Can rear axle capacity be increased?

Tow package and TOW+ mode tow our 8800lb GVWR camper just fine, but camper's tongue weight of only 810lbs with tow hitch and not much else exceed rear axle capacity (3860lbs). I have air bags installed to help the ride, but I know they do nothing to increase axle capacity. Has anyone increased rear axle capacity? How? Can you certify/estimate new capacity?

 

I'm a little surprised you exceeded your rear axle rating with just the tongue weight. Are you using a WDH?

 

Short answer, no. Your payload and tow ratings cannot be increased.

 

The 2/2.5 Gen rear rear axle is listed at a gawr of 4150 lbs. According to folks from the Hino plant that manufacture it, the design gawr is actually around 5500 lbs. Given the component size, this number is not difficult to imagine.

With a pinch of extrapolation, the 3rd Gen axle is likely quite similar in capacity above the listed weight. Can we certify that? No.

 

Yes, we have a ReCurve R6 WDH. We upgraded the mattress (bedroom at front of trailer), have 2 AGM batteries, 2 full propane tanks, but next to nothing in the pass-through storage or bed of truck. It shocked me as to how quickly we consumed the axle capacity. All other weight specs are way under spec. We are anywhere from 80-160 lbs over capacity on rear axle.

 

Could you go nuts and throw a dana 60 under there with gearing to match to front with a custom 4 link and new drive shafts? Sure that would do the trick. Would that do anything to certify the truck now has a higher capacity? No It won't and you would have to have Toyota certify it and they are in the business of selling cars and will never entertain recertifying your truck for any modifications you do. What you're asking isn't possible to re-certify anything, you get the rating you get from the factory period.

Curious where did you find your axle capacity (the source for that rating) and how are you verifying your axel has that weight? by taking it to a scale?

 

Oh yeah, we also have a metal bed cover on the standard bed, so that surely is a weighty factor.

 

The axle capacity comes from the nameplate inside the driver door. We've weighed at the nearby CAT scale several times as we've used the trailer. We've pretty much moved everything you would put in the pass-through and the truck bed into the trailer directly over the twin axles or behind them. Including all our clothes; they're not even in the bedroom. This is sad, because the trailer is marketed as a "half-ton".

 

Teab - what's that trailer size behind your (really nice looking) truck?

 

Any travel trailer over 6000 lbs dry marked as "Half-ton" is a myth when they are fully loaded with water and all the shit we bring into the woods. You always run out of payload in a half ton before you ever reach the "MAXIMUM" towing capacity for a properly weighted tongue.

You might want to stop by the RV dealership and have them look at your WDH hooked up to your trailer to make sure its set up right too as a suggestion that might help put a little more load on the front tires.

 

About the only way to increase rear axle capacity is to go dually. Just slapping on adapters to add a second tire would not be safe. Axle capacity has more to do with just the amount of tires distributing the load. Axle tube thickness, ring and pinion size, bearing size, yada yada yada. About the only way to safely do it would be to swap out the rear for a Dana 80 dually. Not something I'd try with the link suspension. If it still had leaf springs like the previous generations, it would be much easier.
I'm assuming you have the 6.5' bed and not the 8', I'm also assuming it's a gas model and not a hybrid model. If so, according to Toyota's specs a tundra SR5, double cab 4x4 can tow 11,200 (11,090 if 8' bed) with a max payload in the bed of 1,885 (1,810 with 8' bed). Toyota rates tongue weight at 11% of the trailer weight. Since your truck is rated to tow 11,200 the max tongue weight would be 1,132, well within your 8,800-pound trailer.
The standard for proper tongue weight to avoid trailer sway is 10-15% of the trailer weight, I personally go 12% at the least. Tongue weight is easier for me to adjust since I'm towing a 24' car trailer. If tongue weight is too low I just move what I'm towing forward on the trailer a little. For you to increase tongue weight to avoid sway and get to the 12% tongue weight I'd throw all my heavy stuff like bottled water, loaded coolers, etc at the front of the trailer and not the back bedroom. Might not add much but you don't want trailer sway.
Where did you get the calculation that the rear axle has a capacity of 3,860, haven't been able to locate it?

 

2200 lbs dry and about 3500 lbs fully loaded if I have two bikes in the trailer. It has a 45 gallon water tank on it so that's a good 300lbs right there.

