ruderunner
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Post by ruderunner on Jul 1, 2018 3:55:37 GMT -8
Note: this is a work in progress and may take a couple revisions. Also while some of these terms have legal definitions, do not take this to mean legal advise. Also many states have variances in towing regulations and whats legal at home may be different in another state. Contact a lawyer if need be.
So in order from lightest to heaviest heres some definitions (we'll get to weighing and calculating numbers later):
Shipping weight: This is the published weight the manufacturer uses for bill of lading when sending product from the assembly plant to the point of sale. Typically the lightest weight you will find for anything (camper, truck, TV or refridgerator) In the case of vehicles, they may or may not be completed. Yes some components may be shipped separately to be installed at the dealer, you've probably seen a semi flatbed loaded with trailers that have no wheels or tires. What's it mean to us? Nothing unless you are a manufacturer or transporter though sometimes it will be advertised as the weight of a trailer.
Dry Weight: Applicable to motor vehicles and trailers, dry means dry. No liquids, no oil, no coolant, no fuel. It also is based on the weight of a vehicle with standard equipment only. Any options will add to the number but you'll need to find out those weights separately and add them in. It's a hassle. What's it mean to us? In the case of the motor vehicle, pretty much nothing as a vehicle without fuel, oil or coolant isn't useable. Different story for campers though, many don't carry liquids anyways. This has historically been the advertised weight of a camper and I feel it's a good number to use for comparison shopping, just don't expect the camper to weight the same when ready for a trip. Best bet, weigh your setup
Curb Weight: An industry standard number for comparison shopping. It's the weight of a vehicle with full fluids and in a ready to drive state. Based on standard equipment for the vehicle, optional parts will add to the number. It does not included passengers or cargo. Of note here is that most payload and tow ratings are figured based off of this number. Also important is that the manufacturer doesn't know the exact weight of the vehicle in your driveway, so once again weigh it. As a bonus for the camping world, regulations went into effect about 10 years ago making this the advertised number for campers and having it clearly marked on the weight tag. I haven't yet confirmed exactly what included in this number but suspect it includes full fresh water tanks. What's it mean to us? A really good number for comparison shopping and will get you in the ballpark of wether or not your rig will handle a specific trailer. Again though the best bet is to weigh because of differences in optional equipment.
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ruderunner
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Post by ruderunner on Jul 1, 2018 4:47:29 GMT -8
This grouping is what I'll term legal limits. You can be cited or worse for exceeding them, and in case of an accident you may be found liable even if you didn't actually cause the accident. Only the vehicle manufacturer and some liscensed outfitters can legally change the limits on any given vehicle. Just because you added helper springs or other equipment does not mean you have increased the limit.
Gross Axle Weight (GAW or GAWR): as implied it's the absolute most weight that an axle is allowed to carry. Most motor vehicle have these numbers on a sticker in the door jamb and will specify front and rear axle limits. Campers usually have a tag or sticker somewhere but you'll have to look for it, on older units it's often near or on the door. Numbers on the internet or even in the owners manual are not vehicle specific. The sticker or placard on your vehicle is your limit regardless of other published information. In the case of tandem axles they are usually stated as a single weight (eg two 3500# axles in tandem will be tagged as 7000# axle) These numbers can vary tremendously depending on how much weight is carried and where the weight is placed. It includes everythng in or on the vehicle including but not limited to: you, your spouse, the hitch, a snowplow and even the loose change in the ashtray. What's it mean to us? Well besides the legal consequences there are mechanical consequences, an overloaded axle is going to wear out faster, bend or break. This is one you have to weigh to know for sure if you are within the limits.
Gross Vehicle Weight (GVW or GVWR): Agan this one seems pretty straight forward, it's the maximum weight the vehicle is allowed to be subject to the limits of the axle weights. As above it includes everything, even the fries dropped between the seats. Of note is the interaction with axle weight rating, you can certainly load the vehicle in a manner that will kepp you below the GVW but still exceed the GAW. You're not legal that way. This is also placarded on the vehicle, almost always the same sticker that states axle weight ratings. What's it mean to us? The same thing as above, and yes you need to weigh it. Note many folks confuse GVW with payload, however the basic calculation for payload is GVW-curb weight.
An interesting phenomenon of the interaction between GAW and GVW that you should pay attention to: most motor vehicles, especially trucks, have higher combined axle weights than gvw whereas most trailers have a higher gvw than axle rating. Why? motor vehicles generally have a much broader range of where and how the weight can be distributed so the axles are designed to account for that. Trailers have tongue weight in which case the tow vehicle is supporting some of the trailers weight and the axle doesn't have to carry all of it.
