My Car So Far...

The best I was able to do was reccess the metal plate a few mm into the control arm and build up several big and very hot welds so that I had enough material, and so that I could wrap around the corners without burning through. Its not too pretty but Im confident they are strong. Plus Im going to grind them back anyways so they look nice

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Dr.Jeff said:
Steve, interesting about the rear control arm bushings. Indeed the dis-similar axis of the two pivots will bind with the arcing motion [who says we'll never use geometry in real life]. For that matter even with stock bushings there will be resistance (to a lesser extent) as the rubber is 'squished' off-axis with articulation. But certainly the less compliant poly will be more so. A spherical/Heim joint should allow better off-axis motion, but it would not be practical for the street.

Over the years I've found "solid" or "firm" (e.g. poly) bushings/mounts are not very livable for everyday driving. And they can cause other problems. However some rubber bushings have too much movement and don't last long. In those cases the rubber is too soft and not enough of it. A couple companies have developed firmer duro rubber replacements with more material for certain applications. One good example is the up-rated rubber upper strut mounts for the X. That is a good compromise but the availability of such items is very limited.
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One of the problems with poly bushings in applications similar to the X suspension, the binding will eventually crack the control arm mounts. Something you certainly DON"T want to happen.

I re-designed and fabricated all new suspension for my MR2 to put the geometry where I wanted it. In doing so I used tubular control arms and spherical bearings to eliminate the issues with bushings. The reduction in friction improved both ride and grip. Of course its a serious competition only car so I don't care about the NVH that results.
 
Ok now Im jealous Ive had a long love affair with MR2s and have always thought a 3sgte with an lsd trans was a more logical leap than the K series in an X. I mean mid for mid to me seems right.
Just a thought, not trying to start a debate

Anyways... moving on to the opposite side of the control arm. Installation and removal of the toe link needs consideration

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The 3SGTE is a great motor but somewhat heavy. I think its kinda odd that Honda is so popular but Toyota's engines are probably as good or better, yet are practically ignored by the generation that fell in love with Hondas and the Civic.

My MR2:

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Nice Aw. Is it the supercharged? I dont wanna turn this into a MR2 forum there are plenty of those but I likey
 
The trans side control arm was definitely the most complex and time consuming. The other 3 should all go much like this one and quicker too

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Damn, I will never ever be that good. Great to watch, I think I will just continue to toddle my unmodified X around the local autox’s on old hard tires to get the feel of that.

Thanks for posting that.
 
Nice work with the arms, Ben. I am going to be doing similar work on the Scorpion later. With respect to the arms mounting in different axis, does anybody know why Fiat/Lancia engineered the suspension that way? It's intentional of course but what's the intent?
 
motoTrooper said:
It's intentional of course but what's the intent?
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Without studying the design of the suspension I'm not sure, but perhaps it wasn't so much "intentional" as it was the path of least resistance. It might have been simpler and less costly to do it the way they did vs redesigning the chassis/drive-train/body/etc to do it differently. Seems that is very often the case in vehicle manufacturing. However the handling is good with the existing design so in fact there might be a good reason to do it the way they did. My point is, when it comes to the automotive industry, never assume there is a good reason for things. Or more to the point in this example, never assume the existing (factory) design is the best design. [Not to imply that you were assuming anything, just say'n]. Its a good question, hopefully someone that has studied the existing design will offer an explanation for why it is the way it is.
 
Paging Bernice! Bernice to the red arcane-historical-suspension-facts phone!

I am curious how the spherical joint arm attachments add NVH to the chassis, seems like it would be a great mod to the suspension. Steve, were your MR2 control arms also like the X1/9's with off axis attachment points too? So much to learn...
 
I wouldn’t use Heim joints on a street car, not anywhere where they are subject to dirt, road debris, snow, salt or other foreign matter. I experimented making end links and rear toe rods on my old Volvo AWD - even buying “high end” joints with Teflon seats (or whatever wear resistant seat they claimed to use, it’s been along time now) - they wore out in very short order in street use.
 
motoTrooper said:
Paging Bernice! Bernice to the red arcane-historical-suspension-facts phone!

I am curious how the spherical joint arm attachments add NVH to the chassis, seems like it would be a great mod to the suspension. Steve, were your MR2 control arms also like the X1/9's with off axis attachment points too? So much to learn...
Click to expand...


I am not Bernice but I can answer the question. All of the road impact harness, especially the high frequency stuff, is transmitted right through the spherical joint into the body. The OE type rubber bushing acts as an isolator and prevents the high frequency, low amplitude, vibration from being passed from the control arm to the body.

The MR2 front suspension is a virtual copy of the X1/9. The rear is similar but has a slightly different architecture which changes how the bushings work. The rear of the MR2 is very similar to how the front is laid out. It has a lower control arm and a radius arm (track rod). And the MR2's rear control arm bushings are actually perpendicular. And the radius arm attaches to the control arm with another busing. Not a great arrangement for a racecar.

For comparison, this is the OE rear lower control arm and radius arm off my MR2. It is fitted with Poly Bushings in this photo.

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This is the unit I designed and fabricated. The new parts provide for a revised roll center height and camber curve. This version has a development version of the upright mount.

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You can clearly see the difference in the architecture of the rear control arm from the X. Although the actual geometry is quite similar.

Here is the new front suspension, a virtual copy of the X1/9.

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And to answer the previous question about the reasoning for having the bushings on different axis': The OE style rubber bushings are not designed to work with axial loading. That is; a load transmitted on the same axis as the bushing centerline. If the bushings were on the same axis they would have to be very close to parallel with the centerline of the car and the bushing would see a tremendous axial load in braking and acceleration and it takes a very sophisticated (expensive) bushing to work in three axis'. With the bushings positioned as they are on the X's rear control arm Fiat could use a simple/common/cheap rubber tube type bushing because the loads are primarily perpendicular to the bushing's axis. So under braking and acceleration the loads are eaily managed.

It also means that as the bushing twists from compression, it tightens up and becomes stiffer and less likely to deflect under side load. In practice, when the car is cornering hard, the body rolls which compresses the outside suspension and twists the bushing. Because of the twist the bushing can't defect as much so the lateral load causes less actual deflection when cornering hard. Pretty ingenious right? :)
 
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