SLP IROC-Z

iTrader: (1)

if all goes as pland my car should be into the 12s next summer. great, but i need traction get me there. ive been lookin all the torque arms out there for our cars and noticed u can get a full length one or a shorter one like a BMR trak pak or global west. would i benefit from a shorter one? the trak pak is only 10 dollars more then the full length but is it over kill? id like to hear some pros and cons of both or maybe one just totally out performs the other?

Dewey316

a shorter one is better, it changes the instant center

of course there is such a thing as too short as you can see in this picture, shortening the torque arm basicly moves the IC rearward, without much effect on anything else, like the roll center ect.

as for the trak-pack, it has always looked like a nice unit, but having to weld in a crossmember for it, has always turned me off.

SLP IROC-Z

iTrader: (1)

i think ill go with the trak pak, i have a welder at my house right now. ill probably just order the trak pak and its only 10 bucks more then the standard bmr torque arm

spartyon

have you looked at spohn's torque arm? it comes with the tranny crossmember and has the arm bolt to the crossmember.

GofasterFirebird

iTrader: (3)

All, I know is that my Jegster Tq arm worked better than my spohn one. The Jegster one is very short. Too bad it hated the 9 inch. And too bad the 9 inch hates my 6 speed and drive-it-like-I- stole it style.

SLP IROC-Z

iTrader: (1)

i think ill go with the BMR trak pak, it looks like a nice unit.

laiky

shorter TA's are better for drag racing but can cause axel hop problems when braking. it seems that the same way it helps to transfer load under acceleration (lifts the car more) it will lift the rear more under braking.

Dewey316

well if you go too short, i doubt that any of these are short enough to cause serious wheel hop issues under braking.

laiky

when i looked into the Tracklink and track pak some people complained about the brake hop issue. i would still like to try the track link but i'm reluctant to spent 600 bucks on it.

JERRYWHO

The shorter the torque arm the better braking you get, Think about it the shorter arm pulls down on the rear of the car not on the front so you have less nose dive and less wheel hop. I have a trac-link and still call it long at 43" most ladder bars are only 32" long for our size cars. Trac-links are a road race part that just works good at the drags.

Jerry

laiky

So is it safe to assume you like the track link? Have you had any problems? have you experienced the braks hop issue? i would like to get one but i have been turned off by some negative experiences. i am running a TKO and think that will add to my issues.

SLP IROC-Z

iTrader: (1)

hmm, well if does cause any brake hop issues, even tho it sounds like it wont, u can get an adjustable proportioning valve ( i got one ) and turn down the pressure to the rear tires.

AGood2.8

Brake hop as you guys call it (I call it skipping) is cause by too much rebound stiffness setting on shock or is caused by old worn shocks with no compression resistence and weak springs (could be other minor things, but those two are the main culprits). The TQarm has nothing to do with it.

laiky

the way i understand it, i could be wrong, is that the same way the torque arm tends to lift the car under power ( shorter arms give more leverage in this case) the opposite will happen under braking. This tends to cause the axel rotation to pull the car down therby "lifting the axel". It seems to make sense to me i know that it is probably a tuning issue more than anything else but i can see where too short of an arm will cause problems. Is the track link too short? i don't know. i liked it because many people say it made a significant difference in traction and putting power down coming out of turns. i also liked the way it cant bind as the axel moves over bumps and as the car leans.

SLP IROC-Z

iTrader: (1)

the other question is how hard of braking, what adjustments can be made to the front end and will less line pressure to the rear brakes, decrease this problem, if it even exists?

laiky

i agree, it may not even be an issue you will ever come across. I still want one but i would like to hear some more experiences with it first

AGood2.8

SLP and Laiky, You either missed my response, or neglected to believe my answer- so I will try one more time.

The TQarm will NOT cause wheelhop under braking whether its long or short. It is irrelevent the wheelhop issues under braking (read my post above as to what causes brake hop or skipping).

