Trailing arms vs. 4 link

[idaho]

So what are the advantages of trailing arms over 4 link? Any disadvantages?

 

[TacoCrawler]

1:1 discussion

 

[idaho]

Still unsure of the benifits of trailing arms after reading that, as it's all dealing with lowered vehicles, I'm wondering more if a trailing arm suspension rig can crawl as good as a 4 linked one.

 

[EeePee]

If anything, and it's a stretch, a shorter shock and trailing arm set up that has the same travel as a 4 link and long shock might weigh less. Otherwise, pointless.

 

[Eric0424]

If the trailing arms are the same length and bolted to the same locations as the lower links, then there's no performance gain. Shock position and shock angle is where you get your articulation and suspension travel, the shape/style of the lower arm doesn't matter. If you like the looks of the trailing arms, then it may be worth the price to convert. Aside from that, there's nothing to be gained from it.

 

[idaho]

Thanks for the input guys, I appreciate it.

 

[89zj]

well as this is actually something i have experience with since i have been working on my fc170 build trailing arms on the rear of the frame have taken away the side swoop of the suspension. if you take a stock crawler and twist it you will notice the axles will shift or swoop side to side as well as twist if you go with a two link trailing arm set up its alot more ridged and does not allow this shift or swoop however it could cause binding if you dont have the right drive shaft and axle angles as in mine i have a 1 inch clearance gain however my axles have to have a 9 degree upright angle to them to eliminate shaft binding. but if you do your trailing arms in a lowered boomerang shape you can have a 1/2 to 3/4s of an inch flex gain the same with downward bent links without the risk of touching your drive shaft its all a case of getting the right angles and positions of everything to either maintain or gain performance. or in my case i lost a bunch of ridiculous flex that made the rig roll over quite often however i gained traction stability weight and control

 

[EeePee]

I could barely read that but if the suspension geometry sucks, trailing arms won't fix a single thing about that. A trailing arm is a link with a shock mount on it, nothing more. If the axle is swinging then the geometry sucks. The geometry on the Losi Comp Crawler sets the standard for kits.

 

[89zj]

il try to simplify this eeepee

for people who have "cheaper" crawlers such as the everest or maxstone when you flex the suspension you also get a side to side twist due to the links all being connected by ballheads pictured in red arrows. if you go with a two link trailing arm suspension bolted to the frame and have it in a boomerang shape as such here



you end up getting a motion pictured in green in the first image due to them being firmly mounted to the frame with alot more flex capability because they are further from touching the frame when you crawl over objects the only downfall is it lowers your available ground clearance between your front and rear wheels


i have purchased a couple cheaper crawlers recently to do builds with and found that i run out of frame space between the links and frame before i run out of shock compression and adding a slightly lower center to the links changes this or changing to hard mount trailing arms changes this

 

[EeePee]

No need to simplify things for me and I'm still not sure how you think trailing arms will be any different than a link. A trailing arm is a link with shock mounts on it. That's it. Who in their right mind would not have pivots at both ends?

Side twist? What?

 

[Eric0424]

well as this is actually something i have experience with since i have been working on my fc170 build trailing arms on the rear of the frame have taken away the side swoop of the suspension. if you take a stock crawler and twist it you will notice the axles will shift or swoop side to side as well as twist if you go with a two link trailing arm set up its alot more ridged and does not allow this shift or swoop however it could cause binding if you dont have the right drive shaft and axle angles as in mine i have a 1 inch clearance gain however my axles have to have a 9 degree upright angle to them to eliminate shaft binding. but if you do your trailing arms in a lowered boomerang shape you can have a 1/2 to 3/4s of an inch flex gain the same with downward bent links without the risk of touching your drive shaft its all a case of getting the right angles and positions of everything to either maintain or gain performance. or in my case i lost a bunch of ridiculous flex that made the rig roll over quite often however i gained traction stability weight and control

Again, the shape or style of your lower link (be it "arm", round, square, rectangle, hex, rod, tube, U-channel, C-channel, angle, etc.) will not change anything.

You simply replaced worn or loose, sloppy fitting rod-ends and pivot balls with your conversion. You probably tightened up some loose screws and replaced some flexing plastic links as well. My crawlers do not "swoop" side-to-side because the rod ends and pivot balls are all snug and the hardware attaching them is tight. When these part wear or the hardware loosens, then you'll see some "swoop"ing.

Hard mounting can be done with the links, if it were of any benefit. Changing mount location can also be done with the links. Links can also be bent to the "specs" you've shown (your green Crayola drawings above).

 

[TacoCrawler]

IMO utilize trailing arm set ups for trophy, short track and hi speed desert racers.

Axle travel and articulation do not generally share the same concept/purpose.

TA advantage:

they generally sit statically lower...
Tend to track flatter and maintain more stability at speed
while still allowing maximum axle travel potential.
Sway bars are commonly utilized to reduce chassis roll.

