Back to Basics: Front Suspension

I'm looking to improve my understanding of suspension systems, specifically Tacoma suspensions, and the myriad ways to improve them (and break them). I've been reading a lot, here and on the internet in general, watched a couple youtube videos, etc. which is a good base level of knowledge. Now I'm interested in learning and discussing the finer points of IFS, how to improve them for specific applications, and the tradeoffs involved.

If you have links to good sources of info, please share! Basically assume I know nothing about suspension, but am reasonably technically inclined, and willing to soak up as much knowledge as possible. Or in less words I am uneducated, but fortunately not dumb or ignorant.

Anyways, to summarize the Tacoma's Independent Front Suspension (IFS)
Consists of an A-Arm (or Upper Control Arm, UCA), B-Arm (or Lower Control Arm, LCA), Spring (or Coil), Shock, and spindle. Attached to the IFS is the steering tie rod, a sway bar, and in a 4x4, the CV axle.

Next, as kind of a check on learning, here's how I understand how the components work, work together, and how to change them to achieve specific purposes (basically increase lift and travel)

Coil and shock -- the most basic part of the suspension. The coil (or spring) compresses to absorb energy from bumps, and the shock acts as a damper to prevent that from happening too fast (resulting in a smoother ride). For the tacoma owner, adjusting the position of the coil relative to the shock sets the ride height, and changing the spring rate changes the compression behavior (typically heavier spring rates for heavier front ends, if you're bolting a bunch of stuff to the front). Tell me more about if changing spring length is a thing.

UCA, LCA, and Spindle assembly -- this defines the suspension geometry angles, and the arc of travel for the wheel. Longer UCA's and LCA's enable longer downtravel, but start pushing out the front track width. Spindles I need more learning on.

UCA's -- enables caster angle adjustment, which basically allows the wheel to move fore and aft within the wheel well. There's stuff about bearings and the joint, but I don't know anything about that at the moment.

LCA's -- I don't know anything about these

Spindle -- You can change the geometry of these, but again I'm uneducated

Notes on connecting components:
Steering -- if you push out the track width, you'll need to extend the tie rods. Tell me more
Sway Bar -- some kind of control thingamajig. Serious off road people have opinions on these, but I have no idea. Educate me.
CV Axle and joints -- this is what transfers power to the front wheels in 4x4. At stock ride height they are close to level. If you lift your truck, this puts them at an angle, adding stresses to the joint. Lifting your truck AND off-roading, well you just add additional wear and tear vs the stock design condition -- not a big deal, but will wear faster. A diff drop kit can help mitigate this (according to strangers on the internet).

Please help me become more educated. I will update this thread with the knowledge, so hopefully others can find it useful.

 

Kudos for the work you put into that post

 

You seem to have a pretty good grasp on this stuff, but I might be able to add a couple of things.

Coilovers: When compressing the spring with clips or threads, you also change how stiff the ride is. As far as I am aware, you are only supposed to use the stock length coil unless you are going long travel with longer coilovers.

UCA: As far as joints go, there are two main types. Uniballs are great for a little extra travel but are high maintenance, as they are exposed and tend to squeak a lot. The other option is the stock style ball joints. Those are sealed so stuff can't get inside, but they typically don't get you quite as much travel as uniballs. The difference is pretty minimal though, I believe it might be an inch max.

LCA: Most people leave them alone, but if you opt for aftermarket options, some have mounts for bypasses and/or use beefed up joints.

Spindle: When you push your truck offroad, it is very possible to bend your spindle, so there are a lot of people who weld on gussets to greatly enhance the strength of the spindle. If you are 2wd, you can buy replacement spindles that move the hubs down since there aren't any CVs to worry about, which is an easy way to get a lot of lift without changing the coilover itself. As a side note, this is where your hub is mounted, and if you have 4wd, you need to have the outer stub of the CV in the hub at all times. If you bust a CV offroad, don't just yank it out and continue, there's a nut that grabs the outer CV stub and essentially keeps your hub clamped in.

