ProFlex_edited-1It’s a universally recognized truism that suspension makes a rally car. While horsepower, flashy liveries, and noise may draw the attention of onlookers, none of the bark has any merit unless that power can be put to the ground. As we know, rallies are run on diverse and adverse road conditions, from well groomed tarmac, to ice and snow, and through the craggy rocks of the desert.

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R.Tec was contracted to develop the recce car suspension for the VW Motorsport and Hyundai WRC recce cars.

Developing a well-tuned and proven suspension system is vital to the multipurpose driving duty of the rally or recce car. We expect to see demanding corners, deep ruts, washboard, stones, g-outs, and perhaps the occasional jump. We have backtracked our suspension to the original supplier of the VW Motorsports recce Golf Rs — ProFlex.

We traced the supply line from ProFlex in the Netherlands to performance racing suspension purveyors R.Tec of Belgium. Gil van den Heuvel of R.Tec took care of our specific needs and walked us through the process of tailoring a coilover system that would suit our application. “We got the deal with VW Motorsport and we offered them ProFlex suspension. We also made recce car suspension for Hyundai Motorsport with ProFlex,” explained Heuvel.DSC00856

R.Tec takes a customer’s specific needs and changes springs and shock valving accordingly. They engineer shocks for different makes and models, for race or recce applications, and optimization for gravel, tarmac, or somewhere in between. We informed van den Heuvel that this was not a racecar, but a recce car and that we wished to have full gravel suspension under it. Our goal is to maximize wheel travel and control on uncivilized road surfaces.

Demands Of Durability 

The construction of most rally suspension appears, at face value, to be massive overkill. Even when looking at off-road suspension designed for Baja and Dakar it is easy to ask: why do these little cars need such robust shock absorbers? The answer is simple, the homologated design and the loads applied. Most WRC cars feature a MacPherson strut designed front, and a single a-arm rear, — meaning that the shock absorber is a structural member in the support of the car — it effectively becomes a dynamic link or control arm.

Rally cars have the unique challenge of contending with unpredictable and unforgiving surfaces, cutting a corner may force a driver to drop a tire in a washout, or a sliding car may strike a curb or berm. These potential side loads threaten to bend shock shafts.

In order to stand up to the abuse of the road, most rally cars employ inverted, monotube struts. This means that the traditionally small-diameter shock shaft is protected inside the shock body and the valve or shim stack remains stationary in regards to the lower mounting point. A large-diameter shaft, usually 36-55 mm, is the one we see moving as the shock is compressed or extended.

In the case of our ProFlex coilovers, a 45 mm shaft resides in the front struts and is capped off with a 7075 aluminum Group A-style top mount. The rear shock is a more conventional design, with a 14 mm exposed shaft that sweeps a 40 mm piston through a 45 mm body. Both front and rear dampers feature corrosion-resistant coatings and external shock oil reservoirs — remote mounted with a flexible line for the front, and piggyback for the rear. This extra oil volume will help increase the thermal capacity of the shock and allow for a huge swept volume cycling over bumps.

Clockwise from top left: front remote reservoir, rear piggyback reservoir and black anti-corrosion coating, front inverted monotube attachment point and air filter, and 45 mm front strut bodies for deflection strength.

The threaded body of the coilover supports the use of a long spring — preventing coil bind, and supporting long wheel-travel, mostly in the form of droop or sag which preserve a low ride height and center of gravity. Tuning the ratio of droop to bump is a key area when setting up a car for gravel handling.

An invisible addition to this coilover system is a hydraulic bump stop, similar to a “bump-can” run as secondary suspension in desert racecars or rally-raid vehicles. This device resides inside the strut and offers an exponential increase in compression valving resistance during the last few inches before the strut bottoms out. This last bit of damping can help soften the landing of a jump and protect the supporting structure by extending the deceleration time of the unsprung and sprung weight.

“There is no picture for the hydraulic bump stop option. It is an internal component that is used to absorb the shock when the damper is fully compressed. We recommend this for rally and rallycross use, but we generally don’t use it for circuit and hillclimb,” Heuvel detailed.

