Introduction
The Firestone Coil-Rite Airbags (model 4135) have been installed by a 6th-generation Toyota 4Runner SR5 owner to address rear suspension sagging and bottoming under heavy load. When transporting camping gear and electric bicycles—estimated to be a combined weight of 600 pounds—the vehicle experienced a 2-inch rear sag, exacerbated by the leverage of the hitch-mounted items. The suspension would frequently bottom out against the bump stops, even on rough paved roads and forest service trails. While long-term consideration includes a lift kit and reinforced coil springs, the Firestone kit has been adopted as an interim solution. The system is documented as compatible with 6th-gen models despite conflicting information found on some external websites, with Firestone itself confirming this compatibility.
This article outlines the usage scenario, reported performance, and compatibility status of the Firestone model 4135 coil-over airbag system as implemented in the user’s Toyota 4Runner.
Understanding the Suspension Issue
The reported problem stems from the stock suspension's inability to support the vehicle's rear-end under significant and extended loading. A camping setup combining gear and e-bikes placed both directly within the truck bed and via a hitch rack has exacerbated the situation. The configuration results in distributed weight—approximately 600 pounds in total—with an additional mechanical challenge from around 150 pounds of leverage applied at the hitch’s extended position. This setup causes the rear shocks to compress beyond their intended range, contacting the bump stops under regular driving conditions and forest service road use.
Without additional suspension reinforcement, this bottoming effect can result in reduced ride comfort, increased stress on suspension components from overextension, and potential handling deterioration. The Firestone model 4135 airbags are intended to supplement the existing coils to reduce or prevent sag and overcompression, thereby maintaining posture control and improved load-leveling behavior.
Firestone Model 4135 Overview and Compatibility
Firestone offers the model 4135 Coil-Rite Airbag set, which is specifically designed for automotive coil-over suspension augmentation. According to user verification and Firestone's official website, this kit is compatible with the 6th-generation Toyota 4Runner. Some online sellers or resellers may inaccurately indicate incompatibility, yet the Firestone website serves as a verified source stating the product is intended for this vehicle.
The core functionality of the model 4135 is to integrate alongside the existing coil springs, not replace them. Users install the units at the rear coil location, where they function to distribute air pressure accordingly to absorb and negate the sagging impact. The airbags are typically adjusted through a remote inflation or pressure control system, allowing users to tailor stiffness based on load and driving conditions.
User Experience with the Firestone Model 4135
The SR5 owner who installed the Firestone kit observed a clear reduction in rear suspension sag when loaded with camping gear and electric bikes. The 2-inch sag previously experienced was reportedly mitigated significantly. The additional support provided by the airbags prevented the rear shocks from bottoming out during heavy-duty driving conditions commonly encountered on off-road or rough terrain trails.
This improvement was noted even during driving on buckled pavement, a situation that typically induces severe cornering impact and weight transfer. While the Firestone system is not intended as a permanent modification to the vehicle’s overall geometry, it is considered an effective temporary enhancement given current market offerings for 4Runner lift options. The modular nature of coil-over airbags allows for future flexibility; should the user decide to install a dedicated lift kit in the future, the Firestone model 4135 can be replaced or integrated accordingly.
Considerations for Installation and Usage
Installation
The user does not provide step-by-step installation instructions within the source material. As such, detailed procedures for the Firestone model 4135 kit cannot be confirmed from this dataset. However, general coil-over airbag systems typically require the removal of the stock rear coil springs to install the airbags alongside or in place of them. Installation can vary in complexity depending on a user’s mechanical experience, and some may opt to have the system professionally installed, as in this case.
The product should only be installed by individuals with prior automotive suspension installation experience or by trained professionals, as incorrect installation may lead to improper function or potential safety concerns. It is also vital that all suspension components, including coil springs, shocks, and links, are in good condition prior to modifying or augmenting the system.
