Ross Brawn was open following the opening test in Valencia, which uncovered a few problems with the car. One being the cars weight distribution, which is reportedly too far forward. With the narrower front tyres and revised rears most teams are playing with this setting. Brawn were one of the team that learnt early last year how a forwards weight bias would work well with the new slick tyres. This year the tendency is to shift the distribution back 1-2%. Which is a relatively simple case of taking ballast from the front wing and splitter and placing it around the gearbox area.
One more visual change is the unique roll structure\airbox, which has been subtly revised. The sculpting behind the roll structure feeding the oil cooler has gained a side panel to enclose the duct, forming a more distinct entrance either side of the main inlet.
Then having had problems with cracking exhausts and the question over the original exposed exhaust design not meeting the R75 bodywork regulations, the car sported new exhausts, twisted near their exits and with slash cuts to make them flush with the bodywork.