Do helper springs change the GAWR?

[Phoebe3]

Yet another one of those "gee, it made sense at the time" questions.

I've been looking at the Transit GAWR ratings and I can't find any rhyme or reason to them.

The 3.73 axle is rated about 500 lbs more in the van than in the passenger wagon (the van with windows) even though the size, configuration and GVWR are the same for both. I'm wondering if that is a function of the springs and, if so, would adding helper springs increase my GAWR?

[booster]

Originally Posted by Phoebe3

Yet another one of those "gee, it made sense at the time" questions.

I've been looking at the Transit GAWR ratings and I can't find any rhyme or reason to them.

The 3.73 axle is rated about 500 lbs more in the van than in the passenger wagon (the van with windows) even though the size, configuration and GVWR are the same for both. I'm wondering if that is a function of the springs and, if so, would adding helper springs increase my GAWR?

I would certainly think that one of the things that set the GAWR would be the springs, but everything else in the system is also taken into consideration. The weakest link is going to be the one setting the weight limitation, so if you soften up the ride a bit to give a passenger van a bit more comfortable ride, you can have the springs setting the max weight for the axle. If you put in a smaller rear axle itself, with smaller bearings, etc, it could be the weakest point and set the weight. In some cases, especially with the old school vans, the rear GAWR is determined by the tires, which are the weakest link in those vans. That could also be the same for the Transits and different on passenger vans.

Trying to guess why the GAWR is what it is can be pretty tough, as even things like weight distribution can make a difference. Passenger vans have gotten into handling issues, even when not overweight, because a bunch of people decided to sit way in back and none in the front.

We have heard of some issues with adding airbags to Transits causing frame damage, which is likely more because of where the extra capacity is supported do to it being a unibody, but it does point out the problems that can arise. In the past, I think many of the 3/4 and 1 ton vans had basically the same structural build, so the running gears, brakes, suspension, tires, etc determined which capacity they were, not frame or body.

There have been a couple of discussions on going over the sticker weights on the forum, by improving the capacity of various parts. One of the concerns that comes up would be if you ever got weighed by an authority and were overweight. ASAIK, that question has never been fully answered, but most seem to think that if it is the tires that are overloaded, you would more likely get pulled off the road than you would if just over sticker weight on the van.

[BBQ]

Originally Posted by Phoebe3

Yet another one of those "gee, it made sense at the time" questions.

I've been looking at the Transit GAWR ratings and I can't find any rhyme or reason to them.

The 3.73 axle is rated about 500 lbs more in the van than in the passenger wagon (the van with windows) even though the size, configuration and GVWR are the same for both. I'm wondering if that is a function of the springs and, if so, would adding helper springs increase my GAWR?

The GAWR is a factory rating. You cannot easily change it.

The spring does not affect the GAWR.

The axle is the part that carries the weight. The spring suspends the "bed" from the axle.



For example:
The Dana 35 axle is rated at 2,770 lbs
The Dana 44 axle is rated at 3,500 lbs

If you change to the "bigger" axle, you can carry a bigger load.
Of course you also have to change the springs and other suspension parts to match the load, which won't be an easy task.

(Not sure how you deal with independent suspensions)

[booster]

Originally Posted by BBQ

The GAWR is a factory rating. You cannot easily change it.

The spring does not affect the GAWR.

The axle is the part that carries the weight. The spring suspends the "bed" from the axle.



For example:
The Dana 35 axle is rated at 2,770 lbs
The Dana 44 axle is rated at 3,500 lbs

If you change to the "bigger" axle, you can carry a bigger load.
Of course you also have to change the springs and other suspension parts to match the load, which won't be an easy task.

(Not sure how you deal with independent suspensions)

It is my understanding that the GAWR is not the rating of the axle assembly itself, which they all have as a standalone component. GAWR is the weight that is sitting on the rear tires, on the ground, and is the weight you see when on the scales. The axle assembly itself will actually have less weight on it than the GAWR, because of the unsprung weight, at the springs, and will have another weight on it that is the axle end loading which will be less than the GAWR by the weight of the wheels and tires.

Changing to a bigger axle assembly may increase your capacity, but not officially unless you can get it recertified, which appears to be very hard to do. You would have to prove that all the other components and structural elements could also handle the added weight, including the unibody in the case of a Transit.

We have the optional Dana 70super in our Roadtrek, but that option would not change any of the gross weight on the sticker because the tires are the limiting factor. So we have an axle that probably has close to 2000# more capacity than the GAWR, but it doesn't change anything in how much we can legally and safely carry.

[PinIN]

49 CFR 571.3

Gross axle weight rating or GAWR means the value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system, as measured at the tire-ground interfaces.

[Phoebe3]

Thanks, since the 3.73 axle is the same between the Transit Van and the Transit Passenger Wagon, I'm going to figure it is the same part.

