Double diffuser a challenge for Red Bull

His design team has been flat out redesigning parts of the rear and the floor of the Red Bull RB5 to incorporate the controversial design, which was ruled legal by the FIA before the Chinese Grand Prix. With only 10 days between Sunday's Spanish Grand Prix and the start of practice in Monaco, it is not certain that it will be ready.

Newey added that the challenge of adapting the car for a double diffuser has been particularly difficult for Red Bull.

"It is very tight for us," said Newey when asked by AUTOSPORT whether the double diffuser would definitely be ready for Monaco. "It's touch and go.

"The double diffuser concept doesn't sit that easily with the packaging and aerodynamics of our car, so it hasn't been easy to get a step forward in performance."

Newey confirmed that the team would not replace its pullrod rear suspension with a more orthodox pushrod system to incorporate the double diffuser. He emphasised that it was not clear how much of the benefit of Red Bull's rear suspension would be lost, if any, due to the new parts.

"It is a benefit to the car," said Newey of the pullrod suspension. "But we don't know how much because we haven't tried a pushrod suspension. We don't know if we would gain more if we had a pushrod. The goal has always been how we adapt our car."

Newey admitted that the team might opt to run only one of its two cars with the double diffuser during the first day of free practice in Monaco in order to evaluate it against the existing design.

"We might well run one car on Thursday and then put it on the other if it performs correctly. One of the things that we don't have is an aerodynamic test between now and then where we will be able to test it.

"When you've got something that is as different as that on the car, you want to know that it is performing as you expect it to. Monaco is not a proper runway test!"

Newey said that Red Bull was still unsure about whether it would race with KERS this year, saying that it could depend largely on how many of the other teams in the field run it.

"It really depends on how many other teams run KERS," said Newey. "The more teams run KERS, the more difficult it becomes in terms of being outdragged down to the first corner.

"KERS performance has been about where we expected from simulation. That's why pre-season we ran it to establish its pace and reliability.

"Strategically, it's great and for overtaking it's a very powerful piece of technology. But in terms of absolute lap time, it's neutral.

"The problem we have with Mark (Webber) as one of our drivers is that it's difficult for us to get under the weight limit with KERS on the car. We really didn't want to go down the route BMW have done of putting it on their lighter driver but not their heavier driver.

"Then, in terms of feedback on how the car is handling and a comparison between the two cars through a race weekend without any testing is very important. To have the cars with two different specs is something that I didn't want us to do if we could avoid it."