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Since 2014, I have the pleasure to drive the Alfa Romeo 4c. However, the longer I drove the car, the more unsatisfied I got with the responding behavior of the factory-installed suspension. I was therefore searching for an aftermarket suspension strut that meets my expectations of a smoothly driving, yet highly precise and responsive sports car. After a long and thorough research, I feel like I have finally found my solution: The Tractive ACE Suspension kit.

In this thread, I would like to summarize my experience with the Tractive Suspension kit for the 4c. This post is a technical overview that addresses the following points:

  • Motivation
  • Mechanical vs active damper
  • The components of the suspension system
  • Construction of the active damper
  • Control unit
  • Input device
  • Functionality
  • Videos


Motivation


It has been claimed many times before, that the factory tuning of the springs and dampers is suboptimal. Like many others, I was searching for a way to upgrade and customize my sports car. I remembered the active suspension used by Formula 1 cars during the most successful years of Ayrton Senna. It would be amazing if something similar were available in the aftermarket. During the investigation, I have found a few suppliers with similar products. The decision was made in favor of Tractive Suspension Company.

Here are the main three reasons, why the active suspension is superior to a passive version:

  • Adjustable while driving
  • The active suspension adjusts to the driving situation depending on the settings. More on that later.
  • It gives our beloved 4c a comparable technology as is installed in the latest top end sports cars — for a reasonable price.
Since the beginning of March, I am in contact with Tractive Suspension by phone and in writing. The suspension struts that we ordered should arrive soon and will be installed ASAP. I will then be able to write a detailed driving report. I would like to share my knowledge about the technical parts of the suspension kit with you.



Mechanical vs active damper

Link to the image: https://tractivesuspension.com/wp-content/uploads/2018/12/TT-4-1024x813.png
(source: Tractive Suspension)

In this picture, you see different damper characteristic curves. These curves describe the relation between damper piston speeds (X-axis) and damper resistance forces (Y-axis).The curves above the x-axis are for rebound, the curves below are for compression. On an adjustable, pure mechanical damper, it is possible to switch between these curves with the setting screws. With an active damper, a software replaces the setting screws and is able to adjust the settings several times per second. This enables a situation specific damping behavior.

The components of the suspension system

  • 4 suspension struts, made of aluminum, MacPherson strut diameter 43mm
  • Control unit – the brain of the system
  • Input device, touch screen display
The four struts and the Input device are wired to the control unit. The weight of the complete system is lower than the stock components.

Construction of the active damper

In general, there are two parts, which control the dampers fluid flow: jets and a valve. The static jets are the same as in any other standard damper. When the valve is closed all the flow goes through the jets, which represents the most resistant damping curve. An electromagnet controls the valve. When current is flowing through the electromagnet, the valve opens depending on amperage. The damper gets softer according to the valve position. This construction ensures that the damper keeps some residual functionality in the cases of power loss or interrupted connection to the control unit. The valve always changes the compression and rebound damping at the same time.



Control unit


The control unit is the brain of the system. It has an accelerometer to measure the g-forces. This delivers the input for the software to calculate the desired resistance for every strut.



Input device


The behavior of the software is adjustable through the touch screen display. There are four values: Front and rear damper stiffness, pitch and roll resistance. Each is individually customizable in five steps. You can change the values while driving. Additionally, five presets can be stored.



Functionality


In general, the dampers try to counteract the g-forces and keep the car flat to the ground.

For example: When you brake hard, the front struts get stiff and the ones in the back soft. This will reduce pitch (nose dive) and the stopping distance of the car.

The front and rear damper-stiffness settings define the behavior of the system, while no g-forces are acting. Regulating this value will adjust the lowest damper stiffness. This is comparable to the adjustments made with the setting screws on a passive damper.

The pitch and roll settings define the behavior of the car, when high g-forces are acting. They define how much the damper tries to counter chassis rotation. Or differently phrased: How resistant the loaded dampers get under g-forces. At same time the load free dampers get softer.

When the stiffness is set to the lowest value and the anti-roll is set to the highest, the controller is enabled to use the full range of the dampers. Consequently, the working range of the dampers can be adjusted on the lower and upper end.



Videos

The first video shows a recorded lap in a data analyzer. At the lower left, you can see the plots for the damper amperage. Remember: low amperage means stiff and high amperage soft. The graphs named “LF RF LR RR” are the ride heights for each wheel. The controller used in this video is from DSC Sport. The function is similar to the tractive controller.


The next video shows a brake test comparison between a stock and modified Nissan GT-R. I think the braking distance difference is impressive.


Last video is a comparison between a stock and modified Ford Focus RS. It is easy to notice that the car with the active damping is calmer. (Turn down the sound. It was a bit windy during filming.)




I hope this summary was insightful and gave you a broad overview over of the Tractive ACE Suspension kit’s abilities. If you are still not convinced, remember this thread the next time you are lying below your car, adjusting the suspension.

Feel free to ask any question! I will update this thread as soon as I can drive the modified car.
 

