Torque arm front mounting location difference? LG vs Spohn
 

I'm in a real pickle here and I'm looking for some experts w/ this one. I've heard the shorter arms are better at 1/4 and things of that nature while longer is for autox etc. LG's arm is preset w/ -.5 degree while a spohn or any other TA you can adjust to your delight. Spohn use to have a slider mount but no longer but LG has some type of slider mech from what I've been hearing allowing for the rear to travel as it's going through it's paces.

Is there really gonna be that much of a handling difference between the 2 and who has 1st hand experience w/ both? I had a short arm which broke and it did fine w/ Road and Drag at least it did for me. 1 thing I like about Spohn you can go dual loops w/ sperical rods etc. What do you guys prefer and why? Hopefully a lengthy discussion will come out of this and I get to learn a bit more w/ susp etc.

Thanks!

I was going to get LG, but I bought Spohn. Spohn really plants the rear down when your on the throttle. But I feel the rear end hops a little more under hard braking. Plus I get a lot of drive line noise from it. I normally dont mind that, but Im hearing my diff spinning, and hear it spool down whenever Im stopping. Maybe my diff is just going? I talked to Lou and he's first comment was that he thought it would break under race conditions. He tends to be a salesman when talking to him most of the time, but I dont know if he has any experience with Spohn's design. It was not really made for road racing like Lou's is. If I was to do it over, I would have bought Lou's or maybe Random Tech's version (its adjustable). I actually kind of like the non-adjustable. One less thing to be messed up. And I dont think that you want it too far from 0* for road racing.

good luck!

--Kevin

Thanks for the response. I've been looking at LG's unit but my only problem is since I had a short arm before I removed all the stuff that went for a long arm. I don't even remember what goes on there now let alone where to get it from cheap.

I just like the fact of having dual loops and heim joints. But maybe I really shouldn't be concerned w/ that as much. My old arm would hop under hard braking as well but nothing that I couldn't predict and correct. I wish he'd sell that thing a little cheaper though. Spohn w/ all the trimmings is 455 at best and w/ shipping probably the total of LG's arm alone. I can reuse my old cross member and front loop and save there but I won't have nothing for the rear. Oh well............

Once I can find out what I actually need for mouting a long arm I'll probably go that route too. I get tired of adj for street/track/strip myself.

How much noise are you actually getting? I'm pretty loud so I probably won't hear much of anything.
Silas,

F.Y.I., LG has a 25% off sale until the end of the month on suspension components. That would make your torque arm $371.25.:D . I just ordered LCAs and a PHR.

Thanks! Ordering now before I miss out!

I replaced my stock Torque Arm 4 years ago with an HPM unit, but am considering replacing it with the Spohn.

The HPM unit is adjustable, tubular and about 1/3rd shorter than the stock TA. The Spohn TA is only about 25% shorter than the stock or LG TAs.

The HPM came with substantial bracing back to the left rear LCA body-mount and has a large driveshaft safety loop. I like the Spohn DSS-Loops better as they restrict the movement of a broken driveshaft. The HPM tunnel brace is significant and ties my Kenne Brown DD Subframe connectors together well. The standard LT1 Spohn TA will give me back about another 1/8" of ground clearance from the HPM.

The only down sides to the HPM design is that it uses a fixed poly front mount, which causes the TA to rotate with a different arc than the rear LCAs and could lead to bind (I have not experienced bind). In addition, the HPM TA is not rated for serious horsepower/torque.

The stock and LG TAs permit some slight fore-to-aft movement (LG like stock through a bushing and Spohn through a short double-pinned rotating link). A HPM TA is the shorter than the LG or Spohn. The LG is stock length, the Spohn front mount is right at the tunnel brace and the HPM is about 10" shorter than the tunnel brace. A shorter arm increases the leverage and rate of planting the rear tires, but lifts the car further back on the chassis. The arm performs well with initial bite, but then seems to taper at greater speeds. It almost feels like it bites hard at first, runs out of travel and then the rear tires break loose as the car crosses the power band. Therefore, I think that a slightly longer arm would work better for non-drag-racing purposes.

LGs comment on breakage: a 1 piece arm won't break rod-ends or couplers. But then again my factory TA came off on me once, when the factory bolts worked loose. At any rate, a TA won't see any more severe service than drag racing, as far as parts breakage. I don't see alot of complaints against Spohn for broken TAs.

Rick R

A Torque arm are a tricky device, and sometimes its used for the wrong reasons.

Going shorter or staying long depends really on how the arm is designed and if it does what its supposed to in the end.

If you use a short arm, you will plant the rear tires more quickly than a long arm, that's a given (anti-squat). If you get traction, well that depends on what kind of power your car has, what tire you're running in the back, how stiff the springs/shocks are, if you're lca's are parallel.

Alot of people ignore this, and think that they can just put a short torque arm and expect that they will get better traction.

The spohn arm isn't significantly shorter than other arms out there. So now you're going to have to see what spring works good. This rotating pivot point they use can cause changes in pinion angle and move the instaneous center forward and backward.
The old style arm made more sense since it used a sliding member but I think this wasn't strong enough.

