Is there anyone out there with a set of plans or that can help me to build a set of A/arms for a new buggy being built. l see that there are a few SORRA members who are into DIY in a big way and would love to talk to any of these guys. l want to run a bushed style set of arms so any help would be great. Thanks Kevin 0418773057
Well guys this must be a first. There are so many regular contributors with so much offroad knowledge and this post has not sparked any interest. If anyone can help or advise please do so by posting.
Its a bit hard because what works on one car wont work on another...
Basically though, there are some essentials if you're going for a true A Arm (such as late model jimcos) as apposed to semi-trailing (Chenowth, early A arm Jimcos).
Top arm should be (depending upon chassis design) between 80 and 88% of the length of the bottom to give camber gain during travel.
Caster should be between 4 and 12 degrees for straight line stability and centred steering.
Scrub radius should be kept to a minimum, hard to do with big offroad tyres though...
Both arms should be as horizontal as possible to keep the roll centre of the car low, preferably lower than the centre of gravity for flatter, more responsive turning.
Anti-dive needs to be considered, as does caster loss during wheel travel.
You also need to consider ackermann angles and bump steer for steering.
The setup on any racecar is a compromise between the basic values above, and many more.
I bought a heap of books and asked a heap of questions before I started the design... but we've not yet raced our car so I cant tell you if it works or not! It should...
My best advice is if you're designing on paper do it in the following order:
Read Chassis Engineering by Herb Adams (the suspension design program SusProg3d is based on formulae in that book) and How to Make Your Car Handle by Fred Puhn to get a handle on the basic theories above.
Design on paper and see if its going to work. Draw full scale (we did it on the garage floor) and see if it works as expected Make a dummy arm from scrap and bolt it all up on the car and make sure it works. (we made a few changes at this point). Make a jig based on the dummy arm. Then build your arms. Its a long process... but a rewarding one.
Alternatively, build it in SolidWorks or any 3d cad program and skip the paper part - but I'd probably still build the dummy arm to test and make the jig.
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Green Sally up. Green Sally down. Lift and squat, gonna tear the ground.
Thanks wolf that gives some numbers to start with and if l get stuck l will post questions and l hope the get answered. Thanks Jones l will call Az to pick his brain if l get stuck. Another question is it legal to roll your main cage like the Kreger class 10 for racing in Aus.
l have seen some photos of a set of arms from Camburg in the states and they use a hiem joint top and bottom with the top hiem having 8 degres of adjustment for fine tuning or re-setting for conditions has anyone seen this before and what do people think.
Well chappo's car has a heim jointed spindle and he was whooping ass at hyden before the power steering went out.
We went with uniballs in the hope that they'll be more bulletproof at the spindle, but use heim jointed chassis mounts on the top arm for adjustment. We used 3/4 x 5/8 moly hiems for these. We actually use those same hiems all around the car.
8degrees of adjustment? wow, thats a biiiig camber adjustment!
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Green Sally up. Green Sally down. Lift and squat, gonna tear the ground.
Thats what l thought wolf 8 degrees is huge so a clown like me building my first set of arms will be able to cheat a bit. If l use the numbers your good self gave me as a starting point l should be able to move in the right direction.