Adjustability For Compliancy And Cornering

[The hydraulic bump stop] is an internal component that is used to absorb the shock when the damper is fully compressed. We recommend this for rally and rallycross use, but we generally don’t use it for circuit and hillclimb. -Gil van den Heuvel, R.Tec

Having the best of both worlds is always a tough balance to achieve in suspension. In our situation, that means soft, compliant suspension over the rough stuff but still having the support to lean on in the corners. Usually these two needs are opposed from each other on the color-me-black and blue wheel of road racing. In order to prevent body roll and limit travel, the circuit racer usually sacrifices compliancy.

Off-road, soft compression rates mean easily compressed shocks for a smooth ride, but lack support for the corners. Rather than relying solely on articulation-limiting swaybars, there is another solution: three-way adjustability.

Three-way adjustable shocks retain the ability to independently adjust high-speed compression, low-speed compression, and rebound. What situations do each of those adjustments correspond to, you might ask? High-speed compression refers to sudden high shaft speeds like rhythmic washboard, square-edged slabs, rocks, bumps, and other road foreign object debris (FOD).

Low-speed compression adjustment is what affects weight transfer in cornering loads, involving slow shock movement and other gradual inputs to the suspension, such as cornering and big-picture contours of the road. Rebound damping controls the speed at which the compressed spring is allowed to unload. By slowing the extension of the strut, the car is not upset by a bucking suspension that can bounce the car off the road. With these adjustment fields at our disposal, we have the best opportunity to tune the suspension to glide over the bumps comfortably and controllably while supporting the chassis roll in the corners.

Getting The Right Stuff Under Our Recce Car

IMG_1844To get the ball rolling with our custom-tailored gravel suspension, we started by tracking down R.Tec as perviously mentioned. With a solid contact, we set out to explain that we wanted to duplicate the VW Motorsports’ recce car suspension, this was not a racecar.

Van den Heuvel and the technical experts consulted their records and contact at VW Motorsports and came up with a valving and spring rate package best suited to our project. The effort and care the Belgian suspension gurus put into making sure we received the right stuff was admirable.

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R.Tec thoroughly dyno tested our suspension before shipping, look closely and you can see the divergent progressive damping curves.

After every iteration of valving and spring length/rate, the shocks took to the dynamometer. Just like the testing performed on an engine dyno, this visualization tool helped the experts evaluate the damping curve.

Our front shocks are part of the EVO line of inverted monotube struts ProFlex has developed for rally and road racing. The damper is optimized for extended travel over a tarmac unit and the spring lengths are matched.IMG_1858

Eibach racing springs coil around the beefy strut and measure 16 inches long, 2.5 inches in diameter, and are a 250 lb/in rate. Eibach race springs are cold-wound, heat-treated, shot-peened, and powdercoated all in-house to preserve sovereignty over the quality control. This long length and soft rate is still an increase over the stock from spring rate of 185 lb/in, but is very soft in the scheme of performance handling — just what we’re looking for to support the car on diverse surfaces.

Our new spring rates are higher than the OEM rates, but are still very soft in the motorsports world, right where they should be.

The rear coilovers feature a ProFlex main spring and tender. These shocks are designed to be supplemental to the OEM coils that remain in the control arm pockets. These secondary springs measure just over 10 inches in length and are a light 26 lb/in spring rate. When combined with the tender and the original spring, we end up with a total of 311 lb/in of rate on each rear corner.IMG_1883

The valving profile for both front and rear was described by Heuvel as “quite progressive.” Generally reserved for off-road and rally applications, a progressive valving curve will increase in damping force over the stroke of the damper. This design will provide the ability to be supple and compliant over small and moderate bumps, but should the suspension be compressed aggressively, say over a jump or g-out, the dampers will firm up like a German officer’s pursed lips at attention. This begs the question how will our little German hatch fly?

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The 7075 Group A top mount is stout, and the uniball it contains is very tight, while the banjo fittings make clocking the hose easy.

The Group A 7075 aluminum top mount features a high quality uniball for a fixed-camber adjustment. It is customary to have a fixed-camber top mount in a rally application, because the potential for side loading presents the opportunity to knock the alignment out of whack.

Both front and rear dampers feature a total of 78 clicks of damping adjustment — 26 rebound settings, and 26 each for high and low-speed compression.

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The ProFlex service kit is a nice little maintenance package.

In order to keep our niche dampers on the up and up, we opted to get one of ProFlex’s service kits. This nifty pick-and-pluck foam box came with a spanner wrench, ProFlex branded T-handled adjustment wrench, a can of lithium grease, and three laminated service sheets to cover the adjustment and maintenance of the dampers.