The LG arm is good because it's like stock, long, and has free movement at the bushing. It is excellent for braking and gets rid
of wheelhop. It's average on putting power down, it just takes a little longer, but you can play with shocks/springs to help that.

An example of a very short arm is the traclink, which has probably the quickest reaction time of any arm out there on the market. It works best with a soft spring, and has excellent side bite, and launch characteristics.
However during braking, the arm lacks the good behavior of the long arm and tends to buckle too much during hard braking causing wheelhop. This can be cured a little with rebound adjustment in the shock, or adding more brake bias to the front. But in general use this arm only if you know what you're doing
and know how to drive the car with it.

Unbalanced Engineering will release soon a de-coupled torque arm which is short for acceleration and virtually long for braking (since it is decoupled).

I've seen the prototype at a local track and the mounting beam is very well designed (similar to traclink) one end mounts to floorpan by drilling holes, and the other end mounts to driveshaft crossmember (like the spohn), instead of the tranny crossmember like the tracklink.
The arm itself is very short and connects to the beam in a special way :)

Steve

Response to Steve C
 

Steve,

Didn't SLP attempt to make a de-coupled TA for track use? Per Steve Spohn, that TA slammed so low on braking, it nearly hit the ground. SLP does not make that anymore. Hopefully, the Unbalanced Engineering design you spoke of won't have this problem, because that would provide the best for acceleration and braking.

I don't believe the amount of fore-to-aft movement of the Spohn TA would significantly change pinion angle. My 60% length HPM TA (fixed front pin design) can hang the suspension to full shock-limited droop (which is alot) and there is still no suspension bind. Similarly, on compression there is no bind. The rear LCAs limit fore-to-aft movement, especially if the LCAs are parallel. Therefore, the Spohn design solves the "pinned" problem without the looseness/noise of sliding member.

As far as the cost differential. With the Spohn, you get 2 DSS loops, stronger tunnel brace, and an adjustable pinion angle. So there is really no difference in price, after buying a DSS.

I am still leaning towards the Spohn, but I can see the merits of a simple LG arm.

Yes SLP had one, it was the Herb Adams torque arm.

I'm not sure how the Unbalanced one will behave, i'm sure they will test it further.

Fore and aft movement is necessary in a torque arm, or else you will compromise the natural movement of the rear suspension components... everything's connected and works in unison.

You can't look at the suspension staticly and make guesses that since you have full limit at droop and under load, everything will work as expected.

Forces act on three planes, you would have to model the suspension in a program and simulate at speed turns, roll, pitch, ect...

The tunnel brace is not a strong area to mount a complete torque arm period. It is cheap stamped steel meant to hold a flimsy tunnel brace with 4 tiny 13mm bolts.
Luckily the arm is not so short to simply rip off the car. If you have KBDD's you're in a better state to mount it but it's not an adequate area.

Also if the arm rips off your car, that fancy loop will take the driveshaft with it... won't that be nice.

A good loop like the LG unit, reinforces the tunnel area and protects the fuel lines from damage.

Clarification to Steve C
 

Steve,

It seems that you misunderstood my last post and I have some clarifications.

The HPM TA that I currently have is a fixed "pinned" design which uses a poly mount. I know that it is not ideal, due to lack of fore-to-aft freedom of movement. Fortunately, in practice the poly mount appears to compensate for it some, as there is no bind. I set the locknut loose to permit some twist of the TA for cornering and I have not noticed any real wheel hop under hard braking.

However, the fixed pin design is why I want to replace this TA. By the way, I don't know if you have seen the HPM TA, but it has all kinds of bracing back to the driver's rear LCA and to the driver's seat belt mount. The HPM TA is very short (about 8" behind tunnel brace - maybe 32" bar length), so it probably needs it. In addition, as you acknowledge, the HPM is mounted through the factory tunnel brace mount and the KBDD subframe connectors, which further increases strength.

My only performance complaint about the HPM TA is that it gives great initial bite, but then appears to soften. This is probably as it plants the tires at a faster rate, but lifts the car further back on the chassis, appears to run out of effective travel and looses bite. A swap back to a longer bar would reduce the initial bite, but keep the forces more linear and lift the car more in the center of the chassis.

The Spohn does include provisions for fore-to-aft movement of the TA so that the differential is not simply rotating around the front mounting point of the TA. It uses a double pinned link "locator". Theoretically, this is not ideal. However, while a up-down deflection would occur as this link rotates from vertical to a slight angle, it would not appear to be significant enough to change pinion angle much more than a stock or LG torque arm mounted using thick rubber or poly bushings. My use of Global West rear LCAs with spherical bearings, further limits deflection.

By ripping the Spohn TA off of the car, I assume that you are refering to a failure of the front chrome-moly rod end under acceleration/braking or the separation of the entire frame from the bottom of the car under braking. Steve Spohn states that the bar is 39" long (not including the distance from the differential mount to the center of the axle "twist" point. This provides pretty good leverage, by reducing the axle ft-lb torque applied by roughly 3.5 times. The factory TA mount point extends maybe another 12" for more leverage (4+ ratio), but mounts to a bracket off of the transmission tailshaft, which is not much stronger. The bolts on the factory TA worked their way loose on my car several years ago and my TA flopped around. Fortunately, the DSS Loop that I was using at the time enveloped it and kept the TA from banging my floorboards up.

