If we are innocent until proven guilty, why do we have to post bail?

Bail implies presumption that there is evidence to take you to court. You are never, ever, ever required to pay bail. You can refuse, and the state will make arrangements to ensure your appearance in court.

Because of the interest in public safety outweighs the presumption of innocence in that context. We still give the accused freedom in the form of bail so long as they are not a flight risk or a danger to the public.

Rules had to be set

presumption of guilt would translate to you being locked up and we will forget about any trial

Bail translates to you accepting there are Legitimate grounds to pursue charges [ not that you accept Guilt] and that you are guaranteeing the court you will attend all related hearings until the Court makes a decision

if you will not guarantee this to the court then perhaps you may be guilty or may plan to flee to avoid prosecution in which case the court is justified to hold you on Remand until justice is satisfied with the conclusion of the Hearings

No, it's just insurance that you'll come back to face the charges.

If they could have the speedy trial, bail wouldn't be necessary.

Bail is created by statute. That statute specifically says that bail is not a finding of guilt.

In reality - yea it is. But we create this legal fiction because 99% of the time those people are actually guilty.

Bail is merely a guarantee that you will appear in court.

Seriously, you've got the internet. Look up the f*cking word.

http://www.merriam-webster.com/dictionar%E2%80%A6