You should take Wheelz up on this one. There's some fantastic rides in The Stellenbosch mountain from Coetzenburg to the old shooting ranges above Paradyskloof !! But you need local knowledge !!
http://www.dirtopia.co.za On the Delvera winefarm (Stellenbosch) there are some nice riding to be done (30min from CT city centre). Also Jonkershoek valley (Stellenbosch - 45min from CT)