The difference between the Van and Wagon is the wagon has seats, windows and side airbags in the rear - otherwise the physical dimensions are identical. However, it is possible that the suspension and tires are designed for a softer ride and that may account for the difference in the rear GAWR. Both vehicles have a GVWR of 10,360.

Coachmen built the Crossfit on the Passenger Wagon so the rear GAWR is 500 pounds less than they anticipated (hence the recall on their placard). I'm going to fill the tanks and take it to get weighed next week. The freshwater tank sits on the rear wheels.

Since I was planning on adding superspring helper springs, anyway, I wondered if that would make a difference. I'll also check to see if the tires are rated differently, but I would expect not since the front and rear tires are the same and the van and wagon have the same GVWR.

[booster]

Originally Posted by Phoebe3

Thanks, since the 3.73 axle is the same between the Transit Van and the Transit Passenger Wagon, I'm going to figure it is the same part.

The difference between the Van and Wagon is the wagon has seats, windows and side airbags in the rear - otherwise the physical dimensions are identical. However, it is possible that the suspension and tires are designed for a softer ride and that may account for the difference in the rear GAWR. Both vehicles have a GVWR of 10,360.

Coachmen built the Crossfit on the Passenger Wagon so the rear GAWR is 500 pounds less than they anticipated (hence the recall on their placard). I'm going to fill the tanks and take it to get weighed next week. The freshwater tank sits on the rear wheels.

Since I was planning on adding superspring helper springs, anyway, I wondered if that would make a difference. I'll also check to see if the tires are rated differently, but I would expect not since the front and rear tires are the same and the van and wagon have the same GVWR.

A couple of points. Just because the gear ratio is the same doesn't mean it is the same axle model. You can have the same ratio on lots of different capacity axles. We know have 4.10 ratio at about 8K# rated and it replaced a 4.10 ratio at about 6K# rated. With only 500# difference in GAWR, it is likely that it would be the same capacity axle, but it's possible it might have some lighter weight internals, although not really likely.

Roadtrek also used passenger van chassis for the Chevy models, and they had a different frame than the cargo vans, so you never know what is under the metal, as they say. Both had similar ratings, though.

Having the front GAWR the same between the two styles will not tell you anything about tires, as the front tires are almost always running way under rated capacity compared to the rear, although it does get closer with duallies.

One big question would be if you need the extra load carrying capacity, or are you looking for more road clearance, or are you looking to handle better? All three are similar, but would generally be corrected by different methods. It would be pretty rare for someone to say their van's rear suspension is too soft, as it is almost always complaints of being to harsh, and too progressive.

[Phoebe3]

Thanks for the clarification.

I honestly don't expect to be near max GVWR, but I do want some clarity on what I've got in case I decide to tow something or carry something on the hitch. Not on a regular basis, but I don't want to wait until I'm in a pinch to discover I can't do it.

The ride is plenty soft and it handles well in the wind, but I am a little uncomfortable with the amount of sway on twisty roads. There is also a long overhang on the Extended model so lifting the rear a little would help with dragging on a driveway. Coachmen now includes the helper springs on most of the new Crossfits and owners say they like them. My version was early and they've made improvements I'd like to copy.

[booster]

Originally Posted by Phoebe3

Thanks for the clarification.

I honestly don't expect to be near max GVWR, but I do want some clarity on what I've got in case I decide to tow something or carry something on the hitch. Not on a regular basis, but I don't want to wait until I'm in a pinch to discover I can't do it.

The ride is plenty soft and it handles well in the wind, but I am a little uncomfortable with the amount of sway on twisty roads. There is also a long overhang on the Extended model so lifting the rear a little would help with dragging on a driveway. Coachmen now includes the helper springs on most of the new Crossfits and owners say they like them. My version was early and they've made improvements I'd like to copy.

Supersprings will lift you up, but will also make it stiffer in almost all cases, so be aware it may get harsher. Stiffening the rear will normally decrease rear traction and increase front traction and improve handling a bit while reducing sway some. I am a little surprised you notice sway, but not wind pushing you around as they commonly go together.

For the sway, nothing is going to work as well as a rear sway bar improvement. Add one if it doesn't have one, or replace it with a larger one if it does. The good thing about sway bars is that the don't make the ride a lot harsher like springs and shocks can. You would not notice a change in harshness with adding a bar, except for when you hit bumps with just on side of the rear of the van, and then it will be a bit harsher, but also much more controlled.

[Phoebe3]

Thanks. It has a sway bar, but perhaps could use a bigger one. Come to think of it, that is also a difference between the Van and the Passenger Wagon - the Wagon has a sway bar.

I think the reason I notice sway in curves and not in wind is because Ford has a braking system that notices gusts and applies independent brakes accordingly. I'm guessing it's triggered by rapid changes rather than just body roll. I was astonished at how well the Transit handled the wind when we drove the I-40 through the California desert last summer.

I should also point out that we have followed Transit delivery vans that took curves a whole lot faster than my comfort level would allow so I don't think we are any danger - it's just for my peace of mind.