I’ll start by saying I am by no means an expert when it comes to vehicle suspensions. Thus by reading this you will not achieve expert status. The goal of this piece is to give you a quick rundown on the common types of suspensions, and some of their advantages and disadvantages. I also would like to touch on some of the common configurations that are out there. Along the way I hope you’ll learn a few new Scrabble words and maybe the answer to a automotive themed Jeopardy question.
|There’s a lot going on here, but don’t let that intimidate you.
There’s also a lot of dirt. Don’t let that intimidate you either.
One of the goals of ECOA is to encourage you to learn what you can to do some things yourself. Again, this won’t make you an expert when it comes to suspensions but hopefully you’ll learn enough to consider doing your own lift kit. So, break out you thinking caps and let’s learn a thing or two.
First up, let’s talk some terminology. I honestly cannot define every component and term used in a vehicle’s suspension. There are a lot of great automotive glossaries out there with much better definitions than I can write. If you see a word you’re not sure of don’t hesitate to select it, write click it, and look it up. I’ll cover what I can here when appropriate, but I’m sure I’ll miss something.
- Wheel Mount Surface (WMS): This is the point of contact between your vehicle’s axle assembly and the tire.
- Track Width: Measurement from WMS to WMS across a vehicle
- Wheelbase: Measurement from WMS to WMS along the length of a vehicle
- Hub (or wheel bearing): This is what allows the tire to rotate and connects tire to the axle assembly
- Solid Axle: A solid beam that connects WMS to WMS across the vehicle. May be powered or unpowered and may have steering knuckles or not.
- Control Arm: Locates a solid axle front-to-rear under a vehicle
- Panhard Bar (aka – Track bar): Locates a solid axle side-to-side under a vehicle
- Note: Leaf springs do not require control arms as they locate the axle front to rear.
- Independent Suspension: No direct connection from WMS to WMS across the vehicle. May be powered or unpowered and may have steering knuckles or not.
- A-Arm: Common type of control arm found on independent suspensions. Named because the arm has three points of contact (two on the body, one for the wheel hub assembly) that locates WMS front the back as well as sets track width.
- Note: There are a variety of different shapes and configurations for control arms on independent suspensions.
- IFS = Independent Front Suspension
- IRS = Independent Rear Suspension
- GVWR (Gros Vehicle Weight Rating): The maximum load of passangers and cargo a vehicle can safely carry
- Curb Weight: The net weight of a vehicle without any passengers or cargo
- Cargo Capacity: The amount of weight a vehicle can safely carry in it’s cargo area.
- Tow Rating: The maximum weight a vehicle can safely tow. Also remember, just because a vehicle can move a heavier trailer than the max tow rating doesn’t mean it can stop it nor control it during evasive maneuvers.
- Springs: The spring, regardless of type, carries the weight load of the vehicle. This effects handing characteristics and also helps set the GVWR of the vehicle
- Shocks (or structs, or shock absorbers): Regulate rebound and compression speed of the spring. In effect they prevent the spring from bouncing out of control, bottoming out too fast, or springing back too fast.
- Bump Stop: Stops the suspension from traveling up into the body or frame of the vehicle
- Limiting Strap (or spring retainer): Stops the downward travel, or droop/extension, of the suspension.
- Coil-over: A three-in-one spring, shock, and bump stop unit.
- Solid/Solid: Pretty much all older 4×4’s were solid axle front and rear. Older vehicles used leaf springs while newer solid axle 4×4’s use coil springs.
- IFS/Solid: Many newer 4×4’s use an independent front for ride quality but still have a solid rear axle for load handling.
- IFS/IRS: Most modern 4wd SUV’s and crossovers utilize an independent suspension for both the front and rear suspensions.
- Solid Axle
- Easy to modify
- Rough ride
- Bulky – requires higher frame
- Independent Suspension
- Great ride quality
- Compact – allows lower body/frame
- Very tunable
- Complex geometry
- More expensive to modify
- OEM components tend to be weak for serious off-roading
- Never use spring rate to give you lift; Never use taller springs to increase capacity
- Most 4×4’s have a ‘rake’ to them because the rear will squat when loaded
- Taller leaf springs will keep axle centered
- Taller coil springs will move WMS toward center of vehicle due to control arms
- Taller coil springs will swing axle to side due to trackbar
- Some IFS springs are a torsion bar which is hard to replace. May be re-keyed to provide a little lift
- Taller springs on IFS and IRS will swing WMS toward frame of vehicle due to A-arm
- Lifting a 4×4 raises the center of gravity and will have adverse effects to handling
- Narrowing track width on an IFS or IRS suspension will have similar effect to handling
- Bump Steer = A negative reaction in the steering system when the suspension hits a bump
- Death Wobble = A negative reaction when a harmonic develops in the suspension between the axle and the vehicle – usually speed proportional
- Never use spring rate to increase height
- Too stiff a spring will cause your vehicle to skip or slide over bumps
- Never use taller springs to increase capacity
- If the spring rate is not sufficient for the load it will be too soft and could bottom out
- Drive shafts – Both front and rear OEM draft shafts rarely work with taller springs. Usually small lifts (1-3 inches) are okay, but anything above that should require new drive shafts
- Control arms – Longer control arms are needed to correct for changes in suspension geometry both in solid axle and independent suspensions. This can lead to things like “bump steer” and/or “death wobble”
- Track bars – New longer fixed or adjustable track bars are needed to recenter the axle under the vehicle on solid axle 4x4s. This helps maintain suspension and steering geometry and prevents lateral-loading of control arm bushings
- Brake lines – taller springs mean stretching brake lines. This could lead to a line failure when a suspension is cycled through full-droop
- Ground clearance: Taller springs allow for larger tires and also raises vehicle frame
- Carrying capacity: Stiffer springs allow for an increase in cargo capacity
- Handling: Stiffer springs help mitigate body roll
- Replace weak and/or fatigued OEM components with better aftermarket replacements
|After installing a modest lift on my LJ
JKS Manufacturing 2″ Jspec lift kit
2″ taller spring, new shocks, new track-bars front and rear, and new sway bar disconnects up front
Stay tuned for a full install writeup
- The combination of 33″ tires and 2″ taller springs should net me an increase of 3.5″ of additional ground clearance at the lowest point on the Wrangler. This additional clearance provides me with a better approach angle, break-over angle, and departure angle compared to a stock Wrangler
- OEM Jeep springs are soft and fade over time. New aftermarket springs are stiffer than the OEM spring rate allowing for a little extra cargo capacity in the Jeep as well as increase it’s handling
- Eventually I’ll replace the weak stamped steal control arms with stronger aftermarket arms. For the time being though the ones on the LJ are holding their own.
- However the key motivator for me to work on my vehicle’s suspension is the stock OEM springs and shocks were beyond deplorable and needed to be replaced