A torque arm lifts the front of the car under power (wheels pushing underneath) but will not cause the reverse effect under braking- why- the wheels are not pushing, they are pulling. Wheelhop physically can not happen from the TQarm under braking- the opposite will occur. The shorter arm will bring down the weight load of the car onto the rear wheel greater with a shorter TQarm (same principle as areodynamic loading) there is greater downforce on the wheels and would be impossible to hop.
What can happen is the brake bias may and probably will need to be changed so the fronts don't lock too easyif the arm is too short. Any over the counter TQarm will not have that problem.

jaredi

This should say not enough rebound stiffness

Sorta. More an effect of Rebound than compression.

Well, if so then you are contradicting yourself because the TA induced wheel hop happens alot easier when you have weak springs, but I thought you said TA induced wheel hop was impossible?

A complete and total load of it too.


Call me the bus driver cuz I'm takin y'all to school.

OK, let me be the first to call out everyone that said a short TA will not cause brake hop. It WILL! Get that point through your head. Let me say it again real loud and clear:

A SHORT TORQUE ARM WILL CAUSE BRAKE HOP.

Now, on to the tech behind it. The TA is a arm fixedly attached to the nose of the diff (when I say diff I am meaning the differential housing... the thing the TA is attached to.), so that it functions as an extension of the the diff. At the nose it is mounted so that it cannot move up and down (or actually move just very little). OK, follow me on this little walk through here. You're staged and the tree is dropping... Third yellow, and you dump the clutch. FREEZE. Now, picture the TA and the rear end at this moment in time, the nose of the diff wants to go up because the rear end wants to rotate the way of least resistance, which happens to NOT be where the rubber meets the road. The TA keeps the rear from nosing up because it is attached fixedly to the mount. This gives the car leverage on the rear and in order for the axle to rotate, which it wants to do, it has to lift the car up.

OK, SLOW MO forward with me, as the diff starts to rotate, it pushes the car up a little. To push the car up, the rear has to push down on the ground, resulting in the car trying to raise up and driving the wheels into the ground harder, causing a good bite.

Here is where the shorter TA comes in handy, the car will have less mechanical advantage over the diff, so the diff will be able to put more force on the car, which means it will be putting more force on the ground also=better traction.

OK Freeze it again.

I'm gonna explain wheel hop briefly, how it happens and why. There are two kinds of wheelhop that I'll talk about, TA induced wheel hop, and surface induced wheel hop.

The first kind I'll talk about is surface induced. This happens when you hit bumps on the track. For our purposes I will use braking as the example.

OK, our car has got to the end of the 1/4 mile and has to slam on the brakes really hard to make that first turn, but all of a sudden a speed bump pops up . Neglecting the adverse effects to the front suspension, when the rear wheel hits the bump, it is already being unloaded by the braking forces and if you have a nice stiff spring and a nice loose shock, you will be screwed beyond all hope. The wheel hits the speedbump, and the heavy spring compresses as the car loses contact with the surface. OK now the rear of the car is up in the air, the wheels have stopped turning, and life is grand, except the spring. It's still compressed and it ain't none too happy about it, so it decompresses, rather quickly. This is where it pays to have a good shock with ALOT OF REBOUND CONTROL to slow the spring's decompression. But our car's shocks are worn out so the spring decompresses and down she goes, driving that tire right into the pavement. Of course the brakes are still on and locked by this time, so it starts the cycle of bouncing which will eventually quit. But all this time it's wreaking havoc on the T5's gears. So, the ideal setup to avoid surface induced brake hop would be SOFT springs and STIFF shocks.

Now, TA induced brake hop. YES IT HAPPENS. Let's go back to the car rolling down the 1/4 at about 80. No speed bump, but a really short TA. All of a sudden there's a deer, and there's a panic braking. FREEZE for a second. What's happening with your suspension? The wheels are torqued the opposite direction and the rear wants to spin but this time it wants to nose down, but the TA won't let it. And with the short TA, the diff is more empowered. It doesn't pull the car down, it pulls the rear up under the car and AWAY from the pavement, gravity pulls the car down. Now, under the panic braking situation, the nose dives a bit and the rear wheels are unloaded a bit, combine this with the upward force compressing the springs and the wheel will lose contact with the ground, maybe only for a split second, but long enough to set off a chain reaction of vicious brake hop. Here again life is grand, the TA is unloaded, there's no upward torque on the rear anymore... and then the spring decompresses. BAM the tire gets hammered into the pavement. The wheel is at a significantly decelerated speed now, if not locked, and slides, but what happens with the TA now? You guessed it, it's loaded again and pulls the rear upward again... It eventually quits. So the ideal setup to counter for TA induced brake hop would be very stiff springs and stiff shocks (both compression and rebound).

