Adding low-end punch to a factory car stereo usually means sacrificing trunk space for a bulky wooden enclosure. A Cerwin Vega spare tire subwoofer solves this compromise by tucking a powerful active subwoofer directly inside the wheel well, preserving 100% of your cargo utility. Whether you drive a hatchback, SUV, or sedan, this setup utilizes dead space while delivering clean, low-frequency response.
Upgrading your sound system doesn't mean you have to give up groceries, luggage, or tools. Let's look at how these compact powered subwoofers work, how to install them without losing your spare tire, and how to tune them for maximum acoustic output.
How Spare Tire Subwoofers Protect Cargo Utility
Traditional subwoofer boxes take up valuable floor space, making road trips and daily errands frustrating. A spare tire enclosure sits flat inside the rim of your spare wheel or replaces the insert entirely, depending on the model configuration.
Because the unit sits below the factory trunk floor or mat, objects placed on top rest on a flat surface just like they did from the factory. You keep your entire cargo area open. If you need to haul large boxes or sports gear, you don't have to unhook wiring or unbolt heavy speaker boxes.
Active Versus Passive Design Choices
Most stealth spare tire units, including options from Cerwin-Vega, are active systems. They feature a built-in digital amplifier matched precisely to the driver's voice coil impedance. This integration eliminates the need to mount a separate outboard amplifier on your rear seats or trunk side panels, saving even more space and simplifying wiring.
Selecting the Right Unit for Your Vehicle
Before buying, you need to measure your vehicle's spare tire well and verify internal wheel dimensions. Spare tire subwoofers generally fall into two categories based on physical size and fitment constraints:
- Compact 10-Inch Models: Units like the Cerwin-Vega VPAS10 are slim enough to fit inside smaller space-saver spare rims or shallow trunk wells. They run on efficient MOSFET power supplies and fit tight spaces easily.
- High-Output 12-Inch Models: Units like the VPAS12ST offer a larger cone area to push more air. These require larger wheels—typically 15 inches or greater—to drop cleanly into the center rim.
Always pull your spare tire out, measure the inner diameter of the rim, and check the vertical depth from the bottom of the well to the trunk floor line.
Step-by-Step Installation Process
Installing a powered spare tire subwoofer requires basic wiring knowledge and hand tools. Setting up the system properly prevents rattles and protects your vehicle's electrical charging system.
- Disconnect the Battery: Always disconnect the negative battery terminal before running power wires to prevent accidental short circuits or blown fuses.
- Mount the Subwoofer: Remove your vehicle's factory spare tire mounting bolt. Place the subwoofer securely into the spare tire well. Many units use a threaded rod system that anchors through the center of the subwoofer down to the factory mounting hole, holding both the spare tire and the audio unit firmly in place.
- Run Power and Ground Wires: Run an 8-gauge (or heavier) power wire from the battery's positive terminal through a firewall grommet to the trunk. Install an inline fuse holder within 18 inches of the battery. Connect the ground wire to a bare, unpainted metal point on the chassis close to the subwoofer, keeping the run short.
- Connect Audio Signals: If your aftermarket head unit has dedicated RCA subwoofer outputs, run a shielded RCA cable to the back. If you're keeping your factory stereo, use the high-level (speaker-level) input harness to tap into your rear speaker wires.
- Attach the Remote Turn-On: Connect the blue remote wire to your head unit's remote output. If your factory radio lacks this wire, use an ignition-switched 12V accessory source so the amplifier turns on only when the car runs.
Tuning and Calibrating for Clean Bass
Once powered up, resist the urge to turn every gain knob to maximum. Proper tuning ensures tight, musical bass rather than muddy vibration.
- Set the Low-Pass Filter (LPF): Adjust the crossover frequency between 80 Hz and 120 Hz. This ensures your subwoofer only handles deep bass notes while your door speakers handle midrange and highs.
- Adjust Input Gain: Play a familiar track with dynamic bass. Turn the gain up slowly until the bass blends naturally with your door speakers without distorting or clipping.
- Check the Phase Switch: Toggle the phase switch between 0 degrees and 180 degrees while sitting in the driver's seat. Choose the setting that sounds fuller and more impactful, which means sound waves from your sub and door speakers are aligned.
Common Mistakes to Avoid
Avoiding simple setup errors saves time and prevents equipment damage.
Don't skip the inline fuse near the battery; running un-fused power through your cabin creates a severe fire hazard if the cable rubs against bare metal. Don't mount the ground wire to painted surfaces or thin plastic brackets, as poor grounding causes engine whine and amplifier protection shutdowns. Finally, don't ignore rattles. Because spare tire wells are made of sheet metal, place thin rubber matting or foam strips under the unit to stop annoying vibrations before putting your trunk floor back down.
Frequently Asked Questions
Do I have to remove my spare tire to install a spare tire subwoofer?
Most stealth spare tire subwoofers are designed to drop right inside the hollow center rim of your existing spare tire. You keep your emergency tire safely in place while adding audio performance. However, verify dimensions first, as some compact vehicles have spare wells too shallow to house both items.
Can I connect a spare tire subwoofer to a factory stock stereo?
Yes. Almost all modern powered spare tire subwoofers feature high-level inputs. These inputs let you splice directly into your car's existing rear speaker wires without needing an aftermarket radio or line-output converter.
Will a spare tire subwoofer rattle my trunk lid?
Trunk rattles can happen because the sub fires inside a metal cavity. You can easily fix this by applying sound-deadening mats (such as butyl sheets) to the spare tire well floor and adding foam weatherstripping around the perimeter of your trunk floor cover.
How do I control the bass level from the driver's seat?
Quality active spare tire subwoofers include a wired remote bass knob. You can run this thin cable from the trunk up to your center console or dash, letting you adjust bass output on the fly depending on the music genre.
