Besides the domineering Sebastien Loeb and Sebastian Ogier duel, Rally Monte-Carlo had a clear theme in the opening stages of the 2022 World Rally Championship.
Understeer.
As Rally1 dawned on Monte’s Thursday night stages the gaps between leading crews were huge.
Loeb and Elfyn Evans were the only two drivers to get within ten seconds of Ogier’s opening stage-winning time. Back in 2021, less than four seconds separated the top five crews on Monte’s opener. And that stage was longer by five kilometres.
Obviously the introduction of hybrid regulations brought a raft of uncertainties and unknowns. It all combined to give different issues for different crews.
Understeer was the one that stood out for me, however. The biggest victim of one of driving’s worst feelings was Kalle Rovanpera.
2021’s two-time rally winner was over a minute off Ogier’s pace after Monte-Carlo’s first two stages, despite driving the same Toyota GR Yaris Rally1.
So, why was understeer such an issue and what had it got to do with WRC’s new regulations?
Several components of last year’s World Rally Cars have been removed for WRC’s Rally1 era. The active centre differential was one such feature to be scrapped in a bid to reduce ever-increasing technical costs.
This is one of the biggest changes that world rallying’s elite faced heading into Rally Monte-Carlo.
What does an active centre differential do, I hear you ask.
First off, let’s cover what the front and rear differentials do.
Each differential controls the amount of power delivered to each wheel. A “locked” differential means both inner and outer wheels will rotate at the same speed while an “open” differential allows them to rotate at different speeds.
A locked, or stiff, differential improves traction under acceleration and stability under braking. But an open, or soft, differential improves cornering ability as the inner and outer wheels are able to rotate at different speeds allowing the car to turn more effectively.
This happens independently across both front and rear differentials. A centre differential then allows power distribution to front and rear axles to be controlled.
For example, it is beneficial to increase the power delivered to the rear wheels when exiting a corner to improve traction.
The active centre differential, which was a key development area in the 2017-2021 generation of World Rally Car, included mechanical, hydraulic, and electronic components.
It allowed engineers to optimise electronic differential maps that opened and locked the differential depending on the driver’s steering and throttle inputs.
This meant at any given point on a stage, the driver was getting a near-perfect amount of power delivered to each wheel across the car. The differentials could be locked coming in and out of a corner to maximise stability and acceleration while they would open up through a corner to help the car’s rotation.
For 2022’s Rally1 cars, there is no centre differential at all. The removal of electronic controls means that drivers’ differential settings are fixed throughout a stage. Any set-up will effectively be a compromise.
So how did this encourage understeer?
If the differentials were too stiff then the Rally1 cars would have been much more difficult to turn into a corner. The additional battery weight and removal of front aerodynamic devices won’t have helped either.
What I was surprised by, however, was that this characteristic wasn’t picked up and cured during testing. The only explanation is that testing was completed in more slippery, icy conditions.
Rovanpera finally got on top of his car balance issues to set three fastest stage times before the end of the rally.
There is a list of set-up changes that can reduce understeer. In general, having softer settings across the front axle with a stiffer set-up on the rear axle will do the trick.
But of course this is a compromise, especially without any electronic niceties. Removing understeer will increase corner-exit oversteer and with the extra hybrid boost kicking in, this will take plenty of skill to control.
Rovanpera managed it though. How teams battle 2022’s set-up conundrum on snow and gravel will provide another intriguing facet to WRC’s exciting hybrid era.
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Photos courtesy of Toyota Gazoo Racing
Please note, this story is only based on my opinion and engineering knowledge.