It's because you'll only have Alternate brakes with no anti skid - so are restricted to a maximum of 1,000 psi (rather than 3,000 psi) brake pressure.
Edit: since you have only 2 spoilers per wing, there is less weight on the wheels initially, therefore less grip with the tyres and consequently much less deceleration.
You will consume runway distance rapidly at the higher speed.
Last edited by rudderrudderrat; 19th Jan 2012 at 07:53.