Build / What the words mean
What the words mean
The words the tools use, in plain language. Anywhere on the site, tap a word with a dotted line under it to see its meaning.
- Airing down
- Letting air out of the tires off-road for more grip and a softer ride. Air back up before pavement.Also: air down, aired down
- Amp hours
- How much a battery holds: a 100 Ah battery can run a 5 amp fridge for about 20 hours.Also: amp-hours
- Approach angle
- How steep a slope the front can climb onto before the bumper hits it. Bigger is better.Also: approach
- Backspacing
- How far the wheel’s mounting face sits from its inner edge. Less backspacing pushes the tire out, away from the suspension.Also: offset, wheel offset
- Body lift
- Spacers between the body and the frame. It raises the body for tire room without changing the suspension.
- Breakover angle
- How sharp a crest the rig can drive over before its middle drags. Bigger is better.Also: breakover
- Build sheet
- The list of every part on your rig, with weights and prices where they’re known.
- Bumpstop
- A rubber or air stop that cushions the axle at the top of its travel, so it doesn’t hit metal.Also: bumpstops, bump stop, bump stops
- Center of gravity
- The point the rig’s weight balances around. Weight up high raises it, and the rig leans and tips more easily.Also: cg, center of mass
- Coilover
- A shock with its coil spring mounted around it, as one unit. Most independent front ends use them.Also: coilovers
- Crawl ratio
- First gear times low range times the axle ratio. The higher it is, the slower and more controlled the rig moves over rocks and down steep hills.
- Curb weight
- What the rig weighs empty, with fuel but no people or cargo.Also: empty weight
- CV axle
- The short axle shaft to each front wheel on an independent front end. A lift makes it run at a steeper angle.Also: cv, cv axles, cv angle
- DC-DC charger
- A charger that tops up a second battery from the alternator while you drive, at the voltage that battery needs.Also: dc to dc charger, dcdc
- Departure angle
- How steep a slope the back can come off before the rear bumper or hitch hits it. Bigger is better.Also: departure
- Differential
- The round gear housing in the middle of each axle that splits power between the two wheels. Often the lowest point under the rig.Also: diff, diffs, differentials
- Droop
- How far a wheel can drop when the ground falls away under it.Also: full droop, down-travel
- Dual battery
- A second battery in the rig for camp loads, kept separate so the starting battery stays full.Also: second battery, aux battery
- Flex
- How far the wheels can move up and down to keep the tires on uneven ground. Also called articulation.Also: articulation, wheel travel, travel
- GAWR
- Gross axle weight rating: the most one axle is rated to carry.
- Gear ratio
- How many times the driveshaft turns for one turn of the wheels. A higher number gives more power at the tires and a higher engine speed on the highway.Also: axle ratio, gears, final drive
- Ground clearance
- The gap between the ground and the lowest part of the rig, usually the axle housings. Only taller tires raise the axles; a lift raises everything else.Also: under the axles, under the diffs, clearance
- GVWR
- Gross vehicle weight rating: the most the rig is rated to weigh loaded, from the sticker in the driver’s door jamb.Also: gross vehicle weight rating
- Independent front suspension
- A front end where each wheel moves on its own arms. Rides well; less flex than a solid axle.Also: ifs
- Leaf springs
- Stacked steel strips under the axle, used on most pickup rear ends.Also: leaf spring, leaf pack
- Leveling kit
- A small lift for the front only, so the rig sits level instead of nose down.Also: level kit
- Lift
- Parts that raise the body and frame higher above the axles, usually taller springs or spacers. It makes room for bigger tires but doesn’t raise the axles themselves.Also: suspension lift, lift kit, lifted
- Load range
- A tire’s strength rating. Range E carries more and rides firmer than C or SL.Also: load rating, ply rating
- Locker
- A differential that can lock both wheels on an axle to turn together, so one spinning tire can’t stop the rig.Also: lockers, locking differential
- Low range
- A setting on the transfer case that gears everything down for slow, steep or technical driving.Also: 4 low, 4lo, 4-low
- Payload
- How much weight the rig can carry on top of its empty weight: people, fuel, gear and parts all count.
- Plan
- A set of changes you’re considering. Calculators save to it; your rig as it is stays untouched until you mark parts installed.Also: your plan
- Power station
- A portable battery pack with outlets built in. It moves between the rig and camp.Also: portable power station
- Ramp score
- A flex test: drive one wheel up a ramp until another lifts. The score (RTI) says how far it got, so a higher number means more flex.Also: rti, ramp travel index
- Regear
- Swapping the gears inside the axles for a higher ratio, usually to get the power back after bigger tires.Also: regearing, regeared
- Roof rating
- How much the roof can carry. The driving (dynamic) figure is lower than the parked (static) one, which covers people in a rooftop tent.Also: dynamic rating, static rating
- Solid axle
- One rigid axle housing across both wheels. Strong and flexes well; rides rougher on the road.Also: solid front axle, straight axle
- Speedometer error
- Bigger tires turn fewer times per mile, so the speedometer reads slower than you’re really going until it’s recalibrated.Also: speedo
- Spring rate
- How stiff a spring is: the weight it takes to compress it one inch. A heavier build needs a higher rate.
- Sway bar
- A bar linking the left and right sides. It keeps the rig from leaning in corners on the road, and limits how far the wheels can move off-road.Also: sway bars, anti-roll bar
- Tire size
- Written two ways: 285/70R17 is width in mm, sidewall as a percent of width, and wheel size in inches; 35x12.50R17 is height, width and wheel in inches.
- Tongue weight
- How much a trailer presses down on the hitch. It counts against payload.
- Transfer case
- The gearbox behind the transmission that sends power to the front axle and holds low range.
- Upper control arm
- One of the arms that holds the front wheel on an independent front end. Aftermarket ones fix the angles after a lift.Also: ucas, uca, upper control arms