Train Horn Spare-Tire Mount — Hidden Bed-Under Install Guide

A spare-tire-mount train horn uses the void above (or alongside) the factory spare tire to host the air tank, with the compressor and trumpets mounted elsewhere. The result is a fully hidden install — nothing is visible from above the bed, nothing competes with cargo space, and the kit doesn’t broadcast its presence to anyone walking past your truck. HornBlasters and a handful of independent fab shops sell bolt-on bracket adapters specifically engineered for this position; the rest is a standard pickup install with the tank in an unusual location.

The trade-off is straightforward: cleaner aesthetic vs slightly tighter tank size. Most pickup spare-tire wells fit a 1.5-3 gallon tank — enough for any typical chord-horn install (8-12 short blasts before recharge), but not the 5-gallon tanks that ship in HornBlasters Shocker XL S6 / 544K kits. If you want both 5-gallon capacity AND hidden install, you’re looking at frame-rail under-bed mounts instead.

Why pick spare-tire mount

Three reasons truck owners choose this install path:

1. Aesthetic. The truck looks completely stock from the outside. No tank visible behind the rear axle, no compressor mounted in the wheel well, no air-line routing along the frame. Show-truck builders sometimes prefer this for cleanliness; daily-driver owners sometimes prefer it for theft deterrence (a visible $1,200 air kit attracts attention).
2. No cargo-space loss. The bed floor stays completely usable. Tools, dirt bikes, bedliners, work-truck gear all fit normally. Compare to a frame-rail-mount tank that occupies ~10% of bed-floor depth at the front of the bed.
3. Cleaner air-line routing. Spare-tire well sits between the rear axle and the rear bumper. Air lines from the tank to the trumpets behind the front bumper run straight along the frame rail, no cross-over routing needed.

What’s actually in a spare-tire mount kit

The dedicated bolt-on kits typically include:

• Mount bracket — fabricated steel, adapts to the factory spare-tire crank assembly. Bolts to the same mount points used by the spare tire’s hoist mechanism. No drilling into the frame.
• Tank — usually 1.5 or 2 gallons; some kits are 3 gallons depending on truck spare-tire well size. Always 150-200 PSI rated steel.
• Compressor mount bracket for engine bay — separate from the tank mount; the compressor doesn’t share the spare-tire well.
• Air line — long enough to reach from rear-of-bed tank position to engine-bay compressor and front-bumper trumpets. 25-40 ft of 5/16” DOT line typical.
• Standard wiring kit — same as a generic pickup install (10 AWG main, 18 AWG trigger, 30 A fuse, relay).

What’s not different from a regular pickup install: the trumpets, the solenoid valve, the wiring procedure, the install time. Once the tank is in the spare-tire bracket, the rest of the install is identical to /vehicle/train-horn-for-pickup-truck/.

Truck-by-truck spare-tire well capacity

The spare-tire well dimensions vary by truck. Approximate maximum tank size that fits the well without spare-tire interference:

Truck	Spare-tire well capacity	Spare access
F-150 (12th gen, 2009-2014)	3 gallon	Spare access slightly reduced; fits
F-150 (13th gen, 2015-2020)	2.5 gallon	Tight; 1.5-2 gallon recommended
F-150 (14th gen, 2021+)	2 gallon	Tighter; 1.5-2 gallon optimal
Silverado 1500 (K2XX 2014-2018)	3 gallon	Comfortable
Silverado 1500 (T1XX 2019+)	2 gallon	Tight; 1.5-2 gallon recommended
RAM 1500 (DT 2019+)	2 gallon	Air-suspension trims have less clearance
RAM 1500 (DS 2009-2018)	2.5-3 gallon	Comfortable on non-air-ride trims
Toyota Tundra (2007-2021)	2 gallon	Tight; check spare-tire crank routing
Toyota Tundra (2022+)	2 gallon	Similar to previous gen
Tacoma / Frontier / Ranger / Maverick	1.5 gallon max	Mid-size pickups have very limited well space

For F-250 / F-350 Super Duty and other HD trucks, spare-tire mount is rarely used because there’s so much frame-rail space available. The HD trucks accommodate 5-7 gallon tanks between frame rails behind the rear axle without any spare-tire trade-off — better all-around install.

