After a slow start, Renault will be looking to make up ground with a new diffuser
By Sarah Holt
BBC Sport in Shanghai
Renault and McLaren will run with updated diffusers at the Chinese Grand Prix, BBC Sport understands.
The two Formula 1 teams are reacting quickly to a decision by the sport's governing body, the FIA, to approve the use of split-level diffusers.
The FIA Court of Appeal this week rejected complaints from rival teams about the design used by Brawn Grand Prix, Toyota and Williams.
The decision will force the other teams to consider a drastic redesign.
Renault were amongst the teams who spoke strongly against the use of the split-level diffuser - an aerodynamic part at the rear of the car which increases performance - at an eight-hour hearing in Paris on Wednesday.
But the French team, who won constructors' titles in both 2005 and 2006, are now understood to have flown in a modified diffuser to the Shanghai International Circuit.
WHAT IS A DIFFUSER?
It is the rear part of the floor of the car between the rear wheels and under the rear wing
It is crucial to the aerodynamics, and small changes can have a big impact on downforce - and therefore grip and speed
McLaren are also expected to introduce a limited update to their diffuser when first free practice begins in China at 1000 local time (0300 BST) on Friday.
The split-level design is believed to give an advantage of around 0.5 seconds per lap, though Renault and McLaren are not expected to make such a leap in performance immediately.
"I do not think it will be a huge gain in the beginning," conceded Renault driver Fernando Alonso.
"It's not only about putting a magic part on the car - the whole philosophy of the car needs changing and that will take time.
"We will be better than in the last race (in Malaysia) but we can still develop further."
The seven teams who ran without the split-level diffuser in the opening races of 2009 in Australia and Malaysia will need both time and money to catch up with Brawn, Toyota and Williams.
Mike Gascoyne - former technical director of Toyota, Jordan and most recently Force India - told BBC Sport: "A major update to the rear of the car requires a redesign of the gear box, the crash structure and the rear suspension.
"While some teams will implement small updates based on the FIA's clarification, without a huge redesign they won't be able to get the full performance effect.
"Over the next couple of races we will see more and more teams making small updates while significant updates will only come in the following months."
The diffuser row broke out when Ferrari, Renault and Red Bull protested against the legality of the split-level design on the eve of the season-opening Grand Prix in Australia, but race stewards in Melbourne rejected their claims.
BMW Sauber then had a similar protest rejected at the Malaysian Grand Prix while McLaren subsequently recently added their weight to the official protest.
The FIA introduced a raft of rule changes for the 2009 season designed to aid overtaking and make racing more exciting - and the teams whose controversial interpretation of the FIA's regulations on the design of the diffusers has now been ruled legal have prospered.
Meanwhile, the teams that have used the new Kers (Kinetic Energy Recovery System) energy storage and power boost system so far this season - Renault, Ferrari, McLaren, and BMW Sauber driver Nick Heidfeld - have experienced little success.
Ferrari, who have failed to score a point in the two races so far, have decided to dispense with Kers for the Chinese Grand Prix because of reliability problems.
Two-time world champion Alonso was this week quoted as saying: "We have done what the FIA wanted us to do and because of that are being beaten by teams that did what the FIA didn't want."