How to resolve a twitchy back-end in 1/8 buggy?

[VintageMA]

The back-end of my XB8 is very twitchy and I am looking for a way to calm it down a bit.

What is mean is that it's almost like an oversteer. When I am running on pavement it isn't a problem at all, but when I am running on grass and there is tons of traction it's almost like there is an oversteer and the back-end just wants to come around too quickly for the turning of the rest of the car. I was studying it a bit this past weekend and you could see that either direction you steered the back end really wanted to swing in that direction and in the grass would tend to grab and hop a bit (my description of twitchy) and generally flip the buggy if you didn't correct for it.

So I an basically looking for a few possible tweaks to mellow out the back end a bit.

I was thinking that standing the rear shocks up a bit may work.

[BrianG]

What diff fluid do you have in the back? Maybe too thick?

[VintageMA]

Originally Posted by BrianG

What diff fluid do you have in the back? Maybe too thick?

I'm trying to remember as it has been a while since I did the setup. I know I changed the fluids a few months back, but can't find the sheet I was tracking the setup on.

I think I am running 5/20/2 (although I may have upped it to 3k in the rear).

[Finnster]

How is the rear sway bar setup? I'm assuming to the toe is locked?

[VintageMA]

Originally Posted by Finnster

How is the rear sway bar setup? I'm assuming to the toe is locked?

Yes toe is locked with kit settings. Not sure what you mean when you ask how the sway bar is setup?

Lengthen the rear camber link

[jhautz]

If the back end is sliding out to easy in turns you can do a few things to try and settle it down. First is to run softer springs/lighter shock oil in the back. This will allow the back end to roll a ltiile more and outside wheel to grab harder. Lighter or no sway bar in the rear could also help. If you are already feeling like the suspension is soft, then stiffening the front end will have a similar effect as softening the rear end. A stiffer front end will "push" a bit more and prevent the rear end from sliding as much also. Another possible solution is to raise the roll center on the rear end so the chassis rolls a bit more in the back and the rear end grabs.
Here is a great manual on chassis setup. It is from xray, but the principles apply to all buggies and truggies. Check it out.

http://www.teamxray.com/teamxray/sho...p?file_id=4461

[Arct1k]

Thanks jeff top PDF!

[Finnster]

Originally Posted by VintageMA

Yes toe is locked with kit settings. Not sure what you mean when you ask how the sway bar is setup?

The amt of pre-load on the swaybar. Like JH said, sounds like you are not getting too little chassis roll.

[VintageMA]

Thanks Jeff - that's a great PDF. I gave it a quick read through and I think I am going to try to raise the rear roll center a little bit and that adjustment most accurately describes the problem that I am having.

[VintageMA]

Originally Posted by Finnster

The amt of pre-load on the swaybar. Like JH said, sounds like you are not getting too little chassis roll.

Gotcha - without having the buggy in front of me I can't say for sure how much pre-load I have on the sway-bar - I'm sure that is a value that changes for every manufacturer out there too.

the one main thing is to run the rear tie rod as long as possible. that will help settle it down alot

[gixxer]

very nice guide. I think I will have to print that out cause most of it will apply to my 10th scale.

[VintageMA]

I took a look and the rear sway bar is a touch tight on pre-load.

I don't want to change too many things at once so I'll probably reduce a little pre-load on the sway bar and then raise the rear roll center a touch and then take it from there.