By now you've heard many times about the revolutionary new coil spring suspension that Dodge engineers put in the back of the 2009 Dodge Ram 1500 pickup. You've also heard us rave about how much we like it, whether driving it around empty, towing, hauling or off-roading.
This suspension played no small part in the Ram's victory in our recent 4-way truck comparison test in which it defeated the other main players in the 1/2-ton truck market from Ford, Chevy and Toyota.
But we've never actually shown you that suspension...until now.
Dodge calls this "link-coil" rear suspension. The name fits because the solid live axle is located by 2 links per side (white) and the truck is supported by coil springs (black) instead of the usual leafs we see in other pickups.
Other manufacturers use the term "5-link" suspension, for reasons we shall see in a moment.
Did I just say other manufacturers? Isn't Dodge out in front of the curve, here? Well, yes and no.
Every full-size SUV on the market had this type of rear suspension at one time, before all of them (except notably the Tahoe/Yukon/Escalade and their long-wheelbase counterparts) eventually switched to fully independent suspension. The Chevy Avalanche and earlier Ford Exploer Sport used link-coil too, because those vehicles are more of an SUV with a portion of the roof cut off than a full-blown pickup truck.
Chevy tried coil springs on the back of their two-wheel drive 1/2-ton trucks in the 60's, but that was a twin trailing arm design. GMC trucks never adopted it, and Chevy later dropped the idea, but the configuration lives on in NASCAR stock cars and numerous hot rods under the name "truck arm" rear suspension.
Dodge is unique here because they've gone ahead and put 5-link rear suspension on their bread-and-butter 1500-series pickups, 4x2 and 4x4 alike. This type of coil spring suspension is actually a boon off-road because it provides better articulation over obstacles than leaf springs. And coil springs are more than up to the task of handling the loads in the back of a 1/2-ton truck such as this.
But the real payoff here is superior unladen ride and improved cornering stability, as coils have less unsprung mass and they have none of the stick-slip friction found between the rubbing leaves of leaf springs.
Dodge retains leaf springs for it's new 2500 and 3500-series trucks because it is easier to progressively "stage" the spring stiffness of leaf springs when payload capacities get extremely high, as they do in these heavy-duty pickup trucks. Besides, these HD versions don't need to be as concerned about unladen ride comfort because they are more highly-focused as work trucks.
Truck-arm suspension uses one massive trailing arm per side, and that means the nose angle of the rear differential (yellow) changes in an unfavorable way. The only way around the problem is to make the truck arms as long as the driveshaft, but that eats up a lot of space and adds a bunch of weight. Space was less of a problem in the 60's when truck gas tanks were placed outside the frame rails, but modern safety practices put those tanks between the rails, leaving no room for so-called truck arms.
But here a pair of shorter links (white) are used on each side. The space between them prevents axle windup and their differing lengths controls the nose angle of the differential (yellow) in such a way that the u-joints in the driveshaft run much more smoothly and with less vibration through their entire range of motion, something that can't be said for leaf springs or truck arms. As a bonus, the links nest up against the natural curve of the frame rails, so they also take up less space.
Leaf spring suspensions attempt to combat windup by using staggered shock absorbers--one leans forward and the other leans back. But the Dodge setup doesn't need staggered shocks, so they both lean forward like the one shown above.
The coil spring (white) sits atop the axle and extends alongside the frame rail so it can be as long as possible. A urethane bump-stop (yellow) sits just inboard.
We've seen the four trailing links (two per side), and this lateral link brings the total up to five. Called a Panhard rod, it attaches to a bracket on the axle on the left side (yellow) and the frame on the right side (white). The panhard rod is the component that carries all of the lateral loads, and that's why these brackets are so massive.
Leaf spring trucks don't have any such lateral link, so the leaf ends and shackles have to hold fast against lateral loads--a job they're not particularly good at. That's one reason why a leaf- spring truck can sometimes seem jumpy or jittery when encountering rough surfaces.
A rear stabilizer bar is another thing you won't see on a leaf-sprung truck, primarily because the leaves themselves and the staggered shocks use up the available space. But 5-link suspension provides plenty of room for a rear stabilizer bar, and all Dodge Ram 1500 trucks have one.
