Patrick G

iTrader: (14)

Longer would be better for road racing. Stock actually works pretty well. The Random Tech is nice for an aftermarket, but don't expect to see much of a gain with ANY torque arm. Money is spent in other places when road racing. (See reply in How to make a FireHawk outhandle a ZO6 thread.

Pro Stock John

iTrader: (34)

Global West Trac-Link is supposed be to be good for 4th gens.

Shorter is better for roadracing, and longer is better for dragracing. Longer for dragracing moves INSTANT CENTER.

ChrisB

[quote]Originally posted by Pro Stock John:
<strong>Shorter is better for roadracing, and longer is better for dragracing. Longer for dragracing moves INSTANT CENTER.</strong><hr></blockquote>

I don't quite agree with that - check out the thread titled instant center. If you have a lower hp/NA car (I would say under 600rwhp or so) then I would lean to a much shorter torque arm - of course it also depends on tire, track. I would only want a longer torque arm if you start talking serious power - Like Billingsley, Sled, Madman, George, etc.

edit: As for road racing - when you go with a shorter torque arm you are also going to tend to reduce your amount of nosedive greatly - because you are reducing your weight transfer to the front, not because the suspension is stiffer. This would seem to me to reduce to total effective braking force of the front wheels and make the rear more important. I think I would go with Patrick G on this and preferr a longer or stock type torque arm for road racing.


Chris

[ December 29, 2001: Message edited by: ChrisB ]</p>

mitchntx

iTrader: (14)

For our cars, 99% of which are producing 375rwhp or less, it's not so much planting the rear on accelertion, rather keeping the rear on teh ground during heavy braking!

I intalled the G2 torque arm and my wheel hop disappeared.

Patrick G

iTrader: (14)

Chris & Mitch,

Thanks for replying to the thread. I'm not sure that PSJ understands the complex dynamics of suspension geometry. Throwing around buzzwords like "instant center" are great when you know what they mean. <img src="gr_images/icons/wink.gif" border="0">

When road racing, you want as little to upset your front & rear balance as possible since both are usually at their limits in a road race. A long torque arm will eliminate most of the "porpoising" that occurs when accelerating and braking in a road race. A short torque arm is great for planting the rear tires, making it great for a drag car, but in a road racer, the body would be going up and down too much...stability is upset and the tires will unload...not good.

Crazyquik

Ok, we've about come to the conclusion that a shorter torque arm is better for most of the cars here drag racing, as it plants the tires harder and makes the nose rise faster. What about for road racing and autox? Would a longer torque arm help keep the rear planted during hard braking when the forces are acting in the opposite direction?

J.

Pro Stock John

iTrader: (34)

It's been a few years since I talked to the guys at Global West. Their trac-link is FOR roadracing. <img src="gr_stretch.gif" border="0">

Longer torque arms are designed for DRAGRACING.

Pro Stock John

iTrader: (34)

It's been a few years since I talked to the guys at Global West. Their trac-link is FOR roadracing. <img src="gr_stretch.gif" border="0">

Longer torque arms are designed for DRAGRACING.

ChrisB

[quote]Originally posted by Pro Stock John:
<strong>
Longer torque arms are designed for DRAGRACING.</strong><hr></blockquote>

Backup this statement please <img src="gr_stretch.gif" border="0">

Chris

Pro Stock John

iTrader: (34)

I will get a few folks to come over and join this thread... A few folks who make the dang things. <img src="gr_stretch.gif" border="0">

ChrisB

Go for it <img src="gr_stretch.gif" border="0">

What mitch said about rear wheel hop is an excellent point and got me thinking. In regards to the road-racing setup I think what you are going to want is a sort-of "decoupled" torque arm setup. The main problem I see is when you get into a torque arm setup that gives you good anti-squat characteristics you are going to also be setting up a situation where braking torque will actually lift up the rear axle as it pivot's around the front torque arm connection.

Now if you had a torque arm that only applied a torque to the rear end in response to accelerating induced torque - say a free floating torque arm with a jounce spacer or somtehing on top, and then a different member mounted above to counteract braking torque - say use some sort of telescoping or sliding uppder link that bottoms out under braking force so to apply the resistive torque to the rear end - under braking only. This should totally eliminate *any* wheel hop, and actually allow you to tune the rear loading under braking.

With a non-decoupled torque arm it seems like you are just asking for brake-hop though.

This would let you setup/tune your rear suspension characteristics independently - the t/a for accelerating, and the upper link for breaking.

I think you are still going to want a shorter torque arm for reduced anti-squat and an ability to apply power sooner out of the corner - since keeping the front wheels on the ground isn't an issue here.


Chris Bennight

[ December 30, 2001: Message edited by: ChrisB ]</p>

1CAMWNDR

iTrader: (21)

In one way or another they BOTH can be for drag racing. IF you already plant the tires and need more weight transfer, then a longer torque arm that connects to the front of the car will raise the front end as the differential rotates.
However, since our cars dont hook very well, a shorter torque arm will actually force the tires into the ground ( it looks like the rear of the car is rising if an A4 is brake-torqued) as the differential rotates.
This is why a torque arm was installed on the Grand National GNX, the stock rear suspension didn't plant the tires or raise the front end for weight transfer.
Did that make sense?? <img src="graemlins/gr_punch.gif" border="0" alt="[fight]" />
<img src="graemlins/formula.gif" border="0" alt="[Pontiac]" />

mitchntx

iTrader: (14)

Not really ....

I mean I understand the physics of how and why a TA is necessary.

But, it's my understanding that weight transfer is not a desired trait.

