ericjon262 wrote:looking at a thread on old europe, I saw where a member built his own cradle, modeled after a 88 cradle. To me, this doesn't seem like a terrible undertaking, but it seemed like a pretty good bit of work for a piece that doesn't offer any benefit over a stock cradle. if you were to engineer a replacement cradle, what changes would you employ to improve handling? doesn't have to be based on a stock cradle either.
Thanks-
Eric
As Series8217 is demonstrating with his car, lowering the outer pivots or raising the inner pivots on an '88 cradle and making appropriate suspension tuning changes (springs, dampers, bars) along with the right tire stagger results in a car that handles very well.
As Guru points out and as Series has also demonstrated, the '88 suspension so modified still doesn't have a very good camber curve and needs to be stiffer than might otherwise be ideal.
A while back I came up with an SLA design based on the '88 rear links, with the strut removed and the body lowered 1 inch. It gave perfect camber performance and kept the roll center in an area the size of the palm of your hand through 5 degrees of body roll. The static roll center was about 5" above the ground, IIRC, so (if used with a front suspension with the roll center at ground level) it also had a roll axis inclination that compliments the Fiero's weight distribution. The knuckle end pieces consisted of plates that would bolt to the camber bolt holes on the knuckle. These plates would carry the ball joint between the rotor and camber bolts while providing the lower pickup for a coil-over shock inboard of the original strut location. This would also allow ~1" wider rear wheels than the strut suspension allowed. The UCA would need to have mounts cut and welded into the lower frame rail... although it *might* be doable with bolt-on mounts that only require holes to be drilled.
I've been thinking I should dust that design off and build UCA's like Series' fully adjustable units (
http://realfierotech.com/phpBB/viewtopi ... =3&t=17936 ) in order to finally make the SLA rear for '88 cars a reality.
At that point the only weakness is the 5x100 hub bearings and small pattern outer CV joints.
ericjon262 wrote:
how about the early model cradles? any real improvement to be made by adjusting control arm/tierod mounts? I know the '88 is considered the ultimate, but I'd bet a second look could come up with something better.
The early cradle is a different story...
By the time you move enough pivots and change enough components to fix the pro-squat, fix the bump steer, fix the roll center and fix the camber curve, it really is more practical to ditch the stock cradle and come up with a clean sheet design.
What I'm intending to do with The Mule is to build two crossmembers, one forward and one rear. The rear would bolt directly to the current cradle attachment points, but would have to be triangulated forward and aft along the frame rails. It would have a pair of powertrain mounts projecting foward, similar to the control arm or cradle bushings that Guru used to mount his LS4 powertrain. The crossmember powertrain mounts would be set up with corresponding brackets on the engine such that the engine could be dropped straight down without removing the crossmember.
This crossmember would interfere with any exhaust that works with the stock cradle, so installing it would mean building a new exhaust system. It also may not work with the common FWD exhaust setups like the LS4 has which merge both banks into a single outlet off the rear manifold.
The forward crossmember would actually fit in between the inboard mounting ears for the existing forward cradle mounts. I'm not sure if it would bolt to anything else to keep it from rotating, or if I could set the mounts up to pull/push straight through it so that it wouldn't need any rotational bracing.
The suspension would be a 5 link per side arrangement with upper and lower lateral links, a toe link and dual trailing arms.
For reasons related to symmetry, I would *like* to have the toe link in plane with the lower lateral link. If the height of the lower link is half the height of the upper link, then the loads on the lower link are twice the loads on the upper link. With the toe link and lower link in the same plane, each one sees half the "lower loads", meaning that all three links see the same loads.
However, packaging may dictate that the toe link is in plane with the upper link instead. The toe link should be in-plane with one of the lateral links rather than being in the middle between the uppers and lowers. It's typically easy to package this way and it completely eliminates bump steer.
Another thing I would *like* to do is use really long lateral links, similar to BMW's lateral links in the E36 and E46 rear suspensions. BMW placed the outer pivots directly above and below the axle centerline, but offset the inner pivots forward to clear the bulk of the diff. A Fiero could do something similar, but offset the inner pivots to the rear instead. I haven't done the modeling yet to know if that will package in the space available without cutting the frame rail.
EDIT: One thing I think will almost certainly be doable is to put the bottom shock mount at the bottom of the knuckle and the top shock mount on a weldment to the bottom or side of the frame rail. This should allow even more backspacing in the wheel, maybe even as much as 11.5 or 12" width. It might even be interesting to pull the hub flange inboard a bit to take advantage of common offsets in 18x11 and 18x12 wheels on the market (I think they're available for Mustangs), but then the left axle gets pretty short, especially if used with the F40 trans.[/edit]
The trailing arms could anchor to a component that would bolt into the front cradle mounts the way the Fiero cradle did. Because it's only anchored on that one bolt, this component may have to have a hefty mounting tab that reaches forward to be bolted to the floor pan--much like a subframe connector on a Mustang of F-body--or maybe upward to the firewall (or maybe both) in order to secure it against rotation. The mounting bolt would be installed from outboard, go through the trailing arm mount and thread into the forward crossmember.
The knuckle would be water jet cut from 1/2" (or thicker) aluminum plate, would have bolt-on mounts for the links and would accept a Corvette hub bearing (like the SKF units for the ZR1), use drum-in-hat parking brakes via ZR1 hats and two piece rotors. Rotors could be dimensional equivalents to C5 or C6 fronts or maybe even ZR1 rears if feeling spendy (and bought appropriate matching front units...)