Anti Squat and Suspension Tech

[TJ_Shunk]

All these drawings are for the rear link set-up.. What about the Fronts?

[crawls2thewalls]

this is honestly the most informative thread ever written..

you guys are awesome..

i'm finally starting to grasp the suspension geometry stuff and plan to dabble a bit myself..

keep the info coming..

[Steveakus]

My scaler is both a bouncer and a back flipper, I added a stiffer rear spring and a front axle limiting strap. Helped the back flipping but I know it can be better with the right set up.

Pics can be found here

Thanks for any info guys,

[levi steele]

so you want to keep the links together on the chassis and appart on the axle for anti

[insanerc]

Originally Posted by levi steele

so you want to keep the links together on the chassis and appart on the axle for anti

Again, this picture pretty much explains the basics of 4 link geometry. Note the difference in the point of convergence and how it affects a.s.

[gadge]

great thread...physics .. love it..just wanted to throw a couple of thoughts out there....convergence point of upper n lower 4 link bars acts pretty much like a torque arm/ladder bar..with a parallel 4-link (drag car) each side can be set to a different effective length also changing the anti squat
.....drag cars do have to deal with torque twist also but gear ratio is much lower ..lessening the effect..
....drag car accelerating is in the same"effect" as a rock crawler on an incline

[STJ7780]

Not to complicate this discussion any further but what about caster. Everyone is trying to lessen the amount of pinion angle when putting together a 4 link but the caster on the front of these trucks is really negative. What kind of effect will this have on the trail. I know on 1:1 cars and trucks alike positive caster helps to track straight, brake, steering return to center and traction on front wheel drive vehicles. We typically shoot for 3.5 to 8 degrees in the front. As for the rear in 1:1 it is not typically adjustable. I am building a clod tuber so I can run whatever caster I want without having to worry about pinion angle. What would be best to run in the front and in the back?

[Desolas]

STJ7780 ... I would personally try 0 degrees, and work my way back to 8-12 and just try it and see what suits your driving style and what works the best for you. I am unsure exactly how caster effects the truck while crawling (I can tell you how it effects a touring car however..) but a lot of setup is based on driving style and how the vehicle feels to you.

As for anti squat, I have been working on link angles with my truck and have learned a lot from reading what your guy's input was and from trial and error. Having the rear upper links higher in the rear, giving it more anti squat really seems to help the truck. I was having front lifting issues yesterday, I moved my front links 3mm higher toward the center of the truck in the rear and now the front sucks down. It's a huge difference. Of course like what was already pointed out it has different effect on different trucks based on CG and ride height.

I will take some measurements and some pictures in the next few days and post them for you guys to checkout.

-Wes

[5150bronco]

Keep us updated wes.....i have learned to that when thinkin of anti-squat/rear link setup......., upper does work, but also reducing the convergence on the rear upper links help with torque twist, but I think is kinda opposite thinking when considering the theory of anti-squat........

any opinions?

[Desolas]

Here is something else that is throwing me for a little twist when thinking about this .... how do bent links effect the geometry? When looking at a bent link, are we thinking the centerline from link end to link end from the axle to the chassis, or using the deviated flatter line of the bent link?

It would seem to me that the centerline from end to end would be the logical measuring point, basically imaging the bent link as if it was a straight link ... that is how I have been doing all of my measurement and theory, but now I am thinking I could be doing it all ass backwards because of this.

In talking to some people they are telling me that having the upper 4 links lower in the rear of the fronts toward the middle of the chassis should push down the front of the truck .... but this is entirely opposite of what my truck does in testing. The more I bring the link down in the rear, at middle of the chassis the more it lifts the front end of the truck up.

[JohnRobHolmes]

Originally Posted by Desolas

In talking to some people they are telling me that having the upper 4 links lower in the rear of the fronts toward the middle of the chassis should push down the front of the truck .... but this is entirely opposite of what my truck does in testing. The more I bring the link down in the rear, at middle of the chassis the more it lifts the front end of the truck up.

Restate this please, I cannot make sense of your statement. I think you made a grammatical mistake or something, maybe I just need clarification.


triangulation of the links affects roll center, not anti squat. If your chassis is raising on acceleration look to your rear links first. You can't dial out chassis rise from the front links, it is a function of the CG (chassis and front axle system) balanced around the instant center of the rear suspension.


If you are lowering your upper rear link axle mount, it will increase anti-squat and make the chassis rise more under acceleration. If you raise the upper rear link axle mount the anti-squat will be reduced and the chassis will want to dive more.