As far as "planting" the rear, at 350hp (like 95% of those here) wheel spin exiting a corner at 40mph on R compound tires is not an issue, at least not for me.

But, again, my issue is too much rear brake bias. I mash the stop pedal so hard, the rear hops terribly. My LG TA has helped tremendously (stock length and mounting points), but the hop is still there.

These cars will go from 100 to 0 a helluva lot faster than they go from 0 to 100 so anything I can do to help the decelleration performance.

1CAMWNDR

iTrader: (21)

Well then, you still could benefit from a shorter torque arm. Look at it like this:
When braking, the differential rotates in the opposite direction from accelerating (nose rotates down). With a longer torque arm, attatched closer to the front of the car, then you are pulling the nose down, and shifting weight to the front---decreasing the amount of traction for the rear brakes.
With a shorter torque arm; attached in the center of the car or slightly behind the center point; instead of pulling the nose down, you will pull the cneter of the car down, therefore keeping some traction for the rear brakes.
This will keep the car from nose-diving so much. The "nose-diving" causes 2 problems. Unloading the rear tires (less Front/Rar breaking proportion) and upsetting the weight balance of the car.
That is how I think of it. <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />
<img src="graemlins/formula.gif" border="0" alt="[Pontiac]" />

[ December 31, 2001: Message edited by: 1CAMWNDR ]</p>

mitchntx

iTrader: (14)

Interesting dynamic ...

As the TA and it's associated mounting point to the body gets shorter, the leverage it has increases.

With the stock mounting location, the effective length of the TA is to the rear trans cross member. The front mount of the TA is the tail shaft of the trans, which is mounted to the rear cross member, the only hard mount to the frame, the motor mounts not withstanding.

Doesn't the GW TA mount utilize the cross member as a mount ... so in effect making it the same length?

LG Motorsports

OK fellas,

Control your wheel spin with your spring rates, and let your torque arm locate the rear suspension. If you have too much torque and you spin the tires out of a corner, you need to soften the rate in the rear. Either with the springs or shocks. If the shocks have too much bump in the rear, then you will have "Transition" oversteer, if it is not the shocks, then it is either the sprrings or the sway bars.

Always work with the end that is not getting grip. Add traction to the problem end. Changing the geometry, (instant center) is something that needs much testing to get correct. Just quoting "rules of thumb", ie; "shorter doess this, or Longer does that" will get you off the mark. Try to focus on the basics and you will get faster, rather than trying to re-engineering the F-body.

In short, the stock length TqArm has the least effect on "Instant center" and thus provides more predictable handling. The car can feel very unsettling if the Inst Cnter is moving around too drasticly.

We are making a shorter adjustable Tq Arm for Drag racing. It will have its own front mount, away from the Trans mount. So stay tuned for the results.

Later
Thanks, Lou Gigliotti LGMotorssports.com

ChrisB

[quote]Originally posted by 1CAMWNDR:
<strong>
With a shorter torque arm; attached in the center of the car or slightly behind the center point; instead of pulling the nose down, you will pull the cneter of the car down, therefore keeping some traction for the rear brakes. </strong><hr></blockquote>

But the "pulling" is leveraged off the rear end - so when pulling down on the center of the car the opposite force is pulling up on the rear end - which gives you wheel hop. I think a shorter torque arm - if it's directly coupled to the frame - is going to have a much greater tendency to wheelhop - for the exact same reasons it hits the tires harder in a launch.

Lou: Thanks for the great info, probably the only actually usefull bit of information on this thread! Looking forward to seeing your new torque arm for drag racing.

Also, since you may have determined it previously, do you happen to know the height of the centre of gravity on a stock f-body?


Thanks,
Chris

1CAMWNDR

iTrader: (21)

[quote]Originally posted by ChrisB:
<strong>

But the "pulling" is leveraged off the rear end - so when pulling down on the center of the car the opposite force is pulling up on the rear end - which gives you wheel hop. Chris</strong><hr></blockquote>

I see your point. HHhhmmm. I guess that the TA can't be the only answer then (Like LG said). Perhaps a TA and some heavy duty LCAs?? I can't think of how to keep the counter-force under braking from causing wheel hop. <img src="gr_images/icons/mad.gif" border="0">
Must have to be in the spring/shock set-up like LG said. I have no idea what to do there; without causing a lose of performance in some other aspect. <img src="images/icons/confused.gif" border="0">
Yin and Yang. Give and Take. <img src="gr_eek2.gif" border="0">

mitchntx

iTrader: (14)

[quote]Originally posted by ChrisB:
<strong>

Of course the practical answer is what lou said - just get a good TA designed with your application in mind and use other factors to tune to your requirements.

</strong><hr></blockquote>

Makes sense ... the TA is more of a location device, rather than a traction aid.

Granted, it can be used for traction, but that is a band-aid.

ChrisB

Decouple it - have the torque arm only apply force when accelerating, and another member that only applys force when braking. The torque arm would have to be free floating with just a rubber snubber on top. When you accelerated it would "hit" something and be stopped, applying force torque to the body. I would stick some link of telescoping linkage mounted high up on the rear end to the frame rail - this would slide until you had a breakign force and would then bottom out. I don't think it should cause any brake hop if it was mounted up high.

Obviously you would want to tune the point of impact and bottoming out on the 2 members so you didn't have a loose feel in the rear of the car. Not something I have the skill to do - just the only way I can think of to keep the TA from trying to induce any kind of wheel hop on breaking.

Of course the practical answer is what lou said - just get a good TA designed with your application in mind and use other factors to tune to your requirements.


Chris