First of all, make sure that all your cups have lids that are on tightly.
If they don't fit tight in the cup holders I suggest you get the holder from them and place this on the floor of the vehicle where it won't get knocked over.
You can buy sleeves from automotive stores that fit into your vehicle's cup holders to change their size. You could also try this.
〉 Answered on Aug 20th, 2008 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines