What's a good down payment for a $25,000 car?

Okay so ever since high school I've been wanting a Honda Civic si. Now that they have made 2018 Honda Civic si I instantly fell in love (I work for Honda and Toyota so I driven one yesterday) I'm 19 years old with about 1,200 saved up, I have no credit but I will be cosigning with my grandpa and he has perfect credit. And he said he will let me cosign a 2018 Honda Civic si for 6 years if I have a good enough down payment. So what's a good enough down payment for the car? I'll be okay with $300 payments but the only problem is that I don't know how much money I'll need to save up for that much.

Slow down sport. Your on your way to the perfect credit score crash. Your down payment, well that should be about $25,000.00, that should keep you out of trouble. But don't listen to me.

Minimum is 10%, you do realize gramps will be a co owner of this car, right? And any mess up you do will affect him. Tread lightly, be good to the old man. He's risking a lot on you.

YOU HAVE NO BUSINESS GETTING A 25K CAR that is over your 7% income clearly which you have NONE you are creating DEBT FOR YOUR GRAMPA ITS IN "HIS" name and he is RESPONSIBLE for the debt (lease) GO GET A JOB AND GET 10K-15k and you will be lucky to have that car because you are not counting INTEREST (LOAN). You are selfish to USE your gramps as your mule to get a car you can't afford. You know what my parents told me when i didn't have credit and went to a car lot THEY SAID TO BAD GET A JOB i suffered 6 years with out a car and another 6 years in a old stupid truck but you know what i learned valuable lessons.

In general, the more you can place down initially the better your overall finance terms will be.

However, do you realize how much it is going to cost to insure this Si? The monthly cost could quite easily be as much as the month car payment note. Before you get too excited you need to get an insurance coverage quote to know what you are up against.

At least $8500 and be able to pay off the balance in 3 years.
If you can't do that you can't afford the car.
The risk is you will get into a financial mess for a tin box.

A good down payment would be $25,000. This way you don't need a loan and you won't be paying any interest on that non-existent loan.

Keep Gramps out of this. If you can't afford the car on your own, you can't afford it all.