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How much does a truck flex

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#1 Tess



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Posted 23 February 2024 - 09:42 PM

When I loaded my Hallmark Guanella camper on my 2021 F350 crew cab, I had only 3/4” clearance between the top of the cab and the camper. Matt at Hallmark said to add a spacer under the camper, so I added a 1.5” piece of foam. I’m wondering how much trucks really flex. Now my truck is long being a crew with an 8’ box. I have no intentions of going rock crawling. Is there a way to measure flex? I don’t like the look of the camper on the truck. The camper is 3” above the top of the bed side rails. I know it is recommended to have 3” above the cab but is that always necessary?

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#2 Bigfoot


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Posted 24 February 2024 - 12:46 AM

The bed and the cab may flex somewhat and differently because they are attached to the frame and not to each other. Depending on your tiedowns the camper may also shift in any axis when you hit a pothole on the highway or negotiate ruts on an unmaintained road. A rule of thumb is 1.5" to 3" cab clearance, so you might try 2" to see if it looks better. I assume there is no bed liner. 

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2014 Ram 2500 Laramie 4x4 CTD, Crew Cab, 8' box, Hallmark Guanella 


#3 Wandering Sagebrush

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Posted 24 February 2024 - 01:34 AM

Tess, first… Welcome to WTW!


With respect to flex, your 3” of clearance should be fine.  I have had the camper touch the cab of a 2014 F350 CC LB, but didn’t have more than 1.5” of clearance.  The camper was 3400 dry, and much more weight high.  The road (hwy 50 near Grand Junction) had LOTS of rollers, and it seemed to set up a harmonic.



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#4 Tess



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Posted 24 February 2024 - 01:39 AM

There is a rubber mat on a sprayed in bed liner and then a 1.5” piece of extruded polystyrene. While I appreciate your commenting, I do not understand what you are saying. The cab and the bed sit on the frame. Isn’t the frame the thing that flexes? I understand that the portion of the camper that overhangs the cab can flex. 
is there anyone out there that has damage to the top of their cab ?

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#5 JaSAn


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Posted 24 February 2024 - 02:04 AM

Easy enough to measure static frame twist for your vehicle:

  1. Truck on flat level surface.
  2. Place jack under spring mount close to rear tire.
  3. Start jacking.
  4. When other side rear tire lifts off ground - measure frame twist any way and where you want.
  5. Repeat on front.

Incline meters are cheap.

Or you can measure vertical inches difference from some common feature on both sides of truck.

I'd recommend measuring at rear of bed, front of bed and roof of truck.


This is a static measurement; I'd give myself a 25% or higher safety factor for dynamic effects (depends on how aggressive you drive undulating terrain).


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Sköldpaddan, a 1977 FWC Grandby
Renovating Skoldpaddan
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1951 Dodge Power Wagon

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