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Old 07-08-2014, 12:02 PM   #1
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K-2 VS K-3 Chassis

We've had discussions on this topic from time to time, so today, while waiting on my coach to be serviced I decided to do some on the ground checking. I went over to MHSRV down the street and crawled under a 2014 Cornerstone....with a "K-3 chassis". The main frame rails are 8x4x3/8 in. C-channel. The longitudinal rails under the basement floor are 3x1-1/2 in. sq. tubing with the TS/Entegra "Patented?" X-bracing amidships in basement and diagonals between the longitudinals below. Most of the main connections are bolted. Floor to bottom of main rail is 23 in.

The 2014 Essex has the same-sized 8x4x3/8 in. C-channel main rails, with 2x2" sq. tubing longitudinals under the floor. Primary connections are bolted, with diagonal angle irons extending out from main rails to minimize cantilevering of the flooring system. Floor to bottom of main rail measures 20-1/2 in.

The K-3 under a 2014 King Aire was quite different, utilizing a 6x3 in. sq, tubing as the "main" rail with 5x3 in. sq. tube longitudinal bottom rails. 2x3 in. cords extend down from top to bottom rails, forming a truss from front to rear on each side of the coach. Cross members between the rails are equally-dimensioned. All connections are welded....no bolting. Basement floor to bottom of top beam measured to be 24-1/2 in.

Of course, we all know the HP ratings of these coaches, the Cornerstone being the anomaly with a 600 HP motor. I believe HP is the reason the claim of a K-3 chassis under a Cornerstone is made, for it IS NOT structurally different from the K-2 Essex and certainly not close to a K-3. No question about it.....the K-3 under the King Aire IS the strongest of these coaches and there can be no question about that.
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Old 07-08-2014, 12:33 PM   #2
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An interesting narrative...and I appreciate the information. It makes me wonder how Entegra can claim a K3 chassis, unless the chassis delivered by Spartan is delivered to Entegra as a "K3" chassis. That would be illegal and false advertising if published (JMHO, as I'm not a lawyer). I have strong doubts that Jayco's legal would allow the published specifications to differ from reality.

That said, we know that Spartan produces its chassis' to the specs provided from the manufacturer of the coach who then makes additions to the chassis as a foundation for the coach. I have seen the K3 chassis on the factory floor at Spartan. I did not see it side by side with a K2 chassis, but I would imagine that adjustments to the engine mount are of the chassis to house the ISX Cummins engine at 600HP would be different that the adjustments to any chassis, I am going to assume the K2 chassis, to house an ISL engine, again I am assuming that is the 500HP engine in Essex.

In your description of the King Aire, the tubing you describe sounds like Newmar's additions to the K3, so I' not clear, from you description if the basic chassis as delivered to Newmar (basically the rails, front end assembly, and rear end engine assembly and housing) is different fro the basic assembly delivered to Entegra. Pls forgive if I am missing something in the terminology you have used.

FWIW, I am not dissing here either...really am interested, and also as it relates to the London Aire (supposedly only available in Freightliner) but with the ISX engine, because I am considering LA against the Cornerstone for an upgrade this fall. One thing I find frustrating is the lack of specs on engines in the Newmar website (maybe I'm missing something) as I try to compare...of course I'm really frustrated that neither newmar or Entegra can get their web sites up with their 2015 offering (I know Newmar has made it to Facebook) even thought they are now selling them. BTW, evidently American Coach can make this leap in marketing:(

Appreciate the good info. Certainly opens to questions in my mind. Just might ask the folks I know at Spartan.
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Old 07-08-2014, 12:34 PM   #3
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Very interesting thank you for your time and making the comparison


