Torque Arm versus 3-link characteristics

[D-Man]

Hi All,

I've narrowed down the choices for the rear suspension on my '70 Camaro to either a Torque Arm or 3-link.

Goals are:
Fit 335 rear tires
Better ride
Better street performance with an emphasis on twisty highway driving
Predictable handling

Not concerned with the absolute lowest lap time potential.
Faster is better obviously, but not looking to win any competitions.
Not interested in a 4-link system - at all.



A Torque Arm has definite benefits that I like:
Fast and easy to install (although I do weld and fabricate)
Little or no modifications to my original body
No intrusion into the back seat or trunk area

However, there seems to be general consensus that overall a 3 link performs better than a torque arm. How much I have no idea. Also don't know if one or the other inherently rides smoother.
So for those with experience with both types of systems what, if any, handling and comfort differences am I likely to notice with spirited street driving? Assuming the same type of joints (say delrin) are used in both suspensions.

Any chance that upgrading from a Torque Arm to a 3-link would have me saying this "is so much better"? Intuitively I'm thinking no, but would like to hear from those with real world experience.

[dontlifttoshift]

It always comes down to packaging. Those upsides you listed are the opposite of a 3 link install. Given your intended usage run the torque arm and go have fun with your car.

I've never had a TA and a link type in the same car but truck arms act very similar and I have had those and a 3 link in the same car, again, for your intended use the added effort of a proper 3 link isn't worth it.

[D-Man]

Thanks. Packaging is one reason I won't go 4 link. Is there anything you don't like about the 3 link?

[c4racer2]

Generally speaking a 3 link is for a race car - no back seat, cage, etc.

[parsonsj]

A 3 link impinges on the rear seat, as the middle chassis link is approximately in the "ass" location for most cars. I got around that in my Nova by using bucket seats and a tall center console in the rear of the car.

The torque arm is the better choice for a street car, I'd agree.

[dontlifttoshift]

Thanks. Packaging is one reason I won't go 4 link. Is there anything you don't like about the 3 link?

Packaging. Past that there isn't a downside, but packaging is a pretty significant down side.

[D-Man]

A 3 link impinges on the rear seat, as the middle chassis link is approximately in the "ass" location for most cars. I got around that in my Nova by using bucket seats and a tall center console in the rear of the car.

The torque arm is the better choice for a street car, I'd agree.

That's what I would do if I go 3-link. Centered and parallel or slightly angled (top view) upper link (I know there are some disadvantages to that) and buckets. 9 inch Ford.

Can you tell me about your system. Did you use a kit or build it? Is the upper axle bracket one hole or the tall multiple-hole adjustable type?

Seems like I would be able to get enough anti-squat without a tall upper axle bracket, but I haven't got that deep into it yet.

Packaging. Past that there isn't a downside, but packaging is a pretty significant down side.

For sure. But if I could use a short bracket on the axle top (and still get good geometry) the intrusion into the rear seat area wouldn't be too bad. I think.

If anyone can speak to packaging/geometry on a 2nd gen I'm all ears.

[D-Man]

Also, packaging issues aside, any other thoughts on torque arm vs 3-link handling characteristics?

[CSG]

I had one of each at the same time both in fox mustangs. Only real world downside on my TA car was a bit of wheelhop when I screwed up. Both did well and ran very close lap times. I would do a TA for your situation.

[Mark@lateral-dynamics]

The biggest advantage to a 3-Link versus a T/A is the ability to tune such factors as anti-squat/instant center - both vertically as well as length. By definition, the instant center of a T/A is where the forward point attaches to the vehicle - again both height and length. As such, T/A systems typically have "short" IC's, which translates into higher anti-squat figures. In the case of really high A/S numbers, under full acceleration the system is nearly locked up due to the torque reaction, and on rough courses can create traction issues, though this is not typical. With high A/S numbers, the downside is that the car will have resulting "poor" Anti-Lift, which is the torque reaction under braking. It's there with all of the systems on the market that I have seen, and people are forced to drive around the issue - which is wheel hop. I don't like anything that upsets the behavior of the car, ESPECIALLY under braking - when you have you hands full hitting your marks, downshifting, trail braking, etc.

A well done 3-Link will allow you to really fine tune the setup to eliminate the downside of the T/A systems. Installation can be significant, or not depending on how the system is packaged, and in some cases means leaving the trunk alone, and allowing a rear seat. If you can do a 3-Link, do it, it is the best stick axle setup in existence.

[another69]

How do you minimize wheel hop under braking with a torque arm system? Most of the aftermarket kits have adjustability built in, but if you are able to minimize wheel hop what is the trade off?

[Mark@lateral-dynamics]

Wheel hop under braking is predominantly due to the geometry of the suspension, with a far lesser influence from the shock package. Fact. The perfect example of this is watching the NASCAR races on road courses, where they have real braking zones. Best example is the hairpin at Sears Point, it gets so violent that they actually brake axles as a result of it, besides the fact that they lose control and get passed. NASCAR use Truckarm suspension systems by the rule book (which is really stupid), these systems have a very similar "Instant Center" that the Torque Arm setups have. So, if the bottomless pockets of those teams can't tune it out, it is highly unlikely that an aftermarket producer can. It's just how the mechanics of the systems work out.

If you can't do a reasonable 3-Link, the T/A is the next best thing, it just isn't as good both in theory and demonstrated in actual real world performance as well.

