If you’ve been following the build of Project Gruppe R, you’re well aware that we’ve taken a 2013 VW Golf R and have been transforming it into a rally/recce car to carve up the tarmac, but transition onto gravel seamlessly.
To date, our R has received new PowerBrake rotors and calipers, BRAID Wheels and Toyo Proxes RA1 tires, ProFlex gravel-spec coilovers, an extensive aero package, and some other rally essentials. But making this concoction of bits all work together, is where testing and tuning enter the picture.
As we mentioned in our coilover install article, suspension makes a rally car. We should amend that assertion to say well-tuned suspension makes a rally car. If the damping and spring rates that control the chassis dynamics are so wayward as to upset the car, we’ve taken a step back.
To leap forward we began to work with in-house R.Tec tuning expert Fabio Lazzerini. Our Belgian friends over at R.Tec made sure we stayed in good hands as our liaison Gil van den Heuvel passed us up the chain to the next phase of guidance.
It can be confusing to determine what adjustments to make when tackling 3-way coilovers – what metering fields influence what handling characteristics isn’t always clear. Our ProFlex coilovers feature low-speed compression, high-speed compression, and rebound adjustment. When referring to low or high-speed it is important to remember we are talking about shaft speed, not vehicle speed. Look for the sidebars with troubleshooting tips from an unofficial ProFlex Tuning Guide, in each adjustment.
We addressed the handling characteristics of the OEM struts in our introductory article, and we were expecting a night and day change with our gravel setup. R.Tec went to great lengths to make sure the initial valving curve would suit our application and even supplied us with a baseline setting for the different metering screws on the dampers.
Per Heuvel and Lazzerini, we would start our tuning from 12 clicks of rebound, 10 clicks of high-speed compression, and 10 clicks of low-speed compression. With a total range of 26 possible clicks in each field, we are left with 17,576 permutations of damping settings. When you add in spring rate changes and ride height as variables, that exponential number becomes an infinite range. Starting in roughly the middle of each field will allow us some room to go softer or firmer without running into a high or low extreme.
“The chassis handling settings of a car are very complex, because a lot of parameters are acting together, and moreover it’s dependent on the driver as well. In order to take advantage of your suspension, every different rally condition needs special fine tuning. The basic setup will be 80 percent ok, and the last 20 percent will need some work,” Lazzerini began to explain.
The chassis handling settings of a car are very complex, because a lot of parameters are acting together, and moreover it’s dependent on the driver as well. -Fabio Lazzerini, R.Tec
The ability to get the car out of the steep driveway without crunching the nose was a pleasant start. It’s about 1,000 feet of undulating gravel from the driveway to the tarmac. Immediately the reduced harshness and increased compliancy was apparent, we could really feel the high-speed compression valving wake up as you transition from rolling over the bumps to absorbing them. Over crests, washouts, and other dirt road imperfections, the ProFlex suspension provided a floaty, almost distant road-feel experience (in a positive way). This abstraction of how the rough terrain is translated makes for a re-assuring but rich sensory experience.
Pulling onto the highway we took the Golf for a shake-down run up a winding hill-side road. On tarmac, the suspension still feels forgiving, but apply a steering input and BANG, turn-in happens in a much more crisp fashion. Body roll through the corners was perceptibly reduced, but the most profound and simultaneously subtle change was the perceived driving envelope.
At vigorous speeds, it just didn’t feel like we were pushing the car anymore. Under driving conditions where the planted feeling begins to give way, there was no hint of insecurity. This suspension inspires driving confidence more than anything. Because the road inputs are not shocking or harsh like a pure road-racing setup of super high rates and damping, there is increased traction along with the stability. Potholes and ripples in the road that previously jarred the car and made noise are nearly imperceptible. Under braking and acceleration there was very minimal dive or squat.
Our initial test run was not without critique, we were not out joy riding. As ProFlex would ask you to do, we analyzed the driving behavior and tried to attribute each quirk to the three different metering fields; rebound, high-speed compression, and low-speed compression.
Turn-in and followthrough of fast and short corners was consumed without any issue, however long sweeping corners with a late track-out would begin to exhibit some body roll towards the end — we attributed this to lacking low-speed compression damping.
Despite the increased spring rates and the counterintuitively compliant ride, the rear end did present one little buck – very minor. We would address this with the advice of Lazzerini.
Setting the ride height of a car is absolutely one of the most crucial areas to address with a new suspension setup. How much air is allowed under the car, how much frontal area is presented by the tread of the tires, how much the center of gravity is raised, and how much ground clearance is needed to clear obstacles are all important factors influenced by ride height.
“One of the most important parameters is vehicle ride height, usually to have the best handling you have to drive as low as possible, but this depends on the rally stage configuration — if they are nice and smooth or bad and bumpy. Practically, you have to adjust the front ride height in order to prevent the front sump guard from hitting too often or heavily on the ground. Certainly you will touch some times but try not to often by adjusting a good ride height,” Lazzerini reiterated.
Before we dove head-first into the install of our ProFlex suspension, we had the forethought to measure the ground clearance, and tire to fender clearance, both front and rear. With this information we can generate our own baseline off of the factory Golf R settings.
Because we have already identified that this car will be a double-duty driver, the existing ground clearance is slightly lacking (I can’t get it into the garage with our steep driveway without ramps). The plan is to build in a modest 1-2 inches of additional clearance, while maintaining the built-in handling characteristics.
After evaluating our initial (new) ride height, we decided it would be wise to approximate the OEM rake. Baseline settings from ProFlex leveled the car a little, but we did not want to reduce the added front clearance. To remedy this situation, we opted to put 1/2-inch of preload on the rear coilovers, this would give us a little more bump travel and positive rake.
