Outer Limits 4x4 Board

hi i'm working on a 3 link calculator to figure out a front 3link set up for my disco,i searched the forum and the internet but what i found is,you must know a lot so you can build your suspension according to your needs and that there is not a good or bad set up but a set up for the kind of thing you're in. so what i got from my calculations is this:

antisquat:107.94 and 93.18%
roll axis angle:5.12 deg
roll center height:15.57 in
instant center x-axis:56.61in
instent center z-axis:18.17in

for antisquat i can go either way, above or below 100% but want to get more opinions on that,
what to have in mind when braking hard so to fight the front end from dive?
any one have a 3link on his rover?how it performs and how predictable is when braking hard on high speed,cornering etc?

the more coments and arguements the better!!

thnx daf.

If i can find the thread on Pirate ill post the link but a couple of years ago Sam on here ( Strang Rover ) spilled all his glorious knowlegde in a link thread over there. If you read it all about 2/3 times it all becomes clear on seting up a bloody good link setup..
Plus on pirate there is links to a heap of link calculaters (basically links for links )

Thats probably this one Nottie - very long read, but if you take the time to understand it, it is pure gold.

http://www.pirate4x4.com/forum/showthread.php?t=168577


I wouldn't have thought that youd run over 100%AS on the front otherwise the front will lift under brakes which is a bit unusual.

I've been looking into this also, and I would personally keep the AS under 100% front and rear so that it feels natural to drive and when you do spin, then its not bucking and breaking.

Yeah that's the thread to read if you're intending on trying to understand link suspension.

Keep in mind though, that thread is the tip of the iceberg. There is so much more to setting up a vehicle's suspension. If this vehicle is going to be road driven, then consulting engineers BEFORE you start is a minimum requirement.

If its off-road only and trailered/trucked around, then go nuts and have fun building it.

Yep thats the one Slunnie.
I had to change computers as the link was saved on a diffrent PC.
Seems i am not the only one who has the link saved and reads it every now and then when theres nothing else to read to get a good handle on it.

Yeah, I dunno why but I've always been fascinated by suspension and as Micka say's its the tip of the iceberg but its great for a fundamental understanding of the concepts and the 3-link calculator to do the maths for you.

youre very helpful boys and i will read the thread,again for 4rth time and personaly i think that i'm a bit stupid for this,
but i'm allready making the brackets, the link it will be simillar to the trailing arms, bush on the axle and pin on the crossmember side but with a 4mm thick wall and 30mm o.d,i know that configuration is not the best for max. travel but all i want is to free the front a bit to get it balanced with the rear.
i'll use a trailing arm mount to fix the arm on the crossmember
slunnie-i'm not worry about that the front will lift when braking (possible?)i'm worried if it dives to much,on the other hand when on throttle the front will push/pull down(?) anyway if it's arround 100% it will be neutral right?

100% shouldn't lift or drop.

Slunnie wrote:100% shouldn't lift or drop.

its anti-dive in the front end. Lowering it like the AS in the rear can help with hill climbs etc, but like everything there are comprimises.

uninformed wrote:

Slunnie wrote:100% shouldn't lift or drop.

its anti-dive in the front end. Lowering it like the AS in the rear can help with hill climbs etc, but like everything there are comprimises.

Its the same thing.

The AS value for the stock radius arms would be a good starting point to consider...so in a 3 link setup that would be upper and lower links converging at the radius arm chassis mount bush. I would imagine the AS value of the stock radius arms would be very high...and this seems to work well on road.

Biggest concern for on-road manners would be the need to keep the link setup symetrical about the centre line of the rig (front to back) cause if you use relatively soft suspension bushes in the links because as you jump on the brakes the bushes will flex and it will steer the axle. So the vehicle will always pull one way under brakes.

Sam

Also with highly convergent links you, again really need to have symetrical links...otherwise the lifting AS force will lift one side of the vehicle more than the other...again making it handle funny under brakes.

I would almost guess that is you were going to run an unsymetrical link setup you could almost be better running a low AS value so that at least the rig will brake in a straight line.

Sam

Sam, taking into consideration that the AS or AD value on a STOCK rover is relatively high, which works well on-road. Compond that by the fact that most rigs getting "linked" will run larger tyres and some amount of lift, which inturn only rasies AS and AD would it be fair to say that you could reduce the STOCK values to compensate for tyre/lift and still remain safe on-road?

within reason of course

strange rover that's what i have in mind,a standard rover set up is a good point to start from and then adjust to my preference,although i don't know how to find the AS of the stock front suspension because of the lack of the 3rd link and the use of the radius arms to control the axle wrap,but what i notice is when hard on throttle the front end is allmost diving instead of lifting,is this means low AS or better, high AD?- i've been driving for some time with the rear prop shaft removed because of a diff breakage when notice this.
yes the link is going to be on the one side due to sump clearance but parallel to the radius arm,so this may cause problems when braking with unpredictable behaviour, so running low AD will it make things a bit better under braking ?
and what do mean by highly convergent links? us i understand it is the angle difference of the lower and upper links from the axle to chassis mounts?


daf.

