Aluminum Cradle

[Dan]

Any chance the cradle could be built with the front cross member moved further forward an inch or two to give more room for mounting larger engines like the LS4 and for most engine swaps the humps for the exhaust would not be needed unless they are following the stock route or running duals.
Also any idea on a cost for an 88 aluminum cradle. Thanks Dan

[aaron88]

Dan;

It's a custom cradle so anything can be moved.  The only thing set is the mounting locations, standard with a bushing delete.  Also I have not recorded the stock 84-87 control arm mounts because I had not anticipated ever replicating the rear bump-steer.

The cradle I'm making for my car also does not have the exhaust humps like this one does.

This layout shows all ball joints but I could easily make a change for rubber or polly bushings.  Although if someone was to do that they might as well just use the 88 rear instead.  Also notable is that I'm using front transmission mounts instead of the rear.  But for my cradle I'm using two cylindrical bushings to mount the transmission.

So everything here works together, and won't work with stock rear suspension.  So the setup comes with: Cradle, Control arms and Knuckle (almost any bearing or breaking system setup you want).

Aluminum or steel cradle, steel control arms, and knuckles, it's about $4500.  Give or take depending on options.  Notably it's designed to work with 250-275lb/in 2.5" ID springs.

At this point I'm not sure when I'm going to have the front end redesigned.  Almost the same as the 88 only with a faster camber gain.

Aaron

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[Fred]

Aluminum or steel cradle, steel control arms, and knuckles, it's about $4500.  Give or take depending on options.

 

I'm sure its worth that much, but I wasn't expecting it. I guess I'll have to save up my money... 

A couple of question though:

Aluminum or steel
-If it's the same price, nearly the same strength, what are the advantages of going with a steel craddle if it has more weight and it can rust?

Geometry
-Does this setup corrects all the geometry problem of the bump-steer and the camber adjustment problem?
-Would going with a wider track setup will affect (For good or worst) the geometry?
-What is the difference between this kit and the "Helm Motorsport Anti Bump Steer" kit? (I'm not an engineer so from my knowledge both of them looks the same)

Great Job Aaron! Your stuff is looking great! As usual... 
Fred

[aaron88]

Your questions are loaded but I will attempt to answer them.

In this application there is one major difference between the Aluminum and Steel that most people are not aware of.  Aluminum and mild steel have very close strengths but the metallurgy works very differently.  With steel; one simply uses as stronger filler rod to achieve higher than base metal weld strength.  With Aluminum; heating the base metal ruins the temper.  Depending on the alloy you don't get any of it back without an exact treatment process.  With 6061 alloys though you do get a good portion of the strength back over several weeks as the metal age hardens back to about 2/3 strength.  So in general to use aluminum in an application that gets welded, you double the thickness of the aluminum and still end up with weight savings (and anti-corrosion, etc...).  Or you re-quench and temper.

With aluminum you can have a stronger, lighter rust-free alloy.

With steel you have great flexing properties and weldability (You can change stuff and move stuff around without affecting the strength). 

The geometry is whatever you want it to be.  Any camber.  Track width is completely compensated for (however make note that I move the knuckle meaning longer axles).  Bump steer is delete.  You can have poly, ball joints or rod ends.

The Helm kit is a bit of a bad idea.  It doesn't delete the bump steer, and it requires a lot of maintenance.  Every time an end gets changed, also requires a re-alignment.  A lot of people that get them end up removing them.  There is only so much you can do without changing the cradle mounts and the knuckle.

I'll post some pics of additional design options in a week or so.

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[Fred]

I don't quite understand why the helm kit it is such a bad idea. 

I am completely awared that it is not the ultimate solution to correct the problem, but isn't it an improvement from the stock attachement with the tie-rod attached from the knuckle to the craddle?

Fred

[aaron88]

There is no doubt that it is an improvement over stock as the bump steer is greatly reduced.  But it's also a high maintenance item.  If you replace the rod ends in that kit with rebuildable ones you should be able to avoid the re-alignment issue.  How many kilometers do you plan on doing per year?  Typical rod ends are only good for about 10 000km. 

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[aaron88]

Here is another design I'm working with and will most likely build very soon.  Poly universal pivot bushings.



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[Fred]

Whats the geometry difference over the other design you have? 

Just wondering, would this one be compatible with a stock cradle? Again, I'm not an engineer but it really looks like the bump steer kit.

In any ways, great job as usual!

Fred

[aaron88]

Both designs I'm using have almost the same geometry but different advantages and disadvantages.  For example.  This design can be altered to fit on an existing cradle.  Also the outer polyurethane can be exchanged for spherical bearings for a tighter rear end.  It's also possible to have the spherical bearings interchangeable with the poly.  That way if you have a track day you can just change them out without having to worry about the alignment.

One of the problems with the AMS bump steer is that it's making a correction to a control arm that is already tilted off the camber axis.  That's why the suspension can't move without affecting steer.  That on top of the flex and wear issues already described.

Once I have a working prototype then I'll be able properly identify the real world advantage.  Anything before that is still theoretical.

Aaron

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