I asked this Q in the other thread but it was kinda lost and off the original topic.

If Smart Struts improve camber control so well and therefore supposedly provide better suspension performance by simply locating the inboard mounting points a bit lower, why didn't GM do this in the first place?

Discuss.

 

The stock geometry was fine for bias-ply tires with 6" sidewalls. The stock geometry helped compensate for the old tires rolling over at speed in the corners. New tires (especially those with shorter sidewalls have MUCH stiffer construction and don't require as much camber change to maintain proper contact with the road during cornering.

 

Your question about "if it's wrong why did GM design it that way?" is a good one and appropriate one. But GM doesn't always design things right. The engineers are not gods but humans. The design process is often constrained by many things including the corporate bean counters, though I don't think that is the case regarding your question. Design is always a compromise and design objectives can vary depending on the type of performance your seeking. Suspension geometery is complicated and involves many compromises. I don't pretend to be an expert in this area but I have learned a little over the years.

I don't know what GM’s design objectives were but this suspension was designed back in the early 60's. Knowledge of suspension systems has progressed since those times. The front suspension has the opposite problem from the rear i.e. not enough camber gain.

The smart strut lowers the inboard strut rod connection about 1 inch. This lowers the instant swing arm center and roll center. So what? Well yes it improves (diminishes) camber gain. There are also other positive affects. Herb Adams notes in his book "Chassis Engineering" page 75 that the stock C3 Corvette rear suspension as a tendency to "jack". This means the outboard side of the car tends to rise relative to the wheel/tire instead of compressing during cornering. This puts the wheel/tire in a positive camber situation which in turn causes a serious loss of traction. This happens because of the high roll center and instant swing arm center.

 

Megawatt,
Very good explanation, but I have a question. The Smart Struts appear to have the cam bolt as well as the threaded rod ends at each end of the strut. One would be inclined to think that the threaded rod ends alone would be enough to adjust the camber settings. Is there something I'm missing? The reason I want to know is that I was planning to build some of my own with threaded ends for adjustment and do away with the cam bolt, as by rotating it, the angle of the strut (relative to the half shaft) changes as well as the "length."
Also, the standard exhaust pipes come out under the struts and both pipes have "dimples" in them from hitting the struts. Putting struts with a lower mounting point will only exacerbate the problem, so the exhaust pipes would have to be lowered or moved in between the inner strut mounting points to provide adequate clearance.

It tends to prove the old adage that you can't improve/modify one part of a car without affecting another.

Just my two cents worth.

Regard from Down Under

aussiejohn

 

John,

I am doing just that. I am moving my exhaust closer together in the centre. I have ordered new sections of pipe to do that. Once I get my pipes sorted then I am installing my Smart Strut bracket.

Cheers,

Pete
Another Aussie a long way from Home!

 

I just bought a set about a week ago over in the used parts for sale section. I have been wanting a set just for the ease of adjustments.

 

Yes there is a vertical slot in the smart strut and if your using rod ends that adjust by turing the sleeve then you don't need the adjustment cam. I pitched mine. I refered to the information on the John Giovani 6 link to see where he located his in board lower strut end. It's about an inch lower. Generally the strut is parallel to the halft shaft.

Yes changing one part of the car can have an impact on other areas. I also had an exhaust interference. Made some adjustments to mine. What worked for me may not work for you.

 

You use both the cam bolt and the adjustable lenght rods to adjust camber. ...and no I'm not crazy. The adjustable rods allow you to set the static camber which is the normal spec. The cam bolts allow you to adjust dynamic camber (i.e. the amount the camber changes with rebound/compression). I have my static camber set at 1/2* NEG camber and an additional 1/4* of NEG camber per inch of compression for the dynamic camber. For drag racing, you wouldn't want additional camber when you launch so that you maintain the maximum contact patch when the rear suspension is under full load. In that case, you would want 0 dynamic camber.

 

Yes of course you can use the cam to move the inboard
strut vertical position and customize the camber curve for what ever particular performance needs you have. I didn't really feel the need because I don't drag race and I don't autocross or track race. I seldom drive my car more than 7 tenths. However I can still make the adjustment by cutting a rectangular washer with the hole drilled in the right location for what ever vertical position I want. I don't trust the cam adjustment thingee. I have had them come lose and my camber go way out of wack.

 

Well, that's kind of like asking "If electronic fuel injection and magnetic liquid shocks are so good, why didn't GM do this in the first place?

 

I think Chev needed to factor in body roll. Keeping the lever arm effect minimized at the diff avoids excessive camber changes when the body leans on a hard turn.

 

Not to try to change the direction of this topic but we need to understand that the engineers at GM did not produce the best car they could have. First, look at the rad, slanting it the way they did makes it almost impossible to get air to flow thru it naturally, even at speed. The air current will do everything possible to flow around that slanted rad than thru it--the ones who designed the body caused the problem and they did the best they could under the circumstances. Then take the steering. I was driving british sports cars years earlier with rack and pinion steering and my 79 vette doesn't have it. This is something that could have been designed into the C3's but wasn't. Dollars and compromises between the different design teams caused the problems that we, as owners, are correcting as we go and when we can. Just because a bunch of engineers created something doesn't make it the only way it should be done or the best way! And that is my .02 cents.

Bernie

 

but the IRS was Zora's baby. it is known that the front suspension was a comprise, but the design of rear was wide open.



ever see an F1 radiator? all you need is a ducted pressure chamber, not direct exposure to the airstream. heck, the opening area does not need to be that big provided it has a shroud.

 

not really. no rocket science required, nor did they require computers or modern manufacturing processes. engineers had ideal suspension geometry pretty much nailed down by the 60s. tire technology may have been the significant limitation at the time though.

 

If they really knew about the best design at the time, it was probably a financial compromise.