This application is about as exposed and easy to see as any you'll ever find, with the stabilizer bar (yellow) bolted to brackets on the axle housing and the end links (white) stretching up to meet fixed points on the frame.
Stab bar 101: As the frame & body rolls relative to the axle (ground), these links impart a twist on the bar, which generates a resistive torque that feeds back through the links. A larger bar will therefore generate more force and offer more resistance to body roll. But no such twist is generated if both wheels strike a bump at the same time and the bar pivots harmlessly in its bushings.
You might think that 4 trailing links, a lateral panhard rod and a stabilizer bar would make this setup weigh more than a simple pair of leaf springs. You'd be wrong. Dodge says this design weighs some 40 pounds less than the leaf spring design it replaced. That's because the leaf springs themselves are solid and HEAVY, whereas the five links seen here are simple hollow tubes.
Rear disc brakes with ventilated rotors are used on all Ram 1500 trucks.
Familiar single-piston (white) sliding calipers are used, but the parking brake is a mechanically-actuated (yellow) drum brake that acts upon a rotor with a drum-in-hat profile.
Up front, the 2009 Dodge Ram 1500 rides on double wishbone suspension with a high-mount upper arm.
The lower control arm (yellow) and the front knuckle (white) are made of aluminum.
The front brakes utilize two-piston sliding calipers and ventilated rotors.
As we've seen before, the upper control arm is angled to provide a fair amount of anti-dive geometry.
The coil-over spring/shock assembly (yellow) and the stabilizer bar link (black) attach at intervals along the lower control arm, meaning their motion ratios are something less than 1:1.
The routing and operation of the front stabilizer bar is nearly as easily to visualize as the rear bar.
Our Ram wears the optional 20" wheels with chrome facings. The tires are P275/60R20 Goodyear Wranglers and the mounted assemblies weigh 76.5 pounds apiece.
As you can see, these wheels measure 20-by-9 inches and they have a 19.05 mm offset. 19.05 mm? Are they serious? Yes they are, because 19.05 mm is exactly 3/4 inches.
The chrome facing is in reality an elaborate plastic wheel cover that is permanently fused to the aluminum alloy wheel beneath. I don't recommend these optional wheels if you plan to go off-road, because a) 20" wheels are not the best off-road choice because they lack sufficient sidewall and b) trailside rocks can easily flip up and create an ugly gouge in the flashy chrome cover. In fact this is precisely what happened to me while off-roading a new F-150 with a similar wheel treatment. And c) these chrome facings fall into that category of "fake chrome" that I hate. This type of plasti-chrome looks no more like real metal than the plastic chrome parts found in your typical Revell model car kit. This wheelmaking trend must die.
Dan Edmunds, Director of Vehicle Testing @ 13,650 miles
hybris says:
03:12 PM, 11/18/09
I will admit that given the fact that this a upper trim 4 door half ton the coil in back make sense.
BUT in anyother cab/trim type the ammount of sagging that occurs under load is unacceptable. How you guys can rave about this when loaded or towing IMHO really shows how little experience in the truck field you have.
I mean no offense just pointing something out.
heidis says:
03:21 PM, 11/18/09
I have to agree on the wheel chrome cladding thing. My Grand Cherokee has those and the fake-o chrome on the plastic disc part has been eroding away in the pockets of the wheel detail since the first year I had it. I was dismayed to see other brands following suit with this cladding technique. It's cheap and tacky. From here on out, I'm buying cars with painted or clear coated alloys or buying aftermarket replacements. This cladding stuff is just poor any way you look at it.
actualsize says:
03:29 PM, 11/18/09
I disagree. If this truck is properly loaded such that the payload, GVWR and rear GAWR are not exceeded, there is no sag problem. But one can't tow the max AND THEN fill the bed up to the max AND THEN put 5 people in the cab without exceeding one of these--on any truck. The weight of people in the cab is considered to be part of payload, as is the trailer tongue weight itself. If one ignores this and then adds a couple of motorcycles to the bed as well, then you'll exceed the payload, the GVWR, the rear GAWR or all of the above.
hybris says:
03:49 PM, 11/18/09
@actualsize
I never mentioned overloading the truck in anyway shape or form.