If you don't believe me do a simple illustration. Grab a pen, or a pencil or something of the like. Grab it with your thumb and index finger. Make kinda like a see-saw out of it with your thumb on one end. Now put the other end under the lip of the table (make sure your index finger is pretty close to your thumb). Now press down with your thumb but don't hold pressure up with your wrist. Feel that? It wants to move your hand down. Your hand is just like the diff trying to rotate the TA under acceleration. Now put the tip of the pen on top of the table and rotate it into the table again. Feel that? It wants to move your hand up. That's the effact a TA has during deceleration. Now, to simulate a shorter TA, move your hand further down the pencil toward the table and repeat the experiment. That's why a short arm works better for acceleration but will screw you over with brake hop.

That being said, if you are building a drag car or a car that's not going to get a lot of brake use, then by all means go for a short TA. You can band-aid the rear braking system to accomodate. Turn the rear brake bias way down and run stiff shocks and springs. You won't have any trouble unless you get on the brakes REALLY hard. But for a car meant for OT or anything like that, a very short TA means turning the bias down which means horrible stopping distances which means you will go alot slower around the track. If you're runnin an auto with a short TA you better pray you have hellacious front brakes and you better be hopin that 700R4 knows how to rev match

and


No, the TA pulls up on the rear end, compressing the springs, pulling it away from the pavement and allowing that thing we call gravity to pull the car towards the ground.

Think about it, what is the torque arm being torqued by? The rear end. For every action there is an equal and opposite reaction, thus by the rear end pulling the car down, it is pulling itself up and away from the pavement.

If you buy an arm that is too short you are going to have to adjust the bias forward to keep the rears from causing brake hop... Band-Aid for a bad setup.

So all you guys who subscribe to this theory of pulling weight down on the rear end you go ahead and run your short little arms and I will be sitting there as your cars brake hop in every braking zone.

And if you guys want me or any other person with a remote grasp on physics to believe that the TA has no effect on brake hop you better come to the table with some solid tech to back it up.

If you guys want more evidence, look at all the guys with Mustangs running MM or Griggs TA's, or Trac Links. If they arent set up right it will cause wheel hop like no other, especially the Mustang Trac Link, it is one hard MF'r to get right, and if it's wrong it WILL cause brake hop. I have no experience with Camaro Trac Link, although when right, the Mustang Trac Link works very good.

Schools out...

You may have a point there...

Jared

Dyno Don

iTrader: (7)

Then how did a Mudstain problem get here?

laiky

what jaredi sais is basically how i understand the problem, but i can't wait for the fireworks.

AGood2.8

Dear misinformed Jared-

Brake skipping is caused by TOO MUCH REBOUND-why?-Because the tire will skip over the pavement when it compresses and can not return to the ground fast enough- I love when some punk 18yr old thinks he nows it all.

My quote(s) above that was one combined combination and YOU separated to try an TAKE OUT OF CONTEXT is ment as a multiple weakness together and will not occur saparate- thank you very much idiot.

My 4th sentence you quoted me and called me contrditing? where did I ever say "A tQarm induced wheel hop"?- Read again idiot- I said rear wheel hop/ or skipping is caused by either a)too much rebound, or b) not enough compression AND weak springs (causing the commonly seen basketball effect.

Frikin moron. Do you realize the caliber of people you are telling your nonsence to? Jerry for one has raced Sprints for years and has built many race car for scratch- I myself have raced for years and am an acomplished driving engineer and mathimatician. From Don's quote, He thinks your quite the prize also- Do you know his reputation and qualification? Lets just say he's probably the most repected on these boards.- there you go. Edit: Let me add Mr. Spohn below as well!

