Weights will not be raised for the Caulfield Cup or Melbourne Cup if the designated topweights do not accept for the respective races.

Racing Victoria announced the changes for the two feature handicaps on Friday.

Racing Australia amended a rule this month to give Principal Racing Authorities flexibility whether they raise weights for Group One handicap races if the highest weighted horse has less than 57kg at final acceptance time.

RV announced it would implement the change for the Caulfield and Melbourne Cups only.

"The amendment to the rule has been implemented by Racing Victoria at the request of the Melbourne Racing Club and Victoria Racing Club and provides certainty for connections around what weight they will actually carry in the Caulfield and Melbourne Cups," RV's Executive general manager, racing, Greg Carpenter, said.

"Under the previous arrangements, the weights to be carried for these two races could significantly change in the week leading to the race and in the case of the Melbourne Cup final acceptances are taken less than 72 hours prior to the race being run.

"An increase in weights for the Caulfield and Melbourne Cups could be viewed as detrimental to those horses higher in the weights, given it has the potential to impact a horse's performance more significantly in races over extended distances.

"Last year's Melbourne Cup, where the weights were raised 1kg at final acceptances, is a case in point.

"It could be argued that the performance of the default topweights, Big Orange and Our Ivanhowe, was impacted more over 3200 metres than those lower in the weights such as the winner Almandin who had his weight lifted from 51kg to 52kg."

Hartnell heads Caulfield Cup weights on 58kg with Almandin next on 56.5kg.

Irish horse Order Of St George, who is not expected to make the trip to Australia, is the Melbourne Cup topweight with 58kg, 0.5kg more than last year's third-placed Hartnell.

Defending champion Almandin has 56.5kg for the Melbourne Cup.