Rear Suspension Movement

[xnamerxx]

I was curious about something, so I took a video of the rear suspension during some "normal" driving just to see whats happening back there. Now the video proved what I was expecting but I'll get to that later.
The video proves that rear suspension bushings could be beneficial if you plan on racing, autox, road course or otherwise.

I know the zip ties look janky but they really don't do anything during normal driving.

http://www.youtube.com/watch?v=504Pl...ature=youtu.be

[CTScott]

Cool video. There is definitely some wiggle due to the large, soft rubber bushings. Did you notice how much the spring perches flex as well?

[Yarflana]

Look exactly like I would expect. Thanks for making the video.

[CoryM]

It's not uncommon for torsion-beam bushings to rotate on different axes. Meaning if you put solid or stiff bushings in, the beam will bind. No idea if the Yaris is like this or not.
I would like to see that view, but heavy loaded in corner. I am curious where the torsion beam flexes and creates (I assume) toe out.

Neat vid, thanks for uploading.

[xnamerxx]

The video was taken in a heavily loaded right hand corner, the trailing links do move at slightly inverted paths so stiffer bushings might create bind.

You can stiffen the torsion beam AKA B-Spec Mazda 2 rear ARB, it will create some bind during compression/bump, but will also toe it out and possibly create good oversteer.

[CoryM]

Originally Posted by xnamerxx

The video was taken in a heavily loaded right hand corner

Yeah I figured that out after viewing it a second time ;)

Also figured the bushings and the angle of the bolts are what control the toe-out already built into the yaris. If you run a stiffer bushing you will see some bind, but maybe the toe-out will be more linear. In my stock yaris it feels like no toe, no toe, LOTS OF TOE! when doing steady state corners. I think the sudden toe change is also what makes the yaris sensitive to fast changes of load (fast slaloms). That being said, the bind might make the car completely uncontrollable in rear.

You might be able to just rotate the OE bushings to get the results you want. They are directional I would have to look at where the bushings are stiff and where they are open. I think someone should try stiff bushings if it hasn't been done yet.....

[xnamerxx]

My end goal is not to run stiffer bushings but I'm going to keep the cards close to my chest for right now.

[Viperoni]

With the angle that the Yaris's bushings are placed, I would NOT run anything that would cause bind, like a poly or delrin bushing.

The only replacement I see working properly is a spherical bearing in place of the rubber bushing.

Great vid OP!

[CrankyOldMan]

Originally Posted by Viperoni

The only replacement I see working properly is a spherical bearing in place of the rubber bushing.

I'm curious about how you would propose to go about this. Calculating the loads to select an appropriate bearing would be beyond my skills as a Junior in engineering school, and the cost of said bearing that could resist road grit (and possibly salt) would be astronomical compared to a delrin/poly bushing. Not knocking/hating, just curious.

[Viperoni]

Originally Posted by CrankyOldMan

I'm curious about how you would propose to go about this. Calculating the loads to select an appropriate bearing would be beyond my skills as a Junior in engineering school, and the cost of said bearing that could resist road grit (and possibly salt) would be astronomical compared to a delrin/poly bushing. Not knocking/hating, just curious.

I've made some rod-end suspension links that have held up quite well in the past... I make sure I'm at least a few multiples of the maximum g-load that the car would ever really be able to produce (so in a Yaris/Echo, let's say 1.5g) multiplied by the car's weight.
So for a Yaris, figure 2400lbs x 1.5 = 3600lbs, and I'd shoot for at least 10k, ESPECIALLY in the rear axle situation where you'd only have the two bushings supporting all of the load.

Here's an example of some ball joint swivel bearings on McMasterCarr:
http://www.mcmaster.com/#rod-end-bearings/=lkzyc8


Even a small bearing with a 1/2" ID and 1" OD has a 19,875lb rating and costs $7.78.
I'd go bigger than this personally: there's a 1" ID and 1.75" OD bearing with a 82k lb rating that's $20.


On top of that, you'd want to get rod end boots or shields to keep the grit out... there's a few manufacturers for these.

[xnamerxx]

Rod Ends don't like side loads which this axle has quite a bit of, so it doesn't really solve any problems. A rod end would work if you have something that can control lateral movement but you don't need a rod end to do that in the first place.

As for rod ends that can survive salt and such, look at what the dirt track racers run, its usually a good idea as to what works.

[Viperoni]

True - something like this joint would be ideal: http://www.rustysoffroad.com/builder...lex-joint.html

The funny part is that particular joint isn't too far off from being the right size either!

[Jason@SportsCar]

Video from my car: http://www.youtube.com/watch?v=Lf67P...ature=youtu.be

This is from back in 2010. First clip is with nearly stock suspension (and car), Tein springs with stock shocks, bushings and no rear bar.

Second part is with AST shocks (with droop limiters) and 600lb Eibachs in the rear. Still no rear bar and stock bushings. Not much movement with this setup.

[Viperoni]

Can't see too much movement because of the low resolution vid Jason.... can't really tell how much movement there is or isn't.

[xnamerxx]

Thank Jason, your video has shown me everything I needed to see.

[NJ Drive]

Thanks to both of you for showing those vids. I really would like to run without the sway bar because I'm running 225s/205s F/R anyway. I just don't see the significance in running one using higher-than-stock spring rates on a torsion beam especially with a staggered tire setup.

[xnamerxx]

It depends on what's important to you. After some very long conversations with my chassis engineer friend who's helping me setup the car the consensus was to keep the swaybar and the 20lb weight penalty that goes with it.

As the swaybar is designed stock it does more than just stiffen the torsion beam it also helps reduce flex between the links.

The main reason it was decided to keep the swaybar was that I could accomplish better bump compliance while still getting roll stiffness I require. He was also pretty sure that I might be about at the limit of roll stiffness I need for the Dunlops, but not at the limit for the Toyos.

[Viperoni]

I find with my current soft rear springs, I unload the front inner tire coming out of a corner. Doesn't matter what kind of tires either (R888's, RS3's, R1R's, even snows lol)