Search for coil spring helper or coil spring spacer. Installing those will stiffen your springs but they will most likely increase your ride height at the same time. Usually they are solid like these. The ones you linked won't provide as much stiffening or lift because of the holes in them...but that might work for you. They're easy to install...so you could always try them.
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View my fuel log 2015 Mirage ES 1.2 manual: 52.2 mpg (US) ... 22.2 km/L ... 4.5 L/100 km ... 62.6 mpg (Imp)