Watts link bar lengths?

[JD'sTT55]

I've done some searches and haven't found any help to figure out how long my bars for my watts link need to be. What I have in process is a 3 link with coilovers behind a 12 bolt axle. I am planning on 5" of suspension travel. My 2 options for the bars to attach to the axle their lengths would be approx 13" each mounting inside of the coilovers or 20" length the outside of the coilovers? Also the length for the center pivot arm. I had read some members had purchased their center pivot arm from Fay's for their custom builds. It looks like a nice piece.
Thanks in advance. Jeremy

[exwestracer]

It honestly does not matter that much with a watts link... 5" of total travel doesn't need much bar or rocker arm length. The limit to the length of the components is how far they can travel without pulling the rocker arm over-center. I'm assuming by your explanation that you are mounting the rocker arm to the chassis and the links to the axle? The key to getting it to work right is to place the link mounts the same vertical distance apart as the length of the rocker arm. The links do not have to be parallel or horizontal at ride height.

[GRNOVA]

I am running 16" eye to eye on my watts link. Fay's 2 universal kit

[JD'sTT55]

Yes I'm planning on mounting the rocker to the chassis and the links to the axle.

[exwestracer]

There is a lot of conflicting, confusing info out there about watts links. I ran one in the supermod in my sig line below for years and we modeled it to DEATH. Turns out it was as idiot-resistant as any suspension component I've ever dealt with. Most of them are also WAY overbuilt, as the loads are divided in half as compared to a Panhard bar. The only place you have a real load concentration is in the rocker arm pivot. If it's adequately braced you should be fine.

As I said earlier, the link lengths don't really matter, just make sure the rocker will never go over center.

[JD'sTT55]

Just to be clear can you explain what you mean by going over center? I would think it would be when the rocker gets close to horizontal when neutral would be resting at vertical. Or the limit of its travel

[JD'sTT55]

That is why I posted this question was to hopefully avoid making my bars to short and not having enough travel and causing it to "go over center"

[exwestracer]

Just to be clear can you explain what you mean by going over center? I would think it would be when the rocker gets close to horizontal when neutral would be resting at vertical. Or the limit of its travel

Pretty much. When the axle has moved far enough where the link bar and the rocker arm form a straight line, it is possible for continued motion to turn the rocker arm around backward, or "over center". In the picture below, we see that the blue and purple (rocker arm) lines are approaching that point. Very unlikely that you will have that problem with travel limited to 5".



Also, note the motion line of the rocker pivot (dashed line). This is an often misunderstood design flaw if the link ends are mounted at the same height.

[Bryce]

The watts links need to be parallel at some point in the suspension travel. It is easy to make them parallel and horizontal at ride height, assuming you have equal suspension travel up and down.

When I designed my watts link I used 14" arms and a 4" bell crank. This allowed me to have zero (less than .001") lateral translation for up to 6" of travel in one direction.

[exwestracer]

The watts links need to be parallel at some point in the suspension travel. It is easy to make them parallel and horizontal at ride height, assuming you have equal suspension travel up and down.

When I designed my watts link I used 14" arms and a 4" bell crank. This allowed me to have zero (less than .001") lateral translation for up to 6" of travel in one direction.

JD, there you have it... your 13" bars should be fine. Bryce, was that 4" link to link, or 4" link to center pivot (8" total)?

[Bryce]

4" link to link.

[JD'sTT55]

Thanks all for your input.