Installation

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Crawling around on the floor is not glamorous but actually lends some utility we would not have on a lift, like the ability to push off the ground and rest hanging components.

Going into the installation phase we were a little intimidated, if we’re honest. There are no precedents online for this sort of suspension application on the Mk6 Golf R. While the process required some customization, nothing would prevent us from getting these shocks under the car.

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The overall length of the OEM and new dampers is very close, but that’s where most of the similarities end.

The biggest concerns we had going into this situation were the CV joint angles, and the overall length of the front struts with gravel springs. Much to our chagrin the overall length of the new struts is very close to OEM — making the packaging concern moot. Where the gains are built into them is in the added stroke, adjustability, and durability.

We commenced the teardown by getting the car up on jackstands (yes we’re going to do all of this on the ground). With all four wheels off we had a clear view of the battlefield, the stock running gear looked bleak, black, grey, and dusty, ready for some new kit.

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An impact makes removing the spindle clamp bolt an easy task.

The first hurtle of the installation was disassembly; we discovered that there’s a distinct order of operations to complete the removal of the old shocks, specifically the front struts. Up front, the first step was to disconnect the sway bar end link from the strut body, and then remove the spindle clamp bolt.

With the spindle hardware removed, we focused our attention on holding it spread open. While this task can be done with a pry bar, holding it open will rob you of a hand and take considerable effort. We opted to purchase Schwaben’s spindle spreading tool. This invaluable little socket features a lenticular-shaped bit, that when inserted into the inboard slot of the knuckle, holds it open.

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Schwaben’s spindle spreader tool may seem like an unnecessary expense if you have a pry bar, but it’s worth it.

At this point, the order of operations became important. First, we removed the strut tower hardware from under the hood, allowing us to drop the strut inside the fender well, however with not enough clearance to extract it. To give us a little more breathing room, we opted to use some spring compressors and detach the inner CV flange — this sounds like a huge hassle, and it is, but less of a hassle than trying to proceed without doing so. While we were at it, we removed the three nuts securing the lower control arm to the spindle.

Clockwise from top left: Tightening the spring compressors, a long extension and an impact help unbolt the CV, removing the nuts under the control arm, prying the spindle and control arm apart.

Now, the intuitive thing to do is to affix the spring compressors with the bolt head pointing down for easy impact access. Don’t do this, because if you do the threaded ends will just drive themselves up into the fender well and jam. In this case, the long, laborious method is the fastest. Using an open end wrench, we took up the spring pressure.

Wrestling the bottom end of the strut from the knuckle can be tedious, so we decided to work smarter not harder, by reversing the above step. We raised the strut back up into the strut tower and re-bolted it in, this way we could relieve the pressure from the jack and let gravity liberate the strut from the spindle. With the CV disconnected, the whole assembly can be lowered well clear of the strut.IMG_2095

Now, we could focus on the installation of the new ProFlex EVO 1 coilover. Before we could consider hoisting the new damper in place, we realized that the strut tower would not present an opening big enough to squeeze the remote reservoir through. Not wanting to release the nitrogen pressure or any oil we set to clearancing the car.IMG_2238

Opening the top of the strut tower was a messy operation, but it was a required step to accommodate the new struts. We opened a three-inch hole and provided a notch for the banjo fitting to clear the steel braided reservoir hose.

With a Sharpie circle to cut back to, we took to the strut tower with a cut-off wheel, grinding stone, and sanding discs. Right: a notch helped us feed the banjo fitting though the hole.

With the lower control arm, CV, and spindle all loosey goosey from the disassembly getting the new unit into place was a relative breeze. After feeding the reservoir carefully through the strut tower, we bolted the aluminum top mount in place to take the weight off of our arms.

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A pry bar helped us separate the lower control arm from the hub assembly.

With the lower end of the strut still outside the spindle, we reconnected the lower control arm. We used a floor jack to support the hub assembly while aligning the new strut bottom into the knuckle. Presto-chango, the strut is located!

We carefully fed the remote reservoir through the strut tower and then raised the shock into the fenderwell, being careful not to damage the banjo fitting.

After removing the Schwaben spindle spreader, we loaded the bottom of the hub to seat the strut, and then tightened down all the hardware (including the pesky CV bolts).

