Roth vs Traditional IRA: Post-retirement tax bracket

I understand that if you plan to be in a higher tax bracket in retirement that a Roth IRA is probably a better option. However, if you’re retired and have no job, are you still in a tax bracket? Should I be looking at the tax bracket I expect to be in before I retire? I’m a little confused because if I retire my only income would be social security, 401k, etc. I’m assuming your tax bracket would be based on the salary you have at the time of your retirement, but I’m not sure.