How to go over speed cushions?

So I just moved into a new neighborhood and it's got a lot of speed cushions. They are positioned weirdly, so in order to make sure all 4 tires go over the cushion you gotta drive dangerously close to the mailboxes. Is there a difference between just letting one side of the car go over (2 tires) it vs the whole... show more So I just moved into a new neighborhood and it's got a lot of speed cushions. They are positioned weirdly, so in order to make sure all 4 tires go over the cushion you gotta drive dangerously close to the mailboxes. Is there a difference between just letting one side of the car go over (2 tires) it vs the whole car (4 tires)?

Also, the sign says 20mph. That seems fast for me I usually do 8~12. Should I go 20?
Update: Speed cushions in my neighborhood are positioned for one side runover, while most of the speed bumps in shopping areas cover the entire road so you're forced to go over with the whole car. So, that's where the confusion comes from.
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