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Each CV joint is secured with six bolts held in pairs with a curved washer.

On To The Rear

Luckily, all the heavy lifting was in the front end of the car. Moving to the rear made for a veritable cakewalk of an install. The inner fender liner was removed by way of a handful of T25 torx screws making the inner workings visible.IMG_2127

The first step to replacing the rear damper with our secondary suspension coilover was to remove the outer control arm bolt, and using a jack, slowly release the spring pressure. The OEM coil spring is retained in this install but is easily popped out of its perch for hardware access.

Removing the rear lower control arm outer pivot bolt is easy, letting the spring down slowly with the jack keeps things safer.

With the control arm released, the urge is to just push it down and out of the way. While this is fine on the passenger side, take care on the driver’s side because a little plastic servo connects to it, and can be broken with very little force. This device is the Adaptive Front Lighting System (AFS) sensor.

With the arm dropped and the spring out of the way, we had access to the lower damper mounting bolt head. This bit of hardware proved to be very stubborn on both sides of the car for us. Neither the (quality) impact or the longest breaker-bar could touch it so, with the top of the shock still secured to the car, we applied the breaker bar and used the jack to leverage the weight of the car and break free the bolt.

The lower shock bolt was too tight to break free, so we used the weight of the car on the jack. The car is still supported by four jack stands so nothing can fall if the bolt breaks free.

Lastly, the two top bolts holding the damper into the fenderwell were spun free, and the shock absorber dropped out easily. With the OEM rear damper out, we harvested the cast aluminum top mount, which we transferred to the new ProFlex shock. We held the keyed shock shaft with a crescent wrench, we can broke loose the 13 mm nyloc nut. If you apply an impact, expect a lot of spinning, as the piston and shock shaft spin internally.

Next, save yourself a hernia and steal this little trick. Don’t try to push the shock up into the fender well, compressing it to align the lower bolt hole. Before you’re on the floor and without the leverage to compress it, plan ahead. We took a length of stainless safety wire, and once again employed gravity and body weight to compress the damper. With the wire threaded through the top mount we compressed the tender spring and twisted the wire around the forged aluminum bottom boss.

IMG_2194With the compressed spring held in place, we re-inserted the bottom bolt with some Loc-Tite. Holding the shock body to aim it, we cut the wire and allowed the top mount to self-locate in the fender well. A little aligning thanks to the pointy end of a pry bar, and we were in business.

After torquing down the three bolts, we reinstalled the spring and affixed the control arm to the rear knuckle.

Tying Up The Loose Ends

Just a few details would bring a close to the installation of our bespoke rally suspension. Because the front gravel springs are 400 mm long, they relocate the top sway bar end link several inches lower than stock.IMG_1020

We removed the stock end links and were able to measure center-to-center the mounting holes. With this new shorter length, we determined that we would need to take about 2 3/4 inches out of the link to meet up to the holes. After some quick math, we had the area to be removed marked in the center of the link and could get cutting.IMG_1022

With the links shortened, we put a healthy chamfer on the end to provide some void for full penetration during welding and then cleaned up the ends. Using a piece of small angle iron, we clamped the rods down to preserve some straightness and made a couple tacks before full welding.

The front struts’ remote reservoirs were routed into the engine bay, and we were tasked with finding a suitable location to secure them. We decided to avoid areas of radiant heat, so the firewall was out as the exhaust and turbocharger are on the back of the EA113 engine.

We opted to snake the braided lines down the inner edges of the fenders and mount the reservoirs in the empty spaces mirrored on both sides of the car — above the accessories on the passenger side, and next to the airbox on the driver’s side.

Driving Impressions

IMG_1048Finally, after three days of work, we could set Gruppe R back on its wheels and assess the new ride height and handling. With the new BRAID wheels and Toyo tires, we set the hatch on the ground and were pleasantly surprised to find we had gained the ground clearance we wanted.

It was time to get out on the road and give the new coilovers a preliminary test drive. As we stated in the beginning, completing the install of a tailor-built suspension system is not the end of a journey, but the start. Next would come tuning and tweaking until we feel the car delivers the best possible handling.

We analyzed every little nuance on our first drive and will reveal them and what we plan to do to improve the adjustments in part two of Gruppe R’s suspension story: Tuning 3-Way Adjustable Suspension. So stay tuned to see how to dial in all those settings.IMG_1041