Steering: Some folks weld on supports for the tie rod ends, as they can get messed up if you beat on the truck. However, if you are pushing out the track width with an LT kit, you really should be upgrading your steering anyways with bigger joints and rods.

Sway Bar: A large bar that resists being deformed when you flex. You can easily remove it if you want to, but it's generally a good idea to leave it on unless you've already upgraded your spring rates to keep up with the body lean. When going to larger shocks in the 2.5" realm, the sway bar typically needs relocating down and forwards with a spacer.

CVs: Most people claim the diff drop doesn't really help all that much. The rule of thumb is don't go past 2.5" without expecting problems. A good way to check is to look at your boots. If the angle is making the fins on the boots rub eachother, then you're subjecting your CVs to extra wear.

 

u know much….but not everything…..listen you must, for it is for the gram, not function and you must learn to harness the power of an external resi for the flex

 

You mention “UCAs enables caster angle adjustment”. Outside of SPC UCAs I don’t think this is true.

Caster and camber are adjusted at the LCA with stock components. If you lift the truck you lose caster by default. Use the LCA cam bolts to push the arm forward to get caster back and provide a bit more clearance for bigger tires.

SPC does make a UCA that allows adjustment and is an option. Other aftermarket UCAs have additional caster built into them to account for the lift. This actually pushes your wheel further back (everything else being equal) which usually hurts clearance. You’ll see a lot of people also mention cab mount chop - cmc - or relocation - cmr - to get more clearance. This all assumes you’re adding bigger tires to the suspension lift.

Also, if you lift your Tacoma you’re putting more stress on your wheel bearings and your needle bearing on DS will likely cause an issue. Common Tacoma issues. Factor in an ECGS needle bearing and budget for new wheel bearings sometime down the road.

Spindles hold the UCA to the hub / wheel so you want those in good shape. Go-fast desert rigs and heavy crawlers need gussets. I think we are now moving down the path of chasing weak links as the mods add up.

 

I'm going to try and help. I'm a vehicle dynamicist that's been involved in performance chassis and suspension systems for over a decade. My approach to these concepts and problems is and has always been to apply the fundamental physics behind the idea before trying to understand the specific application or commonly understood approach. That's how I try and explain these things. Once you grasp the fundamentals you can understand it in all forms regardless of the vehicle or application.

The spring is there to allow suspension movement while applying a restoring force to an equilibrium position. Most people want to think of the spring as just supporting the weight of the vehicle, but the rate is absolute key to suspension tuning. The rate should be chosen to achieve desired dynamic behavior and not to achieve a ride height. Any ride height can be achieved with any rate spring within reason. The shock (doesn't act as a damper, it is a damper) provides another level of dynamic behavior tuning. It controls suspension motion and should be tuned for the desired dynamic behavior and matched to your spring rates. Spring force is proportional to suspension displacement while damping force is in proportion to suspension velocity.

Suspensions classically are tuned to control the following modes: heave, pitch, roll, warp, and one wheel bump. These wrapped up comprise performance, ride, and handling.

Advanced modes tuned for off-road now include anything where wheels or the vehicle leave the ground as it's a special case of the classic modes.

The problem with only having 4 shocks and 4 springs is that all these modes are coupled together and an adjustment made to target one behavior will affect the others. Therefore, classic suspension tuning is about properly prioritizing and compromising. This is one reason anti-roll bars exist, it allows some low level decoupled tuning.

The important rates of note in any suspension are the wheel rates. This is the rate of the wheel center to the chassis as it moves. Due to installation/motion ratios, the installed rates of your springs and dampers don't match the wheel rates and it's the wheel rates that ultimately matter, not the spring rates required to achieve them. The wheel rate as a function of spring/damping rate is k_wheel=k_spring*(ir^2) where ir is the installed ratio of shock travel/wheel travel.

