Obviously, if you aiming to cycle the 'SDW', then you will want to stay on the SDW route. However, you may want an short alternative sometimes for a change. I have therefore made some suggestions below (only 2 at moment!):
Route: Traveling east, at finger post (about 0.6 miles after barn), turn left down steepish chalk descent, gradual right bend. Although a just discernible bumpy track between open fields, there are drainage gullies cut across it, so BEWARE! After about 3/4mile, join tarmac lane, with occasional speed bumps.
At bottom bear right, but SDW is track just to left of tarmac road, with which it joins up in about 100 yards.
Go over bridge (about 1 1/4 mile from leaving SDW); carry on through village, keeping straight ahead. After, 1/4 mile, turn right at T-junction. Keep on wide road (old A24), follow up to top of longish gradual climb to rejoin SDW.
AR2: Section 4, between Beacon Hill (just east of Harting Down) and Treyford, avoiding Pen Hill. Adds about 0.2mile. As noted in 'section', I find Pen Hill too steep to cycle up, so this is an attractive alternative for a change !
Route: Traveling east: At the sharp left turn to the SW of Beacon Hill, go straight on ! Go though the gate( vehicle & person gates). After about 50 yds, changes to tarmac as skirts private house (Telegraph House, used to send messages in earlier times); continue on slight down gradient on tarmac. At a slight right bend, with bungalow on left, go though single gate on left just before bungalow. Grass path, after about 100 yards, turn sharp left on tractor width track; first part usually deepish tyre ruts. Track gradually descends through trees, emerging on to chalk track. At bottom of short descent, bear left, go along wide chalk track, rejoin SDW after old farm buildings barn.
(to add map, photos etc)
To avoid nasty rough 'ditch' out of Alfriston, see below (Thanks to Andy L)