[Karadjas]

Originally Posted by Desolas

In talking to some people they are telling me that having the upper 4 links lower in the rear of the fronts toward the middle of the chassis should push down the front of the truck .... but this is entirely opposite of what my truck does in testing. The more I bring the link down in the rear, at middle of the chassis the more it lifts the front end of the truck up.

Same thing. Pushing down the front of the truck refers to pushing down the front axle. Since it can't go anywhere, the chassis goes up.

I'm a little dumbfounded by the upper 4 link lower in rear of front middle chassis thing too

[Karadjas]

Awesome thread btw, bookmarked

[Desolas]

Hmm. Sorry about that, apparently I did not proof read after I did a edit, cut and paste... But you still managed to answer my question so you get double points for working through my retardation.

In everything below I am only talking about the rear of the truck....

Just talking about the rear, what you are saying then is that the higher the axle mount is on the upper link (the wider the angle from the axle side upper link to your lower link) the more it will push down on the chassis?

So if your links closest to the axle are closer together, and your chassis side links further apart your in effect raising the roll center and decreasing the amount of force applied to the chassis. Yes?

Lets say someone has a truck with their upper and lower links parallel, also parallel with the chassis bottom and on acceleration the front end lifts - you would want to bring the chassis side upper link down toward the the lower link, or raise the axle side (giving the same effect.) to apply more force to the chassis forcing the front end down. Yes?

[JohnRobHolmes]

When the rear links diverge (chassis side vertical seperation greater than axle side) the suspension will just plain suck. The links need to converge towards the front of the vehicle. If the converge towards the rear (divergance) then I believe you will always have a ton of anit-squat (chassis rasing under acceleration or torque).

Roll center is a totally different issue. It impacts torque roll, chassis lean, articulation, and axle steer. It has nothing to do with anti-squat and is really hard to explain for me. It works on the same concept of chassis CG being above or below the convergence point, but triangulation affects the virtual convergence too.

In the case of the rear links being parallel with too much anti-squat, I would either raise the axle mount of the rear upper links, lower the chassis mount of the rear upper linds, or reduce the ride height. You could also play with the lower links, but that is generally not done on RC's since there is limited mounting space for them.

[Mr_Freeze]

I'm having trouble figuring out how I have more torque twist on the rear axle and almost none on the front.

This can be seen by putting the truck on smooth cement and holding one of the axles off the ground with the toe of my shoe and pressing down on the other with my hand. The rig basically spins out but I can see the effects of more traction and increased torque when I load up the axle.

The short of it...
I can push down crazy hard on the front axle while powering the rig and it hardly torque twists at all. It does have some squat so the front of the chassis raises slightly. Note; front shocks have the same weight oil and internal springs.

The rear axle is another story. It is better now using, I think it was, EeePees post with a photo of the asymetrical rear upper link mount and a stiffer internal spring on the right rear. But it still rolls over with little load on the axle.

How can one end of the truck be so different from the other? I understand the differences when talking about anit-squat but this is rotational torque. The links mount to the axles in roughly the same locations. And the shocks are roughly the same angles.

Anybody notice this quirk? I'm wondering if the different pinion angles could be the culprit or maybe the sliiiightly different shock angles... but there is not that much else different except the ends they are on.

Oop... a side note... a buddy came over and suggested trying the truck test in revers. I'll be damned!!! It acts the same way but reversed. In reverse the rear axle, now going forward, is hard to get to torque the chassis. The front, now at the back, torques the chassis over with litte effort.


Any ideas?

[JohnRobHolmes]

The CG of your chassis is above your roll center. Either reduce your chassis CG or increase the roll center by raising your upper links. What chassis is it, got any pics?

[Stormin2u]

I love this thread, yup picture help tell the story.

[Mr_Freeze]

Revised...
You can see the asymmetrical upper links. It seemed to help doing this on the front as well. The spread is about half an inch.

I do notice that the rear lower link comes off the chassis at almost the same height as the driveshaft. The angle of the photo makes it look higher but it's not. Other rigs seem to have the driveshaft output coming out at around the same height as the TOP link.

I was going to try drilling new holes for the rear bottom links on the chassis and moving them down. Also maybe angling the bottom of the rear shocks out a bit towards the wheels a bit. Right now they are straight up and down. Other than that I'm lost here.

Note:
Regarding anti-squat...
The setup as in the photo below has quite a bit of squat in the rear(back end of the chassis sinks down under torque/load. The front has anti-squat(front of the chassis rises up very slightly under torque/load)
Regarding torque twist...
The front has none. The rear does. The more torque the rear gets the more it rolls the chassis over.

[Mr_Freeze]

Close ups of the asymmetrical on the upper links, axle end. And the triangulation / shock mounting and angle.