What do you guys think of this bumpsteer fix I came up with for the pre 88?
I drew it up quick in solid works, I'm not sure how thick the metal piece would have to be and you would have to grind a new notch in the rod part of the balljoint to fit the plate in between it and the knuckle, but this would allow you to use the stock A arm and attach the tierod at the same level as the A arm and have it be the same length. You would have to mount the tie rod next to the A arm on the cradle. This would be easy to make and cheap too and fully get rid of the rear bumpsteer. It would also be way lighter than the held system.
Also it probably doesn't even need all the material I put on there. Nothing is actual dimensions, When I have the chance when I go home I will measure everything out. the tie rod could also be attached right to the A arm if a bracket was welded on. If a tri link system like on the 88 was desired so that the suspension toes in when compressed or when drooping, then the metal piece on the bottom could just be extended to the left side of the knuckle and another link could be attached there and go to the frame which would just aid the bushings during torque steering. And, it would be an improvement over the 88 because the link being attached underneath the knuckle causes the wheel to gain positive camber when turning hard, so being attached at the same level as the A arm would be ideal. I am going to do this to my own car when I can, what do you guys think?
Do you guys think any more bracing would need to be added? like a triangular member perpendicular to both existing members for added stiffness?
And here is what I mean with the balljoint, the bit cut away on the right is the original slot and the slot to the right is the slot that would have to be made however far up from the old slot that the metal piece is thick. Then it would have to be spun around to the other side (obviously)
[This message has been edited by zkhennings (edited 01-31-2012).]
Dont modify ball joints, replacements are cheap pieces of crap, and when one fails on the road, you don't want to modify a new one, I would trim the upright down. But to add, I think the lower plate is a little thin where it attaches to the knuckle, the whole structure reduces to a small cross section there, and your bending moment would be highest there.
trim the upright? if I did that I would want to weld the plate to the bottom of the upright to make up for the lost material, is the upright weldable? and If you think that it will be ~.25 thick steel then I dont think that it will be much of an issue because if you think about how the tierod end will only apply force parallel to the surface of the plate, so a torque will be applied around the original attachment of the tierod end and then the steel oposing that torque is at least 1 inch wide which translates to one inch thick. and I think that the hole where the tie rod end used to attach will be what takes care of most of the bending forces in the direction that the steel is weak
[This message has been edited by zkhennings (edited 02-01-2012).]
Nice. Have you checked wheel clearance (will that work with 15s)? And of course you have tubes to go between the brackets where the long bolt goes... ~ Paul aka "Tha Driver"
Nice. Have you checked wheel clearance (will that work with 15s)? And of course you have tubes to go between the brackets where the long bolt goes... ~ Paul aka "Tha Driver"
Here are the pics from a test fit to a 16x7 wheel. There is a chance it could clear a stock wheel, Once I have it tacked together, I can pull out a stock wheel and test it.
The sleeve for the long bolt has been on order, just not here yet. There is also 1 more part to make that will bolt to the backside of the trailing link attachment. Like I said "Almost" done.
[This message has been edited by fieroguru (edited 02-05-2012).]
I checked last night and with the reinforcing braces coming in from the back side, it will not clear a 14, 15 or 16" wheel. To clear these wheels, the extension to the trailing link would need to be cantilevered beyond the stock location with the side bracing coming in directly across from the bolts (vs. being angled to support the extended end directly). However, it would probably require a thicker piece than the 3/8" that I am using and there still might not be room for the head of the bolt.
You need to run 18's on the 88 to clear the top of the upright/strut mount anyway, so my main priority was to design them to clear some deep 18 (which is also why the trailing link attachment is shifted inboard 3/8" and still might get a small spacer in the 1/2" - 3/4" range to help the wheel clear the trailing link
Here is a 17" wheel - notice that the strut mounting section restricts the backspacing of the wheel:
Here is an 18" - where the wheel can cross over the top of the strut mounting allowing for an extra inch of backspacing:
Cool. Can you play around with it and see if you can somehow fit an upper A-Arm in the back?
Upper a-arm in the rear really is of no interest to me. There is only about 4 1/2" between the frame rail and strut bolts, and that is before I pull the strut in another inch to maximize the wheel size under a stock bodied fiero. That would leave the upper a-arm about 3 1/2" in length, or I would have to hack into the frame rail...
