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Discussion Starter #1
The ’10 rear GAWR is 4100 #s. Assuming the payload is sufficiently increased by air bags and/or leafs, how do I determine the weight of the rear springs, shocks, bed, etc.? Is this information available somewhere? Alternatively, how accurate is it to just weigh the rear-end and subtract the weight of the axel (assuming I can find its weight)?
 

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Air bags do not (GAWR)increase carry capacity. The just help you correct the attitude of the loaded vehicle.
 

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beat me to it. u cant change ratings of the truck. u can just change the way it behaves or handles it. but the ratings are the same.
 

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There should be a sticker on the driver side door jam stating weight limits. The airbags can easily make your truck handle more payload than what the manufacturer originally stated but that is not legal to do so. Think liability.

You can weigh your truck on a CAT Scale available at most truck stops. Weigh the front axle first, then the whole truck, then the rear axle. That's as accurate as you can get it. . Most trucks gain weight. Bigger tires, tool box in the bed, bigger bumpers, etc add weight to the truck.
 

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As others have said, air bags (supplemental springs) do not increase your payload or axle ratings at all. They allow you to handle higher payload without sagging and therefore maintain better balance/control. Payload ratings are somewhat subjective, limited to a large degree by handling/steering/roll/stability when loaded to that amount. So, from that perspective, supplemental springs can help handling w/ higher loads.

Axle ratings are not subjective. They are rated at that load for a certain duty cycle, limited primarily by heat and wear/tear (e.g., bearings). There is nothing you can do to alter those numbers, short of swapping for a heavier axle.
 

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Discussion Starter #7
Art64: I think you are right that weighing the truck is about the only way to determine the approximate weight resting on the rear axel. I want to replace my '01 Tundra with a new one to pull an 8K# TT, whcih will be the first time I have pulled anything with a Tundra. I need to carry items in the bed, so must add springs, but don't want to get close to the 4100# GAWR limit. Thank you, and everyone else who responded, for your comments.
 

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It is very easy, with loading, to exceed the rear axle rating limit.

It is your responsibility as driver to decide what you will do with that information.

The axle itself is rated by Hino to 5,500 lbs, the stock tires however would not last long with this amount of weight. The springs are designed for a comfort load with a payload in the 1,500 lb range. Air bags supplement the spring's carrying capacity. Better tires make load handling much better. Rear sway bar helps in this regard as well. Given the fact that the truck is rated to tow 10,000 lbs, (with properly braked trailer) or 3,000 lbs without brakes on trailer. So neither power nor braking ability influences the payload rating on your truck.

While axles don't generally break on trucks even when loaded well beyond the rating, wheel bearings can and do eventually fail, even if the vehicle has never been overloaded. So that is a maintenance item that requires a bit extra attention if loading at or beyond your rated axle weight.

The legalities of loading beyond your rating, or towing beyond your rating, have been well explored, and don't enter into the picture unless you get into ridiculous territory. Towing up to 10,000 or 12,000 lbs with your Tundra, driving responsibly, even if your payload is over the rating, will not get you any attention. Clearly if you drive like a maniac, and can be shown to be operating your vehicle unsafely, and cause an accident while doing so, then you have a problem.
 

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Discussion Starter #9
Frankenstein-Very helpful comments! Just knowing Hino’s rating (which I couldn’t find) provides the comfort level I was seeking. Therefore, I will purchase the 5.7 dbl cab with the TRD (tow) package and tow mirrors. From what I read on this forum, even though the TRD pkg has better tires and Bilstein shocks, I may still need to upgrade both further. I’m convinced that air bags and/or additional springs are a must. I don’t mind the extra money since the primary concern is the family’s (and other’s) safety.

My TT arrives in 4 weeks equipped with brakes and the weight distribution/anti-sway hitch system. So, I think I am getting set up right. Feel free to give more suggestions.

I also appreciate your reference to “legalities.” While I must yet research these issues, as an attorney, I understand the need to stay within the ratings and drive carefully. Even if not at fault, but over a weight rating, I can see an attorney allege contributory negligence.

Again, thanks.
 

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Hino keeps this pretty close to their vest, and Toyota will not budge from their rating. I happened to be able to reach a Hino engineer to get my information, but there is nothing they are willing to put on paper. As he said it "We build the axle to certain specifications as set by the customer. We then build in a margin for error over their specification. Finally, we have our internal margin for error. Since Toyota spec'd 4,150 lbs static load (dynamic load is quite a bit above that) we add 30% -- about 5,400 lbs. Our margin adds 50% to that, so we would not expect premature failure below 8,000 lbs. Of course I would never advise anyone to load to our engineered breaking point, because if you actually load to 8,000 lbs you WILL see failures." (emphasis is mine).

What this did do was reassure me that I can load to 4,800 lbs for my level of use. And while an attorney may make allegations, one can simply indicate taking appropriate precautions in driving, use of better tires, etc. The most common failure by far is tire failure. The most common cause of accidents is driver error, following too closely, excess speed, or poor balance in loading.

Long story short: enjoy camping! :D
 
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