The 'Tools", What do they do?

[Hoop-98]

I thought this gap in the schedule, might be good for a tech topic.

So, I thought I would start with one of the most common driver "tools" and what it does.

The Tool is the front and rear anti-roll stiffness.

To illustrate what it does I have built a very simplified weight transfer model. It doesn't allow for tire stiffness, caster, aero, only for the difference increasing roll stiffness splits from one end to another.

This would normally be associated with the anti-roll "bar" settings, although in NASCAR they adjust the rear roll stiffness during pit stops (Track bar).

Here is the Chart.



This would be weight transfer during a steady state left hand turn.

Next we can discuss why it works to fix push or loose if there is any interest.

rh

[chuck34]

Hoop I love this stuff. I have done a lot of it myself. But I'm always ready and willing to talk about it with others. Sometimes it's hard to find people who will talk about it. You know "secrets" and all.

Have you ever tried to write a lap time simulator?

[Hoop-98]

Hey Chuck34, not really a lap time simulator per se, but when we raced karts I did a lot of excel stuff, some predictive of Lap Time changes with different power etc. I also tried it with St Pete and a few other tracks with decent correlation. I have some documentation on basic Lap Time Simulators but i am not proficient in Programming, with a few Calculators etc.

Back to the tools, I am just trying to simplify some of the magic/secrets for discussion purposes.

It is important to state up front, this is only the very tip of the iceberg, reality gets about 1 million times (really a million, not exaggerating) and way over my head when you look at all the dynamic stuff. However, IMO, some basic understanding of mechanical grip, tire mu, weight transfer, helps our discussions of say, driver weight.

For example; Everyone grasps the Grid Weight, but what difference does the driver weight make on weight transfer, even if we weigh with the driver.

So I am going to say that Paul Tracy or Justin Wilson cause the CGh to be .4 inch higher than say Da Matta or Patrick.

So let's see what that does to weight transfer.

I am going to pick a number to begin with, then add .4 to it.
Of course there is no Aero Weight Transfer so we will deal only with the Car/Driver/Fuel Weight.

So Car Weight 1790 Pounds, Avg CGh 13, Avg Track 65.5, Rear Weight 59 PCT. These are figures in the same general scale of an Indycar, not exact figures.
So sitting on the grid the wheels scale weight would be.

Wheel Weights LF 367 RF 367 LR 528 RR 528 Left % 50.0% Rear % 59.0% Cross % 50.0%
In a Steady State 2.5 G LH Turn with a 13 inch ACGh the weights would look like.

LF 183 RF 550 LR 264 RR 792
With a 13.4 ACGh

LF 178 RF 556 LR 256 RR 800
This is a small but measurable difference in cornering power. The closer each end is to 50/50 the better it will grip (we can discuss this later.

In the Da Matta/Patrick Example we end up with 25 Pct Left/ 75 Pct Right.
In the Tracy/Wilson Example we end up with 24.2 Pct Left/ 75.8 Pct Right.

Let's take a break.

rh

[chuck34]

Hey Chuck34, not really a lap time simulator per se, but when we raced karts I did a lot of excel stuff, some predictive of Lap Time changes with different power etc. I also tried it with St Pete and a few other tracks with decent correlation. I have some documentation on basic Lap Time Simulators but i am not proficient in Programming, with a few Calculators etc.

That's exactly what I've been trying to do. I'm basically saying that the car will corner at x g's, accelerate at y g's, and brake at z g's. Then making two half ellipses to build my g-g diagram. I wanted to do that for a start, I'll get more accurate later, maybe. Then I start at the smallest corner radius on the track. Set longitudinal accel to zero, lateral accel to max, and work out from there. It works ok, but I run into issues when the corner radius tightens down on exit or entry, but doesn't go to the min value. Basically I need to work on my accel/brake "logic" I think. Either that or fudge my track map so that it doesn't ever have tight radiuses (radii?) on exit and entry.

