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 aluminum vs steel suspension?

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PostSubject: aluminum vs steel suspension?   Wed Jul 09, 2014 4:54 pm

so my old truck f--ked buick is kinda totaled but suspension parts have been swapped from a shop from my old 97 buick to my new 96 supercharged buick. I'm curious about how on paper are they different other than being steel vs aluminum and aluminum is said to be better. How much weight will I save? is the aluminum one a better ride? its really hard for me to tell because my 97 buick always had KYB struts installed since I had it but the super buick had sts sway bars installed unknown to my knowledge and I always thought that the super buick had less body roll because of its steel suspension. There are too many variables for me to really know though.

I'm interested in knowing though.. how much weight will I save and do the aluminum control arms handle better?
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PostSubject: Re: aluminum vs steel suspension?   Wed Jul 09, 2014 7:14 pm

Body roll isn't the result of control arms bending - or "deflection" in engineer talk. Roll is caused by weight reacting to cornering forces in a turn. What allows the body to roll, or sway over is the softness of the spring rates, smallish sway bars, the damping rates of the struts, and to an extent the soft bushings that hold everything together. Even the tires have an impact on roll. The softness of these suspension parts working together is called "compliance". High compliance (rubber) is softer and quieter. Low compliance (urethane) is stiffer and less comfortable. In some cases, metals are used in place of rubber or plastic bushings. This means extremely low compliance, much less body roll, and lots of noise/vibration/harshness (NVH).

As a rule, aluminum is 1/3 the weight of steel. But steel is stronger, so less can be used to achieve the same strength. Most of the time, a stamped steel or cast iron control arm will be heavier than the same part cast from aluminum. The lighter weight doesn't impact roll that much, but it does lower unsprung mass, which improves the handling of the car to be more agile and connected with the road.

Steel tubing can be a lot stronger and lighter than cast aluminum, but tube steel control arms are expensive because they need to be welded up by hand. Tube steel control arms are still considered among the best for race cars, but for production autos, cast aluminum is about as good as it gets. Also aluminum stands up to salt and moisture better than steel or iron over time - another reason you'll see it on better-built cars.

Btw, coil springs and sway bars are usually steel because of its springiness. There are some fancy sway bars with parts made of CNC aluminum, though. Very expensive. Also, many steel sway bars are hollow to reduce weight. By using a slightly larger diameter tube, they can be as strong as a solid bar and much lighter.

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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PostSubject: Re: aluminum vs steel suspension?   Fri Aug 01, 2014 9:16 am

Correct me if I'm wrong but isn't aluminum more rigid than say spring steel or non carbon steel?

And I'm really curious to how my buick reacts to the new suspension. I had my 97 buicks suspension put in by a shop into the 96 supercharged. they swapped the knuckles, the 12inch rotars, rear rotars, all new pads, calipers, full aluminum control arms, brand new poly bushings, my KYB G2 struts, the hubs and everything. They also replaced my water pump, engine belts, ac compressor and ac accessories (i might have to repalce blend doors), and I have STS swaybars. Basically other than the springs it's like a brand new suspension other than my coilsprings.

my car's been in the shop for 42 days so far lol but they had to custom order studs that were really hard to find for my wheels which should improve ride quality too.

I'm hoping it will handle like it's on rails and ride smooth lol.

I may end up going for an adjustable coilover kit, square low profile tires and lowering it a little.

Any idea how that setup would handle with a coilover, square profile tires and performance coilover lowered a couple inches?
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PostSubject: Re: aluminum vs steel suspension?   Sun Aug 03, 2014 11:25 am

Quote :
Correct me if I'm wrong but isn't aluminum more rigid than say spring steel or non carbon steel?

When you say 'more rigid', I think you mean stiffer, or more resistant to deformation (bending). Steel has a much higher stiffness - more than double that of aluminum, but it's also heavier so less is used. Sure, there are exceptions like spring steel, but engineers know to choose the right materials for the application. They wouldn't use a spring or mild steel for a control arm unless it tested well for the application.

The more important thing to realize is that compared to the rigid parts of the suspension, the springs, torsion bars, dampers and bushings are far more compliant (flexible). These are the parts that move, twist, and pivot under load, enabling the car to absorb shock, hug a corner, and resist diving and squatting.

All of that work you mention, swapping the '97 suspension to the '96 will make a difference, but not because of material stiffness - probably weight and suspension geometry will have a greater impact. The aluminum arms are lighter, and that's unsprung weight (mass that doesn't move with the chassis) that should make the car quicker to react over bumps and around corners. However, the 12" brake rotors are heavier, so you gain back a few lbs. Now you can see why GM decided to use aluminum for the '97-up models.

Phrases like "corners on rails" and "smooth ride" can mean different things. Those poly bushings are stiffer and offer less deflection compared to rubber. This will give a more secure feeling turning corners and you will feel the road more, but the ride won't feel as smooth and soft as OEM rubber, which isolates better from NVH (noise/vibration/harshness).

I agree a different set of wheels can impact your ride quality and handling immensely, but the effect depends on the weight of the wheels, the tire profile, width, etc. Swapping to a coil-over spring set will offer even more change to the ride - probably harsher, less smooth depending on the spring rate. What you have right now is a combination of about a dozen variables that are all going to change, so you can't know exactly what's doing what. We can guess on things, but the only way to know which changes are being caused by what parts is to change one thing at a time, test, record. That's what a lot of guys do at the track for "test & tune" days. You don't see them changing out an entire suspension overnight. You see them changing the rebound firmness setting +2% on a 4-way adjustable damper, then go out and test again.

I hope your new set-up is everything you are hoping for. Please let us know what you think when you get a chance to drive it!

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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PostSubject: Re: aluminum vs steel suspension?   Sun Aug 03, 2014 5:21 pm

I guess maybe I was looking at the shape of the control arms difference. The aluminum ones are thicker and more shaped like a bone would be but the steel ones are thinner and flatter for obvious reasons. I was also thinking that if it were stamped out with that thinness, in order to really be rigid, they'd also have to temper the steel properly? I can't see stamped steel being very rigid unless they were tempered afterwords.

You have a really good point about a lot of changes. I think I need to get to know my car inside and out all over again before I decide on any suspension changes but I do think it's really great now. I'll be taking a thousand mile trip to michigan soon as well to visit my dad's family and that's a perfect opportunity in my mind.

I'll update more later on my suspension thoughts, but it's kinda cool to appreciate the car in a whole new way.
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