Minimal Spring Travel at RAWR Limit

[Jerry Burks]

I found with my new F350 and Alliance 310RL 5th wheel I am right at the limit for the door sticker RAWR of 6780 lbs according to CAT scale (Pin weight is about 3000 lbs). So that is kind of O.K. but given the pending axle recall for this truck I looked a little more closely what that means. I installed a small video camera watching what the suspension is doing while driving under load. I did not see anything related to the recall problem but found that the remaining spring travel is maybe an inch or two at best. Even driving on normal city roads, the axle sometimes bottomed out on the yellow bump stops and I don't want to know how that looks at higher speeds on uneven roads with trailer chucking. If I would have loaded it up to the promised catalog spec of 7230 lbs I am not sure if there was any spring travel left.

Well, the truck is going in for recall repair next week but that will not help the issue mentioned above.

My question is if it could be helpful to install air bags and lift the whole thing up a few inches so that the springs have a chance to do their work before being intercepted by the bump stops?

If somebody is interested in the video clip, see here:

https://www.youtube.com/watch?v=f12xX4hPx_k

[Old-Biscuit]

IS this the Door Sticker you are getting the RAWR from?



Is truck/5vr level when towing?
Truck rear sagging?

Air Bags will help 'level' if sagging


I am really surprised with a 2021 F350 you are banging on the bump stops
I have a 2007 3500 SRW and wet pin is 3080# on my 14K 5vr ....not hitting my bump stops. Overloads are just engaging when hitched

????????????????

[Jerry Burks]

Originally Posted by Old-Biscuit

IS this the Door Sticker you are getting the RAWR from?

I wish, but mine is the one shown below. I suspect, when Ford issued the lowered spec replacement stickers last year, they found 7230 lbs is just too much and trucks built after that just got the lower spec sticker from the factory.
FWIW, the Ford web site spec and what the sales man told me was still 7230 lbs for this model. I feel a bit cheated.

Originally Posted by Old-Biscuit

....Is truck/5vr level when towing? Truck rear sagging?...

Yes, 5er is very nice and level. Truck is obviously squatting when loaded but I did not consider it serious until I saw the bump stop contacting.

I am surprised as well that there is so little margin. When driving on totally smooth road, it does not contact the bump stops. But it takes only a modest wave in the road to do so.

I will look into the air bags. No so much out of leveling concern but rather to give the springs more travel to absorb road dips/bumps.

Is there a consensus which air bags work best for an F350?

I will also check into replacing the rather rigid Rotaflex pin box with a cushioned one for additional peace of mind.

[Dieselguy4]

So what is interesting is that you only have 6830 lbs of tire load on that truck. That would be my first worry on hauling that fifth wheel. I had added air bags to my Ram 3500 since it was just above the helper springs and when I went over a bump it would hit the helpers and launch me back up for a very bad ride. I added Firestone airbags and it smoothed the ride out. You may also want to try a set of Timbren rubber springs. I have read good reviews. You will not have to worry about airing them up.

[RVnAggie]

Sure seems odd to be routinely bottoming out on the rubber bumpers if you’re not right at or over the weight rating.

Can you share your axle weights from the CAT scales? I assume you have the weights for truck only and also for truck+trailer? Doing the math with the actual #’s will help understand the “why” behind the issue. You may simply be closer to or over the capacity more so than you think if you haven’t already ran all the numbers.

For example,

If actual weight of the truck is, say, around 8,200lbs, and maybe 45% of that is on rear axle, then you have 3690lbs of truck weight on the rear. Add 3000 lbs of pin wt and you’re basically at the limit. So depending on your real #’s you could be beyond which means truck sag and very little remaining spring is probably reasonable.

As Old Biscuit stated, air bags will level out the truck. However, they will not add capacity.

Forgive me for being redundant if you’ve already done all the math with the specific axle weights….I’m just thinking on the diagnosis rather than the cure.

Safe travels,

[Jerry Burks]

Originally Posted by RVnAggie

....Can you share your axle weights from the CAT scales? ....

Here you go. I had posted that in another thread in the 5th wheel section. I know with 3080lbs pin weight and 6640 lbs axle weight I am right below the spec limits (and probably slightly above when loaded for travel). But as-is I am still below and would not expect that little suspension reserve. I am going to try Sumos and Torquelift spacer blocks and see what works best.

Originally Posted by RVnAggie

...As Old Biscuit stated, air bags will level out the truck. However, they will not add capacity.

I understand. The main goal would not be capacity or even leveling but reclaiming some spring travel. The likely downside is a harsher ride, I guess.

[Rich1961]

Originally Posted by Jerry Burks

I wish, but mine is the one shown below. I suspect, when Ford issued the lowered spec replacement stickers last year, they found 7230 lbs is just too much and trucks built after that just got the lower spec sticker from the factory.
FWIW, the Ford web site spec and what the sales man told me was still 7230 lbs for this model. I feel a bit cheated.


Yes, 5er is very nice and level. Truck is obviously squatting when loaded but I did not consider it serious until I saw the bump stop contacting.

I am surprised as well that there is so little margin. When driving on totally smooth road, it does not contact the bump stops. But it takes only a modest wave in the road to do so.

I will look into the air bags. No so much out of leveling concern but rather to give the springs more travel to absorb road dips/bumps.

Is there a consensus which air bags work best for an F350?