SteveSpohn

Huh????????

laiky

kapow!! Boom!! X^#@$%*. Covering fire!!!

laiky

What i don't understand is how the arm can lift the body on accelleration and NOT tend to lift the axel on decelleration. i assume that the springs and shocks should absorb these forces but at the same time it should cause the spring to compress, loading the rear suspension. I can see how stiffer springs and shocks could minimize this but not how the tendency doesn't exist?

SLP IROC-Z

iTrader: (1)

this is why i like to ask questions, to find the truth

alloy

iTrader: (16)

You said exactly what I was thinking. I'm very interested in hearing the answer to this as I just this last weekend put my new Spohn torque arm on my car, and would like to hear the definitive answer to this debate.

Dewey316

yes dean,

i too would love to hear this explanation, i may not have 'your' credentials, and you know that i usualy listen and learn from you every chance i get. but i too was and still am, under the assumtion that shortening the torque does have an effect on braking. in my not so well trained mind, the effect under braking is the equal and opposite reaction of accell. if you have anit-squat under accell, you have squat under braking, which is what causes the wheel hop.

AGood2.8

Guys, I will say it again-

When the car accelrates, the axle and TQARM is being PUSHED up under the car by the wheels.

When the car brakes, the axle and TQarm is being PULLED from the vehicle.-----Now if the same downloading principle of the car onto the torquearm COMBINED with push of the rear wheels and not pull (under power not braking- a physically impossible feat), the car still would not have wheelhop UNLESS the LCA angle inverted from brake squat AND power whas applied. Wheel hop will only happen under power.

Edit: or if yyou go really fast in REVERSE and hit the brakes hard.

Dewey316

dean,

but in the situation we are talking about, the rear geomitry has been set up , so that the rear is being pushed away from the car under accell. idealy the proper setup would be for zero rear movement? correct? so that under braking and accell there is no rear squat or lift. but that would be a very hard to do.

AGood2.8

There is a push pull priciple here that does not recipricate (meaning to each action the is not always an opposite reaction)

Case in point (I think this will help everyone understand better) Take a car being towed. If the car is hooked to the bumper of a car in front of it and being PULLED it will track right behind the other car without needing to be steered.

Now if the car is being PUSHED- it needs to be steered. Understand now how push and pull can have an effect? - when a whell is the pushing gorce, it can hop. When a wheel is a pulling force Trailing the object its slowing, it cant hop. Stop and pull it in the other direction (Reverse) and now what it is pulling is behind it in the direction intended, then it can hop (i.e.- a front wheel drive car doing a burnout- major wheelhop.

AGood2.8

Guys, I gotta go. Got a boat to catch for the weekend- going scuba diving. I will be back Monday if there is anything I can add or answer.

jaredi

Hang on a sec. Why did I mention a M*stang problem? M*stang doesn't have a TA factory, and from the factory the car doesn't brakehop, or at least mine didn't. When they install an aftermarket TA kit like MM or Griggs, I know the MM TA is very short, 30 something inches I think, if not set up properly they cause brake hop on a M*stang. So if the TA has NO effect on brakehop, then there's no way it could cause brakehop on ANY car equipped with a TA because they all work the same way... Right?

OK, HOW? I really want to know how? What causes the tire to return to the ground in the first place? The spring! If your spring shoots down and rams the tire into the pavement that's only gonna create more problems! So if you have a shock with STIFF rebound control which softens the impact of the tire with the ground and gives gravity a little more time to reset the chassis before impact, making the wheelhop last a shorter time.

Here, take a look here, got it from a quick google search:

http://www.rpmnet.com/techart/shocks.shtml

Read that and think about it then tell me why a shock with less rebound is better to eliminate wheel hop.

I was thinkin the same thing about 37 year-olds. But while we are on the subject, re-evaluate your math skills and tell me what difference it makes if I am 19 or 60 if I have a grasp on the way things work? If there was a 55 year old engineer from F*rd telling you that your car was a mid-engine would you believe him?

