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Thread: Suspension: "Droop" (The What, Why, and How)

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Old 06-11-2015, 02:50 PM   #1
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Default Suspension: "Droop" (The What, Why, and How)

I'm fairly new to the crawler scene (SCX10 for 2 years) and I don't own a 1:1. Droop is something that I'd heard of before, but clearly was not something that I fully understood the benefits of.

I found a few good articles online that I think many would benefit from reading whether as new information or a refresher. Hopefully we can make this a "stickie" and others can add to the wealth of information regarding not only droop but other principles for setting up the suspension on an SCX-10.

One of the links refers to R/C the other to tuning a 1:1 crawler, but I think we can all probably agree that the principles are very much the same.

Onto the links....

Last edited by DowntownScience; 06-11-2015 at 02:56 PM.
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Old 06-11-2015, 02:52 PM   #2
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Default Re: Suspension: "Droop" (The What, Why, and How)

The What...

The deal with droop - RC Car Action

Suspension tuning is not a simple thing. A typical RC car has more adjustments than you can shake a hex driver at, and choosing the right thing to adjust in the right way in the right situation takes years to learn.

One of the more subtle tuning attributes on a car is droop. A lot of people think they understand droop (and some of them actually do), but plenty of others have never even heard of it. In both cases there is a surprising amount of confusion around the topic, which is why I’m writing about it.

The first thing to understand is that droop is not a setting; it’s an attribute. It is affected by other settings, each of which have their own unique names, but at the end of the day droop is a result of the way your car’s suspension has been adjusted. Droop allows (or limits) weight transfer from one side of your car to another – a factor that can drastically alter handling. Adding droop on one end of your car will generally increase grip on the other end, although this is not always the case. Running a lot of rear droop, for example, allows more weight to transfer to the front wheels during braking, which may or may not be desirable depending on what type of driving you’re doing. I won’t go into the nuances of tuning with droop, largely because the effects differ greatly depending on vehicle, surface type, driving style, and more. Just know it is one of many options open to you, and adjusting it can have profound effects.

Ok, let’s get down to exactly what droop is. Put your car down on a flat surface and let the suspension settle; this is your car’s ride height. Now, slowly lift up on your car’s chassis until the wheels just begin to leave the ground; the distance your suspension is able to extend downwards before the wheels leave the ground is the droop value. Put more simply, droop is the total amount your chassis is able to rise above its natural ride height.

Many cars feature screws in the chassis or suspension arms that limit suspension travel. Although often referred to as “droop screws”, these are more accurately described as downtravel, downstop, or drop stop screws. Although downtravel adjustments affect droop, they don’t define it.

Confused? Ok, here’s an example. Let’s say that your sedan’s chassis is 5mm off the ground at rest. You lift up on the chassis, and at a height of 10mm the wheels leave the ground. This means you have a 5mm ride height and 5mm of droop. Easy.

You want to reduce the amount of droop your car has, so you make an adjustment to limit the downtravel of your suspension by 1mm. The ride height of your car remains 5mm, but now as you lift up on your car the tires leave the ground when the chassis is at 9mm, which gives you 4mm of droop. So far so good.

You now decide that you want to raise the ride height of your car, so you add 3mm of preload to the shock springs. Your car now has an 8mm ride height. So far so good, right? You lift up on the chassis, and because of the downtravel adjustment you just made, the wheels again leave the ground at a height of 9mm. But wait… That means you now only have 1mm of droop. Clearly then, both preload and downtravel are unique and independent settings, but both affect droop.

For the most part, any time ride height is changed droop changes as well. This includes spring changes, weight distribution adjustments, shock angle adjustments, and so on. It is worth noting, however, that unsprung ride height changes (e.g., tire and rim changes) do not affect droop. Additionally, any adjustment that limits suspension travel will also change the droop value. Along with downstop screw adjustments, travel limiters can be added to shock absorbers to reduce the amount they are able to extend. Before suspension-mounted downtravel screws became common on RC vehicles, shock travel limiters were pretty much the only way to adjust droop.

This concept can sometimes be a bit confusing, but that’s ok – nobody was born knowing this stuff. Just give it some time and practice and you’ll be a pro before you know it.

Last edited by DowntownScience; 06-11-2015 at 03:37 PM.
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Old 06-11-2015, 02:53 PM   #3
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Default Re: Suspension: "Droop" (The What, Why, and How)

The Why...

