Gvwr

[firebuild]

So... I did find an old thread that sort of addresses my question, but it was so old I thought a new thread might be in order.

My bus has two stickers on the inside of the door, one dated 6/91 from Ford, which lists the GVWR as 9500 lbs. The other is from Lewis Bus, who made the bus body, dated 8/91, and it has the same exact axle ratings but lists a GVWR of 10,000 lbs.

I'm curious - how does the GVWR increase like that? And which would you pay attention to?

[o1marc]

Ford rated it as a van. Lewis added a school bus passenger body, upping the GVWR.
Use the higher one as it doesn't matter in our case until it hits a GVWR of 26K.

[firebuild]

Originally Posted by o1marc

Ford rated it as a van. Lewis added a school bus passenger body, upping the GVWR.
Use the higher one as it doesn't matter in our case until it hits a GVWR of 26K.

Well, I'm not talking about for paperwork. I was thinking more safety. Ford rated it as an "incomplete vehicle." But I still don't get why adding the bus body would up the GVWR. I can see it would up the GVW, but as far as the rating goes, why would it be capable of carrying MORE weight once it has the body on there? Isn't the chassis what is carrying the weight?

[o1marc]

Originally Posted by firebuild

Well, I'm not talking about for paperwork. I was thinking more safety. Ford rated it as an "incomplete vehicle." But I still don't get why adding the bus body would up the GVWR. I can see it would up the GVW, but as far as the rating goes, why would it be capable of carrying MORE weight once it has the body on there? Isn't the chassis what is carrying the weight?

A bus body is designed to carry more weight than a van body because it's normally longer and wider than a van. Ford didn't put a body on the build, so can't determine end use GVWR, so rated it for a van. As far as safety, I doubt you'll find much difference between the 2 GVWR's. That will depend on your build quality.

[rossvtaylor]

As o1marc mentioned, the initial GVWR is determined by the chassis manufacturer based on their assessment as a stripped/straight truck or van. If a bus body manufacturer or ambulance manufacturer wants to change that, they can...but they would need to do some engineering analysis to make that change. These factors include axle, tire, frame, suspension capabilities...and braking, too. Center of gravity and handling also come into play. But, once that's done, the body manufacturer can make the change...and they become responsible for the change.

Here's a good excerpt from a doc I had:

Many incomplete medium-duty vehicle manufacturers include GVWR information as part of the Vehicle Identification Number (VIN) coding in the vehicle description section (4– and, therefore, will not change an incomplete vehicle’s GVWR after it is manufactured as the VIN would need to be updated. Many incomplete vehicle OEMs will provide guidance about changing GVWR for a VIN-specific new incomplete chassis through their dealer network; however, they make the final-stage manufacturer the responsible party. Many times, altering GVWR requires changing key components (such as tires, suspensions or even axles). If a company claims it can change GVWR, consider asking about the organization’s approach to testing, engineering analysis and certification documentation to ensure ongoing compliance.

As an example, we have a flatbed crane truck based on a Sterling "straight truck"...which is really a semi tractor front end and a longer frame. It's currently got a GVWR of 78,000 pounds. But the original Sterling GVWR was quite a bit lower. The manufacturer that bought the original straight truck added an axle, changed the front tires, added additional braking capacity...then put on a flatbed and a crane. At that point, Sterling is essentially off the hook and the new manufacturer would become responsible if there were an issue.

[rossvtaylor]

I should add...darn, kudos to you firebuild...I'm impressed. I wonder how many skoolie builders have even looked at their GVWR and thought to ponder that? I see so many people just jumping in and going...sometimes knowing nothing about their brake systems or weight limits or how tall or top-heavy they're making their rig. So, a tip of my hat to you...

[firebuild]

Originally Posted by rossvtaylor

I should add...darn, kudos to you firebuild...I'm impressed. I wonder how many skoolie builders have even looked at their GVWR and thought to ponder that? I see so many people just jumping in and going...sometimes knowing nothing about their brake systems or weight limits or how tall or top-heavy they're making their rig. So, a tip of my hat to you...

Well... To be fair... This is a rebuild. I didn't think about it for a minute the first time around! My bus is narrow and tall with single rear wheels. I've been having some "wandering steering" issues that remain mysteriously unsolved so I'm just kind of ticking all the boxes to make sure I'm not making my life harder by being overweight.

I got weighed today. Empty weight before the rebuild came in at 7,520, and now, completely full, I'm only at 9000. So all is well!

[rossvtaylor]

Hi Mary...still, that's great and rare that you'd take the time and effort to do that. More should.

Did you get individual axle weights on that weigh? If you have lots of weight behind the rear axle, which will lighten the front axle, that can cause stability issues and might be a factor in the wandering you feel. There are other things to look at, too, but I'd certainly want to know how the front axle weight ends up.

[HamSkoolie]

I'm no longer surprised by how many people don't weigh. It's particularly important in the RV trailer community and yet very few ever weigh. With a trailer and tow rig the minimum knowledge needed is:
Gross combination weight
Each Axle weight
Trailer weight without tow rig
Tow vehicle weight without trailer (calculated from above)
Pin weight (fifth wheel/goose neck) or tongue weight (bumper pull) also calculated from above.


And yet you see people going down the road with obviously improperly loaded and sized rigs.


It's a lot easier with a skoolie.... front axle, rear axle. It would be awesome to get each corner (for CG calcs) or even each side for side to side distribution calcs but those are probably beyond most peoples capabilities.

