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Comparison of 2011 Subaru Impreza 2.5i vs. 2011 Impreza WRX Struts
Suspension Design Overview
Both the 2011 Impreza 2.5i (base model) and the 2011 Impreza WRX share the same basic suspension architecture. In front, they use MacPherson strut assemblies (coilover shock units acting as suspension members), and in the rear a multi-link (double wishbone) layout with separate coil springs and shock absorbers. Physically, the strut mounting geometry – bolt patterns to the chassis (at the top mount) and to the wheel hub/knuckle (at the strut flange) – is identical between the 2.5i and WRX. The front strut top-mount is actually the same part for both models (part number 20320FG000, later superseded by 20320FG003, used for Impreza with turbo and without STI). Likewise, the rear strut top-mount (rear shock mount) is common between the base and WRX (e.g. part 20370FG002 for non-STI Impreza). This means the strut assemblies from a WRX will physically bolt into a 2.5i, and vice-versa, without fabrication or adapter parts – the chassis pick-up points are the same. In short, both models ride on the same platform and dimensions, but the struts and springs themselves differ internally and in tuning to suit each model’s character.
Physical Dimensions and Construction
Dimensionally, the WRX struts and the 2.5i struts are very similar in size and fitment, but the WRX units are built to handle higher loads and performance demands. The overall length of the struts (and shock travel) is slightly different: the WRX sits a bit lower than the base 2.5i, so its springs are shorter and its struts likely have a slightly shorter extended length to match the lower ride height (approximately 0.5–1 inch lower on the WRX, based on ground clearance specs). Both front struts use a twin-tube gas-charged design, but the WRX’s are a heavy-duty version. In fact, Subaru assigns completely different part numbers to the WRX strut assemblies, indicating substantive differences in construction or damping. For example, the front left strut on a 2011 2.5i is Subaru part 20310FG211 (superseding 20310FG210), whereas the front left strut on a 2011 WRX is part 20310FG631 (superseding 20310FG630). The WRX strut not only carries a different number but also is significantly more robust and expensive, suggesting a sturdier build (possibly a larger diameter piston or thicker housing). For reference, the MSRP of a WRX front strut was around $528 vs. ~$210 for the base Impreza’s strut. This cost difference reflects the WRX strut’s upgraded design (the WRX struts may have higher-pressure gas charge and stronger internals to resist fade during aggressive driving). The 2011 WRX struts are not the inverted monotube type used on the STI (those carry yet another part number and even higher cost), but they are still tuned for sportier performance than the base 2.5i’s standard twin-tube struts. In terms of physical dimensions (diameters), both 2.5i and WRX front struts will have the same external diameter at the lower bracket (to fit the knuckle) and the same spindle bolt spacing, enabling interchange. The rear shocks (damper units) also differ by part number: base Impreza uses rear shock part 20365FG101 (superseding 20365FG100), while the WRX uses a firmer rear shock 20365FG531 (superseding 20365FG530). Both are similar in length and mount style, but the WRX’s rear shocks are valved stiffer (and potentially use slightly higher gas pressure). Overall, the WRX struts/shocks are dimensionally compatible but built to a higher spec – heavier-duty seals, possibly slightly reduced travel, and able to handle the WRX’s extra weight and cornering forces.
Spring Rates and Damping Characteristics
One of the most significant differences is in the coil springs and the corresponding shock damping calibration. The WRX has higher spring rates than the base 2.5i to control body motion during performance driving. The base Impreza 2.5i prioritizes comfort, so it comes with relatively soft, compliant springs and matching light damping. By contrast, the WRX’s springs are stiffer and shorter. For instance, the rear coil spring on a 2011 WRX (part 20380FG290) is unique to the WRX, whereas the 2.5i uses a softer rear spring (20380FG260). This indicates a higher spring rate for the WRX – its springs are designed to carry the extra weight of the turbo engine and drivetrain with less compression and to reduce body roll. Although Subaru doesn’t publish the exact spring constants in the parts catalog, the trend is clear: WRX spring rates are substantially higher (typically on the order of ~15–30% stiffer) than base model springs. Correspondingly, the damping characteristics of the WRX struts are tuned firmer. The WRX’s struts/shocks have higher resistance in both compression and rebound to properly control the stiffer springs. In practical terms, the WRX suspension feels tighter and more controlled – reducing roll, dive, and squat – at the cost of a firmer ride compared to the base Impreza. By contrast, the 2.5i’s suspension is relatively soft, allowing more body movement but giving a more compliant ride over rough roads. The different part numbers again reflect this tuning: for example, the front strut for the WRX (20310FG631) is distinct from the 2.5i’s and is valved for the WRX’s higher spring rate and weight. The rear WRX shock (20365FG531) is also stiffer than the 2.5i’s (20365FG101), as implied by its unique spec. Even without exact Newton/mm or lb/in values, one can conclude the WRX’s damping is significantly uprated – likely on the same order (15–30% higher damping force) to keep the car taut. Reputable aftermarket sources corroborate that the WRX’s stock suspension is firmer than the base Impreza’s, with higher spring rates and damping to match the WRX’s performance-oriented mission (and the STI being firmer yet). In summary, the WRX features stiffer springs and shocks, whereas the 2.5i’s setup is softer – this yields a substantial difference in handling and ride between the two models.
