Sway Bar Diameter Stiffness Chart
Sway bar (anti-roll bar) stiffness rises with the fourth power of its diameter, so a small increase in size makes a big difference. This chart shows the percentage increase in torsional stiffness when you go from an original bar diameter (left column) to a new one (top row). For example, going from a 20mm bar to a 24mm bar more than doubles its stiffness, a 107% increase.
The chart assumes solid bars with the same arm length and mounting points. Hollow bars, different arm lengths and adjustable end-link positions all change the actual rate.
Sway Bar Stiffness Chart
| Original / New | 16mm | 17mm | 18mm | 19mm | 20mm | 21mm | 22mm | 23mm | 24mm | 25mm | 26mm | 27mm | 28mm | 29mm | 30mm |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 14mm | 71% | 117% | 173% | 239% | 316% | 406% | 510% | 628% | 764% | 917% | - | - | - | - | - |
| 15mm | 29% | 65% | 107% | 157% | 216% | 284% | 363% | 453% | 555% | 672% | 803% | 950% | - | - | - |
| 16mm | - | 27% | 60% | 99% | 144% | 197% | 257% | 327% | 406% | 496% | 597% | 711% | 838% | 979% | - |
| 17mm | - | - | 26% | 56% | 92% | 133% | 180% | 235% | 297% | 368% | 447% | 536% | 636% | 747% | 870% |
| 18mm | - | - | - | 24% | 52% | 85% | 123% | 167% | 216% | 272% | 335% | 406% | 486% | 574% | 672% |
| 19mm | - | - | - | - | 23% | 49% | 80% | 115% | 155% | 200% | 251% | 308% | 372% | 443% | 522% |
| 20mm | - | - | - | - | - | 22% | 46% | 75% | 107% | 144% | 186% | 232% | 284% | 342% | 406% |
| 21mm | - | - | - | - | - | - | 20% | 44% | 71% | 101% | 135% | 173% | 216% | 264% | 316% |
| 22mm | - | - | - | - | - | - | - | 19% | 42% | 67% | 95% | 127% | 162% | 202% | 246% |
| 23mm | - | - | - | - | - | - | - | - | 19% | 40% | 63% | 90% | 120% | 153% | 189% |
| 24mm | - | - | - | - | - | - | - | - | - | 18% | 38% | 60% | 85% | 113% | 144% |
| 25mm | - | - | - | - | - | - | - | - | - | - | 17% | 36% | 57% | 81% | 107% |
| 26mm | - | - | - | - | - | - | - | - | - | - | - | 16% | 35% | 55% | 77% |
| 27mm | - | - | - | - | - | - | - | - | - | - | - | - | 16% | 33% | 52% |
| 28mm | - | - | - | - | - | - | - | - | - | - | - | - | - | 15% | 32% |
Shopping for a bigger bar? A stiffer rear bar is one of the most effective handling upgrades for reducing understeer on a Subaru. See our 2002-2003 WRX and 2004 WRX STI spec pages for factory bar diameters.