Bill Shoppe, best set up for ladder bars w/ Transbrake??

[cudabin]

Car is a 67 cuda w/ 470 low deck and 727 with alum drum and Transbrake. Strange Dana w/ 4.56 gears and 10.5W -31 Slicks on 12" rims. Current best is 9.91@ 137mph w/ 1.43 60 foot.

Car weighs 2,900 w/ driver and full of fuel. 56% front 1,646#'s, and 44% rear 1,254#'s. Strange double adjustable coilovers w/ 110# hypercoil springs.

1) How would you set up the suspension for a greasy, hot track with poor traction??

2) What set up for sticky good track ?

Currently at level with the ground on the ladder bar, in the middle hole,
with neg 2 degrees pinion angle. Shocks on 3 clicks from full soft on both extention and compression.

Advice and ideas ??

Thanks,

Arnie

[BillyShope]

The best setup is always one in which the rear tires are equally loaded ON LAUNCH. The great popularity of the anti-roll bar is because of its effect on launch loads of the rear tires. I get the impression that many who use the anti-roll bar do not understand how it's helping them. The visible effect...that of reducing front end twist...is relatively unimportant compared to its effect on tire loadings. It accomplishes this because, with its use, rear roll stiffness is increased relative to front roll stiffness. But, since the front roll stiffness can never be entirely eliminated, an anti-roll bar is not the total answer.

You don't mention individual static tire loads. I'll assume that...left-to-right...they're essentially equal. Understand, however, that, upon launch, the driveshaft torque causes them to be anything but equal. In other words, the nice symmetry, that you have statically, no longer exists during launch. So, in order to equalize rear tire loading on launch, you have to build some asymmetry into your setup.

There are many ways to add the necessary asymmetry. At my site, for instance, I have a spreadsheet on one of the pages which describes an asymmetric adjustment of a ladder bar car. This suggestion alarms some who fear a safety and driveability problem. What must be understood is that the asymmetry can solve the loading problem statically or dynamically. For instance, a static solution would be to simply increase the right rear loading and decrease the left rear until, on launch, loading is equalized. Unfortunately, this would mean that...at low levels of driveshaft torque...symmetry does not exist and there definitely could be safety and driveability issues. But, with a dynamic solution...such as an asymmetric ladder bar adjustment..., rear tire loading can be equal with ANY value of driveshaft torque.

It is strongly recommended, however, that the effectiveness of any adjustment be verified with the traction dyno (Pages 5, 19, and 23).

With a fully dynamic solution, variations in track surface conditions do not affect the setup.

Hope this helps.

[cudabin]

Thanks for the input Bill! I have to admit that I find your suspension blog very interesting but i need to read it a few more times to understand all the variables...

The static weights are:

LF= 859 RF= 796

LR= 633 RR= 623

I do not have easy access to scales and am racing next week on a poor traction track, but i will definitely keep reading your site and try to learn.

The car basically launches straight with no excessive roll, and the rear does not rise or squat, but is neutral.

I would rather waste some motion in weight transfer than simply spin the tires, so would a lower ft hole resulting in a negative angle on the ladder bar transfer more weight and increase dynamic rear tire loading?

It is currently level with the ground in the middle hole.

I have adjustable ft shocks currently set at 90/10, but based on your ideas, I should maybe try the LF at 70/30 ???

Thanks for all the help,

Arnie[/img]

[BillyShope]

There is no suspension adjustment which will increase weight transfer UNLESS that adjustment increases the height of the center of gravity, shortens the wheelbase, increases overall weight, or increases the torque output of the engine. Seriously, a change in ladder bar adjustment will not change the amount of weight transfer, though moving it up will cause the rear end to rise and moving it down will cause squat. (Yes, as the front end of the car rises, there will be an increase in CG height and, consequently, slightly more weight transfer, but your ladder bar adjustment has nothing...or essentially nothing...to do with front end rise.)

[jim_ss409]

Bill, I've also been looking at your site trying to gain a basic understanding of suspensions on a drag race car. Am I right in thinking that weight transfer to the rear axle comes mainly as a result of the forward G forces? If so is it right to think of antisquat as a way to drive the tires down to get the initial hook, then hopefully, the weight transfered from acceleration will keep the tires hooked?

[BillyShope]

Bill, I've also been looking at your site trying to gain a basic understanding of suspensions on a drag race car. Am I right in thinking that weight transfer to the rear axle comes mainly as a result of the forward G forces?

Not just "mainly," but entirely. You can calculate the weight transfer by multiplying the forward acceleration...in G's...times the total weight times the center of gravity height and then dividing by the wheelbase. That's all there is to it.

If so is it right to think of antisquat as a way to drive the tires down to get the initial hook, then hopefully, the weight transfered from acceleration will keep the tires hooked?

