Roll Rates, ARB Stiffness, wheel rates

[David Goodwin]

Hi all, im just doing prelim calcs for my setup next year.

Now i have come across a dillema when reading Milliken or looking at the optimum G notes. Now i have the desired inputs of a max lateral accelation, and a max roll angle i want to achieve. From this (using a tyre approximation for stiffness) i have calculated my wheel rate, ride rate, and the spring(s) roll rates. This gives me something which is short of what i want to achieve...Which is where arb's come in (obviously)...Now this is where i have the problem. Is there any problem with simply getting your desired roll rate and subtracting the spring(s) roll rate to give you the required ARB roll rate? Which in turn would give you an ARB stiffness you would require. Optimum G do things slightly different by using an actual formula, i get an answer close to but not the same as optimum g (within i think 20 Nm/deg).

Is there any error in this?

In addition to this, some of the forumlas from optimum g differ from those in milliken. They give similar but not the same answer.

Cheers David

[David Goodwin]

Hi all, im just doing prelim calcs for my setup next year.

Now i have come across a dillema when reading Milliken or looking at the optimum G notes. Now i have the desired inputs of a max lateral accelation, and a max roll angle i want to achieve. From this (using a tyre approximation for stiffness) i have calculated my wheel rate, ride rate, and the spring(s) roll rates. This gives me something which is short of what i want to achieve...Which is where arb's come in (obviously)...Now this is where i have the problem. Is there any problem with simply getting your desired roll rate and subtracting the spring(s) roll rate to give you the required ARB roll rate? Which in turn would give you an ARB stiffness you would require. Optimum G do things slightly different by using an actual formula, i get an answer close to but not the same as optimum g (within i think 20 Nm/deg).

Is there any error in this?

In addition to this, some of the forumlas from optimum g differ from those in milliken. They give similar but not the same answer.

Cheers David

[Silente]

i would advice to go through like this:

you probably have written an excel sheet to work on your car.

Model in it the contribution of all of your suspension components for roll rate to obtain a final value of roll stiffness and roll moment (or wheight transfer). With this numbers, as you said, giving a certain lateral g you can obtain roll angle.

Then put for the now at zero roll stiffness contribution from bars.

Then you can add arb stiffnees till when you obtain the right roll or the right roll gradient etc.

Excel has also a feature which, once you said to him the desired value for on variable, can change another variable to obtain that desired value.

I know Optimumg G give a math model to find a desired ARB stiffness once you choose your roll gradient, but the results of doing in the way i said is the same; the only difference is that you protect more your calculation from mistakes.

[Eklavya Singh]

Thats another problem you've solved for me Silente.

Any ballpark figures for the kind of roll angle desired at what kind of lateral acceleration?

I was starting off with approx. 1.2 g's for 1.5 to 2 degrees of roll.

[Silente]

This matter depends a lot from the surface you're working with.

A lot of teams stay around 1 deg/g.

I cannot say what the otpimum value is, and probably an optimum value doesn't exist.

I would try to have a skid pad and a road course like the endurance one trying to increase or decrease this value to see differences and to understand the otpimum value for both the situations.

One thing i don't know but that has to be in your mind is if the value you're looking for take tyres in analysis or not.
Also with data logging, if you look only at suspension potentiometers, you don't se how much tyres are deflecting under load, and so how much roll you are experiencing from them.

[David Goodwin]

bump