The official distance of the Grand National has been reduced by a furlong after new measurements of racecourses.
Dozens of tracks will be re-classified from 1 June after it was revealed the published distance of a big race at Wetherby was 78 yards short.
The new method replaces a surveyor's wheel in the mid-point of the course with a more accurate assessment two yards outside the inner rail position.
Courses will also be described in yards as well as the nearest half-furlong.
Horses will still travel the same distance but the move by the British Horseracing Authority and the Racecourse Association has been introduced to give racegoers more accurate information.
Previously, the Grand National was advertised as four miles three-and-a-half furlongs, but this has now been reduced by a furlong.
It is now advertised as four miles, two furlongs and 74 yards.
Thirty-five courses including Aintree, Ascot, Cheltenham, Chepstow, Haydock and Sandown will have published distances shortened.
Kempton Park is one of four courses where traditional distances will remain unchanged, while Wetherby is yet to conclude its survey because of its schedule.
In some cases, start lines will be moved but those courses that cannot do so will be given special dispensation to run races under the minimum distance of two miles.
Full details will be published in the Racing Calendar on Thursday.
BHA director Jamie Stier said: "This new methodology will improve the quality and quantity of data we provide our participants and the increased accuracy will be of benefit to trainers, jockeys, owners and betting customers."