Whatever, doesn't really matter because if your theory is correct then a weak spring won't cause wheel hop. I didn't say you said a TA will induce wheelhop. Sorry if it sounded that way. I meant to say that the only reason a weak spring will cause wheelhop is if it isn't strong enough to resist the rear pulling off the ground. But according to you TA won't cause wheelhop. So how does a weak spring cause it?

EDIT: Edited out the useless and rude personal attacks, and again I apologize.

Let me re-phrase that. Under braking the rear end pulls up on itself, the TA is simply an extension of the rear end.

Do you have any idea about wheel hop? Go outside, right now. Everybody that can! Put your car in reverse and dump it, or throw it to the floor. Get that wheel to spin! See if you don't get wheel hop! Now, what's the difference on the suspension whether you are dumping it in reverse or going forward and apply brakes? It's still a torque on the rear opposite of acceleration.

I think I found your primary misconception right here. The TA is pushed forward only when the LCAs move through their arc. The LCA prevents any motion of the rear end forward or backward except when the rear moves the LCA through it's arc of travel But it is of no consequence as the front mounting point of the TA makes sure that it projects NO FORCE EITHER FORWARD OR BACKWARD on the car. It slides. The only force that the front mount allows to be applied is a force UP or a force DOWN. So you see, the TA can't PULL backward or PUSH forward on a car.

Your physics work for LCAs but not for a TA.

I would think that, ideally, the rear should push itself down into the pavement under both acceleration and braking but I think it may, under braking, throw too much weight onto the front of the car...

Comparing a FWD burnout to a RWD TA setup under braking is like referencing apples to find out where your jeans are made. It's a completely different deal. BTW I had an Echo rental car that would smoke the front tires bad and guess what... NO WHEELHOP. How bout that.

Oh yeah, you gotta tell me how the front TA mount will allow for a pushing or pulling force to be applied horizontally.

And you also gotta explain the physics behind a tire being slammed into the ground before the chassis can reset itself helping anything.

Jared

EDIT: Edited out the personal attacks.

TheGreatJ

I have to go with Jared on this. In a braking situation, with the wheels rotating, I don't see how the rearend could NOT try to twist the TA down and consequently compress the springs which will then rebound and induce wheelhop.

It's the nature of how brakes work.....use friction to remove the difference in speed between the rearend and wheels. This means slowing the wheels down, but it also means trying to rotate the rear at the same speed as the wheels. The brakes will try to twist the rear (nose down) just as hard as they will try to slow the wheels. The TA uses leverage against the weight of the car to minimize this twisting. Since a shorter lever means more force applied closer to the rear of the car, it will try to pull the back of the car down more and the front less as compared to a longer TA. This means more compression is applied to the rear springs and less to the front, which means the rear will "squat" more. Since the rear has less inertia than the car (less mass means less inertia) it will pull up toward the car causing a loss of traction. Since a loss of traction causes a loss of braking power, the twisting force is then removed. The springs will then unload driving the wheels back into the pavement and causing a sudden gain of traction and consequent braking power which will start the process all over again. This rapid gain and loss of traction will cause the wheels to skip along the pavement which is, by definition, wheelhop.

Push or pull doesn't make a difference since the LCA's and PHR keep the wheels in alignment with the vehicle (the towing example is inaccurate...a car being towed can swing side-side where a rear end cannot, and a towed car is neither a driving nor a braking force anyway so it just really doesn't fit at all.)

laiky

i gotta do some more thinking on this, i think maybe everybody here is correct in the context they are thinking of the problem but its too late and i don't think i can put my idea into comprehensible words right now

jaredi

First let me apologize for giving out bad advice about going out and throwing you car in reverse and dumping it or flooring it. I don't want anyone to try that because it's been known to kill T5s because the massive wheelhop puts so much shock onto the not-so-stout gears bang bang bang kinda like the equivalent of a N-drop on an auto... You might get away with it a few times but it ain't none too good for it.

