Allison admits flawed Update 18 made championship-winning W17 a late-season handful

Mercedes technical director James Allison has admitted that the team’s late-season aerodynamic upgrade, internally labelled ‘Update 18’, introduced unforeseen flaws that made the championship-winning W17 significantly harder to drive, contributing to the narrowing performance gap seen across the final rounds of the 2026 Formula 1 season.

Speaking on the NU Silver Arrows Radio Show, Allison confirmed that the package — first introduced at the Sepang circuit and followed up with a revised front wing in the United States — did add downforce, but at a cost. “It has given us more downforce, but it has made the car more of a handful,” he said. “It’s got some areas where it has subtracted a bit of performance that we were not expecting.”

Mercedes had opened the 2026 campaign in commanding fashion, securing both the drivers’ and constructors’ championships. Allison, however, pointed to a structural reason why that early dominance was always likely to compress as the year progressed — one that had nothing to do with rivals simply catching up through development.

The 2026 technical regulations introduced a mandatory 30-kilogram reduction in minimum chassis weight, bringing the limit down to 768 kilograms. While most teams struggled to meet the new target at the start of the year, Mercedes arrived at the opening round already compliant. “We were probably the only car on the weight limit at the start of the year,” Allison revealed. “All the folk we were competing with in the championship had a bit of timber to shift, and that was lap time that came to them that wasn’t available to us because we were already skinny and on the limit with the weight.”

As rival constructors gradually shed their excess mass across the season, the field naturally tightened around the W17 — a convergence that Allison’s own admission suggests was then accelerated by the handling compromises introduced through Update 18. The combination of rivals reaching the weight limit and Mercedes wrestling with an upgrade that subtracted as much as it added helps explain why a team that looked untouchable in the early rounds found itself under increasing pressure by the season’s closing stages.

George Russell and Andrea Kimi Antonelli ultimately delivered the championships despite the late-season complications, but Allison’s candid assessment underlines that Mercedes’ engineering path in 2026 was far from straightforward.