getting ready to set up my triangulated 4 link a need to know what angles to put the top bars at. angle up and down and side of frame to axle. I"ve been looking around on some different sights and on here and not coming up with much.
You will get a lot of differing opinions. Many will say 45° from center line of the car for the uppers (for 90° total) but the race car guys seem to set up more around 30° to 35° (or 60 to 70° total). there is less bind in articulation with a lower included angle. The lower control arm should be parallel to the ground at ride height, no more than 1° pointing up at the front, never pointing down. As for the angle on the Upper Control arms, most OE's set them with the front pointing up, but this induces body roll understeer to make the car safer for grandma. I like to see them pointing Down in the front about 5 to 6° on a street rod, 7 to 7.5° on a car that is being set up more for road course type stuff. Anything more than that seems to cause wheel hop under heavy braking. The softer the cars spring rate the less downward angle I would put in the upper arms more angle does induce body roll oversteer (but it also helps with forward bite)
thanks hot rod don. I started to look at some set ups and saw that the top bars were pointing down. I thought I better ask anyway
I would think for the street i'd want he bars parallel with each other. That way when they go thru the full range of motion you want them to travel at the same rate and similar arc. If, for example, the bottom bars pointed upward then when you hit a bump the arcs of the upper and lower bars would be different and can cause what is known as 'rear steer' - ever go watch the latemodels at the local circle track? those cars' rear move quite a bit as the suspension goes thru its motion and the rear steer for them is an advantage. Take a compass and some paper and play with the arcs and you'll see what i mean. Others on here can explain it better.
Top view, 60deg minimum (30 each side of chassis centerline). More if you're going to corner it hard. Side view, lowers level with the ground. Top bars parallel or slightly downhill toward frame.
I've been wondering the same thing..for my street-driven 34 coupe that may see "spirited" driving occasionally....like at the HAMB drags.
Is this for your truck or something else? How far apart are your frame rails? Most trucks, and hot rods for that matter, have a narrow frame rail width that is usually not enough to get proper angle (in top view) and length on the upper bars. So you either shorten the bars a bunch or build with not enough angle, neither of which is good.
It is for a truck and I'm trying not to change the angles or cutting the bars. I working this out on paper so I can get it right the first time.
Try this site; http://mysite.verizon.net/triaged/4linkcalcv15html/index.html It's faster than paper. It was designed for 4x4 off-road linkages, but will work just fine for a street car too. Anti-squat and roll center axis are the primary geometry considerations. Anti-squat helps load the tires under acceleration. Drag cars usually want 100% or more, but too much causes tire shake and brake hop. For street you'll probably want less than 100%. Roll center angle should be as small as possible, negative for roll understeer gives more predictable handling. Roll oversteer feels twitchy. There are lots of "rules of thumb" about what should be parallel or pointing up or down. Mostly it's all bunk. Just do the calculations and design a geometry for the handling characteristics you want. Some adjustability is always a good thing as well. Most any design uses some estimations, and things don't always come out quite right when translated to metal.
One chart has "SF Rod end" and opposite that it says "Rod end breaking" Does that mean the rod end has literally broken or is it a mispelling of "Rod end, [comma] braking"? I see right above is is "Rod end buckling" so maybe it's correct? I'd really like to use this chart for my own car before I begin cutting/welding...er, if I can figure it out.
S.F. is Safety Factor. If the rod end breaks at 20,000 lb and your design loads it to 5000 lbs, you have a safety factor of 4. Safety factor of no less than 3 is typical for automotive design. The calculator is designed for off-road, so the preloaded rod end choices are heavy duty ones. It also has a link bending calculation assuming the rig is hung-up with half the vehicle weight resting on the center of the link. I hope that's not relevant for anyone's hot rod.
I laid it out again and the top bars at 30deg leaves the top bars to long. the top bars are 19" bolt center to bolt center. If I cut 3 1/2" off they will work. Is it possible to shorten the top and bottom bars. The kit I have is for a 32 ford but I don't know good of a fit it is. I don't see how this kit will work 32 measurements. My frame rails are 36" inside to inside and then 16" for the pumpkin. hopefully anyone can understand what I'm saying .