For anti-dive/squat the instant centre for radius arms is at the chassis mount.

I think what Sam means when saying highly convergent links is very small vertical separation at the chassis. i.e. instant centre close to the chassis mounts (like radius arms).

The link calculator is assuming rear suspension and acceleration in the direction from rear to front. If using the link calculator for front suspension, then this direction of acceleration is from front to rear - i.e. braking, so we are talking of anti-dive under brakes.

(Edit) links forces switch from tension to compression or vice versa when acceleration changes direction (rear suspension change to braking or front suspension to acceleration). So the calculations go out the window when this happens. (end edit).

The calculator will not tell you what the anti-squat (during forward acceleration) is for front suspension.

However, for most people the most important issues for the front suspension are during heavy braking.

The important part of Sam's discussion is that with a non-centered middle link, you will get roll during braking. This is worse the farther you are from 100% AS. Make sure you use fairly non compliant links as this is the big problem. Make sure you make it strong enough and weld things to a structurally competent level. There are serious forces involved and serious consequences in the event of a failure.

If it were me... I would design for below 100% and use a system where the change in AS with travel is very low. Single upper, dual lowers.

herdwick. wrote:strange rover that's what i have in mind,a standard rover set up is a good point to start from and then adjust to my preference,although i don't know how to find the AS of the stock front suspension because of the lack of the 3rd link and the use of the radius arms to control the axle wrap,but what i notice is when hard on throttle the front end is allmost diving instead of lifting,is this means low AS or better, high AD?- i've been driving for some time with the rear prop shaft removed because of a diff breakage when notice this.
yes the link is going to be on the one side due to sump clearance but parallel to the radius arm,so this may cause problems when braking with unpredictable behaviour, so running low AD will it make things a bit better under braking ?
and what do mean by highly convergent links? us i understand it is the angle difference of the lower and upper links from the axle to chassis mounts?


daf.

If you're running it like that, have you considered running 5-link - ie an upper on each side to provide better control under brakes?

to calculate anti-dive you need:

wheelbase
tyre size
link postions, both axle end and chassis end, heights off level ground and lenghts from axle centerline
COG
front and rear brake percenatges

uninformed wrote:to calculate anti-dive you need:

wheelbase
tyre size
link postions, both axle end and chassis end, heights off level ground and lenghts from axle centerline
COG
front and rear brake percenatges

and a calculator

using std radius arms I think you will find the AS values more in the region of ~170% (std height) and up to ~200% (for a 4-5" lift). Also there is lots of other stuff to consider and you can caluculate it all day and there will still be stuff you haven't allowed for. Its very hard to get a good balance of all the characteristics you 'think' you need. Even AD is a minefield, eg in some offroad race vehicles the AD is very low and this then is counteracted by driver skill to some point - they 'pitch' it in early (hit the brakes and load the front end) then use a combination of brake/steer/throttle to drive it through a corner. Then add suspension setup to the equation..... faaaark good luck.

1MadEngineer wrote:using std radius arms I think you will find the AS values more in the region of ~170% (std height) and up to ~200% (for a 4-5" lift). Also there is lots of other stuff to consider and you can caluculate it all day and there will still be stuff you haven't allowed for. Its very hard to get a good balance of all the characteristics you 'think' you need. Even AD is a minefield, eg in some offroad race vehicles the AD is very low and this then is counteracted by driver skill to some point - they 'pitch' it in early (hit the brakes and load the front end) then use a combination of brake/steer/throttle to drive it through a corner. Then add suspension setup to the equation..... faaaark good luck.

All very true, but for anything driven on the road, it doesnt hurt to have a starting point and the Stock stuff has to be OK as it is allowed to be driven on road. yes its not the best off road, but gives you an idea of whats going on. measureing the car static on level groud is only 1millionth of whats going on as you say. but you have to start somewhere

slunnie a 5link is almost impossible due to space,i will stuck with the 3link and see how it goes,the link is at the machinists shop and will post an image as soon as i can,and then start making the crossmember.


daf.

sorry for the hijack but a lot of the guys in this thread have a good feel on rover stuff.
Q - would there be any interest / market in making superflex arms for rovers. A lot of design and development work goes into getting them right so its a big investment in time and money if only 1 or 2 guys were ever interested in them.

They work exceptionally well in the cruisers and patrols and have racked up an amazing amount of comp victory's since released. But rangies and discos seem to work well stock, does the front end need just that bit more flex?

any feedback greatly appreciated
Greg

Greg, you already know I am interested to compare them to my current custom cranked and holey bushed configuration.
I wouldnt mind fitting out Fluffy with the new shocks and then doing a comparo with the standard, current & superflex arms!

I could potentially be interested too Greg.

Another interested in superior arms for rovers.

Im interested in a set too, my county has nothing front end flex wise...