When you adjust the coil relative to the shock (threaded spring perches, snap ring adjustments, etc.) you are just traveling the suspension and changing ride height. It is the exact same effect as installing a longer or shorter spring. Both are changing the suspension's position relative to the spring equilibrium position thus lowering or raising the vehicle by traveling the suspension. It's easy to visualize if you understand the spring is always carrying the same static weight (minus small cross weight changes suspension height adjustments make) and therefore the spring does not change its loaded length at ride height when you make any of these adjustments. Therefore, what does change is the length between the spring mounts (the shock in this case) and because it attaches to the chassis and the suspension the suspension must travel. That's basic ride height adjustment. Changing the length of the spring has the exact same effect.

The UCA, LCA, and spindle do define the path the wheel will travel. It will also define how wheel angles change. As the wheel travels vertically it will also move in and out in the front view (scrub), fore and aft in the side view (precession/recession), and camber, caster, and KPI will change. Longer arms, typically, allow for more linear suspension travel, but it's not a guarantee they push the front track width out. That will depend on the starting angles of the arms. For example, if they start parallel and horizontal the track width would narrow with bump travel. So think about it in terms of the fundamentals and then realize what the results would be for the application.

The spindle is also known as the upright or knuckle. It is just a rigid unit that bridges the outboard points of the UCA and LCA and carries the wheel hub. It is this item that connects to the steering rack, pivots on the outboard points, and allows the front wheels to steer. By moving where the hub is carried in the upright you can effectively raise or lower ride height, which will also change some fundamental suspension and steering parameters like scrub radius and mechanical trail. It's worth noting that changing tires size also changes these parameters as it moves the distance of these axes from the contact patch.

So that's a generalization and not fundamentally correct. There's no reason UCA adjustment couldn't be designed to change any suspension parameter. A UCA could be used to move instant center, change anti-dive, adjust camber, or other things. Yes, it can be used to adjust caster. Caster is just the angle of the steering axis in the side view. Changing caster doesn't mean the wheel has to move fore or aft in the wheel well, but if done solely at one pivot then yes, that is likely a small byproduct.

LCA's can have adjustments designed to make all kinds of changes as well. For Tacomas adjusting the front inboard pivot has a large change on camber and small change on caster. Adjusting the rear inboard pivot has a large change on caster and small change on camber. Read the link below for a good description of how the specific Tacoma layout works to adjust alignment parameters.

https://www.tacomaworld.com/threads...d-love-alignments.594309/page-7#post-20252854

Mentioned above, they're pretty simple.

Track width pushed out means you've probably installed longer control arms. Now the spindle is farther away from the rack. The tie rod connects these components so the rack can steer the wheel through the spindle. If it's farther away the connecting item needs to lengthen.

Sway bar is an incorrect term that's been used so prevalent it's now accept as correct. It is technically an anti-roll bar. It is a torsion spring mounted in such a way that is twisted as the vehicle rolls. Opposing wheels traveling in opposite directions (one up and one down) constitutes roll motion and the bar twists to resist that movement creating a resistance to the vehicle rolling. When both wheels travel the same direction you have pitch or heave and in this case the bar pivots in its mounts and doesn't twist so doesn't provide any resistance. This is the decoupling I mentioned earlier as an anti-roll bar only resists certain kinds of chassis and wheel motions and not all. The downside is that off-road you typically want warp travel (flex) and this anti-roll bar resists that type of wheel motion causing tires to unload or lift over uneven terrain. Also, anti-roll bars affect one wheel bump and are an additional roll spring typically with no roll specific damping which may require more compromise with increased overall damping rates.

CV axles are just that. They transmit power from the diff to the hubs. They need to be the right length, have adequate plunge for the amount of suspension travel you have, and do operate best a low angles of misalignment. They can survive just fine at higher angles depending on the quality of the joint and severity of the angle.

 

@ShimStack are you around tomorrow to work on my truck?!

 

These videos explain Toyota IFS very well:

https://www.youtube.com/c/TinkerersAdventure/videos