Usage Adjustments
Adjusting the air pressure in the Firestone model 4135 system likely involves an external control module and air valve connections (standard to most coil-over airbag installations). Users can vary pressure settings based on the intended load, with a fully loaded configuration requiring higher inflation than a lightly used or unloaded setup. While no specific instructions for this method are provided in the source, adjustment is generally performed for each drive session or load configuration.
No mention of automatic or electronic leveling systems is included in the dataset; if such a feature is provided in higher-tier versions, it is unclear here. The manual adjustment of pressure may be the expected user practice for this particular model and installation.
Performance and Safety Considerations
The Firestone airbags offer enhanced suspension control under loaded conditions but do not provide rigid structural replacement for stock coil springs. For long-term use or for users subjecting their 4Runner to significant off-road use, the airbag system may serve as a stopgap solution until a comprehensive lift kit with stronger suspension hardware is available on the market.
Safety considerations include ensuring all mounting points are properly torqued and that the airbags remain pressurized at proper inflation rates during operation. Over- or under-inflation may shift the vehicle’s center of gravity or compromise the airbags’ integrity, leading to reduced effectiveness or potential failures. Users should consult Firestone's documentation or installation instructions for recommended air pressure ranges and maintenance schedules to ensure optimal performance.
Compatibility Discrepancies and Vendor Reliability
Despite Firestone’s confirmation of compatibility with the 6th-gen Toyota 4Runner, some websites may misrepresent the product’s applicability. As the Firestone website is the sole authoritative source referenced in the material, and it explicitly states that the model 4135 is intended for use on the 6th generation TRD SR5 model, users should prioritize purchasing from Firestone-affiliated or verified dealers.
Unverified third-party retailers or independent forums may disseminate outdated or incorrect information due to lack of access to updated OEM compatibility data. Therefore, it is strongly advised that users cross-reference compatibility with Firestone's documentation rather than relying solely on third-party product descriptions or user claims.
Alternatives and Long-Term Solutions
The Firestone airbag system is presented by the user not as a direct permanent upgrade but as a functional enhancement until a full lift system with heavy-duty coils becomes available. Such lift kits are generally engineered for extreme off-road use and offer more robust and rigid suspension reinforcement than modular support systems like coil-over airbags.
Until the market provides proven long-term lift solutions, coil-over airbags remain a suitable alternative for users seeking to maintain load capacity and handling without major structural modification. However, users should be aware that coil-over airbags are not typically suitable for extreme off-roading, trail racing, or heavy towing beyond moderate levels. Their primary benefit lies in leveling and supporting load distribution rather than significantly enhancing ground clearance or suspension travel.
Summary of Key Features and Benefits
The Firestone model 4135 coil-over airbag system allows the user to address rear suspension sagging under heavy load conditions in the 6th-gen Toyota 4Runner. Key features include:
- Compatibility with 6th-gen models as confirmed by Firestone
- Reduction in rear-end sag with consistent heavy loading (600 lb. total estimated weight)
- Prevention of rear shock bottoming on both paved and off-road conditions
- Potential as a stopgap solution until a full lift system is available
- Requires manual inflation/pressure adjustment (as implied, although no specific mechanism is described)
- Supplemental support to stock coil springs rather than full replacement
Conclusion
The Firestone model 4135 Coil-Rite Airbag system has provided a notable improvement in rear suspension handling for a user equipped with a 6th-gen Toyota 4Runner SR5. By reducing rear sag and preventing shock bottoming, the system has enhanced both comfort and usability during loaded driving situations. Despite some conflicting reports on external websites, Firestone confirms its compatibility with the 4Runner model, making it a reliable option for those seeking supplemental suspension reinforcement.
Users are advised to install the airbags only via a professional or skilled technician, ensure all suspension components are in good condition prior to installation, and follow Firestone’s pressure and maintenance guidelines. While the kit is not a long-term replacement for structural suspension upgrades, it presents a viable solution for load-related sag control and offers a flexible alternative to permanent modification.
This user experience underscores the effectiveness of airbag-based suspension augmentation for off-road and heavy-use applications, serving as an interim enhancement until more specialized systems reach the market.