Pitch And Rake
Taking a step back, before the overall ride height can be locked-in, the pitch or rake of the car needs to be established. Looking through the profiles of OEM car stances it’s common to see some traits between brands and nationalities. The Golf comes from Wolfsburg with a considerable amount of positive rake — meaning the nose is lower than the tail.
The second very important parameter is the rear to front pitch or rake, this will determine the corner in/out balance of the car. -Fabio Lazzerini, R.Tec
“The second very important parameter is the rear to front pitch or rake, this will determine the corner in/out balance of the car. If the rear is too low versus the front ride height, the car will not turn, it will understeer. If the rear is too high versus the front the car will want to oversteer when you corner in,” Lazzerini projected.
We don’t want to completely go against the chassis geometry VW built into the Golf, so we took tried to approximate the original rake. Lazzerini emphasized that the preload adjustability on the rear damper is not intended to be used for adjusting ride height, and a spacer should be placed under the main spring in the control arm to boost height. Our change in ride height was minimal, so for the time being we will demonstrate how to adjust ride height with the coilover.
Luckily the threaded shock bodies of our ProFlex dampers mean that we have considerable control over the preload supporting Gruppe R. The plan initially was to retain most of the positive rake VW engineered into the chassis from the factory. With the propensity for understeer, already identified on both our NASA HPDE and NASA Rally Sport/California Rally Series schools, we don’t want to make anything worse.
Lazzerini recommended that we proceed in small increments, “try to adjust the rear by steps of +/- 5 mm, for this you just need a little bit of straight to get speed and cornering. Once you have the right rake you can start lifting the car up or down, keeping it at that rake.”
“When this is not so bad we can start playing with the other parameters: springs, dampers, clicks, toe, camber … But first of all try to adjust a good ride height, if this is not good, you will never compensate with damper adjustments,” Lazzerini warned.
High Speed Compression
Too Soft HS-Comp
- Damper bottoms out easily
- Wheel disconnects from the road over high speed obstacles
- Potholes are not absorbed without bottoming
Too Stiff HS-Comp
- Overall harsh feeling
- Car tracks grooves in the road too much
- Hits are transferred to the bodywork and passengers
- Loss of traction
- Whole car comes off the ground over obstacles
Gruppe R will see a fair amount of gravel on a regular basis, so making the suspension as forgiving as possible will go a long way to preserving control, comfort, and longevity of the vehicle. The baseline setting was a step in the right direction for the undulating surface or dirt roads but we want to push that boundary.
Low Speed Compression
Too Soft LS-Comp
- Excessive body roll
- Excessive squat under power and acceleration
- Excessive dive under braking
Too Stiff LS-Comp
- Small bumps still harsh
- Loss of traction under acceleration
- Loss of traction under braking
- Sloppy corner turn-in
Low-speed compression is the adjustment more people encounter with 2-way adjustable dampers. This compression circuit works with managing vehicle weight transfer over subtle movements of the shock shaft. As you smoothly turn-in to a corner and track-out, the low-speed compression helps to prop up the weighted (out)side of the car, reducing body roll.
In addition to Gruppe R’s gravel duties it will carve up windy roads, and circuits, we don’t want the prevailing tendency to be a mushy roll through the corners. The baseline turn-in was very crisp, but track out could use a little tweaking.
“For sure the cars handling behavior and the feeling you will have with this kind of suspension is a lot different than a reinforced stock suspension. The way we prepared (valved) the dampers gives more low speed bump but still retains good progressivity,” Lazzerini assured.
Too Soft Rebound
- Car bucks after hitting an obstacle
- Car feels loose on its springs
- Excessive body roll
Too Stiff Rebound
- Suspension ‘packs’ i.e. does not have time to extend before the next bump
- Car feels too hard
- Car skates across the road surface too much
- Loss of traction
- Excessive braking distance
- Whole car falls into potholes instead of just the wheel
The rebound adjustment controls the speed at which the springs are allowed to unload as the unsprung weight comes off the ground or the sprung mass of the car lifts over a crest. Keeping that tire in contact with the road surface as much of the time as possible is the name of the game. A rebound that is too slow will not allow the wheel to return to Earth fast enough, but a rebound setting too gentle may cause the car to buck or chatter in terms of traction.
Rally falls somewhere in the middle, too savage for the circuit racers and too European and regimented for the desert rats. We felt like the baseline rebound was nearly spot on, perhaps needing a touch in the rear after our little bounce off the bump stop, and possibly in tandem to help the sweeping corner track-out.
Round Two Settings
For our second go around of adjustment testing, Lazzerini advised us to retain the baseline high-speed compression setting of 10 clicks and only address the other two fields. We would only adjust the front shocks to start and then once we found our favorite combination leave it alone and repeat the same process for the rear. After progressing through Lazzerini’s three tests we felt better educated to make some informed tests ourselves. We logged our findings in a journal for future reference, find it transcribed here:
Manufacturer to manufacturer may differ in the number of clicks per turn of the screw, but in the case of ProFlex, there are six clicks per revolution. They are defined detents and in the case of the low-speed compression nuts, even give an audible click. Don’t force adjustments, light pressure is all it takes to turn a screw.
In rally we are fighting for traction over loose and rough surfaces. On the tarmac we are fighting for cornering stability. The ability to make the best of both worlds makes rally cars unique.
It’s a good practice to keep a little log book of the changes you make, make notes of how the car felt different. That way you can always return to a known quantity if further adjustments feel like backwards progress.