I am trying bloke but I am not as fast as ...

Shannon Campbell
http://www.gondwanaracing.com.au/predator/shannon.jpg

and Walker Evans
http://www.gondwanaracing.com.au/predator/walker.jpg

Jeff, have we met?

The Predator is a very skinny car.

The yellow car had a poor roll centre. But it is important to distinguish between body roll and roll centre. Torsion anti sways can reduce body roll into the camber but they don't correct a poor roll centre.

I reckon roll centre needs to be the subject of its own thread or article. Jeff, is this worth writing up or will most folks use it as an insomnia cure?

I will go with the flow, I reckon it is worth writing up, what do you think?

I would like to follow it there too 4zee, I am sorry I take so long sometimes :wink: We recently had a photographer come one board so hopefully we can get some good pics coming. If there are any guru mini DV folks on here, geez, they would be very welcome in the shed as it would be great to put a little Predator workshop history onto mini DV I reckon.

Thanks heaps for the encouragement. I reckon there must be other folks on AJOR who are doing the home-fab thing also. So, where are you all?!?!?!

They are not spacers Jim, they are floating joins that keep the mains and tenders together so that both springs work in unison to achieve their combined spring rate.

i for one would like to see a write up on this, i thought they were the same thing?

well im kinda getting there, very slowly though, so far i have 302W/AOD/NP208, allong with Dana44/9" , but i need to learn alot more about cage design and link design before i dive into it, hence the reason why this thread is so helpfull. ;)

I am going to post something that Sam/strangerover (mogrover) said on pirates as I can't be bother typing out a massive essay.

I am sure Pete can shed plenty more light on this subject as well :D

<snip>
The roll centre is the point that the body wants to rotate about on the axle or the point that the axle supports the body laterally (or supports the body in a sideways direction). The simplest example is a triangulated 3 link with the upper links triangulated to a single point on top of the axle. This point is the roll centre. If you are talking about roll centre what most people are concerned about is the height of the roll centre. If the roll centre is high it will reduce the amount of body roll that you get when on side slopes. This is a good thing because it keeps everything stable in the off camber stuff and is why a lot of people try to get their roll centre up high - to reduce body roll. The roll centre can be thought of as the point where the body is supported laterally (or sideways). So that if the body is supported laterally up high it wont have as much tendency to induce body roll than if it was to be supported down low. If a rig uses a panhard rod then the roll centre is the mid point of the panhard rod.

When you start to look at triangulated 4 links things start to get a bit more complex and you should be really talking about the roll axis as apposed to a single point. But in simple terms if only the upper links are triangulated then the roll centre is high (means less body roll) and if only the lowers are triangulated then you get a low roll centre (means more body roll). If both the uppers and lowers are triangulated then the height of the roll centre will still be high and the angle of the roll axis will be more horizontal. Now without going into it too much a horizontal roll axis produces little roll induced rear steer (which may or may not be usefull on a rock crawler). Also if you can get the roll axis to be sloping down a bit (going from the rear to the front) then it will behave better on the road (again this may not worry you on you trail rig)

Again this is hard to explain without going into things too deeply or writing 1000 words.

To further complicate things a high roll centre (or axis) isnt the be all and end all of rock crawler suspensions because what a high centre also does is if a wheel moves upwards (over a bump) then the body must move sidways as well (really should be drawing pictures here to help explain this). Now as you go faster for the wheel to move upwards quickly it must push the bodysidwards quickly as well - which is hard to do. What this means is that when you are throttling up a climb quickly (still talking rock racing speeds here ie say 40:1 and 4000rpm) when you hit a bump on one side your springs wont want to compress when you have a heigh roll centre because to compress a spring it must move the body sidways as well so you may as well think of it as having no springs at all and the rig will just bounce off the tyre.

Running a low roll centre will let a wheel compress much more easily without pushing the body sidways as much.

Lots of successful comp buggies run high roll centres and lots of then run low roll centres. One isnt definately better than the other.

So in summary:

If you want a high roll centre trianglate the uppers.

If you want a low roll centre triangulate the lowers.

If you want the rig to behave well on road at speed then you should look at triangulating both the uppers and lowers and try to get your roll axis sloping downwards a bit towards the front.

If you want to minimise roll induced rear steer then you should also do the double triangulated thing to get a flat roll axis (although having the axis a bit up hill or down hill wont matter just as long as its flattish).

If you want your suspension to work well on the heigher speed throttling climbs and soak up bumps then you should go for a low roll centre.

If you want your rig to work well on the slower crawling speeds and reduce body roll and remian stable in the off camber stuff then you should go for a high roll centre.

Finally the hieght of the roll centre or the angle of the roll axis wont really make a huge difference to the capability of a rig - we are only talking degrees here. Lots of very good comp buggies run every variation of roll centre and axis.

<snip>

Clear as mud?? :mrgreen: