3-link or 4-link rear?

...This is the same suspension I had on the the rear of my tricked out spridget. Nice low roll center & never picked up a wheel.

Kendall

Kendall:

Do you have any photos of this suspension on your spridget? I'm doing a Miata-engined midget, and I'm currently going through the same struggles as Keith: what type of rear suspension. Any pics are well-appreciated.

--Thanks, Chris

Although not often seen, a Watt's linkage can also be set up so that the bellcrank is mounted to the chassis instead of to the axle, with the lateral links attached to the ends of the axle instead of the chassis, one running parallel ahead of the axle, the other behind it. This works best when the bellcrank is laid flat (horizontal), and mounted above the axle. The bellcrank itself can be made U shaped to wrap around bulky axle items like the pumpkin. Since the bellcrank is not sprung, it can be made beefy enough to take the bending loads, along with suitably sized pivot bearings. The advantage is in packaging, with an added potential bonus of lower unsprung weight. Not always the right answer, but a handy trick when needed.

Lot's of interesting variations in Watt's links are possible. Check out what they did on the rear of the PT Cruiser, the bellcrank and links are asymetrical. One side is larger than the other, but the ratio of the bellcrank arm to link length is the same on both sides. The links themselves are not parallel, they angle upward from the bellcrank to the chassis:

http://www.chrysler.com/en/2009/pt_cruiser/performance/handling/

Carter Shore.

If you mounted a Watts bellcrank to the chassis, would that still keep the R/C at the center of the bellcrank? Meaning that the roll center would move in relation to the axle?

I have not done analysis, but seems like the RC would remain at the center of the bellcrank to me. Or perhaps at the intersection of the projection of the axes of the lateral links onto a vertical plane. Either way, the RC would be relatively static with respect to the chassis.

I considered such a setup for my Spitfire DeDion project. Packagng is a real bitch in that tiny space when you have decided there will be no chassis cutting.

Carter

Thanks to all the help and advice, I'm currently leaning towards a 3-link with Panhard behind the axle if I can package it. I'll look at the under-axle Watts setup, but I like the fact that I can make a 3-link / Panhard completely and utterly adjustable for roll steer, anti-squat and roll center. I have more faith in my chassis tuning ability than my ability to get it right on a sheet of paper

Keith;

Just for my own clarification, when you are talking about a 3-link, are you going to use three forward links + a lateral link (pan hard bar)?

--Thanks, Chris

An alternative is a torque arm with built in watts link instead of the third arm of a three-link.

See what Paul Bird did with his Mustang. He incorporated the watts into the third link. The topics are sort of long, but dig around in them for the rear suspension info.

http://forums.corner-carvers.com/showthread.php?t=30257

http://forums.corral.net/forums/showthread.php?t=660756

chrisf wrote: Keith; Just for my own clarification, when you are talking about a 3-link, are you going to use three forward links + a lateral link (pan hard bar)? --Thanks, Chris

Yes, a three-link really has four. Unless it has a Watts, in which case you might say it has five.

And a four actually has five, unless two of the four are angled in which case it has four.

3-link plus panhard (or watts) FTW. check out speedway motors for all sorts of cool devices to decouple the acceleration versus braking reactions through the upper link.