Second let me apologize to AGood2.8 for the personal attacks which I am going to edit out. 1. Because all it will do is clog the post with useless 2, It's just not cool. I'm sure he's a good guy and for all I know he is everything he claims. I don't have solid information to make me think otherwise so I can't really dispute it.

[EDIT, see below post.]The more I think about it now, the more I am tending to think the wheelhop problem would only show up when using engine braking. So that if you were to push the clutch in the rear wouldn't be torqued as much and the TA wouldn't load up and work either way. [/EDIT]

Any ideas on that?

Jared

SLP IROC-Z

iTrader: (1)

thats what i think, i also think we should talk to people that are using these torque arms for the real world story.

MrDude_1

heh, took me a min, but i get what hes saying about the push pull effect and wheel hop.


lets pretend the wheels are slowing. im sure you can envision the axle trying to twist and that makes the TQ arm push down on its mount and lift the axle.. thats what you're seeing right?

well what about the LCAs... the wheel is slowing... the car still wants to move, so the LCAs are being pulled apart.. the tenson on them makes them want to stand out as far as they can...

if they are on the correct side of the arc(or perfectly flat) that force would counteract the TQ arm effect.

think about this... the car weighs alot and is putting alot of stress on the arms pulling the axle along. meanwhile the TQ is trying to be rotated upward..... if you have ever had the TQ arm disconnected with the weight of the rear on the tires, you would find that with your pinky finger you can pull down and lift the rear of the whole car.... the leverage is that great.

now, the axle is trying to overcome that leverage...and it would take alot of force to over come that since its so long... the greater LCA pull causes the axle to stay put under braking.




atleast thats how i visualize it after reading this thread... prior to that, i never gave it too much thought.

Hunter Motorsports

FOR EVERY ACTION THERE IS AN EQUAL AND OPPOSITE RE-ACTION
This is a LAW of physics. It is a LAW - because it cannot be broken. The statement that this is a "push pull that does not reciprocate" is simply ludicrous.

The "towing the car" analogy is not really applicable here - as the axle in a moving car that is being driven is WORKING - applying acceleration and braking forces called "torque".

The Torque Arm is NEVER being pushed or pulled - it is not a ladder bar - it is a torque arm. The Torque arm controls axle torque in the following way: When a forward or accelerating force is applied to the wheels the opposing force is trying to rotate the axle in the opposite direction, which wants to swing the pinion upwards, and thus the torque arm upwards. Under braking - the opposite is true - the brakes are applying torque to the wheels and the axle wants to rotate in the opposing direction trying to pull the front of the torque arm downwards. This is why Torque Arms have some sort of slider system - rotator, tube, bushing or whatever - because the only force the torque arm is supposed to react to is a upwards or downwards force as a reaction of axle torque.

It is the job of the trailing arms (more commonly known as lower control arms) to transfer the forwards or backwards force from the axle to the chassis of the car, thus accelerating or decelerating the car.

Torque arm length and instant center position, and trailing arm angle BOTH determine how a suspension reacts to acceleration and braking. Short torque arms provide more anti-squat by moving the instant center rearward at the expense of braking performance. Yes - short torque arms are MORE prone to wheel hop under decelleration than longer torque arms. This is just a function of how the suspension works - as in how it reacts to the forces that are applied to it. Longer torque arms do not have as much anti-squat but are more stable under braking. Anti squat can also be added by changing the angle of the trailing arms. Having the front of the arm mounted higher than the rear provides this function. Having more anti-squat "plants the tires" harder under acceleration - but has the opposite effect under braking - effectively trying to compress the suspension as a reaction to braking torque. This is what can cause wheel hop or "brake skip". Look at a car that has alot of anti-squat built into the rear suspension - under acceleration it de-compresses the suspension pushing the rear end of the car higher into the air. The opposite happens under braking (remember - this is a LAW of physics) and the brake torque results in the suspension compressing. Once the wheels start to hop it is a cycle that can only be stopped by reducing brake torque until the suspension stabilizes.

I will not go into how wheel hop can be caused by deflection and wind up. Save that one for another day.

Of course - if the torque arm decouples under braking and acts as a 3-link (Herb Adams torque arm) it becomes a whole different game.

