Dear Driving for Dollars, 
I am a server in a restaurant. I make good money when you count my tips, but on paper my income is much less, so I am having a hard time getting a good interest rate on a car loan. I think I have a friend with great credit and a good income to co-sign for me. How much does my income matter with a co-signer? 
-James
Dear James, 
When you get a co-signer for a car loan, that person's income, credit score and history are taken into account. In short, the lender will be looking at your friend's ability to repay the loan entirely on his or her income and credit profile. If the friend has the income and credit that you say, you should be approved for a better interest rate than on your own.