OK here's one that is often confused,
Gross Combined Vehicle Weight (GCVW): This is the maximum weight of tow vehicle and trailer, subject to axle limits and gvw limits of the individual components. It IS NOT the combination of tow vehicle GVW and trailer GVW, it IS NOT how big a trailer you can tow. It IS the limit of the COMBINED package with all options and cargo.For example, a truck loaded to it's GVW of 9000# and has a GCVW of 10000# can only pull 1000# of trailer, no matter what the GVW of the trailer is. Conversely, a 4000# truck with a 6000# GVW and a 8000# GCVW can tow up to 4000# of trailer but you can't exceed the trailer GVW to max out the GCVW. What's this mean to us? More of the same legal and mechanical problems. And the remedy is the same, weigh it to know for sure.
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ruderunner
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Post by ruderunner on Jul 1, 2018 5:18:37 GMT -8
This section I'll call Advertised and calculated weights. Indeed many of the advertised numbers are caluclated and can be used for comparison shopping. But as mentioned in the first section, advertised numbers don't necessarily mean that what's in your driveway matches that. Also something to keep in mind, advertised numbers are usually calculated to give the most impressive ratings not necessarily what is real world.
Payload: this is a calculated number that is advertised. The calculation is GVW minus Curb Weight. Notice that one number is a legal limit and one is an advertised number, this trips many people up. Also many people think GVW=payload, it does not but it's a bigger number to brag about in advertisements. Remember the definition of curb weight is for an empty unoptioned truck, this being the lightest truck they can sell will inflate the payload number. Best bet, weigh your truck as you normally drive it and subtract that from the GVW to calculate your payload.
Towing capacity: This is another calculated number that is advertised and again the calculation is done in a manner that advertises the biggest number. It usually has a disclaimer or asterisk about being properly optioned and equipped. Unfortunately this number is usually not placarded on the vehicle and is buried in the owners manual, as are the required options and equipment. Generally speaking the advertised number is based off of a truck with all the towing options and the correct hitch with weight distribution and sway control, but no other options in order to keep the truck as light as possible. This weight is then subtracted from the GCVW to give the calculated towing capacity. Does your truck weigh the same as the one used for the calculation? Probably not. As with payload the best bet is to weigh your truck as normally driven then subtract that from the GCVW to find your towing capacity.
It is important to note that towing capacity is not based on GVW of the tow vehicle or trailer but you cannot exceed either of those numbers. Along with that, just because the gvw of the trailer is higher than the capacity does not mean you can load the trailer to the max. The other way is also true, you cannot load the tow vehicle to its GVW and still pull the max capacity.
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ruderunner
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Post by ruderunner on Jul 1, 2018 5:49:11 GMT -8
Finding your weights: Generally speaking the GVW and GAW are listed on stickers on the vehicle. Most other numbers can be found in your owners manual but some you need to weight for yourself. The ones in the owners manual are going to be fairly generic for the type of vehicle you have and will have lots of little details about how those numbers are figured. For example tow capacity has disclaimers about special options and equipment and you will need to follow those guidelines.
As for actually weighing your vehicles and setup, the first hing you need is a scale. These usually aren't too hard to find, most aggregate suppliers have scales (sand and gravel yards) some landscape supply places, some lumber yards, truck stops occasionally, scrap yards usually but i'd recommend avoiding highway weigh stations until you know you're legal. Unless you're running a commercial liscense you shouldn't need a certified scale (call the lawyer) most others are close enough for this.
You'll also need a notepad and writing insturment. A calculator can be handy but most of this is basic addition and subtraction.
Here's the procedure I use. Note some of the abbreviations I use here have no definition other than what I say. Meaning there's no industry standard or legal standard, it's just 4 letters are easier to write vs a bunch of words:
Drive truck and trailer to scale. Ask to use the scale. I've never been rejected nor charged but a certified scale probably will charge.
Disconnect any weight distribution device (this can adversely affect the tongue weight calculation later)
pull slowly onto the scale until the rear axle of the tow vehicle is almost on, write down the number you see on the display. Lable this FAWT (front axle weight towing)
Pull forward until the trailer is almost on the scale, write down the number on the display. Label this TVWT (tow vehicle weight towing)
Pull forward until the whole rig is on the scale, write down the number on the display. Label this GCVW (gross combined vehicle weight)
Pull off the scale and disconnect the trailer.
Pull on the scale slowly until the rear axle of the tow vehicle is almost on, write down the number on the display and label FAWC (front axle weight curb)
Pull forward until the whole tow vehicle is on the scale. Write down the number on the display, label it Curb Weight.
Pull off the scale and reconnect the trailer including any weight distribution you have. At this point you can head home or show yourself how weight distribution affects the tow vehicle. If you want to see what happens repeat the test with the trailer connected and mark down the numbers indicated. What you should see is the FAWT increase and a smaller reduction in RAWT(TVWT-FAWT).
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ruderunner
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Post by ruderunner on Jul 1, 2018 6:24:59 GMT -8
OK now you have a page full of numbers and we can figure all sorts of things from here. It might be easier to do the calculations in a different order than they were weighed.