Justins86bird

Wow, long thread going on here. Without repeating what was said, Hunter above pretty much sums it up.

Alot of the 4th gen 98+ guys are having rear brake hop (LS1 rear brakes). Some of the solutions were less aggressive rear pads or a stronger, but stock length torque arm. Some of the guys who had put in a shorter TA got more brake hop and changed back to a stock length TA just to rid the brake hop. For drag racing, a short arm will help plant the tires. After all, you just need to go straight and fast. For road racing, a long arm since not only acceleration, but braking and turning play an important role. While I'll agree the the tranny ain't the greatest place to mount the arm, it is a pretty good design. Not only was it used in 3rd gens, GM engineers designed it into the 4th gen suspension, which shares almost all the same parts as the 3rd gens. The stock length arm is fine, it just needs to be stronger.

As for the orig poster SLP IROC-Z, sinces he's in the 12's and wants to go faster, I'd assume he's mainly into drag racing, where a shorter arm would be better.

Dewey316

hard to argue with that,

thanks Karl. as always you put the concept into words very well. what you are saying is what i was thinking.

jaredi

That's what I've been trying to say, however (in)effectively.

Jared

Chickenman35

And if you don't believe Karl...go out and Buy Herb Adams book "Chassis Engineering" . Explains quite clearly the Pro's and Con's of Long and Short Torque Arms. Pages 70 through 72 .Specifically mentions that Short Torque Arm can provide more Anti Squat during acceleration but at the expense of Wheel Hop under Braking. A Decoupling Torque Arm is the preferred method of curing Brake Hop with a Short Torque Arm.

Paul Van Valkenburgh's " Race Car Engineering and Mechanics " also clearly explains how short Torque Arms can cause rear wheel hop under braking. Page 22.

Too much rebound in the rear shocks causes rear wheel hop under braking? Highly unlikely on Asphalt.

I've been Road Racing\Autocrossing and Hill climbing for close top 30 years now. I run a TON of rear brake ( helps the car turn in and optimises braking ). Any time that I have had rear wheel hop it has easily been cured by adding MORE rebound to the rear shocks... not less. That info's also available in Herb Adams and Paul's book if you care to look it up.

Edit: Fat fingers ...Spelling

jaredi

Nevemind guys, just dismiss that thought... I wasn't thinking right...

Jared

SLP IROC-Z

iTrader: (1)

i havent hit the twelves yet, but if i had traction id be close. i do want a good balance of handling,braking and acceleration from this car. its my daily driver and its fun to carve corners and im putting in 1LE brakes so its gonna stop.

maybe a stock length torque arm will better suit me.

Hunter Motorsports

Go with the Spohn Performance Torque Arm AND the LCA Relocation brackets. Together they will still be way cheaper than the TracLink - and in my oppinion for what you want to do they will perform better.

For street and performance driving set the trailing arms up to be level or for the rear of the arm to be slightly higher for a bit of roll understeer.

When you go to the strip set the rear of the trailing arm to its lowest possible seting for traction. Adds more anti squat, and plants the tires harder on the launch.

Sure the BMR stuff is a bit cheaper, but I have personally had excellent results with Spohn products, and hey - can you say "board sponsor"

Seriously - the stock length torque arm like the Sophn (relocated from the trans tailshaft of course) is the best overall design in my oppinion. It works on the street. It works at the strip. It works on the track (road course).

And if you are really interested in what is happening in the rear suspension when you mash the throttle or stand on the brakes - read some of those books that Chickenman recommended, and add to that list "How To Make Your Car Handle" by Fred Puhn.

Good luck.

laiky

Thanks for clearing that up guys, Hunter and Chickenman you guys are always helpful. BTW Chickenman your spring advice was dead on.

If anybody has a pic this Herb Adams decoupling torque arm i would love to see it. Also does anybody know what happened to Herb Adams and his suspension parts business??? He used to make some great stuff.

Justins86bird

Oops, I thought you were building a car just for the drapstrip. Thats why I recommended the short arm.

