it pulls the shock out. edit: i.e., the answer to your question is "yes"

you can't have prodive and antidive on the same wheel. % anti/pro dive is based on the SVSA. the attaced image (not mine, found on google but good example) is for a double a-arm suspension.


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Cosworth
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Re: Advanced Suspension Geometry and Design
February 04, 2014 08:47PM
Quote
Reamer
I believe what happens is it binds up the susp in rough situations. Compresses the softer spring then stays bound up while braking, eliminating travel to soak up the bumps. As soon as the tire skips a bump you loose all grip. If the road were smooth the wieght would stay planted until the surface lost grip and then you would skid the tires.

With no anti dive I believe the tire would soak up the bumps stay in contact with the road and you could still be hard on brakes with out locking them up. At least until the surface lost grip.

On Ice you would have almost no wieght transfer do to no grip so you would constantly be locking your tires.
Exactly, thanks for splaining it in better English than what I did.
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Cosworth
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Re: Advanced Suspension Geometry and Design
February 04, 2014 08:54PM
Quote
Iowa999
I agree that a lot of these things are less than useful because you can't use the information, even if you wanted to, but this is an example of something that wouldn't be too hard to try, which is why I dragged it in. For example, instead of placing the two ears on the bottom end of the shock in symmetrical locations, move both a bit towards the rear of the car, shifting the axis of the shock to be in front of the axle, to increase the leverage from LFBing. You couldn't move it much, because, without making a new knuckle from scratch (or fabbing a new lower LCA), you'd end up moving the wheel back, but even a little bit has a huge effect on leverage. This is something that I really want to try.
Quote
Iowa999
OK, I'll bite.

The reason is that the torque-based part of anti-dive is directly related to the value of LFBing. Assume a balanced use of throttle and brake such that the front wheels are providing neither acceleration or braking. The geometry of the lower LCA is, therefore, doing, nothing, but there's a lot of torque on the hub. With the correct shock geometry, the front wheels are pressed into the ground, providing grip.

At least, that's my current understanding (which is quite different from the weight-transfer story that one gets from trail-braking on pavement). Thus, any discussion of messing with the geometry of front struts cannot be divorced from a discussion of LFBing. In fact, the slight disagreements that you see in this thread about whether you want more or less anti-dive could very well be explained by differences between drivers in the use of LFBing vs, for example, the hand-brake.
Quote
Iowa999
I much prefer to think about the two sources of anti-dive separately. There is that which comes from the fore-aft force on the hub, and there is that which comes from the rotational force (i.e., torque) on the hub. The second requires the brakes, but the former does not. Anti-dive from fore-aft force and the angle of the lower LCA occurs whenever the tires are slowing the car.

(If we can somehow morph this into a discussion of how left-foot braking really works, I'd be very happy.)
I think John is right, you need to start your own thread. You're going off way to far off topic and you're doing nothing but pondering and theorizing about things that don't even make sense, and on top of that you're begging to confuse what these features are for and in what axle they belong. Please stop this and lets keep this relevant to GEOMETRY AND DESIGN.
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Re: Advanced Suspension Geometry and Design
February 04, 2014 09:01PM
boyfriend



Edited 2 time(s). Last edit at 02/05/2014 08:28AM by Iowa999.
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Cosworth
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Re: Advanced Suspension Geometry and Design
February 04, 2014 09:09PM
Quote
Reamer
In oval track cars the #1 thing every team adjust to help the car turn is done in the rear of the car. I say this meaning quick adjustments to dile in a ill handling car. I know you dont all watch Nascar but for you closet guys you always see teams on pit road doing 90% of there work in the rear of the car.

It may just follow? If that were the case then they wouldnt adjust and turn bolts or raise lower the panhard bar in EVERY single pit stop. It maybe #2?Air pressure is probably #1 adjustment.

The point is at least the rear roll center of the car is crucial on making a car do what the driver wants. Getting the front and the rear to work together would be the ultimate goal.

I think this maybe why the gc,gd work well. The strut tops are close to the same hieght. Where as the 08 up the rear spring susp mounts are at least a foot lower. This is so you can get your lugage in the trunk with out those pesky strut towers.
OK the NASCAR rear adjustments are made because its the quickest they can make. Its something that can alter the fore/aft balance of the car and its easier than changing anything in the front suspension close to the flaming headers and brakes. One of my best friends, Joey Knuckles a multiple Daytona 500 winner as a crew chief back with Davie Allison has mentioned numerous times that the rear is only there to drive the car and keep the gas tank off the ground. They have gone as far and running rear coil bound and with 0 rebound shocks. And funny enough running on the bump stops in the front. NASCAR has loads more tech than people think. BUT its not relevant to rally suspensions. So back to talking about what can make a FWD or RWD car put the power down better.

Some percentage of Anti Lift and 0 anti dive seems to be what engineers are aiming for in the FWD cars.
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