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The dream is becoming a reality..Thank you for posting, Dr Duke. Waiting with eager anticipation the fitment of these to your 4C. I hope they are everything they’re cracked up to be. Are they rebuildable and are parts readily available? Sorry if that has already been explained.
 

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Stupid question here, but what do these do for feel?

The 4C is such a visceral car that it absolutely screams at you as to what it is doing.
For better or worse, the longitudinal weight transfer is dramatic, and lateral is quite controllable. Changing to stiffer or statically adjustable shocks doesn’t alter this, just the amount that the body moves around and how much the wheels lose contact with the road.

Having dynamically changing dampening must change the feedback you get, along (I assume) with how you have to drive the car (on track, or auto-cross - there is no other reason to get these). I’m sure that it makes it easier to drive corners quickly.

Not saying that these are a bad idea. On the contrary, I very much want something like this. Just curious as to what all they mean in terms of how you drive the car approaching 10/10.
 

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I know of many on the Viper forums that loved their Tractive (aka DSC Sport) setup and said it didn't take away anything, just made driving better for the purpose they were adjusted for. I might look at this for the 4C....
 

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What are input signals for this active dampers?
As far I know, all the cars with active suspension have an armada of sensors to actively control the damper. What possibilities are offered by the 4C?
 

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The dream is becoming a reality..Thank you for posting, Dr Duke. Waiting with eager anticipation the fitment of these to your 4C. I hope they are everything they’re cracked up to be. Are they rebuildable and are parts readily available? Sorry if that has already been explained.
Fingers crossed that they hold up with the expectations. I do not doubt Tractive. Finally the shocks offer a broad range of (hard- and software) adaptability. Therefore, I am not concerned.

The order cycle time is around 4-6 weeks. The kit is “built to order”. I can ask how the current situation is.

The dampers are fully serviceable. During service, Tractive may also change the configuration (expansion reservoir) or tuning of the dampers. For road use, the dampers need a service every 60’000 km.

Factory warranty is 24 months for road use – any form of motorsport is excluded from this.

The big question is

How much does it cost?
I have the prices in euro, the trading currency of Tractive Suspension.

TRAC-AR-Axx03, Tractive ACE suspension kit, 4 dampers including springs €4725,- ex MwSt

TCU-S15, Tractive controller, wiring harness and touch screen display €995,- ex MwSt


What are input signals for this active dampers?
As far I know, all the cars with active suspension have an armada of sensors to actively control the damper. What possibilities are offered by the 4C?
In short: 12V DC 0.6-2A. The input signal for the solenoids is ampere. There is no logic in the damper itself.

The Tractive ACE Suspension kit is independent of the car electronics. In general, it is possible to use the data-interface of the car to control the dampers. We discussed that possibility already. My impression is it would work. One of the concerns is the update rate / signal delay of the car systems. I will look at it as soon as I have gained experience with the Tractive control.
 

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...

In short: 12V DC 0-2A. The input signal for the solenoids is ampere. There is no logic in the damper itself.

The Tractive ACE Suspension kit is independent of the car electronics. In general, it is possible to use the data-interface of the car to control the dampers. We discussed that possibility already. My impression is it would work. One of the concerns is the update rate / signal delay of the car systems. I will look at it as soon as I have gained experience with the Tractive control.
So it's based on an accelerometer in the control unit, and whatever settings you give that controller?
 

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Discussion Starter #10
Stupid question here, but what do these do for feel?

The 4C is such a visceral car that it absolutely screams at you as to what it is doing.
For better or worse, the longitudinal weight transfer is dramatic, and lateral is quite controllable. Changing to stiffer or statically adjustable shocks doesn’t alter this, just the amount that the body moves around and how much the wheels lose contact with the road.

Having dynamically changing dampening must change the feedback you get, along (I assume) with how you have to drive the car (on track, or auto-cross - there is no other reason to get these). I’m sure that it makes it easier to drive corners quickly.

Not saying that these are a bad idea. On the contrary, I very much want something like this. Just curious as to what all they mean in terms of how you drive the car approaching 10/10.
You are spot on with your thoughts!

I think in general driving will be much less surprising and a little less scary. Bumps should be better absorbed. In fast S-turns the car should roll less. A new feature: "pitch stabilizer" gets added. In general, stability through the suspension is better than a hard stabilizer - the suspension remains more independent. I'm curious too!


These two clips are from a rally event. The videos are cut the same. In the individual camera settings, the cars are well comparable.

Tractive Lotus

Passiv Lotus
 

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Yeah, 0:57 in the first video and 0:35 in the second one - although I think that the blue car takes the bump a bit faster, the way the car unsettles when compared to the white Tractive car is quite obvious. Good comparison!
 

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Thanks! These two corners are also nice to watch: white 1:48 vs blue 1:39 and 2:36 vs 2:47. The white car won the race and the blue became third.
 

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Discussion Starter #18
Weight difference to stock?
When I remember correctly:

The front shock absorbers are about the same weight. The Tractive rear ends should weight 6.3 kg each. The stock is around 9 kg.

The control unit weights 0.7 kg together with the display and wiring maybe 1.5 - 2 kg.
In total 3 - 4 kg weight saving.


I think @Y Cymro will update us soon.
 
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