Citroën will not look back on its 2017 FIA World Rally Championship season with fondness, and that might just be the understatement of the year. What should have been the season in which the Versailles outfit returned to prominence has instead been blighted by poor reliability, unpredictable results, and a number of truly scary crashes. For a team with a whopping seven titles under its collective belt this isn’t merely unacceptable, it’s downright inexcusable, more so when you remember the depth of talent at its disposal and the fact that the team opted to miss most of last year in order to fully develop the C3 WRC.

While the C3 was developed over the course of the year and did indeed improve as it progressed, a number of fundamental issues rooted deep within the car remained, with both the suspension and ‘diff being key areas of concern. There have been flashes of speed and of course the odd good result, most obviously in Mexico and Spain (out and out victories for Meeke), results made all the more frustrating for occurring on both gravel and (largely) tarmac – it proved that the C3 could indeed win on all surfaces, just not with any regularity.

The source of the gremlin that’s caused Citroën so much head scratching has long been the source of much paddock gossip and intrigue, with the rear suspension at one point thought to be to blame. What was clear was that the issue was at its most insurmountable on gravel events with especially low levels of grip, a problem seemingly exacerbated as the event progressed and the condition of the stages degraded. These loose-surface events are also the rallies which demand a driver have complete trust in what the rear of his car is doing in order to succeed, Meeke’s Mexican success notwithstanding. The majority of Citroën’s biggest crashes took place on low-grip events, with Meeke forced to drive at the very edge in order to remain within touching distance of his rivals – all too often with predictable, bodywork-shedding results.

Inside sources have recently shed some light on the possible cause of the issue, with the finger of suspicion instead falling on one of the new for 2017 components, the hydraulic active centre differential and the manner in which it is effectively actuated. Active diffs were de rigueur in world rallying from the mid ‘90s to the start of this decade, before being phased out in 2010 as part of the FIA’s attempt to drive down costs in the wake of the global economic crash. The decision to re-introduce them in time for this season was one made partly at the behest of the manufactures themselves, with many believing that they would help reduce costs by cutting down on component failure in other areas of the drive-line, namely the drive-shafts.

One could argue that Citroën, a team which utterly dominated the WRC for the majority of the ‘active diff’ era’, should have been better placed than most to re-unlock the secrets of an active setup, but this evidently hasn’t been the case. Now, after months of trauma and dozens of frustrating results, the problem appears be an inability between the front and rear diffs to communicate. The root cause of this could be down to one of any number of things (or even a combination), with both software and hardware issues both potential trouble spots.

While the exact cause of Citroën’s diff woes isn’t currently public knowledge, its impact on the car has been about as far from subtle as it’s possible to get! The issue has manifested itself in spectacular (not to mention deeply unnerving) fashion; the front diff has supposedly been routing power to the rear under deceleration for a corner, then failing to transition the other way when accelerating out of it. Just to compound matters, the exact opposite of the situation outlined above has been occurring when accelerating uphill.

As we’ve already seen, the C3 seems to be at its most troublesome on gravel, specifically those low-grip gravel surfaces prone to significant degradation over the course of a day’s rallying. The control issues highlighted above might well go some way towards explaining why the car has appeared to be such a handful in low grip situations, with rutted gravel, mud and snow looking to be the most troublesome. The Monte, Sweden, Argentina, Italy and many of the loose surface events which make up the bulk of the current WRC calendar have exposed the car’s flaws in stark fashion, while the C3’s ‘twitchy’ character might also explain some of Kris Meeke’s more heart-stopping moments.

The issues facing Citroën in its quest to turn the C3 into a consistent winner seem to be down to either the software or hardware governing the active differential, and also the manner in which said differential is utilised by the crew. The two of course are linked, with software governing the differential’s behavior perhaps lacking the degree of scope required to be truly effective on all surfaces and in all conditions. The crew’s inability to make the minute adjustments required to dial the C3 into all conditions has imbued it with a very narrow window of optimum performance. To put it bluntly, it has proved very tricky for Citroën crews to find the C3’s ‘sweet spot’ and to put it to good use, with not enough graduation built into the system. While Versaille’s technical understanding of the science behind electronic differential trickery is beyond reproach (it was a strong point of both the Xsara and C4 WRC), it has taken the team longer to reacquaint itself with making the active centre work in all conditions.

Quite how the problem came to light isn’t currently known, though one can speculate that Sebastian Loeb’s gravel test might well have played a part in shedding light on the issue. Fully resolving the problem will be a task for the off-season though, with talk of Citroën adopting a new, clean-sheet approach when it comes to developing its differential control system. While only Citroën can know for sure what form the revised differential control interface will ultimately take, one can be certain that it will be easier for the crew to access ‘on the fly’, that it will be better integrated with the diff itself from both a hardware and a software perspective, and that it will give a broader scope for more precise control of the differential on all surfaces. The 2018 C3 WRC must be an easier beast to setup, the team’s continued success, not to mention its reputation, demands it.

The discovery came far too late to rescue Kris Meeke’s season, though the last two rounds have brought cause for guarded optimism as to the state of the C3, especially as both Wales and Australia are made up of precisely the kind of variable grip stages which have been the car’s bug-bear so far. The C3 preformed doggedly if not spectacularly in the Welsh forests, though there was no doubting that all three cars looked far more planted, predictable and indeed drivable than they did at the start of the season. Australia must surely have tempered any mounting enthusiasm though, with all three drivers out thanks to a mixture of rear suspension failure brought on by collisions with the scenery (Meeke and Leferbvre), and a dramatic crash (Breen). The team’s public announcement that it was allowing its drivers ‘off the leash’ in the lead up to the event surely played a part in this (and in Breen’s in particular), and they will no doubt have procured valuable telemetry from having all of its crews driving in such an uncompromising fashion, but it’s also further evidence that finding the C3’s illusive sweet spot remains a tricky proposition.

The C3 is fundamentally a decent car – has to be, modern WRC events aren’t won by machines with at least a kernel of brilliance buried within them, but much needs to be done if it is to enable Citroën to take the fight to Hyundai, Toyota and M-Sport next year. Meeke, Breen, Lefebvre and anyone else likely to find themselves tasked with driving the C3 will hope that Citroën channels its immense experience into resolving the issue over the winter break, and that the car which emerges at the Monte is a far more polished machine than the one which flung Meeke into the scenery the last time the WRC pitched up at the principality.