So we have Curb Weight and FAWC. Cubr weight is just that, the curb weight of your vehicle. FAWC is the amount of that weight carried on the front axle of the vehicle. Subtract FAWC from Curb Weight to find RAWC (rear axle curb weight) This is handy info not just for towing but for hauling home improvemnt supplies etc. It also tells you what your actual payload is versus the advertised number since you weighed your vehicle not the theoretical vehicle.
Do the same calculation with FAWT and TVWT. This tells you how much weight is on the rear axle when hooked up (call this RAWT). Compare this to your stickered GAW for the axles to be sure you're not over the limit on the rear. Also compare TVWT to GVW to make sure you're just not completely overloaded.
The GCVW you wrote down needs to be compared to the GCVW in your owners manual. If you're over you need to lose weight or get a higher rated tow vehicle.
Subtract TVWT from GCVW to find trailer weight. Now you know what the trailer weighs and can calculate the ideal tongue weight.
This gets a bit more complicated because division is involved...and there's more steps to find out what your tongue weight currently is.
Ready? ok take your trailer weight and divide by 10. That's the minimum tongue weight you should have (10%) Now take the trailer weight and divide by 6. This is the maximum tongue weight you should have (actually just a bit over at 16.?% vs 15%) I want to keep the math simple.
OK now you know the range for tongue weight, but still not what it is. We can calculate it just use the numbers you got without weight distribution. We'll do this in steps rather than one long algebraic equation.
1. subtract FAWT from FAWC 2. subtract the result of 1 from RAWT 3. Subtract RAWC from the result of 2
If I did the physics correctly that should equate tongue weight
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Post by bigbill on Jul 1, 2018 9:41:23 GMT -8
I would also like too add this thought. Now you are ready to load and go. As you add things to your trailer you and your helpers may make several trips to the trailer with must take items take don't weigh much but keep in mind what a loaded suitcase weighs or a large sack of groceries or a case of soda/pop. Are you starting to see what I am talking about? It is real easy to add 500 to a 1000 pounds without thinking about it. If you put everything in one end of the trailer you can drastically change the balance causing too much or too little tongue weight. A simple way to make sure you are loading right is have your trailer hooked to the tow vehicle the before loading measure from the tongue to the ground. Once you are loaded remeasure, these numbers should stay fairly equal to what they were, if it changes then you may be out of balance. If the front distance increases you have decreased the tongue weight which could result in sway. If it front measure decreases just a little you are probably fine but it means you are increasing tongue weight which could overload your hitch. This is just a simple way to see if you are in the ballpark.
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ruderunner
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Post by ruderunner on Jul 1, 2018 15:38:19 GMT -8
Good point and part of the reason I tried to show folks how to calculate tongue weight the way I did. There's an easier way but I wanted to emphasize that where the weight is us as important if not more important than how much weight.
That said I'm still trying to figure out a good way to explain what WD hitches do and how they effect the tow vehicle. I know what they do and how, just trying to figure out a simple way to explain it.
Teeter totter has come to mind. Any suggestions?
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Post by bigbill on Jul 1, 2018 18:08:24 GMT -8
The spring bars act as a lever using the weight of the trailer tongue to load the levers which transfers part of the weight to the front wheels of the tow vehicle. Years ago they showed a front wheel drive car towing a trailer with the rear wheels removed to demo how they worked. The car and trailer sat perfectly level. They also told you not to do it as it was just a demo to explain how the hitch worked.
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roadtripper
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Post by roadtripper on Nov 6, 2018 19:36:53 GMT -8
Thanks for the detail here. I've always just taken a wild guess at my trailer weight. I'm thinking 3500 is on the safe side. I might be way off. I'm hoping to get to the scale over at the gravel yard soon and see for sure. I'm in the market for another tv and thinking 7k tow rating would be good which makes the colorado look nice. Have a question on the tongue weight. How far back on the trailer is it affected? Is everything half way from the ball to the axel part of tongue weigh or do the wheels carry the load farther forward due to the balance of the load behind them? I saw a ball with built in scale on etrailer where you always have an accurate read on tongue load. It cost about $120. Looks like a nice safety feature. Any one ever tried on of these? Thanks.
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ruderunner
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Post by ruderunner on Nov 15, 2018 8:18:55 GMT -8
Tripper, tongue weight is the effect of how the load of the trailer is positioned relative to the axle centerline.
Think of a teeter totter or old school balance scale with the axle as the pivot. Weight added to one side will bring that side down and the other side up. Placing weight directly over the axle has no effect on which end is heavier.
Let's try an example: For the sake of this lets say we have a 15 foot camper, 10 feet between ball and axle and 5 between bumper and axle. Lets place 200# over the axle, there it makes negligible difference in tongue weight though of course it does increase total trailer weight. Now put that 200# on the tounge (think a couple batteries) you've increased the tongue weight by rougly 200#. OTOH if you put that 200# on the bumper of our theoretical camper (bike racks etc) you actually unload the tongue by 100#. (5 feet being half of 10)
The important thing to keep in mind is that tongue weight is more like a measure of force needed to tip the trailer front to rear. All else being equal, the longer the tongue the less force needed to tip the trailer.
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