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Page 20
3LINK SETUP

NEW

I believe you'll find the spreadsheet, at the bottom of this page, much more "user-friendly." I've attempted to anticipate matters such as body interference and have provided quick solutions.

The idea of a 3link, with its ability to provide equal rear tire loading on acceleration...regardless of driveshaft torque...and also provide no squat or rise, is tempting, but there are other matters to consider. Those of you who presently run 4links might get the idea that you can "try out" a 3link by merely removing the upper left link and rearranging the other three. FORGET ABOUT IT! A number of years ago, I was working with the tech editor of "Hot Rod" magazine on a 3link article. We found a racer who was willing to do exactly that. He removed the upper left link and set the other links as I directed. While testing on the street, there was a suspension failure. Fortunately, there was minimal body damage and noone was hurt. I had failed to make any stress calculations. Yes, even engineers...with all their "book larnin"..can make some very stupid mistakes! Many commercial 4links are "borderline" on link strength. Simply compare some of those "spaghetti" links with the links of a stock suspension. Feel free to use the applicable brackets from your 4link with Heims (though I prefer you'd use the rubber bushings from the front eyes of leaf springs), but be certain to use some "beefy" tubing.

Then, there's the matter of braking safety. Since the 3link provides equal rear tire loading during acceleration, it follows that, during braking, the rear tire loading is unequal. So, is this dangerous? I could point out, as I have in the past, that the C Type Jaguar, with a 3link suspension, won at LeMans, where braking performance is critical. This statement omits, however, some important information. If you're good enough to drive at LeMans, you know the value of NEVER locking up the wheels... especially the rear ones...during braking. With hydraulic brakes, the braking EFFORT is essentially all on the front wheels, but, if you are concerned about this matter, I would recommend a telescoping FOURTH link, in that upper left position, which will "bottom out" on braking and provide some stability in those panic stop conditions.

The offset of the upper link is measured, if a symmetrical weight distribution is assumed, from the center of the car. If the car is heavily weighted to one side, the car centerline should be biased accordingly.

Some of the numbers you input, such as those for wheelbase and axle ratio, will always be positive. With some, the positive sign direction is obvious, such as those described as "distance forward." For vertical distances, some assumptions are made. Vertical distance to the upper link from the axle centerline, for instance, is assumed positive with the pivot point above the axle centerline. Though the lower link pivot is typically below the axle centerline, the measurement is still considered positive. In those unusual instances when the lower link pivot is above the axle centerline, a negative sign is required. The signs output in ANSWERS are significant. A vertical position that is positive means a distance above the axle centerline; a negative number means below.

rear track=

wheelbase =

axle ratio =

effective rear tire radius =

center of gravity height =

lower link length =

upper link length =

upper link offset =

weight of rear axle assembly =

total weight =

axle centerline forward to
rear of upper link =

axle centerline vertically to
rear of upper link =

axle centerline forward to
rear of lower link =

axle centerline vertically to
rear of lower link =

ANSWERS:

axle centerline forward to
front of upper link =

axle centerline vertically to
front of upper link =

axle centerline forward to
front of lower link =

axle centerline vertically to
front of lower link =

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