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Field Tools

Overlander
toolkit.

Six precision calculators built for serious expedition travel. Size your rig, plan your provisions, rig your recovery — before the road disappears.

Air Suspension
14,500 lbs
Solar
1,350W
Winch
13,500 lbs
Water
91 gal

Air Suspension & Tongue Weight

Calculate optimal PSI for each preset and verify tongue weight distribution.

Trailer Setup
8200 lbs
4000lbs16000lbs
lbs

75% of GVWR · enter what your trailer actually weighs loaded (from a scale)

1T15ZR-6 reversible sleeve / rolling lobe · 70 in² effective area · 15–100 PSI

Tandem Axle (4 bags)

Air Suspension Bias — RREV ISA

Adjusting front vs. rear air spring pressure shifts the load distribution along the trailer chassis, directly changing tongue weight at the hitch.

50 %
0%100%
Tandem Axle (4 bags) · Bias: Equal
22 psi3,075 lb22 psi3,075 lb615 lb10% tongueTANDEMFIG. 01 — SIDE ELEVATION
615lb
Tongue Weight
10% — within spec
10%
Tongue %
Of loaded weight
22psi
Front Spring(s)
At current bias
22psi
Rear Spring(s)
At current bias
Pressure Presets by Terrain
Camp / Loaded
22 / 22
F / R PSI
Freeway
25 / 25
F / R PSI
Off-Road
30 / 30
F / R PSI
Loaded Weight6,150lbs
Per-Spring Cap @ Max7,000lbs @ 100 PSI
Total Spring Capacity28,000lbs
Load Ratio22%
Front Spring Load (ea)1,538lbs
Rear Spring Load (ea)1,538lbs
Tongue weight 615 lbs (10%) is in the ideal 9–15% range. Bias: Equal.

RREV ISA uses the Firestone W01-358-9781 (1T15ZR-6 reversible sleeve) — ~70 in² effective area per bag, 100 PSI max. At spec, a single bag supports ~4,250 lbs at 60 PSI and ~7,200 lbs at 100 PSI. Bias adjustments made via the RREV HUB app — independent per-wheel BLE control. Pressures are estimates; always confirm with RREV HUB readouts.

Methodology & Safety
How PSI is calculated
PSI per bag = (per-bag load) ÷ (effective area in²). With the W01-358-9781 at ~70 in² effective area, a fully-loaded rig typically sits at 30–60 PSI — well under the 100 PSI ceiling. The legacy "load ratio × 100" mapping ignored bag size and pegged the meter at max.
Firestone load chart
Per single W01-358-9781 spring at design height: 40 PSI ≈ 2,800 lbs · 60 PSI ≈ 4,250 lbs · 80 PSI ≈ 5,700 lbs · 100 PSI ≈ 7,200 lbs. Effective area varies ~70.0 → 72.0 in² with stroke; treated as constant here.
Tongue weight target
Industry standard is 9–15% of loaded trailer weight. Below 9% causes sway; above 15% overloads the tow vehicle rear axle and hitch receiver. Cargo position dominates — air bias is a fine-tuning lever, not the primary control.
Bias adjustment safety
Never set any individual spring below 15 PSI — minimum pressure to maintain bead seal. Always adjust pressure with trailer on level ground and unhitched from tow vehicle first.
RREV HUB app
RREV ISA suspension adjusts all four corners independently via BLE. Use the three saved presets (Freeway / Off-Road / Hitching) — do not manually adjust while moving.
Triple axle note
Triple axle configs distribute load across 6 springs. Middle axle carries the highest load at neutral bias — monitor center spring pressure first when diagnosing uneven wear.
Field Notes

The 70% Winch Rule

Never run your winch at full rated capacity. Work at 70% maximum to protect the motor, rope, and your recovery anchor.

Air Down Before You're Stuck

Airing down on sand or loose terrain is easier before you're in trouble. Carry a quality compressor — recovery is faster than getting unstuck.

Water Is Weight

Water weighs 8.34 lbs per gallon. A full 65-gallon tank is 542 lbs. Factor this into your payload calculation before loading other gear.

Tongue Weight Kills

Too little tongue weight causes sway; too much overloads your tow vehicle's rear axle. Target 10–12% of loaded trailer weight.

Plan Solar for Cloudy Days

Size your battery bank for 2 days of no-sun autonomy. Desert sun is great — Pacific Northwest or mountain valleys, not so much.

Navy Showers Save Trips

A navy shower (wet, off, soap, rinse) uses 6L versus a normal shower's 60L. Master this and triple your off-grid water range.

Built For Your Mission

Configure your RREV.

Every RREV is engineered around the numbers that matter — the same ones these tools help you calculate.

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Expedition Calculators | Suspension, Tire, Winch, Solar & Water Tools | RREV — Roam Resilient