I see the merits of both LG and Spohn designs and disagree with your condemnation of any tunnel brace designs.

However, 1 point taken is that if I chose to go with another tunnel brace TA, I will consider welding bracing around the factory tunnel brace mounts to strengthen them and adding more welds to the KBDD subframe connnectors in the immediate area.

Have a good weekend.
Rick R

Man that was some great information! You guys really you your stuff. Well after long debate and reading the posts above I cancelled my order. I'm gonna get more info into to this debate as I see more may be in store.

For my application though it's primarily a daily driver when the sun is out of course and lots of track time (road course Nurnburgring & Hockenhiem. Local roads are a dream w/ twisties, blind curves, etc. SO that's where I roam. I run 150 rear springs w/ 3rd Gen bilstein shocks for anyone that maybe curious.

I also was waiting around for UBE to have their's for sale soon but I'm not into the drilling, I like to keep it simple so their TA for now it seems it tossed out of the equation. Still between the 2 mentioned.

Hopefully the debate will continue.......
thanks again!

Any TA with a fore aft movement built in (which is almost all) will have a changing pinion angle. The only way the TA could move for/aft in its front mount is if the entire axle move front to rear. Or the pinion angle changes. We know which happens.

The old Spohn arm had some breaking problems. The new design has fixed the problem and is probably a little lighter to boot.

Putting on a aftermarket TA does not change anti-squat directly. It changes instant center. Which will change the percentage of anti-squat. Because of this just putting on a shorter TA WILL increase straitline traction. The Traclinc is a drag racers dream. Granted LCA angle changes will add traction too.

Of the Torque arms that I know that have won a National Championship at the Solo 2 Nationals are the Random Tech which is stock length and the Traclinc which is the shortest available.

The Spohn is the best comparmise. Short for more traction. Longer than some to keep brake hop and funky corner exit problems to a minimum. Go with the Spohn. I am. And I will weigh in on how it peforms. At the National level.

The Unbalanced Eng. decoupled arm sounds similar to what I'm building, except rules force me to keep the stock arm. I'm hoping that this will increase rear brake performance without the lovely axle hop we all experience.

I think I broke my HPM megabite TA last night.

It is not totally separated, but it sounds like 1 of the members is sliding/grinding, when I back up the car and it did not track straight on my last launch. It makes a sound of a long steel bar grinding axially against metal. Maybe I pulled the adjustable coupler apart and its sliding out, when I am backing up the car. Once work obligations are reduced, I need to get under the car to inspect.

I am not surprised, as the HPM are is not rated for more than 450 flywheel hp or slicks. I don't have slicks, but the 315mm Kumho Victoracer 700s launch pretty well when warmed up.

At any rate, my question is this. As my broken TA still works better in the forward direction (compressed coupler) than reverse (coupler in tension), how strong does a TA have to be for hard-braking/de-celleration?

Spohn says, their TA floats on hard braking/engine deceleration, and does not exert appreciable downforce. Its a fact that I can stop much much faster from 100mph than I can accelerate from 0 to 100mph. Therefore, I would reason that the TA would exert more tensile force on the tunnel brace mount under braking, than compressive force on the tunnel brace during a drag launch.

Steve C brought up the point that the tunnel brace factory mount only uses 4 13mm bolts to mount to a stamped steel brace welded on the body. The last thing that I would want to happen is have then entire TA assembly with brace rip off the bottom of the car and dig into the ground.

I may need to dig up my old statics problems, but it seems to me that the forces (excluding front brake force) would be equal and opposite for acceleration and deceleration. The only variable is the location of the rear LCAs.

What do you gentlemen/ladies think?

Rick R

ICORNER i've never seen the HPM arm before so I can't really comment on how it works. Furthermore I've never installed it on
my car so I can't tell really what it's doing.

As for your argument about the rotating bracket member not causing changes in pinion angle, well remember the last time you adjusted pinion angle on your car. How long did it take you to get your 0, -1 or -2 angle? Remember how little you had to rotate the heim joints or hex bolts to get it right? This bracket is moving at angle every time you accelerate and brake. Try to measure the changes in pinion angle (you can't ). So how will you know what it's dialed into? Setting it when the car doesn't move, doesn't tell you in this case what pinion angle you're left with.

Fore and aft movement of the torque doesn't change pinion angle. It doesn't change the angle of the torque arm because the whole arm slides together which is connected to the pumpkin and it slides with it, there's no rotation.

I don't see the point to go to the Spohn I've had it, it's moderate at traction, depending on how much pinion angle you put it gets better or worse. But then again you can adjust pinion angle with other arms.
Corner exit is again moderate, nowhere near the Traclink's performance.
And braking... well remember, a longer arm is always better so again no advantage there.

I just think that if you're going to spend the money, you might as well find more significant advantages to a product.