Reading your last quote, you'd definately want a stock length arm. Make sure you get an adjustable one like Spohn's or Random Techs.

SLP IROC-Z

iTrader: (1)

i was thinkin of goin with a BMR unit

AGood2.8

I'm back.
Hunter, You and I in essence are saying the same thing only in dfferent blame catagories.

You blame the torque arm, I blame the spring rates and dampen forces. Fact is, the torque arm does not control wheel contact patch, the shocks and springs does. Wheel hop is a result of insuficiant shock and spring control. Now granted, the shorter torque arm will induce greater rear downforce in braking (less bias shift), But the chassis weight on the rear bais(just like downforce I mentioned above) needs to be further dampered by increased compression- just like an areodynamic road car needs greater sping rate to counteract the increased downforce. With higher spring rates- higher damping is required. Other wise the tire will bounce off road defects (bumps-big or small) and ground out or overtravel its intended geometry.

When the torque arm length is decreased, the spring and shock rate needs to be increased due to the lessening of geometry leverage-

In conclusion- The TQarm will cause an alteration of chassis balance that will change the spring and shock rates- its the spring and shock rates that become insufficiant and cause wheelhop. Up the rates to control this?- no problem-however it will unsettle your balaced cornering weights. This is why I have stated in the past and I will quote: " A little shorter can be fine, but too short of a torque arm can cause havoc. Any over the counter TQarm is long enough not to suffer from any problems"

Hunter- what I meant to say is that the action- reaction sinerio in this case does not INVERT because of one way is push, and the upside down forward reaction is pull (so the wheel hop known to all is not the same cause inverted). Sorry, I was not clear. Also never said the torque arm is pushed or pulled- the wheels are pushed or pulled under the torque arm and chassis (the tail bones' connected to the........ you get my drift, everything lifts together, everything dives together. ) My push pull sinerio was to help explain how the same force going forward can be alter if pushed rather than pulled- I know it has no relation to TQarms, it had a relation to the understanding of how a push and pull can effect things differently- And I said that above! read my above post again- it discribes wheelhop from thrust (bad LCA angle) This can not reciprocate.

Here's the biggy- Too much rebound CAN cause brake skip- how- what is not talked about in any sentence above is the fact that roads are uneven- that is why cars have suspensions. this "brake hop" under brakings is caused by too little rebound force. The geometrys has been changed, SO, the compression needs to be bumped up in equal relation to the rebound (torquearm leverage before and after need to be factored and reajusted to proper proportions. When a car is brakings hard and weight is transfered over that tire (whether front or rear), THEN the tire is absorbing defects in the raod surface, it will compress and return to the ground after the road defect. If the rebound damper is set too high, the tire will NOT return fast enough to the back side of the bump (in essence "skip")- this in repetition (I shouldn't need to tell you Hunter) causes "brake jacking" and bottoming out will occur if action occurs long enough.
Not enough compression will cause grounding out as well and too LITTLE (not too much) rebound will cause brakehop- "the basket ball effect" I discribed above

I plan to get HERBS Adams book an interpet what is said, I have never read it.

Every car is different because every driver has modified it with different aftermarket parts, some this with that, others that with that- so many combos- It can work for some, but not for others based on what rates and setting are inherent on their particular car.
Thank you, Dean

Edit; Jared I respect your apology, you are a gentleman to do it first and I must also apologise- p.s.- I will work on my typing ski;;s, I have been out of any school for years and my spelling is getting worst over the years- lack of read literature I guess- I'm a talk radio junkie

SLP IROC-Z

iTrader: (1)

i was lookin more into BMR stuff, i want to get their non adjustable LCAs, adjustable PHB, relocation brackets and their torque arm. i also plan on usin air bags in my rear springs, and a pair of 255 50 16 BFG drag radials.

the trak pak i was interested in because it was shorter and stuff. i wasnt aware of the brake hop that can happen tho. how severely do u have to slam on the brakes for that to happen? and is a minor adjustment of lowerin the raer line pressure (i have a wilwood adjustable prop valve) gonna do the trick? like i originally asked on the top of the thread is the trak pak over kill for what i have?