For Silverado 2500HD / 3500HD, spare-tire mount is also rarely used for the same reason.

The mid-size unibody pickups (Maverick, Santa Cruz) have spare-tire wells but typically don’t accommodate even 1.5-gallon tanks cleanly. Drop-in electric horns (Stebel Nautilus, Wolo 619) are the practical install path for those chassis.

Spare-tire-mount install procedure

The tank-side install adds roughly 30-45 minutes to the standard pickup full-air-kit procedure. The full sequence:

1. Jack up the truck and secure on jack stands with the rear wheels off the ground. Crank down the spare tire and remove it from the truck.
2. Inspect the spare-tire crank assembly — the cable, the spool mechanism, the mount points to the frame. Note the bolt pattern; this is what the spare-tire-mount bracket bolts to.
3. Bolt the spare-tire mount bracket to the same factory mount points as the spare-tire crank. Use the supplied hardware (typically 7/16” Grade 8 bolts). Torque to manufacturer specification.
4. Mount the air tank to the bracket — orientation matters: the tank’s drain valve must face down (gravity-fed moisture removal), and the pressure switch port must NOT be on the bottom (moisture damages it). Most spare-tire-mount brackets are designed for one specific orientation; follow the kit’s instructions.
5. Plumb air-line out the frame-rail side of the spare-tire well. Most kits route the line forward along the inside of the frame rail to the engine-bay compressor.
6. Re-mount the spare tire on the bracket assembly if the kit accommodates both — some brackets relocate the spare to a cargo position; others share the well with the tank in a stacked configuration.
7. Continue with the standard pickup install — compressor in engine bay, solenoid forward of the trumpets, wiring per the main install guide.

Spare-tire vs frame-rail mount — when to pick which

Spare-tire mount is the right choice when:

• You want a completely hidden install with nothing visible behind the truck
• Your bed real estate cannot lose any space (work truck, dedicated cargo use)
• You have a 1.5-3 gallon tank in your kit (or are shopping for one)
• Your truck is light-duty (1500 / 150 class)

Frame-rail mount (between rear axle and rear bumper) is the right choice when:

• You’re running a 5-gallon or 7-gallon tank — won’t fit in spare-tire well on most pickups
• Your truck is HD (F-250+, RAM 2500+, Silverado 2500HD+) where frame space is generous
• You want the fastest install — frame-rail mount is typically 30-60 minutes faster than spare-tire mount because no spare-tire-crank work is needed
• The extra exposure of the tank doesn’t bother you visually

Common pitfalls specific to spare-tire-mount installs

• Forgetting where you put the spare. If the bracket relocates the spare, document the new position and confirm tire access before driving away. Owners have called for tow trucks because they couldn’t find their relocated spare during a roadside flat.
• Over-tightening the spare-tire crank bracket bolts. Factory torque spec on these bolts is typically 25-40 ft-lbs; aftermarket kits often ship with Grade 8 hardware rated for higher torque. Use the kit’s spec, not the higher-strength bolt’s max torque, to avoid distorting the frame mount.
• Mounting tank with pressure switch port on bottom. Moisture pools into the switch electronics; switch fails in 6-12 months. Always side-mount or top-mount the pressure switch.
• Cutting air-line at an angle to fit the tight routing. PTC fittings need square cuts to seat properly. Route through the tighter spare-tire well clearance with extra care; use a proper tube cutter not wire cutters.
• Skipping the manual shut-off valve at the tank. Useful on any install but especially on spare-tire mount — having a shut-off lets you bleed pressure to service the tank without crawling under the bed.

For the complete 15-step pickup full-air-kit install procedure (which adapts directly to spare-tire mount with the tank-mounting steps replaced by the spare-tire procedure above), see /guides/how-to-install-train-horn-on-truck/.

