Adrian Newey suspects Christian Horner did not "fully understand" his "pain and frustration" during Red Bull's fallow years with Renault engines after criticism of him in the former team principal's new book.

Horner as team principal and Newey as technical chief worked together with huge success across 19 years at Red Bull, enjoying two periods of sustained title-winning form with first Sebastian Vettel in 2010-2013 and then Max Verstappen in 2021-2024.

But between those periods Red Bull took a back seat to Mercedes' dominance of the sport following the arrival of turbo-hybrid engines in 2014.

Red Bull initially continued to be powered by Renault, as in their four title-winning years under the previous rules era, but the French manufacturer struggled with the new regulations, which compromised the performance of the team's Newey-designed car.

Writing in his newly-released autobiography, Drive, Horner recounted a period mid-way through 2014 when he became disappointed in Newey after the legendary designer had received an offer to join Ferrari and was mulling whether to leave.

Horner wrote: "I stood behind him and believed that he stood behind me as well. But at the first sign of adversity, Adrian wanted to abandon ship. I felt very sad about that."

Horner added that, despite Newey's importance to the team, "I could no longer rely on him. Our partnership was not as solid as I had previously believed."

Horner's comments were put forward to Newey in Friday's team principals' press conference at the United States Grand Prix.

"You're quite right in saying that, no, I haven't read any of it [the book] yet," replied Newey.

"I think 2014, as a chassis designer, if the PU [Power Unit] manufacturer has a bad year, that happens and you accept it.

"If the PU manufacturer has a bad year and doesn't appear to have any intention of trying to address the problem, that's altogether a different matter and that's quite bleak at that point. And that's the situation that unfortunately we faced in 2014.

"And as it turned out, that situation didn't really change with that supplier until we changed to Honda in 2019.

"So, you can imagine my pain and frustration at that. I don't think Christian fully understood that, perhaps. But I was in conversation."

Ultimately turning down Ferrari's offer in 2014, Newey signed a new contract to stay at Red Bull but began to split his time with other projects at the company outside of F1.

Newey stayed a further decade at Red Bull before leaving eventually in 2024 to join Aston Martin the following year, where he is team principal and managing technical partner.

Newey added: "The rest of it [in the book] I really can't comment, but Christian and I remain friends. As many of you know, I am godfather to his daughter Olivia, so, yeah."

In interviews publicising his book, Horner said he saw similarities between Newey's current experience of trying to turn around a struggling Aston Martin team to their early years at Red Bull following the energy drink's buyout of an underachieving Jaguar outfit in 2005.

It was a comparison that Newey agreed with.

"I think there are actually a lot of parallels between when I started at Red Bull and when I've started at Aston Martin," said Newey.

"Both teams that through their history had had quite a lot of turmoil with changes of owners, changes of senior managers, etcetera.

"It's then really trying to, as we've spoken before, get everybody working together, try to break down silos, improve the culture. And that's been exactly the same again."

Speaking to Sky Sports News earlier this week, Horner said: "Adrian is without doubt the best designer that Formula 1 has ever seen. His track record speaks for itself.

"Lawrence [Stroll] is a very successful guy. He's a very driven guy and has obviously invested heavily in that team. Honestly, I think they've got their own journey that they're on, and it'll be interesting to see how it plays out."

Saturday October 24
6.15pm: United States Grand Prix Practice Three (session starts at 6.30pm)
8.30pm: United States Grand Prix Qualifying build-up*
10pm: UNITED STATES GRAND PRIX QUALIFYING*
12am: F1 Academy Race 2*
12.45am: Ted's Qualifying Notebook*