Do Your Wheels Hang Low? Compression vs. Droop for Rock Crawling - Auto Trends Magazine

Do Your Wheels Hang Low? Compression vs. Droop for Rock Crawling

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.

Last edited by DowntownScience; 06-11-2015 at 03:37 PM.
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Old 06-11-2015, 02:54 PM   #4
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Default Re: Suspension: "Droop" (The What, Why, and How)

The How...

In the "What" we found that droop is basically the fully extended ride height minus the static/settled ride height.

In the "Why" we found that we want to shoot for a 60/40 compression to droop ratio.

So how do we do that?

We need 3 measurements....
  1. Ride height when shock is fully extended
  2. Static/settled ride height
  3. Ride height when shock is fully compressed or chassis bottoms out

If we know the amount of droop we have we can find it's percentage of travel by dividing it by the full shock travel amount.

NOTE: I used the extension height minus the compressed height. It may be better to use the known piston travel value for your particular shock. Either way will be close to getting you to 60/40.

Example from my SCX10:

I placed my SCX10 on a flat surface and using digital calipers measured to the same spot on the top of my rock slider. Doesn't matter where you measure to as long as all 3 measurements are to the same location.

Measurements:

Extended: 3.9 inches

Static/Ride: 3.5 inches

Compressed: 2.5 inches

With those measurements I found my droop to be .4 inches and my full travel to be 1.4 inches. This would mean that I also have 1 inch of compression.

.4 divided by 1.4 equals = .285 or around 29% droop.

I needed more droop!

Based upon my full travel of 1.4 inches I would need around .56 inches of droop to be at 40%. (1.4 x .4 = .56). That means that my ride height with 40% droop should be around 3.34 (down from 3.5 inches).

3.9 (extended) - .56 (target droop) = 3.34

How do you get more droop? Less pre-load. Need less droop? More pre-load.

My shocks aren't threaded so I played with spacers until I got to that magic number.

Last edited by DowntownScience; 06-11-2015 at 03:40 PM.
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Old 06-11-2015, 03:41 PM   #5
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Default Re: Suspension: "Droop" (The What, Why, and How)

Observations...

So some of you may have noticed that I was quite the droop skeptic before educating myself and talking a bit about it with others. Not anymore! I've seen it work with my own eyes! My truck handles so much better now!

COG - Your center of gravity is now lower.

Self Balancing - So we're 60/40 compression to droop now. What does that mean exactly and what does it do? This is the coolest part that I observed!

When you ride up onto an obstacle with your left front tire (driver side) the obstacle will begin using the compression of your shock. When that 60% compression is used up by the obstacle your passenger side shock will begin to extend! That extension is from the droop and your suspension geometry that is all connected by the axle. When the low side (passenger side) extends (by around 40% of the shock travel) it actually levels the truck's chassis out.

Traction - You'll be amazed at what your truck is able to traverse with the ability to step down/break the ridge/etc. coming over an obstacle (shock extension) to get grip! That just wasn't possible when you were at 100% compression because your shock couldn't extend before. Instead of extending then balancing you would just roll over to the low side.

Last edited by DowntownScience; 06-11-2015 at 04:06 PM.
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Old 06-11-2015, 04:47 PM   #6
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Default Re: Suspension: "Droop" (The What, Why, and How)

I remember when we said droop, we were talking about shocks fully compressed with springs inside, under the pistons...

And sag was the word we used referring to what you're calling droop.


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Old 06-11-2015, 04:53 PM   #7
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Default Re: Suspension: "Droop" (The What, Why, and How)

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Old 06-11-2015, 04:53 PM   #8
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Default Re: Suspension: "Droop" (The What, Why, and How)

Quote:
Originally Posted by EeePee View Post
I remember when we said droop, we were talking about shocks fully compressed with springs inside, under the pistons...

And sag was the word we used referring to what you're calling droop.


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... the good old days...
I'm really glad that you brought up the springs behind the shock piston thing! That was also one of my confusion points. "Full Droop" is what's I've seen it referred to, but based upon my reading I'm not sure of the benefits!

If one side can't compress then the other side can't droop...right? I guess there is still a little room for compression but I keep reading that too much isn't want you want...just like too much compression.