Cost on a spare-tire-mount install

The bolt-on bracket adds roughly $80-150 to a standard pickup full-air-kit cost. Using the cost guide tier numbers:

• HornBlasters CS232 + spare-tire bracket DIY: $580 + $100 (bracket) + $0 install = $680
• Kleinn HK7 + spare-tire bracket DIY: $840 + $100 + $0 install = $940
• Shocker XL S6 + spare-tire bracket is not recommended — the 5-gallon tank doesn’t fit in the spare-tire well on most light-duty pickups. Step down to the CS232 (2-gallon tank) for spare-tire mount.

Add $100-200 for shop install if you don’t DIY — the spare-tire-bracket portion is usually flat-rate $50-100 on top of the standard install labor quote.

Frequently asked.

01 What is a spare-tire-mount train horn?

A train horn install where the air tank mounts in the void above the factory spare tire, using a bolt-on bracket that adapts to the spare-tire crank assembly. Compressor stays in the engine bay; trumpets mount behind the front bumper. The whole install is fully hidden — nothing visible from above the bed. Typical tank size 1.5-3 gallons; 5-gallon tanks don't fit in most pickup spare-tire wells.

02 Will a 5-gallon train horn tank fit in a spare-tire well?

No — not on most light-duty pickups. F-150 12th gen (2009-2014) gets close at 3 gallons; T1XX Silverado 1500 (2019+) and 14th gen F-150 (2021+) max out around 2 gallons. The HornBlasters Shocker XL S6 5-gallon kit needs frame-rail mount instead. For Silverado 2500HD / 3500HD or F-250 Super Duty trucks, frame-rail mount is the better choice anyway because frame space is generous.

03 Do I lose my spare tire with a spare-tire-mount kit?

Some bracket designs relocate the spare to the bed cargo area; others share the spare-tire well with the tank in a stacked configuration that retains the spare in place. Verify what your specific kit does before ordering. F-150 owner manuals explicitly note that the spare can ride in the bed cargo area as a documented alternative; same is true for Silverado / Sierra. RAM 1500 air-suspension trims have less spare-tire well clearance, making spare relocation more likely on those trucks.

04 How long does a spare-tire-mount install take?

Roughly 30-45 minutes longer than a standard pickup full-air-kit install. The standard install runs 4-5 hours per the HornBlasters CS232 manual; spare-tire mount adds the spare-tire-crank work, the bracket bolting, and the spare relocation if applicable. Total install time 4.5-6 hours for a typical pickup.

05 What kits are available for spare-tire mount?

HornBlasters publishes truck-specific spare-tire mount brackets for several common pickups. Independent fab shops also sell bolt-on adapters specifically for F-150 / Silverado / RAM 1500 platforms. The bracket-only purchase typically runs $80-150 separate from the kit; pair with any standard 1.5-3 gallon air kit (CS232, Kleinn HK7 or smaller, Vixen mid-tier kits). Start by visiting hornblasters.com/pages/manuals-schematics for the current bracket lineup.

06 Is spare-tire mount harder to maintain?

Slightly. Tank drain (recommended every 2 weeks) requires crawling under the bed and reaching past the spare. Auto-drain valve upgrades ($69.99 HornBlasters Electric Drain Valve Kit) eliminate this — the valve drains automatically each time you cycle the system, so you never need to physically reach the manual petcock. Spare-tire mount installs benefit from the auto-drain upgrade more than frame-rail mount installs do.

07 Can I install spare-tire mount on a Tacoma or Tundra?

Tacoma — 1.5-gallon tank max in the spare-tire well; tight install. Tundra — 2-gallon tank max across all generations. Both are viable but you're working with limited tank capacity. Drop-in electric horns (Stebel Nautilus 134 dB at $40-65) are often the better path for these mid-size and tight-engine-bay pickups; spare-tire mount works but the trade-offs are more pronounced on smaller chassis.

Sources

• HornBlasters install manuals & schematics index
• HornBlasters Conductor’s Special 232 manual
• HornBlasters Electric Drain Valve Kit

Pricing is current as of April 2026.

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