The Rr shock's mounting position allows for more progression
allowing a softer more compliant absorbing ride.
It's pertinent that the CO's are sprung and valved accordingly.
( ^ more leverage )

The axle's pinion angle remains constant/in line through out it's travel.
^ (radial arc).

TA disadvantage:

the axle's radial travel (arc), during it's up/down travel,
can alter wheel base length excessively at full droop.

TA suspensions do not support a load as well...
so a lightweight chassis would be preferable.

Chassis roll is excessive unless a sway bar is utilized.

-----------

IMO 4 or 3 link is best for a slo mo crawler chassis.

3-4L advantage:

The wheel base length remains more constant (for the most part)
As the axle's radial arc moves more vertical in it's up and down travel.

A sway bar is not necessary nor advantageous to a slow mo crawler.
Unless it's street driven and/or driven at higher speeds.

3-4L disadvantage:

The axle's pinion angle will not remain constant (in line) during the axle's travel
so that could be considered a travel limitation.

link ends will likely be under more leverage stress.
But if built well should hold up fine.


in ending...

RC crawlers are not subject to the same stresses
that a 1:1 crawler might be subjected to or need endure.

^ just what I know.

You know more !? post it or stfu :mrgreen:

 

[fr8cture]

I put trailing arms on my 1.9 wraith purely to have the Ultra4 look. It crawls good and does great hill climbing.

 

[Eric0424]

I put trailing arms on my 1.9 wraith purely to have the Ultra4 look. It crawls good and does great hill climbing.

That's the same basic reason (looks) others are doing it, some just have a hard time admitting it.

 

[EeePee]

Or have no idea what they're actually talking about. Red arrow path is completely wrong and so is the green arrow path. How in the heck is a green arrow going to articulate if it only goes straight(ish) up? It won't. Your red arrows don't even follow the path of the articulation, which is clearly defined by the tires in the picture, which is a Losi truck.

 

[Eric0424]

Yeah, those guys are everywhere.

 

[binaryterror]

if you go with a two link trailing arm suspension bolted to the frame and have it in a boomerang shape as such here

There is not way to make a 2 link (no upper link) trailing arm system. It will always need something at top to hold the pinion angle. Double mounting a trailing arm makes it a Ladder Bar style, still needs upper links.

Everyone here is spot on, Trailing arms are just links with shocks mounted to them, not mounted to the axle. Nothing else.

To fix axle twist in a true 4 link, you need good triangulation at the chassis and axle. Also helps to have the correct geometry as well. This is true for Trailing Arms or Link systems.

 

[89zj]

well ive come to a decision either no more alcohol or no more internet.....sorry eepee and everyone else I have no idea what i was trying to explain at all last night and it doesnt make sense to me either "which is rather embarrassing for someone who went to college for automotive technician" . so i will correct what mess up i was doing and i apologize ( if you are trying to have a trailing arm system "2link" you would require a leaf and shackle spring system) which you would lose flex that you would have with coilover suspensions due to leaf suspensions being firmer and having limited spring rates ,trailing arms are intended in full scale vehicles to eliminate wobble and axle shifting under torque force weight same as ladder rails EX: when your hard accelerating and your tires are not getting traction as they should you will have wheel hop and quite possibly a forward and backward twisting motion that causes stress on your axles drive train suspension and frame, a 4 link for a crawler is the best way to go due to its ability to have a lot more flex than a stiffer leafspring setup most set ups are a 10-35 degree angle from frame to axle for the upper links and a 0-15 degree angle for lower links creating a triangulated system ( old saying triangles are much more stable then a square) however eepee i do kind of understand what i was trying to say about the side to side sway of the axles but thats only on 3 link suspensions for cheaper rc crawlers i have 2 everest 16s that have a 3 link and the center link is connected with a ballhead to the center of the axles which only allows for so much movement before it tries to move somewhere else but the side to side shifting is only like 3/16 of an inch so its not really much to notice unless your REEALLY paying attention to it. but anyhow sorry for my drunken rant i will try refraining from that in the future unless you all enjoyed me making myself look like a moron

 

[Del Monte]

There is not way to make a 2 link (no upper link) trailing arm system. It will always need something at top to hold the pinion angle. Double mounting a trailing arm makes it a Ladder Bar style, still needs upper links.

Everyone here is spot on, Trailing arms are just links with shocks mounted to them, not mounted to the axle. Nothing else.

To fix axle twist in a true 4 link, you need good triangulation at the chassis and axle. Also helps to have the correct geometry as well. This is true for Trailing Arms or Link systems.

Exactly.

Most trailing arm setups in RC are still 4-link suspensions, just with the shocks mounted on the lower links. Link and shock geometry still make a big difference in handling and predictability of the truck.

The further from the axle the shock is mounted, the more leverage the axle will have on it. The axle will also be able to react faster in a trailing arm setup than it would if the shock was mounted directly to the axle. This means more body roll or torque twist if everything else is equal.

 

[802coma]

I haven't done the "geometry" on this but I feel like trailing arms climb better than traditional link suspension. Think the shock position gives great anti squat characteristics.