I like the Bi-Folds. tri-folds are finger pinchers.
http://www.fleetfarm.com/catalog/product_detail/atv-motorcycles-snowmobiles/atv/accessories/raider-6-ft-x-48-in-bi-fold-atv-ramp-bcs1007?utm_source=googleps&utm_medium=shopping%2Bsearch&utm_campaign=google%2Bproduct%20search