Anyway, sorry to hijack your thread. I really enjoy that sort of stuff. As you can probably tell from my sig. If you don't have a copy of the Milliken book you really should pick up a copy. It's great for this sort of thing.

[chuck34]

Perhaps one thing that you might want to point out for those new to this is tire load sensitivity.

Basically a tire produces more cornering force if it has more normal force on it. Normal force being what you measure with a scale. So the more "weight" on a tire, the more cornering force it can create. The problem with this is that you don't gain as much by loading a tire as you loose by un-loading a tire.

So using Hoops first example, you have 394lbs on each front tire statically. Then in a 1.8g turn you now have 276LF 512RF. That means that you have gained 118lbs on the RF, and lost 118lbs on the LF.

Using made up numbers, because I don't know the tire properties of an IC tire. That means that you have probably gained about 100lbs of cornering force on your RF (compared from static), but lost about 120-150lbs of cornering force on you LF (again compared from static).

What that boils down to is that you want to have your tires evenly loaded (side to side) in mid corner. In that situation you will have the most cornering power. That is why oval track cars have more left side weight. They start with more weight on the left side so that when load is transfered in the corner (from your left side tires, to your right side tires), they end up with even tire loads under cornering.

Clear as mud?

[Hoop-98]

Perhaps one thing that you might want to point out for those new to this is tire load sensitivity.

Basically a tire produces more cornering force if it has more normal force on it. Normal force being what you measure with a scale. So the more "weight" on a tire, the more cornering force it can create. The problem with this is that you don't gain as much by loading a tire as you loose by un-loading a tire.

So using Hoops first example, you have 394lbs on each front tire statically. Then in a 1.8g turn you now have 276LF 512RF. That means that you have gained 118lbs on the RF, and lost 118lbs on the LF.

Using made up numbers, because I don't know the tire properties of an IC tire. That means that you have probably gained about 100lbs of cornering force on your RF (compared from static), but lost about 120-150lbs of cornering force on you LF (again compared from static).

What that boils down to is that you want to have your tires evenly loaded (side to side) in mid corner. In that situation you will have the most cornering power. That is why oval track cars have more left side weight. They start with more weight on the left side so that when load is transfered in the corner (from your left side tires, to your right side tires), they end up with even tire loads under cornering.

Clear as mud?

Much lower opacity than mud!

For example:



or



So the bottom line we want to minimize weight transfer either by,

Wider Track (Not Allowed)

Lower Center of Gravity ( Newer tub or lighter driver allows ballast placement)

Driver with Lower CG ( Additional ballast, or lower upper body weight)

We can't stop Left to right weight transfer, but with roll stiffness we can make wither the Outer Front, or Outer Rear carry more of the transferred weight.

More front resistance loads the RF, unloads the RR, reducing the spread (difference)across the rear and increasing the spread across the front, or more rear grip.



rh

[chuck34]

Thanks Hoop. I usually try to use charts and graphs when explaining this stuff. But I don't have anything at my fingertips here at home. :-(

[Chamoo]

Well this stuff is very interesting. You guys obviously know a lot more then the average joe.

Keep doing things of this nature. I don't know what all of it means, but I'll learn a hell of a lot faster reading these messages then if I never see them from you guys.

These technical talks add a nice element to these forums.

[chuck34]

Well this stuff is very interesting. You guys obviously know a lot more then the average joe.

Keep doing things of this nature. I don't know what all of it means, but I'll learn a hell of a lot faster reading these messages then if I never see them from you guys.

These technical talks add a nice element to these forums.

What don't you understand? Ask questions. There really are no dumb questions, so ask away. That helps you learn, and therefore enjoy the racing more. And it'll help me to better understand as well. Teaching is the best way to learn something. :-)

[Hoop-98]

I'll echo what Chuck said, we aren't high muckety engineers, just fans with some understanding and tons of questions.

rh