Again, it's the acceleration...vertical, this time...which determines the loading. As the rear of the car is accelerated upwards, the rear tire loading is increased. Unfortunately, this time interval is extremely short, for the rear of the car must then be DECELERATED as it approaches its upper position limit. This deceleration then UNLOADS the rear tires. Any net gain...if it exists at all...is very, very small. And, an oscillatory loading has been introduced, which is usually something to be avoided. I would strive for a neutral (100% anti-squat) condition on launch.

(A bit of history: If you go back a few years, dragracers generally avoided anti-squat over 100%. Instead, they favored a car which squatted severely. When they saw the car loading the tires as it bottomed out, they reasoned that this was to their benefit. In other words, they were making the same mistake, but in reverse. They didn't realize that, as the rear of the car was accelerating downwards, it was unloading the rear tires. Now, it's realized that, as the rear of the car is being pushed upwards, it's loading the rear tires. This attitude change was most likely brought about by the successful Mopars of the sixties. Anyway, now they're missing the unloading as the rear of the car is decelerated as it approaches its upper travel limit. This squat/rise business is simply a game you can't win.)

[John Wallace]

Here's an article that may be of interest.

Leaf Spring Traction

[BillyShope]

Yes, it's possible to calculate the load imbalance of the rear tires, during launch, of a symmetrical car. By "symmetrical," I mean that no efforts have been made to cancel the effects of driveshaft torque. But, it's necessary to consider only the dynamic forces, which greatly simplifies matters.

The forward tractive force, at the rear tire patches, is equal to the effective coefficient of friction times the sum of the static rear tire loading and the weight transfer. This is equivalent, in magnitude, to the inertial force acting at the center of gravity and directed backwards. The product of this inertial force and the center of gravity height must equal the product of the weight transfer and the wheelbase. From the preceding, it is possible to calculate the weight transfer and then the left and right rear tire loadings EXCLUDING the effect of driveshaft torque.

To determine driveshaft torque, it is only necessary to multiply the tractive force times the effective rear tire radius and then divide by the axle ratio. Note that the engine torque is not used, for the tractive force is limited by the friction coefficient and NOT by the engine torque.

It is the driveshaft torque, of course, which upsets the loading of the rear tires, but we cannot apply the full calculated value of driveshaft torque, for a portion of the reaction torque absorbed at the engine/transmission mounts is fed back to the rear suspension where it cancels the driveshaft torque effects. The remainder of the reaction torque goes to the front suspension. In other words, the reaction torque is split in proportion to the relative front and rear roll stiffnesses. This is why the currently popular anti-roll bar works so well. It greatly increases the rear roll stiffness, meaning a higher proportion of the driveshaft torque effects are canceled.

So, if it assumed that 60% of the roll stiffness is at the front of the car, the calculated driveshaft torque would be multiplied by 0.6 and then divided by the rear track. The answer would be the disparity between left and right rear tire loadings.

[jim_ss409]

Bill, Would asymmetrical four link settings be the preferred method of canceling the effects of driveshaft torque? http://home.earthlink.net/~whshope/id8.html
As I said, I'm new to this subject but most of what I've been reading has suggested things like pre-loading, anti roll bars and spring rates.
Here's another thing that I hadn't really considered...
"As any oval track racer will tell you, maximum performance from a tire pair is achieved when they're equally loaded."
Would it be correct to think that a drag car would achieve maximum traction with both rear tires loaded an equal amount,,, as opposed to 60% left, 40% right for example.

[BillyShope]

Bill, Would asymmetrical four link settings be the preferred method of canceling the effects of driveshaft torque? http://home.earthlink.net/~whshope/id8.html
As I said, I'm new to this subject but most of what I've been reading has suggested things like pre-loading, anti roll bars and spring rates.

The driveshaft torque, with a RWD beam axle car, provides asymmetric tire loading. The only way to correct this is with asymmetry in the chassis. Asymmetric adjustment of the 4link is one way of accomplishing this. This is certainly to be preferred over preloading, which provides driveshaft torque cancellation at only one value of driveshaft torque. The anti-roll bar is better than preloading, but, since all of the roll stiffness cannot be removed from the front suspension, it isn't the total answer.

Here's another thing that I hadn't really considered...
"As any oval track racer will tell you, maximum performance from a tire pair is achieved when they're equally loaded."
Would it be correct to think that a drag car would achieve maximum traction with both rear tires loaded an equal amount,,, as opposed to 60% left, 40% right for example.

Absolutely!!! This is why the anti-roll bar is so popular, though many, I'm afraid, don't really understand its benefits. Yes, it keeps the front end from twisting, but the real benefit is that it provides more equal loading of the rear tires. The problem is that unequal rear tire loadings cannot be easily "seen." Unfortunately, many dragracers feel that, so long as they can stay in their lane, the only thing they need is more horsepower. As indicated above (and at my site) complete cancellation is possible and will yield maximum benefits.

[jim_ss409]

Thanks Bill.