There are countless ways to customize a 4×4: lifts, tires, shocks, light bars, armor – and that isn’t even touching on what you can do under the hood. With many modifications, a cursory Google search will turn up some ideas on the best build for a specific type of wheeling. This is not the case with the argument of compression vs. droop — not even close.
This is despite how important droop and compression are in any off-roading vehicle. As Dylan Peterson, content specialist at 4 Wheel Parts puts it, “Proper droop and compression ratio is just as important to a 4×4’s setup as lift height and tire size, but it’s usually just an afterthought once those parts are already installed.”
Every forum member has a different idea of what the best compression and droop ratios are and half of their opinions consist of “Well, it depends.” It is important to know that neither compression nor droop are the “most” important for wheeling: the truly optimal ratio would be 50-50.
However, a true 50-50 compression to droop ratio is virtually unachievable. Instead, for rock crawling, a 60 percent compression to 40 percent droop ratio is the number to aim for. Based on personal preference, there is plenty of wiggle room, of course. Generally speaking though, a crawler wants more compression than droop. Here’s why.
Compression, a/k/a “Stuff”
Compression, or how far up a wheel can be “stuffed” into the wells, is not only important for smooth riding, but also vital for an even distribution of weight.
Consider a Jeep JK attempting to crawl over a large rock, left front tire on the rock, right front tire on the ground. Having 60 percent compression means the body of the JK will remain almost straight while the axle tilts, stuffing the left front tire into the wheel well. This insures the JK’s center of balance remains stable, decreasing the likelihood of a roll or flop.
A high percentage of compression also means maximum traction while wheeling. If a wheel droops down, while it may be able to reach the ground, it may not be able to gain any traction because of uneven weight distribution.
Mike Finch, content specialist for 4 Wheel Parts says, “A stuffed tire has more traction than a drooped tire. By the nature of a vehicle, it takes a lot of psi to force a tire up into the well. That force is transferred into the traction patch. Any time you droop a tire away from the rig, you lose psi on the traction patch.”
With plenty of compression, all four tires are more likely to stay on the ground with the weight of the vehicle evenly distributed amongst them. Even if a tire were to lift from the ground due to extremely uneven terrain, with a good set of lockers (or even using the emergency brake to force the free wheel to stop), there will still be enough weight distributed amongst the other three to pull the vehicle forward.
Without the right exterior accessories, a high compression ratio does mean too much upward motion would mash bits together, bend metal and rapidly wear down parts. However, there are aftermarket accessories to prevent damage like this, such as bump stops, which work very well to protect precious parts.
Aftermarket fenders and a small to medium lift kit also serve to increase the amount of upward travel available to a 4×4, while a high percentage of compression decreases the likelihood of jamming an axle against the bump stops and losing control.
Additional benefits of a high compression ratio include a smoother ride and a decreased likelihood of bending or breaking an axle on whoops, drops and other obstacles.
Droop
Droop is downward motion – how far the suspension will allow a wheel to reach down below a vehicle, and it’s important for reaching into dips or crevices and maximizing axle tilt.
Without enough droop, the axle does not have enough room to move and the obstacles a 4×4 can take on will be severely limited. Without droop, a 4×4 wouldn’t be able to climb onto an obstacle on one side and keep its wheels on the ground on the other – they just wouldn’t be able to reach.
Without droop, the axle would compress excessively, sacrificing ground clearance.
Consider the same Jeep JK as before, crawling over the same rock. Without sufficient droop, as the left wheel climbed the rock, the right would be very quick to lift entirely off the ground. Even on relatively flat terrain, if the JK went through a dip or crevice on one side, not having enough droop would mean leaving at least one tire to dangle in space.
Droop helps with crawling obstacles and managing rough terrain. It increases a 4×4’s reach, so that at extreme angles of terrain the body can remain relatively level. However, droop in and of itself is not enough, just like compression would not be much use alone.
60-40
With too much droop over compression, a 4×4’s center of gravity climbs as the wheels climb, putting it at risk of a roll. Weight will not be evenly distributed, disrupting traction, and every bump and hiccup in the trail would be jarring.
“The farther up your axle can travel without disturbing the weight patch of the tire on the low side, the more stable your Jeep or truck will be and the more flex you can get before pushing the center of gravity of the rig higher,” says Finch.
With too much compression over droop, the vehicle’s reach would be severely compromised, meaning wheels may not be able to reach the ground on rough terrain and ground clearance would be sacrificed with every obstacle.
A rock crawler needs to be able to make the most out of the amount of static travel its axle has. A 60-40 compression-to-droop ratio does exactly that by ensuring weight remains evenly distributed and the greatest amount of traction is achieved. This ratio decreases the likelihood of a roll, makes for a smoother ride which is less likely to damage parts, maintains good ground clearance and increases driving control.
The Gist
Lowering compression to less than 50 percent of total travel sacrifices traction and evens weight distribution. It would be the equivalent of someone trying to walk down the stairs while only being able to bend their knees part of the way. It would make him uncomfortable, put him off balance and more likely cause this individual to go tumbling down the more his range of motion was limited. No matter how far his other leg might be stretched to reach the step below, he would be hindered by not being able to bend his knees completely.
Having less than 40 percent droop means sacrificing tire reach. Like someone walking down the stairs while only being able to extend their legs halfway, hopping step to step. They are only one wrong hop away from slipping and sliding down the steps on to their backsides because no matter how far their knees can bend, they cannot reach the next step with their other leg only partially outstretched.
Droop and compression work in tandem and optimally in equal amounts. However, not living in a perfect world means 60 percent compression, 40 percent droop is the most realistic way to maximize static motion and crawl the rocks like a pro.
Photos courtesy of 4WD.com.