I am using a 60" Gearmore tiller. I had to replace the tines after two years of use. I talked to Gearmore about getting replacements. The person at Gearmore (theey are in California) said that one customer, a city that uses their tiller to help clean up the beach, replace their tines every week. the lifetime really depends on the soil/dirt. the 90 degree tines are typically called "L" tines and the curved tines are called "C" tines. I replaces my C tines with L tines. The L tines would stall the tractor where the C tines had no problem. There is more tine in the dirt with the L tines. The cost is about $5.00 to $6.00 per tine. My tiller has 40 tines. Use gloves when you remove the old tines, save cutting up your hands
carl