Originally posted by Will: This looks like it's only about 1/4 of interference, but would probably reduce max possible wheel width by 1/2" to assure adequate clearance.
"Just" build a bent/cantilevered trailing arm.
I have a Percy's Wheel-Rite also.
The clearance to the trailing link will be one of the easier things to "fix" The Percy's tool is pretty handy. Been thinking about making one out of steel so it is more precise.
I think this is great exploratory work fieroguru, but I would like to point out what appears to me to be a weakness. Perhaps it's only an illusion given the angles of the photos, but the area pointed out in the picture below seems to be quite small in cross section. All of the accelerative and braking forces are going to be transmitted from the wheel to the lower of the two holes in your bracket where the trailing link is now attached. This is going to create a moment about the upper hole in your bracket that is now used to attach the bottom of your bracket to the old trailing link hole in the knuckle. The only thing that appears to counter this moment is this small area pointed out in the photo. It seems to me that the area pointed out in the photo will bend as the trailing link tries to pivot the piece of steel that it's mounted to, about the upper hole. (I did my best to explain it, but I know it may not be clear.)
That area would be a weakness if that was the only attachment. The other side of the trailing link extension is welded along the full length (on both sides) and the backing plate is also there to help spread the loads and act as a reinforcement.
The other factor at play is the side with the notch, is in a plane about 3/4" from the centerline between the two trailing link bolts, so it will not be very effective in resisting the acceleration loads that will want to rotate the 3/8" piece backwards. The plate on the other side angles back and attaches to the upright in a plane that is about 3 3/8" from the centerline between the two trailing link bolt, so it is much better suited to resist the acceleration loads. The backing plate also ties into this rear plate to help spread the loads. The only reason I put the front plate on, was to help stabilize the extended portion of the 3/8" plate and to keep the lower edge from twisting since the trailing link is cantilevered off to the side.
[This message has been edited by fieroguru (edited 02-09-2012).]
Here are some quick mockups. I did shim the wheel about 3/8" outboard to clear the new lateral link bracket on a 16" wheel.
With 6 1/2" between cradle and floor (1/4" higher than stock ride height specified in Bloozberry's drawings) or 28" to center of wheel well opening:
Stock (lateral links are almost level):
With fieroguru lateral link relocation (lateral links angle down, will kick out the bottom of the tire for positive camber gain under compression):
With 5" between cradle and floor (1 1/4" lower than stock ride height) or 26.5" to center of wheel well opening: Stock (lateral links already pointing up to the wheels) With fieroguru lateral link relocation (lateral links close to level again - restores to stock suspension geometry with 1 1/2" lowering):
With 3 1/2" between cradle and floor (2 3/4" lower than stock ride height) or 25.0" to center of wheel well opening:
Stock (significant negative camber gain... definitely not good)
With fieroguru lateral link relocation (less bad - pretty much the same as the stock suspension lowered 1 1/2"):
I am planning to start a separate thread specific to this lateral link relocation.
Umm... depends on your definition of "grip". The textbook definition of "grip" is the ratio of normal force to the lateral force that a tire can take. With that definition, the inside tire has the most grip.
However, because most of the car's weight is on the outside tires, they are responsible for the vast majority of the lateral force that makes the car turn.
Like austrianimport, i have been bitten hard by the "double wishbone rear suspension" bug. guru's huge contribution with the lowered pivots, is still sinking in, and blooze's magnificant draftings have me scribbling at a furious rate. then i bumped into more lamborghini pictures . . .
my drawings stink, so . . .
please let me know if the geometry is as good as i think it might be, and where i really screwed things up.
it starts with guru's lowered pivots bracket, but the front pivot gets changed to a ball joint. the trainling link pivot on the bottom of the knuckle is eliminated and instead the trailing link gets fused to the forward lateral link very near the joint at the knuckle. similar to this drawing, but only involving the forward pivot/link, and the forward link's mount. Originally posted by aaron88
the forward pivot would be kept at ~4.5" (or more) higher than the others to maintain anti-squat, and continue to use rubber. the rear link stays the same, and is soley used to set toe. i would prefer to use tie rod ends where the heims are being used. i think they will last 10x longer, cost the same, and still be rigid.