Its a 6x12 toyhauler (a little shy of 14 feet from hitch to back) with two tip outs beds that fold out of the sides. I had one of the big boy 8.5' x 24' campers and ran into the same bullshit you're going through (also marketed as "Half-ton") and moved up from my half ton ram 1500 to a F-250 3/4 ton (for only 8moths and hated that POS Ford) and decided I hated all that shit and found something that is easy to pull and fits what I'm after and is well within the half ton range. My previous Silverado with the 6.2 (replaced the F-250) and pulled it great and the Tundra doesn't even hardly know my current trailer is there especially considering it has trailer brakes too.

*edit also don't have to use a WDH which is another bonus of less shit to deal with
**edit#2 For those looking for this it was a one off prototype from a now folded company "VRV" and the closest would be to look at ATC trailer company who has a few models a little bigger they've made over the years.

 

When you've gone to the scales did they measure steer axle and drive axle separately? If you really want to know what's going on you need to fill it with whatever your bringing on your trip plus passengers. Weight the whole truck, then steer axle, then drive axle. This will tell you how much weight is on each axle. Then do this again after making sure your WDH is set up properly with your camper loaded with everything you'd be travelling with, food, supplies, coolers, water in tanks, etc. Go back to the scales and weigh it again and see where things are at. Problem you'll have is weighing drive axle because the camper will still be hooked up and on the scale. Or possibly the trailer store has scales that go under each individual tire. We use these to weigh our competition rigs and can weigh every corner individually.

 

I'll also add that your WDH probably weighs a good 120 ish lbs right? There goes about 10% of your payload before you even hook up the trailer. Throw you and the wife/kids/dog and now you barely have enough for a couple coolers let alone a travel trailer.

Exactly as @ColoradoTJ said you got dooped into "Half-ton". The only people I trust less than an auto-dealer would be an RV-dealer.

 

Oh yeah and nobody said it yet....Also your/our 3ed gen is going to explode and you should have bought a 2nd gen.....glad we got that out of the way.

 

How did you get the 810 pounds of tongue weight? Just what the manufacturer says? Is that actually measured on a Cat Scale?

I would imagine and 8,800 lb. Trailer would be in the 1,200 to 1,400 pounds of real world tongue weight. Add in the WDH, and the 200 lb. Metal bed cover and you are already at 1,500 lb. Tongue weight. Throw in passengers and you are up there as far as payload goes. With that much tongue weight and a WDH not setup correctly you could be over axle ratings.

There is no way 810 pounds of tongue weight would cause you to be over axle ratings.

 

Yep, "marketing" is usually just a fine line and a technicality away from outright lies. It's downright predatory and kinda' pisses me off.

When I bought my trailer (3,800 dry & 5,500 GVWR) it was listed on Lance Camper's website, brochures, etc. as being suitable for tow vehicles with a 5,000 lb. capacity.

The 4Runner I used to have had a towing capacity of 5,000 lbs. and there's no way in Hell I'd want to tow my trailer with that... not even empty.

Fortunately I knew a little, and I generally don't believe much of what I see in "marketing" and brochures, but there are plenty of people who go "Hey, let's buy a trailer!" and just look at numbers on paper or ask the trailer salesman for advice.
A couple of camping trips later they're asking the truck salesman for advice.

OP, are you inflating your airbags before or after you set up the WDH? Are yours inflated manually or auto leveling (I didn't see what year Tundra you have)

Somebody correct me if I'm wrong, but I think airbags can actually work against the WDH by pushing that weight down onto the axle, especially if they're inflated before you hitch up.

I'm thinking your tongue weight might be more than 810 lbs. How did you determine that number?

And if that number IS correct, that's less than 10% TW, and asking for trailer sway.

 

Lots and lots and lots of Tundra drivers are over GVWR when towing. I’m overweight by 200 lb when my gas tank is full and we’re loaded up to go tent camping with no trailer. If that is something that bothers you, you picked the wrong truck.

 

OK, the only way to figure out what your towing on the axle is to go back to the scales with the truck and trailer loaded for vacation. When you get to the scales only pull the (1)front axle of the tundra on the scales. After they get that weight drive the (2)rest of the truck onto the scales but do not let the trailer wheels go on the scale. After they get that calculation pull it (3)all on the scale, truck and trailer, that'll give you the full weight of both truck and trailer loaded for vacation with supplies and passengers.
Get your scale ticket and deduct the front axle weight (1) from the total weight of just the truck (2). This will give you your rear axle weight with the trailer connected and your truck loaded.