to-fst-4u

iTrader: (35)

I also posted this in the Suspension section, but I figured I would get more of a response if I posted it in here.

My torque arm queston/theory

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I have been studying the torque arm issue here lately, one of my classes is Chassis and Handling Engineering, where we set up race cars and what not. In the room, we have a brand new late model dirt car chassis that we mess with the set up and what not trying to learn how to set it up. Well yesterday, I got to noticing that this perticular car went with a torque arm setup instead of a four-link or truck arm system.

I asked my instructor why this was and he said it was because these cars have so much horsepower, around 800, and weigh like 2300-2400 pounds, it is easier to get them to hook up with a torque arm. Well the design of the torque arm is something that I have never seen before. It is just a regular bolt on torque arm on the axle, but in the front, it isnt solid mounted like our cars with the drag race style chassis mounted T/A. It is mounted with a adjustable spring and strut. I was asking my instructor why it was done this way instead of mounted solid.

He said that if it was mounted solid, when all the power was put to the rear wheels on the straight it would "shock" the suspension causing it to break loose, so with the spring and strut, it lessens the shock therefore hooks up better. My question is on our cars, why isnt something like this offered or been tried? Seems logical to me that it would work better. Just my .02 though. Sorry for the long post.

Zach

Empatho

iTrader: (16)

it makes sence, maybe someone will come in and tell us why they dont do it with cars

to-fst-4u

iTrader: (35)

Yes, I need someone smarter than me to explain this to me more in depth than my instructor could. I asked him why they wouldnt do that on our cars and all he could come up with is "I dont know"

3.4camaro

iTrader: (1)

cost.

And the stock one bends enough to get the kind of shock releif you are talking about.

to-fst-4u

iTrader: (35)

Regardless of cost, on a high horsepower application like some of these members are running, I think they would spend the extra money to hook up, if this theory would work on our cars. Sure on a stock car you are probably right, but how many cars over 500 rwhp are still running the stock T/A?

modracr62

iTrader: (12)

You are talking two different worlds when comparing a dirt late model T/A with a camaro T/A.... On a dirt late model you have a true floated 4 link with several inches of travel that WILL be used. Those type of suspensions hook up so hard that with a solid mounted T/A it would actually hook to hard to soon. The reason the shock and spring is there is to dampen the load so it will hook longer.

to-fst-4u

iTrader: (35)

Makes sense. I realized that it was quite a different set up from our cars, I was just talking about the design of it and why it wasnt used on our cars. So if the shock and spring are there to dampen the load to hook longer, why wouldnt this also do the same thing on a F-Body?

tee-boy

iTrader: (8)

Seems to me that hooking on a dirt track is quite different from hooking on a straight/flat piece of pavement.

black_z

iTrader: (4)

A dirt car that only turns left is going to have a vastly different suspension setup than a car with suspension for a drag car or street car.

to-fst-4u

iTrader: (35)

Holy cow, I was waitin for someone to say that. I was referring to when they romp on the throttle on the straights, kinda like a drag race. I know dirt cars only turn left.

Old SStroker

The whole torque arm issue is complicated.

To get more "forward bite" as Tony Stewart is always asking for, we want increased anti-squat in the rear suspension. That's a whole subject in itself. We can do that by shortenng the torque arm, but that leads to both power hop and brake hop in an F-body style of rear suspension. If we start moving the rear lower control arm angles we screw up the roll steer...and the beat goes on.

One solution: "Decouple" the torque arm from the rear suspension geometry. You can do this with 4-link suspension with "floater brackets" or "birdcages" and a separate torque arm. The spring/shock combination at the front torque arm mount does indeed soften the shock to the tires when copious amounts of torque are applied. This is great on dirt, but can also work on pavement.

The secret is "decoupling" the drive torque reaction from the braking torque reaction and the roll steer geometry. If you do this you can adjust everything independently, which is something you CANNOT do with an F-body rear suspension.

Here's a discussion of this on the "other" forum. Read carefully what Jon A says.

http://web.camaross.com/forums/showthread.php?t=391537

FWIW, I strongly recommend the book Race Car Vehicle Dynamics by Milliken and Milliken published by SAE. If your instructor isn't using it he should. Read everything you can written by Terry Satchell. You (and perhaps your instructor) will learn a lot.

We are just scratching the surface of this subject.

Jon B.

to-fst-4u

iTrader: (35)

Great post man. Very informative. Thanks alot. Just a FYI, we are using the book Chassis Engineering, by Herb Adams.

Zach

Old SStroker

That's a good basic book. I was fortunate enough to know and work with Herb "back in the day". Herb knows way more than he put in that popular book, but it wasn't written as a textbook.

Race Car Vehicle Dynamics, on the other hand, 'follows a path between a "theoretical" textbook on vehicle dynamics (which could miss the unique needs of racers) and producing a "popular" book on handling (skipping over the engineering details).' Quoted from the preface of this almost 900 page beauty. Chapter 17 is worth the price of admission.

I highly recommend it to you.


Jon

FASTFATBOY

iTrader: (23)

A buddy of mine has a pavement late model, it as the GM truck style lower arms, but on the top center of the rear end is has a horizontally mounted(front to rear) coil over deal mounted to the center of the top of the housing and to the roll cage bars,also has a panhard bar, man I saw this and was fascinated by it....I layed under the car and checked it out......Those roundy round boys got it goin on.

It does the same thing, gently applies power to stop tire spin, also helps the shockload when letting off the gas and braking into the corner also.


Global west makes a "de-coupled" torque arm for our cars, but it is for road racing.



I have a question, why does a dirt late model's suspension "twist" in the car in the corner when gas is applied? That is REALLY weird looking.


David

ssvert99

iTrader: (26)

the "fifth arm" setup you are talking about does in fact soften the hit at the tires and works as its supposed to. why we haven't used it on street/strip cars is this... where are you gonna mount a 13-16 inch long coil-over shock assy in the middle of the car?

borninatransam

iTrader: (4)

with people cutting 1.3x 60 ft times i dont think youre going to get too much improvement. if it aint broke, dont fix it.

black_z

iTrader: (4)

We are using the same book for my chassis class.

uncle ray

the main reason is that on dirt trying to put down even 200hp is quite difficult. the set up you describe is designed to limit the initial shock to the contact patches and gradually increase the forces applied to them.

on the street, or better yet at the track with a prepped surface, this would translate into unwanted slop. engineers spend thousands of man hours tuning out flex and slop. at the strip the suspension should transmit as much shock to the tires as the tires can handle. while a huge horse power street tired car could benefit from this design (minus its inherent handling issues) a nice wrinkle walled drag radial/ slick serves the same purpose only at a much more desireable location. right at the end of the powers travel to the ground.

besides... imagine having to tune your tires, shocks, springs, instant center, differential, clutch, and then throwing another huge variable right smack in the middle!

bottom line... transfer full power to the tires and tune with tire pressure and shock/spring settings on grippy surfaces.

absorb as much EXCESS power as linearly as possible on slick surfaces
( i would assume that its designed to take up the initial shock of the pedal going to the floor right out of a turn, keeping the car from looping. then maxing out the spring rate and putting down full power to the straights. not to mention absorbing some dive when letting off the power into turns as well)