Alpha Tauri turned down the opportunity to update its car for 2021 with last year's rear-end and gearbox of sister team Red Bull.

Amid the pandemic, and apart from an aerodynamic rule change, chassis design has been essentially paused between 2020 and 2021 apart from a complex 'token' system.

However, as a technical partner of Mercedes', Aston Martin got the green light to upgrade to the 2020 title-winning rear-end without spending a single token.

A similar rear-end upgrade would also have been available to Alpha Tauri.

"We decided to leave the rear of the AT01 as it is," said Alpha Tauri technical director Jody Eggington.

"It wasn't an easy decision," he told the Japanese source as-web.jp. "We considered the positive and the negative sides.

"It was certainly an attractive option to switch to a new gearbox without using tokens, but it was the front of the chassis that I most wanted to develop."

Eggington said the decision was also guided by the sweeping new regulations for 2022.

"Next year's cars will be drastically different," he said. "So we have to concentrate our resources there as well.

"Last year's AT01 was very complete - especially the rear stability was fully satisfactory. So we decided that we didn't need to (change it)," Eggington added.