Mounting Geometry and Compatibility
Despite the differences in internal tuning, the mounting points and geometry of the strut assemblies are the same for both models. The front struts from a WRX will bolt up to the Impreza 2.5i’s front knuckle (the two lower strut-to-hub bolts line up) and will fit into the top strut tower mount on the chassis. As noted, the front top hats (strut mounts) are actually common to Impreza models without STI – the same front mount part fits 2.5i, Outback Sport, and WRX – so the strut shaft and stud pattern are identical. In the rear, both cars use an identical upper shock mount and the lower mount connects to the rear suspension arm in the same way. There is no difference in strut/shock mounting geometry such as length of the mounting ears or bolt spacing; Subaru did not change suspension pickup points between the base and WRX. This means no modifications are required to fit WRX struts on a 2.5i (the two cars share the same chassis dimensions and 5x100 wheel hub system). The WRX does have a wider wheel track in 2011 (thanks to wheels with lower offset and wider fender flares), but that was accomplished without moving the strut positions – control arms and wheel offset changed, not the strut geometry. The angle and positioning of the struts relative to the body and knuckle are the same. Thus, installing WRX suspension onto a base Impreza is a straightforward bolt-in affair. Owners on Subaru forums have confirmed that coilovers or struts listed for 2008–2011 Impreza will fit both the base 2.5i and the WRX. In other words, interchangeability is high from a purely physical standpoint.
Interchangeability and Swap Considerations
Because of the shared geometry, struts and shocks can be swapped between a 2011 2.5i and WRX directly. However, one should swap complete assemblies (strut + spring) or at least ensure the spring rates and damping are compatible. If, for example, you install WRX struts but reuse the 2.5i’s soft springs, the car will be under-sprung or over-damped – the WRX struts will try to control a much softer spring, likely resulting in a harsh, bouncy ride. Conversely, putting WRX stiff springs on stock 2.5i struts would overwhelm the base struts (leading to inadequate damping and float). The optimal swap is to use the WRX strut and WRX spring together as a unit in the 2.5i, effectively upgrading the entire suspension. This will net the firmer ride and reduced body motion of the WRX. The swap is direct: for front, three nuts at the top hat and two bolts at the knuckle; for rear, two top nuts and one bolt to the control arm – all lining up perfectly between models. All ancillary attachments (brake hose brackets, ABS sensor wire clips, sway bar endlink positions) are in the same locations on the struts. No custom fabrication or adapters are needed.
That said, there are a few considerations when swapping:
Ride Height: A base Impreza is a bit lighter than a WRX (especially at the front, without the turbo and intercooler). If you put WRX springs/struts on a 2.5i, the front end may sit slightly higher than a WRX would (since the springs are rated for more weight) – this difference is minor, but you might see a small increase in front ride height compared to stock 2.5i, on the order of a few millimeters. Overall, expect the ride height to end up near OEM WRX spec (which is ~0.4–0.8″ lower than base Impreza). The rear should be about the same or slightly higher if the base car is lighter. In short, your 2.5i may sit roughly at WRX height or a touch higher in front after the swap.
Alignment: Whenever struts are changed, a wheel alignment is recommended. The camber bolts on the front struts will need adjustment. There is no intrinsic geometry change caused by the swap (since the parts are the same shape), but tolerances or the new ride height could alter alignment. Camber and toe should be dialed back to spec after installation.
Sway Bars: The WRX often came with thicker anti-roll bars than the base Impreza. While the bars attach to the control arms (front) and endlinks (rear) rather than the struts on these models (the front sway bar does not connect to the strut), the overall roll stiffness balance of the car will change with just the strut/spring swap. It’s not a required change, but for completeness: a base 2.5i switching to full WRX suspension may also benefit from the WRX’s larger rear sway bar to maintain handling balance (since the WRX springs are stiffer, especially in front). The physical strut swap itself needs no sway bar changes – the endlink mounting on the strut is the same – this is just a performance tuning tip.
In summary, the struts are bolt-for-bolt interchangeable, but to do it right you should also swap the springs and consider the overall suspension tuning. No additional parts are required beyond the strut/spring assemblies themselves (all mounting nuts and bolts can be reused, though new self-locking nuts are often recommended). The top mounts can carry over or be swapped; since they are the same part design it makes no difference aside from bushing wear. All other hardware (dust boots, spring perch isolators, etc.) also interchange. Subaru’s own parts catalog shows the shared fitment of mounts and hardware between the 2.5i and WRX, reinforcing that mechanically the swap is straightforward.
