FAWR+RAWR less than GVWR?
01-19-2019, 05:54 PM
#1
Senior Member
Thread Starter
FAWR+RAWR less than GVWR?
Hi All,
I am trying to understand why GVWR < (FAWR+RAWR). The FAWR and RAWR specify how much each axle can carry, yet each vehicle I've seen itself can carry less than their sum. Can anyone help me understand what part of the truck becomes over-stressed if I ask both axles to simultaneously carry the weight they are each individually rated for?
Thanks,
-kehyler
I am trying to understand why GVWR < (FAWR+RAWR). The FAWR and RAWR specify how much each axle can carry, yet each vehicle I've seen itself can carry less than their sum. Can anyone help me understand what part of the truck becomes over-stressed if I ask both axles to simultaneously carry the weight they are each individually rated for?
Thanks,
-kehyler
01-19-2019, 08:53 PM
#2
Grumpy Old Man
Frame, brakes, maybe other components.
Ford has rGARW that can be used to haul heavy on the rear axle, such as a heavy gooseneck equipment trailer loaded to the gills. And they have fGAWR that an be used to haul heavy on the front axle, such as a snowplow. But you cannot max out both the fGARW and the rGAWR at the same time because some components of the truck cannot handle that much weight. Frame is probably the main culprit.
So GVWR is the limiter. If you require more GVWR, then you need more truck. Ford makes it.
Ford has rGARW that can be used to haul heavy on the rear axle, such as a heavy gooseneck equipment trailer loaded to the gills. And they have fGAWR that an be used to haul heavy on the front axle, such as a snowplow. But you cannot max out both the fGARW and the rGAWR at the same time because some components of the truck cannot handle that much weight. Frame is probably the main culprit.
So GVWR is the limiter. If you require more GVWR, then you need more truck. Ford makes it.
01-20-2019, 06:36 AM
#3
“There’s a common misconception that a truck’s GVWR is determined by adding gross axle weight ratings (GAWRs) together for all axles. Although this was a common way of calculating GVWR many years ago, it’s no longer an accurate method. The chassis manufacturer task of establishing a vehicle GVWR is much more difficult today due to advancement of safety system standards and how vehicles meet these requirements. This is why many trucks have a GVWR much lower than the combined axle ratings. It is not uncommon for a truck with a GVWR of 19,500 pounds to have a front axle rated at 7,500 pounds and a rear axle rated at 14,700 pounds. Safety standards that apply to braking, vehicle stability, and chassis manufacturer internal standards for durability, dynamic stability and handling can restrict GVWR even though the sum of the axle ratings exceeds 22,000 pounds. In this instance, the OEM set the GVWR at 19,500 pounds based on test results and vehicle dynamic performance to ensure a safe, reliable truck.
Bob Raybuck
Director of Technical Services
NTEA”
01-21-2019, 10:31 AM
#4
Senior Member
You could take it a step further and consider the tires too.
Example:
My current truck is an F250 with a GVW of 10,000
FGAWR: 4800
RGAWR: 6100
275/70/18 tires are rated for 3,195 each.
Basically, each individual component has to be rated beyond the part it needs to support. The tires on my truck are rated for 6,390 per axle or 12,780 combine. So, both axles will never have "not enough" tire to carry the rated load. Same with the GVW on the truck. The axles will always have enough rating to carry the GVW of the truck.
And, the higher axle ratings allow for some wiggle room in loading the truck. My truck has a payload capacity of 2,766 pounds. If I were to load exactly that in the bed of the truck, the weight would not distribute perfectly 50/50 even between the two axles. It's likely that the rear axle would take more of the weight. So, the balance could actually be the front axle carrying 4100 pounds and the rear 5900. Both axles would never be overloaded.
Or, add a large tongue weight that pushes down on the rear bumper. In that case, the rear axle is now a fulcrum point that is carrying weight. The tongue weight may force 6600 on the rear axle but the fulcrum point of the rear axle would actually lift weight off the front axle (think light feeling steering). So the front axle could go from 4100 to 3400. But, again, both axles would still be in compliance without the GVW of the truck being exceeded.
Example:
My current truck is an F250 with a GVW of 10,000
FGAWR: 4800
RGAWR: 6100
275/70/18 tires are rated for 3,195 each.
Basically, each individual component has to be rated beyond the part it needs to support. The tires on my truck are rated for 6,390 per axle or 12,780 combine. So, both axles will never have "not enough" tire to carry the rated load. Same with the GVW on the truck. The axles will always have enough rating to carry the GVW of the truck.
And, the higher axle ratings allow for some wiggle room in loading the truck. My truck has a payload capacity of 2,766 pounds. If I were to load exactly that in the bed of the truck, the weight would not distribute perfectly 50/50 even between the two axles. It's likely that the rear axle would take more of the weight. So, the balance could actually be the front axle carrying 4100 pounds and the rear 5900. Both axles would never be overloaded.
Or, add a large tongue weight that pushes down on the rear bumper. In that case, the rear axle is now a fulcrum point that is carrying weight. The tongue weight may force 6600 on the rear axle but the fulcrum point of the rear axle would actually lift weight off the front axle (think light feeling steering). So the front axle could go from 4100 to 3400. But, again, both axles would still be in compliance without the GVW of the truck being exceeded.
Last edited by clarkbre; 01-21-2019 at 10:36 AM.
01-22-2019, 11:54 AM
#5
Besides the issue of the truck physically being able to handle and brake at the full GVWR, if your GVWR wasn't less than the GAWR's then you would run into issues where you would exceed one of the GAWR's before GVWR. Imagine your F150 had a 3750 and 4050 lb GAWR and a GVWR of 7800 lbs. Your GVWR would suggest that you could attached a 5th wheel with a 2000 lb pin weight, but the rear axle would have far exceed 4050 lbs.
Meanwhile, most of our F150's can actually handle nearly the full payload on the rear axle alone. Mine is 4050 lbs and has a 2700 lb empty rear axle weight with a payload of 1539 lbs.
Meanwhile, most of our F150's can actually handle nearly the full payload on the rear axle alone. Mine is 4050 lbs and has a 2700 lb empty rear axle weight with a payload of 1539 lbs.
01-22-2019, 06:47 PM
#6
Senior Member
Thread Starter
I was hopeful that we could understand which part in particular was the weak link. If its a dynamic stability concern, that would obviously be difficult to tell.
01-23-2019, 09:17 AM
#7
Hi All,
I am trying to understand why GVWR < (FAWR+RAWR). The FAWR and RAWR specify how much each axle can carry, yet each vehicle I've seen itself can carry less than their sum. Can anyone help me understand what part of the truck becomes over-stressed if I ask both axles to simultaneously carry the weight they are each individually rated for?
Thanks,
-kehyler
I am trying to understand why GVWR < (FAWR+RAWR). The FAWR and RAWR specify how much each axle can carry, yet each vehicle I've seen itself can carry less than their sum. Can anyone help me understand what part of the truck becomes over-stressed if I ask both axles to simultaneously carry the weight they are each individually rated for?
Thanks,
-kehyler
I would be perplexed if it was the other way around.
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01-23-2019, 06:51 PM
#8
Senior Member
Thread Starter
01-24-2019, 05:50 AM
#9
Senior Member
My 2014 F150 4x4 w/ HDPP has a GVWR of 8200#. The FAWR = 4050#. The RAWR is 4800#. The OEM LT 17" tires total 9600# (2400 x 4). And to cap it off, 2286# CC.
01-24-2019, 07:40 AM
#10