[CSG]

I agree with what Mark has said but I want to ad that typically you have to be driving harder than most people do to hop a well designed TA car. We are talking about track only hard core driving and even then my car only hopped when I screwrd the heel toe downshift and only around 25% of those.

[D-Man]

I had one of each at the same time both in fox mustangs. Only real world downside on my TA car was a bit of wheelhop when I screwed up. Both did well and ran very close lap times. I would do a TA for your situation.

Thanks for the real world experience feedback.
Do you know how long your T/A was?

The biggest advantage to a 3-Link versus a T/A is the ability to tune such factors as anti-squat/instant center - both vertically as well as length. By definition, the instant center of a T/A is where the forward point attaches to the vehicle - again both height and length. As such, T/A systems typically have "short" IC's, which translates into higher anti-squat figures. In the case of really high A/S numbers, under full acceleration the system is nearly locked up due to the torque reaction, and on rough courses can create traction issues, though this is not typical. With high A/S numbers, the downside is that the car will have resulting "poor" Anti-Lift, which is the torque reaction under braking. It's there with all of the systems on the market that I have seen, and people are forced to drive around the issue - which is wheel hop. I don't like anything that upsets the behavior of the car, ESPECIALLY under braking - when you have you hands full hitting your marks, downshifting, trail braking, etc.

A well done 3-Link will allow you to really fine tune the setup to eliminate the downside of the T/A systems. Installation can be significant, or not depending on how the system is packaged, and in some cases means leaving the trunk alone, and allowing a rear seat. If you can do a 3-Link, do it, it is the best stick axle setup in existence.

I'll need to do more reading to understand that fully.

Reading between the lines a 3-link can have the same (high) A/S as a torque arm but without the brake hop issues?

I found pictures of your old 3-link and didn't think it was too bad as far as cabin intrusion with the centered top link.

How do you minimize wheel hop under braking with a torque arm system? Most of the aftermarket kits have adjustability built in, but if you are able to minimize wheel hop what is the trade off?

Which kits are you referring to?
The only adjustment I've seen on the T/A kits I've looked at is pinion angle. Which is set at the differential.
T/A overall length and front attachment height are all pre-set, non-adjustable.
Diff attachment height is also preset, but I don't believe that adjustment would make any difference anyway.

Wheel hop under braking is predominantly due to the geometry of the suspension, with a far lesser influence from the shock package. Fact. The perfect example of this is watching the NASCAR races on road courses, where they have real braking zones. Best example is the hairpin at Sears Point, it gets so violent that they actually brake axles as a result of it, besides the fact that they lose control and get passed. NASCAR use Truckarm suspension systems by the rule book (which is really stupid), these systems have a very similar "Instant Center" that the Torque Arm setups have. So, if the bottomless pockets of those teams can't tune it out, it is highly unlikely that an aftermarket producer can. It's just how the mechanics of the systems work out.

If you can't do a reasonable 3-Link, the T/A is the next best thing, it just isn't as good both in theory and demonstrated in actual real world performance as well.

Would this be reasonable geometry for a 2nd gen F-body street car?

Centered top link (between the rear seat buckets).
Top link situated as tight as possible to a Ford 9" housing (i.e. only one mounting hole in the bracket).
Trailing arms in basically the factory leaf spring mounting location at the front.
Adjustable trailing arm brackets at the axle.
For a starting point.

I agree with what Mark has said but I want to ad that typically you have to be driving harder than most people do to hop a well designed TA car. We are talking about track only hard core driving and even then my car only hopped when I screwrd the heel toe downshift and only around 25% of those.

Was that on race tires and would street tires (335s) make any difference?

[another69]

D-man,
The adjustment I am referring to is on the Speedtech TA system. The lower links can be adjusted (they say make them parallel to the ground I think) as well as the panhard bar & of course pinion angle. Not nearly the adjustment of the 3 link, but I wonder if any of the adjustments affect wheel hop?

[Rod]

fun thread....

[CSG]

Sorry, I do not know the length of mine. It was a custom piece that Roush did.

I never hopped mine on street tires only on stickies. That may not mean anything though as I was not driving hard into turns with the street tires. I was fastest qualifier at nearly every race with that car in my rookie season so the design can get it done well. I don't think I could have done that in a car that was not really good.

[D-Man]

D-man,
The adjustment I am referring to is on the Speedtech TA system. The lower links can be adjusted (they say make them parallel to the ground I think) as well as the panhard bar & of course pinion angle. Not nearly the adjustment of the 3 link, but I wonder if any of the adjustments affect wheel hop?

That's good. Inclination of the lower links would change instant center if I'm not mistaken. Not sure what else?

Sorry, I do not know the length of mine. It was a custom piece that Roush did.

I never hopped mine on street tires only on stickies. That may not mean anything though as I was not driving hard into turns with the street tires. I was fastest qualifier at nearly every race with that car in my rookie season so the design can get it done well. I don't think I could have done that in a car that was not really good.

I don't doubt your torque arm car was really good. It's actually rare to find negative comments online regarding T/As.

This may be wrong or too simplistic, but my understanding is that short arms hook up better (more AS) and longer arms have less wheel hop.
Last night I was doing some napkin engineering for an adjustable length T/A. It's actually quite feasible.
That said I'm sure someone (racer or vendor) has played around with T/As enough to know what length approximately is best for a 2nd gen road car.

[SSLance]

We tried for a couple of months to design an adjustable length TA for my G Body and just couldn't find room under the car for an adjustable forward mount.

The sweet spot for a 108" WB car is somewhere between 45-55" long from our calculations.

[Rod]