Rear suspension suggestions / examples

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busman

Well-known member
Joined
Dec 29, 2007
Messages
147
Location
Beloit, Kansas
Hi guys, looking for some ideas on rear suspension. I am wanting to run a rear buggy spring with a short rear frame section. Which is going to limit the distance from the diff to the frame kickup. I am also going to run an explorer 8.8 rear axle, this axles center section is offset 2 7/8". Which makes it harder to run a triangulated four link. What I'm looking for is some suggestions as to what works and what doesnt. Short link four bar unit, triangulated 4 bar, ladder bar, radius rods? Trying to keep this on the cheap but want a safe and dependable driver. I have searched for days and have found a few examples but havent really found any pros and cons of different examples. I would like to end up with somthing like Donsrods T, but not sure about the strength of the rear radius rods.

Thanks for your time.
 
Why does an offset pumpkin make it difficult to run a 4-link? Your link bars should be wide on the axle anyways.
5282008113923PM64461.jpg

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I may be confused but wouldn't the lowers be in tension under acceleration and the uppers in compression. I'm not trying to start anything it just makes me wonder if I should reinforce MY uppers a little more.

Sean
 
Keep in mind that ladder bars lift the car under acceleration and factory Mopars used a pinion snubber on their drag cars. That means the axle housing is trying to rotate the pinion up, which puts the top bars in tension under acceleration. Right, eh?
 
MMMMMMmmmm.:eek:

I'm backwards, I hope mine are strong enough:D. They're the mounts that came with the kit so I'm sure they're okay, but I just like to beef things up so I never have to think about it again.

Sorry to jack the thread.

Sean
 
The crossmember is thick tube, to prevent deflection. The upper bars will pull on it, while the lower bars are pushing, but either way there is stress on the crossmember. There is more force in the lower bars however. In a car with higher horsepower I support the crossmember to another point on the frame to stiffen it up. I didn't feel it necessary on a 45 HP vehicle. :p I posted a picture below of a truck pushing more horsepower, with more triangulation and support for the upper bars.


Thats a good looking setup. Most of the time you see the upper bars opposite yours. Thanks for the reply.

Yes, generally you do. "Technically" (and I use the term loosely) that is not the correct way to set up a 4-link. In theory the bars should be wide on the axle, for more support, and to eliminate or reduce torque steer. Especially on higher horsepower cars. They also are supposed to be wide on the axle, and narrow on the frame so that the roll center of the vehicle is located on the frame. When it is located on the frame, the roll center stays in the same place in relation to the vehicle. So the vehicle will perform the same in every corner, at every speed. With the bars narrow on the axle, the roll center is located at the axle, and it moves with the suspension. This means it will perform differently depending on how the car is loaded, how the body is rolling, how the suspension is compressing, etc. Its not a big concern to some people, but I really like to drive my cars hard. With the bars wider on the axle, it also produces better roll steer characteristics, which also keeps the suspension very predictable in turns.

You can also triangulate the lower bars, which is known as a Satchell Link. This creates a much lower roll center. I like this setup, because most vehicles have a low roll center in the front, and lowering it in the back makes the car feel more balanced. Here is an example.
1292007101836PM4081.jpg


I plan on using this setup on my 30 Chevy. If you have a transverse front spring, your front roll center is very low, sometimes even at the ground. I want my car to feel as balanced as possible, and handle as well as ti can on straight axles. :D


Another thing you need to consider, is your instant center. This is the point where you link bars would intersect if they where extended out into space past their pivots. The "technical" way once again, is to find the vehicles center of gravity and put the IC there. This is kind of aggressive for a street driven car, and provides a lot of anti-squat, to the point that the rear of the vehicle will lift up (pushing tires down for more traction). I set my roll center on most vehicles around the bumper or grill area if its under 120" wheelbase, because it provides a pretty neutral easy to drive setup that is daily driver friendly. Here is a view from the side.
123200710655AM82551.jpg

1292007102431PM39951.jpg


You don't want your IC behind the axle. Your car will squat hard under acceleration. I like a vehicle that launches hard without lifting or lowering the rear end much at all.

Hope that helps a little bit. I'm glad to answer any other questions, and take criticism as well. I try to spread the word about 4-link geometry, because it seems to be something often overlooked.

-Edit- Pay no attention to the fruity colors. Not my pick, lol.
 
I really like your work, if nothing else it looks cool. I'm sure the handling is also great as you seem to have done a lot of research.

I used the calculators from that "earthlink" link that I posted above to try and figure out my suspension for zero anti-squat and went through some of the ideas you talked about. I guess the only way I can know if it worked is to drive it once I'm done, here's hoping.

Thanks for the info and pictures, I find this very interesting, I never knew how much science went into suspension.

Sean
 
I really like your work, if nothing else it looks cool. I'm sure the handling is also great as you seem to have done a lot of research.

I used the calculators from that "earthlink" link that I posted above to try and figure out my suspension for zero anti-squat and went through some of the ideas you talked about. I guess the only way I can know if it worked is to drive it once I'm done, here's hoping.

Thanks for the info and pictures, I find this very interesting, I never knew how much science went into suspension.

Sean

Thanks.

I feel that zero anti-squat is a bit neutral. I try to aim for a low number of positive anti-squat, which generally achieves the no dive launches. Somewhere around 15% is what I try to average. But every setup is different.
 

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