I'm talking about the amount of sag seen in some of the first posts for the Ram when towing in this case, since none of the editors have put over 500-750 lbs in the bed I can't say I have notice any sag in the pics but none the less I'd bet that the Ram would sag more than anyother pickup made simply because the coil-springs aren't made for anything more than moderate loads at best.
bodyblue says:
03:51 PM, 11/18/09
Great post as usual, Dan. Ram looks to be solidly engineered. Oh what about the promised post on the Rambox replacement?
bankerdanny says:
04:02 PM, 11/18/09
I have not heard about the fake chrome clad wheels before. I can't agree more that this is a trend that should die. Real chrome or polished wheels can be re-chromed or polished to repair scratches, but a plastic coated wheel would probably have to be replaced.
Sounds like planned obsolescence to me.
frazier500 says:
04:25 PM, 11/18/09
@ hyrbis
I think you just completely disregarded the comments made in the post you're referring to.
"More importantly, the amount of supposed sag had no effect on the truck's driving dynamics. Light front-end feel? Nope. Excessive or uncontrolled bounce over bumps? Nope (coil springs were not an issue here). Reduced braking force from lack of weight transfer to the front tires during braking? Not that I could tell. The Ram stopped right now whenever I needed it to."
DCuerpoJr says:
04:29 PM, 11/18/09
Thanks for the post Dan! Much appreciated.
I think the "link-coil" rear suspension on this 4-door Ram 1500 Laramie makes sense. With the bed as small as it is, especially with the RamBoxes narrowing it down even more, and the fact that this is the luxury model...I doubt an average owner will load the bed with more than 500-750 lbs.
It's too small to load up an ATV and probably too short to load up a dirt bike or motorcycle. And I doubt they'll haul stones or slabs of rock with concerns of scratching the bed. All those duties rest in a real workman's truck.
jkavanagh says:
05:28 PM, 11/18/09
hybris,
frazier500's quote summarizes the situation well.
Rear end sag, in the absence of any dynamic tradeoff, becomes strictly an aesthetic thing. That's pretty much the long and short of it.
hybris says:
05:37 PM, 11/18/09
@Frazier500 @jkavanagh
You may have legit points and since I don't have a 09 Ram to do tests on I will leave this train of thought alone for now.
bodyblue says:
06:43 PM, 11/18/09
The bed is not too short for a motorcycle if you use the bed extender.
vt8919 says:
08:31 PM, 11/18/09
My uncle would love to see this walkaround. He drives an 09' with the Big Horn package.
actualsize says:
09:13 PM, 11/18/09
@bodyblue: The RamBox replacement parts are in, but we have not yet taken it back in for the install. Stay tuned.
bimmerjay says:
12:55 AM, 11/19/09
What happened with the RamBoxes?
I like the idea of the coil suspension on the light duty truck - it makes sense. As for those wheels, horrid. Obviously the plasti-chrome is intended to keep the cost of the 20's as low as possible, because real chromed aluminum 20" wheels would probably cost thousands. Still, they're cheap and tacky. This truck needs a serious chromectomy.
rsholland says:
06:17 AM, 11/19/09
This Ram suspension is just a preliminary step before we actually see an IRS setup in a full-size 1/2-ton pickup truck. Many full-size truck-based SUVs already use that setup. Pickups are next. ...And of course, the naysayers will scream foul (as is the case here).
actualsize says:
06:38 AM, 11/19/09
@bimmerjay: One of the RamBox liners cracked inside from having a trailer hitch ball and mount--the part that plugs into the receiver--bounce around inside. This is a 100% legitimate and logical use for these storage compartments, in my opinion. The plastic that makes up the inner floor is supported by steel, but the end-walls and side-walls are pure plastic, and that's where it cracked. I think the material needs to be changed to something thicker and a little less brittle. I'll do a before and after post after it is repaired. Once it is fixed, we might cut some foam inserts to hold the hitch pieces in place--the type of restraints you'd see around camera lenses inside a pro camera case.
actualsize says:
06:44 AM, 11/19/09
@rsholland: Agreed. There is no reason why IRS can't work on a 1/2-ton pickup. Aside from customer acceptance, I think cost is the main obstacle. And the only full-size SUVs that have NOT gone that way are the GM offerings--and they suffer for it. Every other full-size ladder-frame SUV has IRS.
rsholland says:
06:49 AM, 11/19/09
Foam inserts in the Rambox sounds like an excellent solution. It should also reduce movement of said items as well as reduce noise.
