Radius Arm Suspension - Mistake or A Move in the Right Direction?

M

Mr. Valvetrain

Engineer
Maybe I am just looking for an outlet to ***** about another change in the wrong direction (AAM for example) but the recent change to the basic design of the front suspension to a radius arm from a five link has me questioning the compotency of the engineers in Auburn Hills. How could this possibly be an improvement other than from a piece price and assembly cost savings for Chrysler? I understand when you are designing the next econobox to a price point you'd go away from a double wishbone to a much cheaper and clearly inferior MacPherson srut arrangement, becuase you are not concerned with details like geometry change throughout travel. However, I'd prefer my $70k truck have a bit more focus on function. I'd like to hear some commentary on this subject if anyone else has an opinion either for or against this new (to Dodge) design.

Thanks.
 
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There really isn't enough travel to matter much. I've seriously thought about changing mine to super duty style radius arms for the ride and simplicity.

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As said above the radius arms are there for ride quality. As far as proper geometry for all out offroading?! Probably not so much. Not in factory form anyhow. Also as stated above the amount of factory travel really isn't going to make a big difference as for performance whether control arms or radius, but the radius will help smooth the ride. Same reason they went with coils in the rear.

Now can a properly designed radius arm perform?! Absolutely! If you doubt that check out: http://www.carlisuspension.com/dodge-ram/components/6inchradiusarmsystem.html

Grant you that's a 6" lift but it's all the same in theory. It's still a long travel suspension that functions well (for a 7000+lb truck)


As far as your comment about AAM axles being a bad decision, I'm curious as to why you say that was a poor decision? They deliver more power to the ground due to less driveline loss and with the exception of bending the front axle, when the truck is driven HARD or jumped, or maybe even the lack of free spin hubs, I really don't see the change being a bad decision.

Like I said though, not trying to criticize, but rather merely curious as to why you said it.
 
Bull**** they drive like a truck. My 2011 ford rode better than my Infiniti. And why can't my truck ride like a Cadillac? I'm getting to old to put up with a harsh ride. I'm dropping some serious coin on my suspension to make it ride like a caddy.

And why the hate on the aam? You saying the dana was a better choice? Why?

I think folks forget sometimes that the manufacturers build for the masses and we aren't the masses.
 
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BgBlDodge said:
Bull**** they drive like a truck. My 2011 ford rode better than my Infiniti.
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Then you must have a phucked up infinity. No they don't ride like an old leaf spring truck, but there wasn't a significant difference in ride quality in the '08 ford I use for work and my '01 dodge. Plus the ford has the turning radius of a barge


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Then your ass must be numb because there was a HUGE difference in ride quality between my 01 dodge and my 2011 ford. And my 06 dodge. Guess we will just agree to disagree.
 
Surprising how what tires and at what pressure those tires are at..... I know when I bought mine off the lot the tires were a bit low on pressure, but the test drive was comfy....... figured out what pressure the tires were supposed to be at, set em there, and hello stone stiff ride. Bigger tires helped a lot, stockers were the worst.
 
mikmaze said:
Surprising how what tires and at what pressure those tires are at..... I know when I bought mine off the lot the tires were a bit low on pressure, but the test drive was comfy....... figured out what pressure the tires were supposed to be at, set em there, and hello stone stiff ride. Bigger tires helped a lot, stockers were the worst.
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The 08 I drive for work is on stock wheels and tires (275/65/18) and the dodge is on 285/65/18. Both aired to ~70psi, both ride like a truck. I haven't had a lot of seat time in my friend's 2011, but didn't blow my mind with the difference. I guess I don't have a sensitive, sore old ass that can pick up on minute differences in how a truck rides. Honestly I really don't care how it rides. If I want a soft, smooth ride I drive my car.



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In a perfect world, we'd all only perate on best practices. Keeping in mind I'm an engineer in Detroit, I could go on and on and on about engineering principles and test facts (that to some extent only impact theory and not so much pratical use of automobiles) to justlify why I dislike radius arm suspensions and AAM, the fact of the matter is that trucks are consumer products where cost, marketability, etc. all come into play. Engineering fudementals are only a foundation for all of that other hoopla. Look at the load bearing points on the AAM knuckles; 1 ball joint bears weight, the other "ball joint" (a king-pin really) is off axis and bears no load. Just a poor design on a fundemental level and a miss on "best practices". Yet, the switch to AMM was a big cost savings. Go figure. I don't expect to convince anyone here, just looking to provoke some conversation. And as you can tell by the wide variety of opinions in the replies, making a vehicle isn't as simple as focusing on one particular area.
 
A radius arm suspension won't ride any differently than a 3 or 4 link suspension that's setup with the same anti-squat, roll axis, ect. The difference in ride qualtiy comes from spring rates, bushing and isolator material and location, tires, shock valving/oil, ect. There are so many factors that play into how a suspension "rides". Performance wise: radius arms are a step up from leaf srings only. a 3 or 4 link suspension is dominant in every way besides maybe cost. If it rides rough, it's either not setup properly, the spring rate is too high or linear, the dampening/rebound of the shock isn't matched/tuned well, ect ect ect. This is all basic suspension design stuff, I'm shocked there's even an arguement about this....

That being said, a flat and long set of raduis arms with proper separation at the axle will ride and perform just fine for a street driven rig.
 
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