[firebuild]

Originally Posted by rossvtaylor

Hi Mary...still, that's great and rare that you'd take the time and effort to do that. More should.

Did you get individual axle weights on that weigh? If you have lots of weight behind the rear axle, which will lighten the front axle, that can cause stability issues and might be a factor in the wandering you feel. There are other things to look at, too, but I'd certainly want to know how the front axle weight ends up.

Unfortunately the scale near me, which is at a moving company, can't do axle weights. But the wander is there even when the bus is empty. I was involved in a freak accident - a truck dropped a load of concrete and rocks on the freeway - and I hit the debris and blew out my back tires (about 50 people did - shut the freeway down). The bus was completely stripped empty at the time because I was redoing the floor. That's where the wandering started in earnest, though it was actually present to some extent beforehand.

I can't even tell you how many things have been done in an attempt to correct this problem - Max (my bus) literally spent seven weeks at a spring shop, where the owner basically made it his life's work to figure the problem out (without charging me a dime). I would say through his efforts, the wander is about 85% better, but it's still there. He fixed or replaced pretty much anything that could be causing the problem - I now even have airbags in my brand new front springs! The one thing that has been suggested that I haven't really been able to sort out is, shortly BEFORE this happened, I had my steering box replaced. It was suggested that it's maybe not the right steering box. My bus is an E350 but apparently the one for a bus is different than the one for a van? I dunno. I have not been able to really dig in to research this yet.

The wander is definitely coming from the rear, but like I said is not any different with no load at all.

[o1marc]

Why can't they do axle weights? You drive onto the scale with just the front wheels and take a reading. Drive off the scale so just your rear wheels are on it and take a reading. Axle weights.

Any salvage or scrap yard or dump has a scale to drive over. Our local one could even do side to side.

[firebuild]

Originally Posted by o1marc

Why can't they do axle weights? You drive onto the scale with just the front wheels and take a reading. Drive off the scale so just your rear wheels are on it and take a reading. Axle weights.

Any salvage or scrap yard or dump has a scale to drive over. Our local one could even do side to side.

The scale is like a tight lane with guard rails on each side. The guy said he couldn't do it. I didn't get into it with him.

[LargeMargeInBaja]

firebuild,
As I understand the process, the vehicle manufacturer establishes the vehicle maximum capacity (GVWR, GCWR) based on the type of frame, axles, brakes, and the engine/tranny for that specific vehicle.
.
After the vehicle leaves the manufacturer, would mounting bigger tires increase the manufacturer's maximum capacity?
I fail to see any way adding/removing/modifying the vehicle could change the frame capacity, the capacity of the brakes, or the engine/tranny combination.
.
For example, in 2003, we converted a 1997 Ford CF8000 commercial truck to our concept of an ExpeditionVehicle.
At the time we acquired it, it had a 24 x 8.5 by eight foot tall reefer box with a 8k lift-gate... with a GVWR of 29,000#.
.
We swapped that yuge heavy box for a 12 x 7 by seven foot tall dry-van box... a difference of an honest four ton across the scale.
Simultaneously, we whacked about nine feet off the rear of the frame.
Did our modifications change the capacity of that shortened frame -- nope.
Did a different box change the brakes -- nope.
Although years later, we went from the stock 22.5 tires/wheels to 24.5 -- adding a squidgen over two inches to our ground-clearance -- the vehicle manufacturer was not involved in our decision... and the certified GVWR remained intact... 29,000#.
.
An 'incomplete' vehicle is (usually...) not able to be licensed for on-road.
An incomplete vehicle (usually has little utility outside basic transportation, and requires a 'body up-fitter' -- mounting a hitch, box, tank, manure-cannon -- to create a viable vehicle.
.
We delivered RecreationVehicles -- and heavy-trucks such as cranes and concrete mixers -- manufacturer-to-dealer and dealer-to-shows.
Often, while waiting for paperwork at a RecreationVehicle manufacturer, we wandered the assembly line, watching frames get components mounted.
.
Looking at one segment of the up-fitter industry:
* a RecreationVehicle relies on the body for the vast majority of the completed vehicle rigidity.
We watched a forklift raising a rolling chassis -- no engine/transmission, no body -- higher than we are tall to clear the tires from dragging.
Droop city!
In this genre of vehicle, I think the base vehicle provider -- Ford, Freightliner, etcetera -- relies on the engineering honesty of the finished vehicle manufacturer -- Winnebago, ForestRiver, etcetera.
.
A bus body is engineered to complement the frame beneath it.
Although I have no first-hand engineering experience with verifying the modifications of raising a roof or shortening a bus into a crewcab fifth-wheel toter, I am pretty sure:
* no changes to a completed certified vehicle can alter the maximum capacity of frame, brakes, or engine/tranny.
.
firebuild, I wonder if -- in your case, Ford -- established their potential GVWR/GCWR based on a shoe-box up-fitted body, a completed vehicle with the wind-drag of a parachute.
I wonder if your bus up-fitter engineers used an aerodynamic 'slippery-er' body shape to change the established GVWR/GCWR.
.
Unless you get The Word from the up-fitter about your V.I.N., this just might remain a mystery for the ages.

[firebuild]

Originally Posted by LargeMargeInBaja

firebuild,
Unless you get The Word from the up-fitter about your V.I.N., this just might remain a mystery for the ages.

I actually put in a call to them out of curiosity. They don't make buses anymore, though, they just sell them now.