Is it more of a Comp. Crawler thing instead of a scaler thing?
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Old 06-11-2015, 04:58 PM   #9
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Default Re: Suspension: "Droop" (The What, Why, and How)

That was called semi droop cause it still has a spring keeping it up. Or 50/50 or 60/40. Droop, semi droop or not at all, I guess. I started messing around with that mid 2007 with a TLT. We had no idea what we were doing.
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Old 06-11-2015, 05:01 PM   #10
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Default Re: Suspension: "Droop" (The What, Why, and How)

Quote:
Originally Posted by DowntownScience View Post
If one side can't compress then the other side can't droop...right?

Is it more of a Comp. Crawler thing instead of a scaler thing?
All the shocks do is extend, there's no compression at all.

I suppose it's more of a comp thing though I've seen it plenty of times on scalers, but it doesn't make much sense to me.
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Old 06-11-2015, 05:03 PM   #11
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Originally Posted by Dad,Canyoufix? View Post
That could work too. I see you not only have spring below but also above the piston. Is that really the true full diameter of that piston?
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Old 06-11-2015, 05:09 PM   #12
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Default Re: Suspension: "Droop" (The What, Why, and How)

Quote:
Originally Posted by EeePee View Post
All the shocks do is extend, there's no compression at all.

I suppose it's more of a comp thing though I've seen it plenty of times on scalers, but it doesn't make much sense to me.
+1 on that one!

Not after seeing how the suspension needs to be sitting somewhere near the middle of the full travel of the shock to take advantage of the suspension geometry.

Kinda like a see-saw! One side goes up and the other goes down. I know there's gotta be a better way to describe. I'm not a physics major or mechanical engineer so I'm not sure if this is right, but it's like a lever system...No?
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Old 06-11-2015, 05:28 PM   #13
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Default Re: Suspension: "Droop" (The What, Why, and How)

Quote:
Originally Posted by DowntownScience View Post
That could work too. I see you not only have spring below but also above the piston. Is that really the true full diameter of that piston?
The bottom spring is pretty close, the top is a little off, 1-1.5mm. I run my scx's with shocks set up like that(80mm gmade transitions, and stock shocks converted like above). It is a preference thing(IMO), I don't think it is a better set up for all, I just prefer it since trying it out.
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Old 06-12-2015, 05:01 PM   #14
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Default Re: Suspension: "Droop" (The What, Why, and How)

I run boom racing boomerang droop shocks, and love them, like he stated though there are pros and cons! The stock shocks are a good way to go if you don't want to mess with anything.
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Old 06-12-2015, 07:36 PM   #15
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Default Re: Suspension: "Droop" (The What, Why, and How)

Static ride height must first be determined
and that static result is established by the 60/40 travel split.

Droop is simply the distance of travel the axle will drop (extend lower),
below the chassis's established static ride height,
allowing the shocks their full extension. (40/60)

While compression is the distance of the axle's upwards travel,
above the chassis's static ride height
allowing the shocks to compress upwards fully. (60/40)

Solely lowering your suspension is not droop.
It's simply lowering the chassis COG

It's how it is with 1:1 rigs... why should rc crawlers be any different ?

One can run a crawler without any springs at all, if they wanted.
That set up would be considered all droop and offer no compression.
Friend of mine does that... but crawls considerably slower then most.

If yer gonna hammer down or bash some...
some established compression is a must.

My 1:1 rig rolls fairly close to 60/40

But RC crawlers don't have living occupants...
so 50/50 works better for me.

Last edited by TacoCrawler; 06-12-2015 at 08:42 PM.
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Old 11-11-2015, 07:20 PM   #16
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Default Re: Suspension: "Droop" (The What, Why, and How)

In the motorcycle world this is referred to sag. On a dirt bike sag is 100-110mm on a 12" shock or 25% static sag. This is likely a good setting for fast rigs like a Yeti I imagine. Crawlers need a softer setup so I guess that is where the 40% comes in.
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Old 11-11-2015, 10:02 PM   #17
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Default Re: Suspension: "Droop" (The What, Why, and How)

Nice read... for my wraith/deadbolt/ and wroncho I like 40/60 with light springs and heavy weight oil to slow the shock down. I also have my shocks slanted inward to the center of my rig. This does decrease the reach of the tire.

Wroncho numbers

Extended 3.75
Static 3.0
Comp. 2.5

.75 divided by 1.25 = 60%

Crawls great.

Last edited by k goodrich; 11-11-2015 at 10:39 PM.
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Old 05-22-2018, 08:35 AM   #18
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Default Re: Suspension: "Droop" (The What, Why, and How)

Thanks DowntownScience for posting this info! It was extremely helpful! Have a great day!
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