Frankly I'm surprised the Rambox isn't coated with a 1/16" of rubber liner, which would also do the same thing—and would take up less space than a foam lining.
bumpy says:
09:03 AM, 11/19/09
Just a quick note- the sub-1-ton Chevy trucks used trailing arms and coil springs 1960-72, while GMCs used them 1960-62 and 67-72, with a leaf spring option in the latter period.
dg0472 says:
09:49 AM, 11/19/09
Thanks for clarifying that bumpy. I was pretty darned sure my (uncle's/)dad's(/brother's) 1972 GMC had rear coils.
chunky_azian says:
10:16 AM, 11/19/09
Ditching leave springs for links is great. Semis have been rolling around like that for a while. But I don't think pick up trucks should have IRS. Truck based full size SUVs are different; they are the new non-minivan minivan where ride quality matters. Trucks are meant to go off road and they need the articulation.
I'm all for IRS in cars, but trucks need a solid axle somewhere. Perhaps trucks should have a DeDion like the Smart or a twist beam setup similar to Suzuki. Either one of which would not have to carry the heavy differential as an unsprung weight and reduce damping requirements.
rsholland says:
10:48 AM, 11/19/09
chunky_azian
There are plenty of heavy-duty off-road trucks with IRS. Just look at what the military are using. Oshkosh, the maker of severe-duty trucks for the military, offers a number of trucks that have fully independent suspensions.
http://www.oshkoshdefense.com/defense/products~mtvr~home.cfm
Also of interest, the military is in the process of re-fitting a lot of their solid-axle trucks from Iraq to IFS/IRS for use in Afghanistan, because the IFS/IRS-equipped trucks work so much better in that rugged terrain.
As actualsize stated: It's merely a matter of customer acceptance, and not capability, that's the stumbling block here. Slowly but surely that will be overcome.
rsholland says:
11:00 AM, 11/19/09
Here's a link on the military trucks with the IFS/IRS suspension swap:
http://online.wsj.com/article/SB124450375989595981.html
actualsize says:
12:06 PM, 11/19/09
@bumpy: Thanks for clearing up that historical detail. My various sources were contradictory and dad never owned one of those.
rick8365 says:
07:43 PM, 11/19/09
I'm surprised at the thinking that went into the material used for the RamBoxes. I would think that they would have made them of a material similar to what bedliners are made of. It is very apparent in the photo of the broken one that it is that thin brittle type of plastic - strange decision IMO.
Thanks for another great walkaround, Dan. I have had many trucks, all with leafs, but seeing this design up close with your explanations.......I might be a convert in the making.
One question came to mind - I think I understand the angling of the front shocks but I don't understand why the rears are at such an angle. I would think at some point in being angled that their effectiveness would diminish or be comprimised. I have seen that shocks can be mounted horizontaly "off site" like in an open wheel car but of course there are always a series of links/levers connecting everything as if they were bolted directly to the axle and frame. With the Ram, the ends of each shock are bolted directly so I would think this angle would be somewhat counter productive. What is the purpose of such an angle here? Space considerations? And why not a coil over set up in the rear too? I would think that the truck arms and panhard rod would be handling all of the fore/aft/lateral axle location duties so that doesn't seem to be a reason for the degree of angle with the shocks.
bimmerjay says:
11:34 PM, 11/19/09
@actualsize,
Thanks Dan. Sounds like a poor design decision - you'd think based on their location in the bed they'd be made with a much more durable plastic.
threemopars says:
05:20 PM, 12/28/09
There are leaf sprung trucks out there with rear stabilizer bars, my 02 Dakota had one. My 2006 Dakota has one.
threemopars says:
05:25 PM, 12/28/09
@hybris
This question was posed to Dodge when the Ram was shown about ride height with a load on the back. Truth be told that when the truck was designed from the get-go, it was given a level ride height. The back end is not "jacked up" for lack of a better term, resulting in what appears to be significant sag under load....and thats what it is, an appearance. The rig handles heavy loads quite well.