djbxp

Special Thanks to Toyoter91, clarkie_ni and Frank_L.
I went to the track and do some setup changes with noticeable improvement on the clock. I will post my setup when is ready.

Now i will give one more try on finalizing the setup for the track and then practice for the race. The only thing i didn't fully understand is the front end geometry in relation to the caster adjustments. We have the lower roll center and also we can add caster from lower arms, we have the upper roll center and again we can add caster, and the king pin plates. also we have the 2X1mm and 1X2mm spacers on the upper arms adjustment. Too many areas to setup and i don't know where to focus for what reason...

When do we change caster from below and when from upper arms? Why to do this and why not doing that ? What are the side-effects of each change? When to adjust from upper arms spacers and when to adjust from eccentric bushings lower or higher? Please give some examples.

toyoter91

iTrader: (47)

I try and isolate the lower arm to kick up needs and change it based off that more than using it to adjust overall caster, even though it will alter caster if you don't adjust the upper arm position along with the lower arm angle change. You can also introduce active caster (caster change through travel of the suspension) if you don't change the upper arm angle along with any lower arm angle changes.

If I only want to make a caster angle change I use the upper arm position to do that. (moving the upper arm forward or back)

King pin angle is something different from caster. It will change the way the steering feels. Not an adjustment many cars have so its not something I have played with very much as I dont actually have a XB8

3DRCRACER

iTrader: (1)

The king pin plates do not alter caster on the XB8. They only affect the upper arm length. It can be misleading because the differentiation between the plates is in degrees. If you lay a 6, 10 or 14 on top of each other, you will see the difference in the mounting hole for the upper arm which only makes it shorter or longer.

djbxp

In different web sites terms in roll center are written opposite!! Even in some setup guides and famous web sites of pro-drivers! Let's clear this guys !!

In the Hudy off road setup guide for roll center is stated:

The amount that a chassis rolls in a corner depends on the position of the roll axis relative to the car’s center-of-gravity (CG). The closer the roll axis is to the center of gravity, the less the chassis will roll in a corner.

Please open attachment and notice roll center transfer from green to orange.
We come to the conclusion we all know, moving the links on the tower up, roll center is getting lower!! No doubt about that! Also no doubt that higher links on the tower we gonna have less roll!! SO ??

The drawing and practice show that: The further roll axis is from center of gravity, the less the chassis will roll in a corner!! (green lines). Opposite from what is stated in the hudy manual. Maybe i'm doing something wrong??

In order to accept the above statement we have to assume that center of gravity is below the car... this is the only way to go closer to the center of gravity and the less the chassis will roll in a corner. Where is the center of gravity? must be on the car ... What's going on?

masher81

iTrader: (16)

The higher the link is on the tower, the lower the roll center and the more the car rolls. What you said here is wrong.

djbxp

i feel like is rolling LESS when have the links high on tower. no one agrees with me ?

Tijuana_Taxi

iTrader: (4)

Watch this video, it makes it pretty clear. https://www.youtube.com/watch?v=tWdRQaz_Xq8

kuruption

iTrader: (24)

I threw this together really quickly to explain how I see roll center.

I'm not an engineer... but this is how I visualize it in my head.

Roll center is in relation to the Axis of the pivot and the Center of Gravity. The CG of a car will usually exist somewhere between the pivot of the A-arm and the pivot of the upper camber link / a-arm. In fact, I believe that in most cases, the camber link / a-arm pivots are a lot closer to the CG, so the effects of changes are smaller.

Green represents low roll center and red represents high roll center, where the horizontal lines represent the pivot horizontal axis (i.e. hinge pin / shock mount positions) and the angle demonstrates the amount of roll associated at with pivot point.

Where the angle is greater, there is more roll. Thus, lowering the A-arm pivot or raising the camber link pivot would increase the angle and increase the roll.

This assumes one pivot point. In the case of an A-arm or camber link, there are obviously two pivot points which make it more complicated..

kuruption

iTrader: (24)

Just want to add... even pro drivers have a problem with roll center. Jared Tebo posted a video a couple years ago showing how he finally figured out roll center... mostly because he had to start doing setup for himself.

rick oxley

my car also felt like this, the exact oppersite to how it should and how it felt
on the xb9/808 sorry no explanation as to why?

masher81

iTrader: (16)

There are other factors in play. When you change the camber link you also change the camber gain. Moving the link up may change the camber change in such a way that the rear has more traction.. more traction = more roll.

OleC

Even better explanation: https://www.youtube.com/watch?v=44AlYI6lSX4

clarkie_ni

https://youtu.be/yU2c03KkF6k

This is the best explanation on YouTube. You will understand it after watching this one guaranteed.

rick oxley

at the euros some of the team drivers were using 5mm of bumpsteer
shims at the hub, can anyone please explain the reason for this?

shesha

iTrader: (1)

+1 on that vid explains the theory spot on.