Well I'm not sure if you'll have to, depends on the credit and what the seller wants.
But if you were to put a down payment, it would affect monthly payments because you'd have a lower overall cost...
Example: 10,000 dollar bike at 12 mo without a down payment would be 10,000/12 per month
10,000 with 2,500 down payment would be 7,500/12 per month.. so basically less per month
Obviously there's a lot more to it, but yea.