next we construct an adapter for the top of the knuckle similar the the adapter on the bottom (using the strut bolt holes). this adapter places a pivot ~2" outboad of the knuckle/strut bolts. it provides a place to mount a triangular arm just like the lower one. it's forward mount would also be ~4.5" higher to maintain anti-squat? and end up just about on the firewall. (also in rubber) it's outboard mount would be a ball joint as well (to take accel/decel forces) it's inboard mount would be a tie rod end, and as you know the real trick is where to mount it. using blooze's drawings (thanks again is not enough). i calculate that we can keep the arm parallel with the lower one. and give it a length 2/3 as long as the lower arm. is 2/3 length good? it is very close to the ratio/angles of a late model chevy pickup i was just looking at. this length places the pivot just inside the upper frame rail and partially through the top of the frame rail. i have drawn a braket for the top of the frame rail that includes reinforcemnt around the cuts, and a top half to the pocket cut out for the arm to pass through. there would be no need for a rear lateral link on the top ./?
rear scrub radius. i may be way off here, but it appears the stock rear scrub radius lands at about the inboard edge of the tire. (using the top of the strut as the upper pivot and the middle of the trailing link at the knuckle as the lower pivot.) i know the lateral links take up all the force, so it will not affect steering, but 400hp pushing 2500 pounds seems like a lot of "turning" force applied to the lateral links. this revised suspension uses upper knuckle adapter pivot for the upper scrub point, and the lower knuckle adapter pivot for the lower scrub point. the effect is to move the scrub radius very close to the middle of the tire. improvement?
i have this all laid out on the graph paper, and it looks good to me, but this might help a lot.
aventador underside arrow is pointing to the rear. (alot better than my drawings ehh!) it appears to me that the forward mount is raised significantly from the others. the rear link is similar to fiero. the front wishbone replaces the forward lateral link and the trailing link. here is a top view obscuring the rear link, but on the lower arm shows the front mount being higher, and notice the upper arm, different from the proposed design, but the its mounts are cut into the upper frame rail similar to what i had envisioned. more/larger pics here http://blogs.insideline.com...sion-walkaround.html
if you are still listening after the frame rail discussion, then lets move on to the other big hurdle to double wishbone (type) conversion . . . carring the weight. i would propose a cantilevered inboard coil over design. in the vacant spot left by removing the upper rear lateral link, use a member similar to the omitted link, but longer and with three pivots. the outboard pivot would be located on the upper knuckle bracket 4" behind the ball joint used for the upper control arm's outboard joint. the middle pivot is on top of the frame rail 5" behind the other frame rail pivot. and the inboard pivot would be in the engine compartment more or less straight up from the spot on the cradle where the lower rear lateral link attatches. the inboard pivot is used to attatch to a coil over shock. the body of the shock is vertical. mounted low on the cradle at this spot again . in this shot the shock would go on the right side of the picture, just behind the cv joint. (remember his bracket sits higher than normal) Originally posted by bse53:
the shock is right side up, has lower center of gravity, and has reduced unsprung weight. its length would be about 14", and only need ~3" travel. the height adjusters are easy to get to as well. the cantilever link would be parralel with the upper control arms rear bar, until it hits the second pivot, then it would bend up towards the sky at a ~45* angle. this geometry should give increased spring rate with suspension compression. it would require roughly double spring rate because of the leverage. room? - there is plenty of room on the drivers side!, but on the pass side my alternator is in the way (3800 conversion.) i will gladly move it. i can see the middle pivot binding. it would require a sliding roller.?
after thinking last night, i wonder if the upper arm could carry all of the anti squat (acel) and the lower arm could be left level. this would give anti dive to the rear under braking?
so gentlemen, here is hours of my time. maybe number the critisisms so we can keep track of them all!?
[This message has been edited by ricreatr (edited 02-15-2012).]
I think If a double wishbone setup were done then either a bracket should be welded to the bottom of the strut hat to attach a coil over and then it could attach at the top of the knuckle via bracket.
