Outer Limits 4x4 Board

ok, so we are trying to design a 4 link for the rear of my mates crusier. it is a 75 series rear diff, under a 40 series chassis, on saw airshocks, behind a 350chev to t700 and willl be making around 500hp

now, been reading all last night and morning on pirate, specially the 'link suspension for dummies' thread -> http://www.pirate4x4.com/forum/showthre ... oll+centre

and now have some questions

it will be a 4 link with the uppers triangulated, i gather this will give us a high roll centre which should help i think cause this cruiser doesnt have the lowest CG on earth. is this correct?

what sort of vertical seperation should there be at the axle (keeping in mind the power of the motor)....would 6 inches be enough or should we go for more?

whats the minimum angle that the upper links can be (off the perpendicular line forward) to hold the axle laterally

after reading the thread on pirate, many suggest makin the uppers adjustable at the chassis end to adjust the anti-squat. should we mount the upper and lower links paralle when viewed from the side, in the top hole of the mount, and have 2-3 other holes below to play with the anti-squat?

and finally, for the moment anyway. what percentage should the uppers be shorter than the lowers? i've read everything from 65% through to 90% any magic number?

anyone........?

antt wrote:anyone........?

hi antt .just went and had a look and mearsure off me buggy and the cruiser . buggy , lower links are 1250mm and tops are 850mm thats centre off bolt holes to centre off pin where it mounts on the chassie . crusier ,lower are 1500 mm and top are 1000mm . distance between [parallel] the links is 9.5 '' sittin at the ride height of the rig .hope this helps . antt this thing looks great carn't wait to see it done

u gunna triangulate the lowerrs?

mine has 9.5 -10" seperation at diff

humphey wrote:

antt wrote:anyone........?

hi antt .just went and had a look and mearsure off me buggy and the cruiser . buggy , lower links are 1250mm and tops are 850mm thats centre off bolt holes to centre off pin where it mounts on the chassie . crusier ,lower are 1500 mm and top are 1000mm . distance between [parallel] the links is 9.5 '' sittin at the ride height of the rig .hope this helps . antt this thing looks great carn't wait to see it done

thanks for that humphey, helps a lot. do you street the cruiser much now? how does it behave?

redzook wrote:u gunna triangulate the lowerrs?

mine has 9.5 -10" seperation at diff

just depends on space. may be getting a complete tube rear end now, so can easily triangulate the lowers if that happens

antt wrote:

humphey wrote:

antt wrote:anyone........?

hi antt .just went and had a look and mearsure off me buggy and the cruiser . buggy , lower links are 1250mm and tops are 850mm thats centre off bolt holes to centre off pin where it mounts on the chassie . crusier ,lower are 1500 mm and top are 1000mm . distance between [parallel] the links is 9.5 '' sittin at the ride height of the rig .hope this helps . antt this thing looks great carn't wait to see it done

thanks for that humphey, helps a lot. do you street the cruiser much now? how does it behave?

antt it dose'nt see much black stuff any more but it had 2 years road use before i started compin it .it drove the same as it was on leaf springs .

antt wrote:

redzook wrote:u gunna triangulate the lowerrs?

mine has 9.5 -10" seperation at diff

just depends on space. may be getting a complete tube rear end now, so can easily triangulate the lowers if that happens

Triangulating your lowers usually lowers and flattens your roll centre.

with airshocks at all 4 corners, wouldnt' it be desirable to have a high roll centre for stability?

antt wrote:with airshocks at all 4 corners, wouldnt' it be desirable to have a high roll centre for stability?

Yes high will help for stability. But then it is usually less flexible as well. Also depends where the weight is and how high it is. I have a high roll centre at the front and a low one at the rear. 70% of my weight it at the front and one 30% at the rear so the end with the high weight (front) has the high roll centre thus aiding stability. With the rear low, it doesn't adversely effect stability much but it is able to be very flexible and supple when powering up a hill and thus flexing/twisting the axle instead of pushing the chassis up and down. This keeps the power to the ground and keeps the rig stable whilst powering on.

See - easy!

Now the difficult part is that every vehicle is very different and there is no right and wrong - enjoy!!!

cheers dave.

well this thing is running an 80 series front end (radius arms), so i guess they have a high roll centre. so we could probably aim for a lower roll centre in the rear to give it a bit more flex

anyone else have info re the other questions bout minimum angle on the links for lateral control of the axle? and the whole antisquat debate?

antt wrote:cheers dave.

well this thing is running an 80 series front end (radius arms), so i guess they have a high roll centre. so we could probably aim for a lower roll centre in the rear to give it a bit more flex

anyone else have info re the other questions bout minimum angle on the links for lateral control of the axle? and the whole antisquat debate?

The magic quoted value for the convergence of the upper triangulated links is 40 degrees. So that means the links need to be further appart than 40 degrees at the diff.

I would also argue that the proportional length of the upper and lower arms is not as sifnificant as you are making out. Considering all forces are either compression or tension in the links, the length of them is non important. The length significance is due to rotation of the diff as the syspension cycles. In reality, your actual diff centre may only have 4-6" of vertical movement. This is not enough to cause pinion bind in most circumstances.

So once again you get back to the rule of thumb of keeping the links as long and as flat as you can.

thanks again dave.

one final question, what have all u guys done with the brake proportioning valve? just made up a way to mount it with the new setup, or gotten rid of it all together?

anyone.......

antt wrote:thanks again dave.

one final question, what have all u guys done with the brake proportioning valve? just made up a way to mount it with the new setup, or gotten rid of it all together?

I run a Willwood adjustable proportioning valve. I would have kept the existing one but the fuel tank doesn't leave it enough room to function and besides - i broke it getting it out