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Old 07-08-2014, 01:49 PM   #4
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so here are some shots I took of the Cornerstone chassis. it shows the 8" main rail and the longitudinal bottom rail. 2014 model, 600 HP
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Old 07-08-2014, 01:52 PM   #5
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Thanks, but can you differentiate the KA K3 chassis from the Cornerstone K3 in these pics. Are you saying that the front to back main rails are different?
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Old 07-08-2014, 01:54 PM   #6
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I had the opportunity to see The King Aire and Essex chassis "Naked" at the factory this Summer and the difference is striking, The KADB is much heavier duty. At one time Spartan had the specs for both K3 chassis, K3LT and K3GT on their web site but then it was taken down. I haven't checked tom see if they put it back up.
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Old 07-08-2014, 02:03 PM   #7
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So here is the K-3 under a 2014 King. The main rail is now a 6x3" BOX tube as opposed to a C channel in the Essex and Cornerstone. Bottom rail is a full 5" deep! All connections are welded.
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Old 07-08-2014, 02:22 PM   #8
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What we used to call a K3 is now the K3GT. The new "K3" is more similar to a K2 than a K3GT, but it's NOT the same as a K2. The K2 couldn't take the ISX engine, only the ISM. So to put an ISX in a frame lighter than the old K3, Spartan had to develop a new chassis. The are differentiators, but you either need to look underneath or see them side-by-side. The K2 has the upslope at the back end, while both K3s are straight back under the engine. That's the ISM vs ISX difference.

The (new) K3 isn't as tall in the basement as the K3GT. Not easy to see unless you have two coaches pretty much side-by-side, as we have here at Hearthside Grove this week.

The London Aire is on an FL chassis with the same ISX-15 engine as the KGDB and EXDP. The Mountain Aire is also an FL chassis (not sure if the same), but has the ISX-12 engine (500HP) instead of the ISM.

Nice pictures on this page: http://spartanchassis.com/rv/rv_chassis.asp
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Old 07-08-2014, 02:27 PM   #9
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Quote:
Originally Posted by DSL417 View Post
In your description of the King Aire, the tubing you describe sounds like Newmar's additions to the K3, so I' not clear, from you description if the basic chassis as delivered to Newmar (basically the rails, front end assembly, and rear end engine assembly and housing) is different fro the basic assembly delivered to Entegra. Pls forgive if I am missing something in the terminology you have used.
Take a look at the pictures in post I linked in the previous post. The differences are obvious. On anything other than a K3GT, there is no bottom framing as provided by Spartan. It's all added by the RV manufacturer.
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Old 07-08-2014, 02:38 PM   #10
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Here are some shots of a K-2 under a 2014 Essex. Note the same 8" main rail as the Cornerstone and 2x2 " bottom rails, sans the Cornerstone's diagonal lacings. The diagonal angle iron is to offset the load bearing on floor joists as they carry the perimeter walls.
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Old 07-08-2014, 02:41 PM   #11
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Fascinating...thanks Slabman & FlyingDiver!
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Old 07-08-2014, 02:55 PM   #12
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Yes, Dave. BIG difference in engineering performance. We studied this kind of stuff in engineering school, but I realize it may not be as obvious to a more "normal" human being. The square tubing by itself is normally superior to C-channel, but the real key is how its integrated into a truss as they have done with the King Aire chassis. Again, this is NOT present under the Cornerstone. So while the K2 utilizes a deeper C channel as a "backbone", the K3 relies on a much stronger backbone-a truss to carry the loadings. You can see extra steel at the rear which appears to have been deployed to carry that big isx.
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Old 07-08-2014, 03:42 PM   #13
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The '15 LADP is on the Freightliner SL chassis similar to the '14 Essex option. Engine is the cummins ISX15 Diesel with 600HP and 1950 lb/ft torque. Same as the KADP and ES Cornerstone. Allison 4000MH six-speed trans. ZF 20K LB Front axel. Just configured a '15 LADP and it was $15K Retail more than a Cornerstone with almost every conceivable option including a $12K upgrade to the Girard Nova awnings. Much better value IMHO.
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Old 07-08-2014, 04:55 PM   #14
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Quote:
Originally Posted by slabman View Post
Yes, Dave. BIG difference in engineering performance. We studied this kind of stuff in engineering school, but I realize it may not be as obvious to a more "normal" human being. The square tubing by itself is normally superior to C-channel, but the real key is how its integrated into a truss as they have done with the King Aire chassis. Again, this is NOT present under the Cornerstone. So while the K2 utilizes a deeper C channel as a "backbone", the K3 relies on a much stronger backbone-a truss to carry the loadings. You can see extra steel at the rear which appears to have been deployed to carry that big isx.
Thanks...there you go...dad gum mechanical engineers...versus us fluid engineers. You probably made more money than I did as well.
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