we have three thunderbirds in our house I own one and my son has two thay have a slight reflex when unstrung but when strung resume a d shape on ours we use 7- 71/2 inches have always worked the best you will find these bows are very good performers will handle the modern string materials and will give most longbows a run for there money in the speed department I have had mine for 5 years and only switched to drop pounds when my son grew out of his 41# I asked him what he would like most and he said another thunderbird I think that says it all I know mine will never leave my house. If you need any more help just ask Delin