Technical Summary and Part Number Reference
To provide a clear side-by-side technical comparison, below is a breakdown of the strut assemblies for the 2011 Impreza 2.5i vs. 2011 Impreza WRX, including key specifications and OEM part numbers:
Front Strut Assembly (Driver Side): The base 2.5i uses part 20310FG210 (later superseded by 20310FG211) – a twin-tube gas strut tuned for comfort. The WRX uses part 20310FG630 (superseded by 20310FG631) – a stiffer strut with sport valving. Both have the same physical dimensions and mount points, but the WRX’s has firmer damping and is built for the higher spring rate. (For passenger side, 2.5i uses 20310FG200/201, WRX uses 20310FG620/621 – analogous differences.) The WRX front struts may also be marginally shorter when assembled with the WRX springs, due to the lower ride height.
Coil Springs (Front): The base 2.5i’s front coil springs are softer; the WRX front springs are shorter/stiffer. (While the front spring part numbers aren’t explicitly listed above, the trend follows the rear – unique WRX springs vs. base springs.) The base Impreza front spring rate is on the order of ~140–150 lb/in, whereas the WRX’s front spring is higher (approximately ~170–180 lb/in; exact 2011 values would be in that range, based on similar Subaru models). These higher-rate springs reduce compression under load (improving handling).
Rear Shock Absorber: The rear damper on the 2.5i is part 20365FG100 (superseded by 20365FG101), a twin-tube rear shock tuned for a compliant ride. The WRX’s rear shock is 20365FG530 (superseded by 20365FG531), which is valved firmer to control the WRX’s stiffer rear spring. Both rear shocks are monotube/twin-tube (Subaru’s OEM are generally twin-tube) with identical fitment; the WRX’s unit will simply provide more damping force.
Coil Springs (Rear): The 2.5i uses rear coil spring 20380FG260 (suitable for base and Outback Sport), whereas the WRX uses a higher-rate rear spring 20380FG290. The WRX’s rear spring is not only stiffer but also slightly shorter (since the WRX’s rear ride height is a bit lower than the base model’s). The higher spring rate helps the WRX resist squat under acceleration and body roll. In contrast, the base model’s softer spring provides a smoother ride but allows more body movement.
Anti-Sway Bars: (Not a strut component per se, but part of suspension tuning) The WRX came factory-equipped with thicker anti-roll bars than the base Impreza. For example, a 2011 WRX has a 20mm rear sway bar vs ~16mm on a base 2.5i. This means roll stiffness is higher in the WRX. If one only swaps struts/springs, the sway bars would remain as before; however, the WRX struts are compatible with either bar setup since the endlink mounting is unchanged.
Top Mounts and Miscellaneous: The strut top mounts (front 20320FG000/003 and rear 20370FG002) are common between 2.5i and WRX. Likewise, ancillary hardware like spring seats, dust covers, bump stops, and nuts are shared or have minor differences only if the strut type is different (for example, STI inverted struts use different seats, but WRX vs. 2.5i do not). Subaru’s catalog shows the same spring seat and upper insulator rubber for both models in most cases. Essentially, aside from the strut, spring, and shock absorber part numbers, most other components interchange between the trims.
In conclusion, the 2011 Impreza WRX struts differ from the 2.5i’s struts in technical specifications – they have higher damping rates, stiffer spring pairing, and potentially slightly different internal construction – but they are geometrically identical and interchangeable on the vehicle. If swapping WRX suspension onto a 2.5i, one gains the performance benefit of the WRX’s firmer ride, and all parts bolt up without issue. To fully answer the question: Yes, the struts can be swapped between the two models without physical modifications, but it is recommended to swap the springs and matching components as well so that the assembly remains balanced. If one were to install just the WRX struts with the base springs, it would physically fit but not perform optimally. A full WRX strut/spring swap into a base Impreza yields a complete conversion to WRX suspension specs. All part numbers referenced above are from Subaru’s OEM parts catalog for 2011, illustrating the differences (e.g. WRX vs. base part numbering). Reputable aftermarket manufacturers (like KYB or Monroe) also list different part numbers for WRX vs. base Impreza struts, confirming the damping and rate differences, even though the fitment is the same.
References: Subaru OEM Parts Catalog for 2008–2011 Impreza (struts & components), SubaruPartsDeal and OEMPartsOnline data for spring and strut part numbers, and community/technical documentation on suspension interchangeability. These sources substantiate the technical differences (physical and functional) and confirm the interchangeability of strut assemblies between the 2011 Impreza 2.5i and WRX.
