The best replacement for coil springs is leaf springs.

The best alternatives to coil springs are rated as following:
★★★★★  leaf springs
★★★★  torsion bars
★★★★  coilovers
★★★  shocks
★★  spacers
★  air bags
★  air shocks
★  pocket springs
★  torsion bar
  620 coil springs
  air springs
  constant
  sinuous springs

Your alternative for coil springs is not listed? Suggest!
Speaking about coil springs, one probably shouldn't forget about air bags.

Other search terms related to coil springs and their ratings are:
★★★★★ air bags
★★★★ struts
★★★ shocks
★★★ leaf springs
★★★ air springs
You have in mind a companion for coil springs and it is not yet here? Propose!



Google Trends

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coil springs
leaf springs
torsion bars