Just my opinion, but I don't think that is wide enough to effectively triangulate the bars without shortening them a bunch. You say your pumpkin is 16", what kind of rear end? If it is a 8" or 9" Ford and you can weld on the pumpkin that will help. If it has a cast center that you can't weld to that makes the problem even worse. I would really run a parallel style 4 link with a panhard bar. You can use the kit you have with a little work. Lower bars mount just as described above, either directly under the frame rail or outside of it. If you are running coilovers and have the room they can be mounted vertically outside of the rails as well. The upper bars mount to the top of the axle housing and go straight forward. The upper bars can mount inside of the frame rails. The difference in length from top to bottom is actually a good thing and gives you progressive antisquat. Add a universal panhard bar behind the axle and make it as long as you can make it to minimize side to side movement with travel.
i'm about to fit up a trianglutated 4 link in my 31 roadster, thinking about shortening the lower bars a couple inches, is that ok? also what degrees should i put the diff at?
i agree with hotroddon, the lower bar should be level with the ground at ride hight my 29 coupe tho has a 3 bar setup and the lower link bars i have at a angle,the top bar is straight
I did a bit of research prior to installing mine. The bottom bars should be paralel and horizontal at drive height. (I'm using airride.) The top ones on the pumpkin I placed at 90 degrees and level as well at driving height. Make sure you can adjust the bars in order to change the pinion angle if needed and so that you can adjust the rear axle/wheels to sit evenly in your fenders. Hope this helps a little. The pic shows the frame in its lowest position, not driving height.
Zion, halfway 'tween chicago and milwaukee. Us guys in the trailer park think its a little ghetto in some parts. Good choice going parallel......now you won't have to replace bushings every 5,000 miles.
if I use what I have with the shorter bars on top were do I mount the top bars on the axle? do i mount them vertical with the bottom? I'm talking about were the bars bolt on to the rear end. and do I still point down 5 to 6 deg
You can mount them inline vertically with the lower bars ore you can move them in. We set up a 55 pickup with the lower bars under the frame and the upper bars inside the frame rails. As far as angle, google antisquat calculator and you can input some dimensions and it will spit out information for you. Move things around and see what will work best. There is no absolute "you should always mount these bars at these angles" just some guidelines. To your question, 5 or 6* down seems aggressive, and without knowing how the rest of the truck is set up it is hard to say.
yhis sounds like a dumb question to me but here goes, how do you determine the centerline of your car....... sheepishly waiting.... thanks
It's in the middle. If you were to measure the width of your frame, we'll say its 24" wide in the front and 40" wide in the rear, measured at crossmembers. The front center would be 12" in from the outside and the rear centerline would be 20" in from the outside. Connect those two points with a theoretical piece of string front to back and there is your centerline.
Sorry for revivig this old post; im installing a triangulated 4 link on my 40 Desoto Coupe and was wondering if these specs would be considered too extreme. At ride height, rear to front, Bottom bars are 1 degree down and upper bars are 5 degrees up. Any input is greatly appreciated.
This is a professionally built frame, if you are interested I can measure all the angles and lengths tomorrow. It's a '32 frame. Notice they don't go to the top of the center section, it helps with floor clearance. SPark
As an example, here are measurements for a 32 frame but yours would differ. Remember to ensure axle is centred in frame and your wheelbase is correct and the axle isn't biased to the front of rear or to one side more than the other. Also make sure you pinion angle is correct. Measure twice, cut once. Once welded up it's too late. I already see that it was tack welded.
The lower bars only have compression loads from pinion torque reaction in his build. [and tension loads during braking ] The triangulated bars are mounted directly in front of the axle and are subjected to compression loads due the axle thrust [every ft/lb of torque at the tyre footprint equals the same amount of thrust at the axle centreline] These thrust loads are better off being controlled by arms closer to the wheels to prevent the wheels trying to toe-in [bending the axle tubes, or torque steer] 3rd gen F bodies have these arms out wide for that reason. Axle thrust loads are always greater than pinion torque loads due to mechanical gearing.
Thank you LM14. Unfortunately my frame has an X crossmember, if thats the correct term., in the middle therefore Im unable to attach the lower bar bracket to the frame as in the pictures you provided.
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