triangulated 4 link help
- Thread starter brewil
- Start date
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brewil
Well-Known Member
Unless you go with a parallelogram linkage you're going to have some pinion angle delta. That's OK as long as it is kept to a minimum. Which shouldn't be too hard with the small range of motion involved. Some pinion angle delta is preferable to the traits of a parallelogram.
Ideally the torque arm design will have a CVJ of some type at the trans end of the drive-shaft. It's pinion angle delta won't be seen by the pinion UJ, so all of the operational angularity will happen at the trans. Without a CVJ there the potential for some nasty vibes when not at the set height will be quite large.
Ideally the torque arm design will have a CVJ of some type at the trans end of the drive-shaft. It's pinion angle delta won't be seen by the pinion UJ, so all of the operational angularity will happen at the trans. Without a CVJ there the potential for some nasty vibes when not at the set height will be quite large.
brewil
Well-Known Member
Is there a way with a 3 link, not a torque arm, to minimize the pinion angle?
Does the top link need to be a straight bar? Please see my curved top bar diagram
to deal with space issues, would this work?
Do you agree that the top bar should be parallel to the bottom links for a street/cornering car
as in the original diagram?
Does the top link need to be a straight bar? Please see my curved top bar diagram
to deal with space issues, would this work?
Do you agree that the top bar should be parallel to the bottom links for a street/cornering car
as in the original diagram?
Use the ExcelCAD file. It will show you why you don't want a parallelogram linkage. You want the Instant Center's location to give you some Anti-Squat. This is more important for how the car launches and comes out of a corner than change in pinion angle.
Hyper-Performance
Late Apexer
As far as effect on pinion angle, the torque arm will have less impact on the change in pinion angle over the travel of the suspension than the 70% type 3rd link. Its a matter of how much the third member will rotate during the travel up and down, the longer the triangle the less of a change of angle.
Your "curved" 3rd link is OK so long as the "imaginary straight line" through both end links are where you want them to be. The curves, bends, etc. that you add only add to the flex allowance and change the stress vectors.
As a rule of thumb the control arms and 3rd link should be nearly parrallel with suspension in the static state. I like to make the 3rd link mounting point adjustable so that I can fine tune my anti-squat/dive based on particular tracks.
The 3rd link design places a LOT of stress on the upper 3rd link during hard acceleration and hard braking. If you are thinking of drag racing, the torque arm is much preferred. For road racing, I like the 3rd link for adjustability.
With either design and panhard bar or watts link is essential to keep the axle housing centered under the body during cornering. I prefer to mount the frame end of the panhard to the passenger side as most road race tracks have more hard right handers (panhard under compression).
Your "curved" 3rd link is OK so long as the "imaginary straight line" through both end links are where you want them to be. The curves, bends, etc. that you add only add to the flex allowance and change the stress vectors.
As a rule of thumb the control arms and 3rd link should be nearly parrallel with suspension in the static state. I like to make the 3rd link mounting point adjustable so that I can fine tune my anti-squat/dive based on particular tracks.
The 3rd link design places a LOT of stress on the upper 3rd link during hard acceleration and hard braking. If you are thinking of drag racing, the torque arm is much preferred. For road racing, I like the 3rd link for adjustability.
With either design and panhard bar or watts link is essential to keep the axle housing centered under the body during cornering. I prefer to mount the frame end of the panhard to the passenger side as most road race tracks have more hard right handers (panhard under compression).
hum, I'd want the panhard to be under tension more than compression. In tension the strength is a direct factor of the cross section only. In compression you get buckling loads and now it's a lot more complicated. Steel is also better in tension than it is in compression.
Regarding bends in locating links, each one makes the link more of a spring than a rigid member so cross section and diameter must be increased to compensate. I'd use a bent design only when a straight design just won't work.
Regarding bends in locating links, each one makes the link more of a spring than a rigid member so cross section and diameter must be increased to compensate. I'd use a bent design only when a straight design just won't work.
brewil
Well-Known Member
I would beef up both the top arm and the attachment points on the chassis and diff.
Much appreciated guys
Much appreciated guys
Mad Dart
Nothing to see Here!
The pinion angle is not going to change as much as you think. Maybe 1* using poly urethane bushings. Solid rod ends it's not going to move at all. A body's and coil overs the max the suspension will move during travel is about 2 1/4" each way from ride height. IF it does move then you have your bars in the wrong spot or the bar length is incorrect and it is set up wrong.
I built 2 different triangulated 4 links and my pinion angles did not move enough to even think about it after they were set up.
I built 2 different triangulated 4 links and my pinion angles did not move enough to even think about it after they were set up.
brewil
Well-Known Member
aaah thanks MD!!!!
nm9stheham
Well-Known Member
Hope you don't mind my disagreeing on this item as a practical matter. I have dealt with the "tension better than compression" arguments for years in roll cages and it is mostly 100% inconsequential the way people tend to shop-build things. If you are going for the ultra-thinnest parts, then yes, but just thicken up the wall thickness (like .095 or .120) and never worry about it. The unsrpung weigth contribution is tiny.
I have built upper bars with an small OD, thick wall tube, and tapped it for large heim joints. Strong as a bull!
nm9stheham
Well-Known Member
As far as parallel for the upper and lower links, that was the conclusion I came to for a 4 link parallel arm design for a rally car car. Moving angles to get anti-squat is good for circle track corner lauch, but you pay for it in hard braking. I'd stay parallel for the street. You can always build in an anchor point with multiple vertically spaced mount points and play around with it.
If you get started on this, it would be good to hear and see how it works out.
If you get started on this, it would be good to hear and see how it works out.
No disagreement on my part, but given that there is a bias in the direction of the loadings it makes sense to optimize for the more prevalent loading.
Jo Diesel
My other car is a Dodge
The reason I went to a torque arm is this is a street car and I feel this is the best for my application. The eng I am using is a turbo big block with 600+ ft lbs of torque. the trans cross member is one of the strongest points of the car. Our cars are prone to a lot of flex and I felt this would move some of the stress to a better area.
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