And one question... say the car rolls 3 degrees in a turn... do you assume that the wheel on the inside has dropped the same amount as the wheel on the outside has compressed? ie they are at the same angle to the ground as the car is without any correction from the suspension?
one thing you should get rid of if you go to a upper A arm on an 88 suspension is the trailing arm .it just is not needed with an unequal length upper and lower A arm suspension . make the lower arm one piece with adjusting bits and problem solved .i think the aventador suspension is way more complicated than a fiero suspension needs to be .more weight , more horse power wider wheels and people that pay a lot of money for a car wont even accept tubular steel arms any more .even a vette has aluminum arms .
foooey! thought maybe i could twist your arm to give up what you have in your head. cant blame me for trying.
excellent point, a clean sheet design sounds great, but i wouldnt know how to start a project like that.
wftb, no trailing link sounds good to me, but i have talked to a couple people that like the fact that all of the forward motion of the car is in one link that can have rubber bushings (to help with wheel hop), and the laterals can have hard/precise joints for steering. me . . . i dont know.
i like aluminum . . .
[This message has been edited by ricreatr (edited 02-26-2012).]
The trailing arm bushings contribute to wheel hop because they allow torque to put load into the suspension in a direction that's not specifically damped.
this awsome thread had me thinking something simpler.
quote
Originally posted by 88lambo:
what about leaving the guru lower mod in place. using the big 18" wheels, and drilling/tapping the knuckle for a large heim such as the drawing?
the upper arm is 19cm (7 1/2") long, compared to the lower that is 31cm (12 1/4"). this keeps an upper to lower ratio of 62%. very close to the ratio of the front arms. i think i would use more suspension drop (2" total). the drop would make the lower arm higher than level at the knuckle. the upper arm gets steeper down.
is the geometry any good? i can see camber out on an inside tire, and a good bit of camber in on the outside tire.
is this enough info to run it through a program?
edit: should work with early cars too.
[This message has been edited by ricreatr (edited 03-01-2012).]
1. I'm not sure that you could get away with drilling and tapping the upper part of the knuckle since the threads of the heim joint would place the casting under tension. You would need to drill right through and use a hardened nut on the backside to avoid the problems of relying on the porous casting.
2. Where do you plan to attach the coilover/shock/strut to the arms/knuckle?
3. I understand that the geometry needs to be worked out first and foremost, but something you should keep in the back of your mind is that the lower frame rail is fabricated from two 18 ga stamped steel Z sections spot welded together along the flanges. You would want to consider the loads and how they will be applied to this type of frame especially after you've cut into it to fabricate your pocket mounts.
Edit to add:
4. the lower frame rail isn't parallel to the centerline of the car when viewed from the top as you've sketched. In fact, it's wider at the front and narrows towards the back considerably. There is approximately a 110 mm difference in the width between the LH and RH lower frame rails where you've proposed the forward and aft mounts for the upper control arm (dimensions taken from inside the engine bay). This might complicate locating your mounts.
[This message has been edited by Bloozberry (edited 03-01-2012).]
2. Where do you plan to attach the coilover/shock/strut to the arms/knuckle?
The way he's depicted it, the load on the rod end would be in compression rather than tension (at least on the outside wheel)
What's pictured is essentially the first avenue I considered for improving the Fiero rear suspension. The intelligent way to make that work is to fab a bracket (can be *VERY* simple--two plates with 4 holes each) that would be secured to the knuckle via the stock strut bolts. The bracket would connect to the outer pivot of the upper control arm outboard of the stock strut mount, while providing a location inboard of the stock knuckle to bolt the lower pivot of a coil over assembly. Obviously this would be used in conjunction with an upper coil over shock mount that would bolt into the stock strut tower bolts.
quote
3. I understand that the geometry needs to be worked out first and foremost, but something you should keep in the back of your mind is that the lower frame rail is fabricated from two 18 ga stamped steel Z sections spot welded together along the flanges. You would want to consider the loads and how they will be applied to this type of frame especially after you've cut into it to fabricate your pocket mounts.
Also keep in mind that a large fraction of the lateral suspension loads on the cradle go through the lower frame rails via the rear cradle mounts. As well there is a component of the vertical load of the suspension delivered to the lower rail by virtue of the fact that the strut tower is connected to the lower rail.
IOW, the lower rail is far from being tissue paper... However, to properly support an UCA, some insightful design of the pivot locations would be necessary in order to fully tie them in to the rail.
[This message has been edited by Will (edited 03-02-2012).]
Would you please slow down... you're making the rest of us look bad. 
I was starting to worry I was the only one.