I will also check into replacing the rather rigid Rotaflex pin box with a cushioned one for additional peace of mind.

You have the smaller of the two 18" tire options on your truck, which is why you have the 6780 rear axle weight rating. The 275/70-18E tired truck has the 7230 rear axle weight rating. I installed the SuperSprings Super Sway stops for the upper overload spring perch to contact the spring sooner. Instead of the truck dropping 3 inches to contact the spring, it now only drops an inch before contacting the upper overload spring.

[RVnAggie]

Thanks for sharing the scale tickets. You’d obviously already gone through the math on the actuals.

Would be good to hear from others who are that close to the limit to see if they are also that tight on spring travel.

The air bags or other similar alternatives should certainly help the situation. I doubt the ride will be any worse; likely better since you’re currently hitting the bumper stops some.

I put airbags on my prior truck, 2016 F250 with a 15k fiver & about 3,000lbs on the pin…..shame on me for sure for that match up. Only pulled it once without the bags, about 85 miles from dealership home, so trailer had no personal gear at all other than the washer & dryer added by dealer, but truck sagged like an overloaded baby diaper.

I ordered and installed the bags immediately, so I don’t really have a good reference point to compare before vs after bags. With the bags, I had a nice level truck that didn’t look overloaded and the ride wasn’t stiff at all when pulling the trailer. However, was stiff as a board though with no trailer unless I let out most of the air which was to be expected.

My bags were Firestone Ride Right. I also added a small on board compressor under the bed so I could deflate when unhooked and then air them back up easily for towing.

Best wishes on whatever specific remedy you choose.

[Jerry Burks]

Originally Posted by Rich1961

You have the smaller of the two 18" tire options on your truck, which is why you have the 6780 rear axle weight rating. The 275/70-18E tired truck has the 7230 rear axle weight rating. ....

Thanks for this information. You are right, I checked the tires are only rated 3415 lbs each.
So I learned now that you can not trust what you read on a Ford data sheet or hear from a sales guy about a spec that is not on the window sticker.

Does not change much the fact, that even at my reduced axle weight rating, the F350 is more than maxed out and does not have much reserve, let alone at the higher tire specification of over 7000 lbs.

[Bhidalgo]

Jerry - you've really got me thinking here about truck cargo capacity issues regarding the 2022 310RL we're due to pick up in a few weeks, or so. I have a 2021 F250 currently, but due to cargo capacity limits with the Alliance, we have ordered a 2022 F350 SRW 160" WB, w/6.7L Diesel to use to pull the 5'er with. I've ordered the truck with the 11.5K GVWR package, 5th wheel prep, 3.55 locking axle, but am getting LT275/65R20E OWL All-Terrain tires vice the 18" ones i understand you may have on your F350. I'm wondering now if I am just wasting money and potentially facing the same rear axle issues you are dealing with.
I am looking to see how you resolve this spring bottoming just in case I need to turn around and address the same issues with the 2022. I'll be keeping an eye on this post for a while at least. P.S. I've attached a copy of the order sheet for my 350 if anyone in the know can tell me if I may have weight capacity towing issues or not based on what I've ordered. Thanks and good luck.

[Jerry Burks]

Well, I think the higher rated tires may give you more peace of mind regarding their own capability and whenever I have to replace mine I may buy those as well.

But it does not change the fact that even at the lower tire rating the F350 suspension as delivered is struggling with my 15,000 lbs GVWR 5th wheel. I hope I can improve that with the suspension add-ons because I am not going to trade for a dually (even if there were some available).

That is not to say that the truck feels bad when towing. Actually I found it a revelation in terms of stability and wind effects compared with our previous F53 base Class A. It is a great truck that tows nicely. I have the 3.1:1 diff and given the huge torque I find it a perfect match. Driving up and down Vail Pass with cruise control and auto engine braking at decent speed and barely have to touch the brakes. Cruising along on flat highway at 65mph and about 1400 rpm is quite efficient.

[JIMNLIN]

Fleet Ford specs shows the F350 SRW can have a 6340 or 6780 or 7230 rawr depending.....and around a dozen different gvwr packages
The specs also show a 4 leaf rear spring pack and a 5 leaf rear spring pack depending on gvwr....gas or diesel.....17" vs 18'/20" wheels and probably other criteria.
Of course the 5 leaf pack (7230 rawr) has a higher deflection rating.

And all this may change depending on year model. IMO for the most actual rear axle payload the higher gvwr package and the 7230 rawr in the lightest cab selections.

[Rhagfo]

Well it is beyond me why you would have bought a 2021 F350 SRW with the limited 11,500# GVWR, when in 2021 the F350 was available with a 12,400# GVWR. I realize it is the short bed so not available, but the LB would have got you the 7,230# axle and a GVWR of 12,400#.

[VanDiemen23]

I don't see anything odd here. You are at the limit. There's suspension travel, but not much. That's the way it works.

On a light duty truck, running at the limit is supposed to be the exception, not the rule. The minimum travel remaining is there for basic safety. It's not a commercial vehicle designed to run at that limit for the life of the truck.

You can play around with springs, tires, etc to get to the highest rating the truck was designed to handle, but your axles, R&P, bearings, brakes, etc will still be at the upper end of their designed range unless they were brought down from a bigger vehicle line.

If you intend to haul that load and expect to get a normal service life out the the truck you need a bigger truck.