How does a truck manufacturer determine the Gross Vehicle Weight Rating for a Truck?

MikeRMurphy

New Member
By way of introduction, I am a research engineer at the University of Texas - Center for Transportation Research. I am currently working on a study regarding use of Specialized Hauling Vehicles which includes either newly constructed or older vocational trucks which one or more lift axles. A newly constructed truck has the GVWR identified on a plate or sticker mounted to the door panel or perhaps under the dash. What considerations are evaluated when setting the GVWR for a dump truck? I would expect the GVWR for a SU 5 dump with two lift axles would be larger than the GVWR for a 3-axle dump. I would expect that safety considerations such as braking capacity and structural capacities of the axles are part of this determination.

The reason I am curious about this is that based on field data collection there are many older trucks that have been retrofitted with one or more lift axles. However, I am not sure how the increased GVWR would be determined after the lift axles are added. The Texas Deparment of Motor Vehicles states in their Vehicle Registration Manual that a truck cannot be registered to haul more Gross Vehicle Weight than the GVWR shown on the data plate. Thus, when a truck is modified, how is the GVWR recalculated? Who would place the new GVWR plate / sticker on the truck?

Thanks very much for your help.

Mike Murphy
 
You can get a permit in Texas for overweight with extra axles on a county-by-county basis.
 
Rodger -

Thanks very much for your reply - I am aware of the TxDMV overaxle, over gross vehicle weight permits. However, the TxDMV Vehicle Registration Manual specifically states that a truck should not be operated at a GVW that exceeds the truck GVWR. This led to my question about how truck manufactuer's determine GVWR for a new truck. Older trucks have lift axles fitted which would increase the allowable GVW under the Federal Bridge Formula - but unless the truck's GVWR is modified to reflect the increase in allowable GVW - how can this be done legally?

Thanks again,

Mike
 
Rodger -

Thanks very much for your reply - I am aware of the TxDMV overaxle, over gross vehicle weight permits. However, the TxDMV Vehicle Registration Manual specifically states that a truck should not be operated at a GVW that exceeds the truck GVWR. This led to my question about how truck manufactuer's determine GVWR for a new truck. Older trucks have lift axles fitted which would increase the allowable GVW under the Federal Bridge Formula - but unless the truck's GVWR is modified to reflect the increase in allowable GVW - how can this be done legally?

Thanks again,

Mike
The manufacturer issues a GVWR. So when you add axles the installer will have a new manufacturer plate with the revised GVWR. They are certifying it can now carry said weight legally.

The advantage of buying a truck fabricated with the higher weight in mind is it will in general have a double frame, and heavier build. This will prolong its service life. But the GVWR is about how many points of contact you can make with the ground, and how much the weakest part can hold each.

Much the same is done in light trucks when you add lift, change to taller tires etc etc. Reputable shops will have these plates to reflect changes.
 
Tazz

Thank you very much for your reply - this is helpful. However, I still do not know the process that is used by the installer to arrive at the new GVWR. If the installer simply adds the lift axle manufacturer's recommended maximum load (say, 8,000 lbs) to the original trucks GVWR (say 54,000 lbs) the new GVWR is 62,000 lbs. However this determination was made solely based on lift axle manufacturers statement about the lift axle maximum load. No consideration was given to the total truck braking capacity when carrying 62,000 lbs with 4 axles, compared to carrying 54,000 lbs with 3 axles. I have heard truckers say that by simply dividing the GVW by the number of axles the 4 axle truck works out to be 15,500 lbs per axle whereas the 3 axle truck is 18,000 lbs per axle so there is more braking capacity with the 4 axle truck. Is this logic also used by the lift axle installer when preparing the new GVWR value?

I am just trying to understand which factors are considered when the new GVWR is calculated.

Thanks again very much,

Mike
 
I am sure they have some engineers crunch numbers to arrive at the new certified weight. Braking is part of it, and road weight is another factor.

Getting above my pay grade on that.

@Hammer166 might have some insight, or @AK7
 
I know for sure there's gov't regs on braking performance that have to be met, and I'd imagine there's regs on component ratings being adequate. I'm not sure if the gov't applies a performance standard or if they use some industry standard, as far as which engines get what tow rating (up to chassis capabilities.)
 
You can add all the axles you want,but the DOT will only recognize the factory vin plate,unless you get it recertified.
And the only way they are doing that is if the dealer does the install.
 
AK7

Thanks very much for your comment - it is helpful to know that the dealer must install the lift axle and then re-certify the truck. I will check with local major truck dealers that I know add lift axles to determine how the re-certification is performed.

Thanks again,

Mike
 

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