Determining actual weight on tow vehicle tires - Fiberglass RV


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Old 02-06-2016, 04:32 PM   #1
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Determining actual weight on tow vehicle tires

Sorry if this has been discussed a lot already but my search didn't really come up with much.

I was starting to get scared that the brand new C range tires I just bought were going to be pushed really far past their load rating, but maybe there's hope...

So each tire has a max of 1,985 lbs. I know my truck weighs about 4,000 lbs. I would guess more of that weight is in the front because of the engine, but to be on the safe side and to make it easy, I'll just divide that four ways.

So there is already 1,000 lbs on each tire. Now if I buy a trailer with a gross weight of 3,300 lbs, say, that would be crazy! Way over the weight.

But then I started thinking what I need to look at is tongue weight, right? Not total weight.

So most of our trailers, in the 17ft and under category, aren't more than 400 lbs tongue weight. So while I'd be on the safer side running a D range tire, or a tire brand with a slightly higher C weight , I'm still under the max weight, and not pushing the limits too much, right?

I wish I had looked a little more into this before I bought my tires. I just looked at the old ones, and they are load range C, but have a max rating of 2245 lbs or something.
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Old 02-06-2016, 06:21 PM   #2
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Unless you're planning to carry a lot of cargo weight in the back of your truck, I think you should be fine. I'm sure you're well under 1000 pounds/rear tire empty, and you're adding less than 200 pounds of tongue weight on each tire. And yes, it's tongue weight that matters, not the total trailer weight. The rest of the weight is carried on the trailer's tires.

It wouldn't hurt to upgrade when you are due for new tires, but it doesn't seem urgent enough to throw out a perfectly good set now. It also wouldn't hurt to increase the pressure a little when you get ready to tow.

The fact that you'll be going at a slower speed when towing helps with the demand on the tires. Trailer tires are only speed rated to 65 mph, so you probably shouldn't be going any faster than that (and some states have even lower limits for towing).
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Old 02-06-2016, 07:15 PM   #3
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Keep in mind that while your truck may weigh x so many pounds it is pretty well always going to weigh much less on the rear axle than the front... just the nature of the design of a truck - so dividing the weight of the truck over all 4 tires is not going to give you much in the way of factual weights.

The tongue weight of the trailer is going to be carried on the rear axle/tires as well.
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Old 02-06-2016, 07:30 PM   #4
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Ok, thanks!

Yeah I knew dividing by all four tires evenly wouldn't be quite accurate, but by doing it that way, if I come out still under the max weight, then I know I'm well on the safe side and I've got some wiggle room. Plus the math is easier

I have a fiberglass topper on my truck and I will have some stuff in the back, but nothing crazy. But I'll bet the topper weighs almost 200#.
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Old 02-07-2016, 10:08 AM   #5
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Accurate axle weight

Semi trucks are taxed, and fined both by total weight and per axle weight, I think. Most truck stops (and grain elevators) have scales. You can get an accurate weight of each axle by weighing the entire rig, then in succession pulling an axle at a time forward off the scale. Truck stops are quite familiar with this. I think it costs around $10. By the way, many highways have accurate scales built into the roadway near weigh stations. These metal plates are used to pull trucks in or let them PrePass with a transponder.
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Old 02-07-2016, 01:48 PM   #6
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I've also considered going to the local transfer station/landfill and having them weigh me. That's how I found my truck was 4,000#. But I'll bet if it wasn't busy, they'd humor me and let me weight each axle, for free.
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Old 02-07-2016, 01:59 PM   #7
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Quote:
Originally Posted by ZachO View Post
Ok, thanks!

Yeah I knew dividing by all four tires evenly wouldn't be quite accurate, but by doing it that way, if I come out still under the max weight, then I know I'm well on the safe side and I've got some wiggle room. Plus the math is easier

I have a fiberglass topper on my truck and I will have some stuff in the back, but nothing crazy. But I'll bet the topper weighs almost 200#.
I guess the bigger question is what truck do you have and what does the manufacture suggest the tires should be and its pay load? No one knows a vehicle better than those who built it so their advice is probable much better than any you would get here without anyone knowing even what make/model of truck you have.

Many of the mid sized trucks do not have an overly large payload and with two passengers, the family dog and the topper on the rear you may not have as much as you may think left over for the trailers tongue weight.
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Old 02-07-2016, 02:47 PM   #8
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I've also considered going to the local transfer station/landfill and having them weigh me. That's how I found my truck was 4,000#. But I'll bet if it wasn't busy, they'd humor me and let me weight each axle, for free.
Scales like that would not be very accurate, perhaps only calibrated to read in increments of 100 lb. They get a lot of rough use, and may not be checked for accuracy very often. A grain elevator or Feed store should have better scales.

To get accurate axle and wheel weights, you need a scale where the approach and departure ramps are level with the platform, and long enough so the truck/trailer stay level at all times. Your most accurate reading will be with the entire rig on the scale. Then, when you pull forward or back to weigh one axle, go just far enough to get the other wheels off the platform. DO NOT TURN THE STEERING WHEEL. DO NOT HOLD THE BRAKES. DO NOT PUT IT IN PARK. JUST PUT YOUR TRANNY IN NEUTRAL AND LET IT ROLL TO A STOP. Otherwise, the scale can be pulled sideways and you get a false reading.
You individual axle weights should add up to within one half of one percent of the total weight.
After all that, There is no need to split hairs here. "Close is Good Enough"
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Old 02-07-2016, 02:56 PM   #9
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Cool, thanks.

I know my max tongue weight is 500#. I'll have to look into the rest of it. My truck came with load range C tires. With the trailer I get, I don't expect to have a ton of extra capacity, but I don't expect to be right at the limit, either.
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Old 02-07-2016, 03:00 PM   #10
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Ok, thanks!

Yeah I knew dividing by all four tires evenly wouldn't be quite accurate, but by doing it that way, if I come out still under the max weight, then I know I'm well on the safe side and I've got some wiggle room. Plus the math is easier

I have a fiberglass topper on my truck and I will have some stuff in the back, but nothing crazy. But I'll bet the topper weighs almost 200#.
The load added at the rear, on the hitch ball, is some distance behind the rear axle. So, there will be a transfer of weight off the front axle as well as adding weight on the rear axle. Trucks are designed so that with the maximum payload in the box, the load on all four wheels is the same, to somewhat more on the rear. the only way to know for sure is to weigh all axles under as loaded conditions.
For example: say your trailer hitch weight is 200 lb. and the ball is 2 ft behind the rear axle, and the truck's wheel base is 10 feet. (200 x 2) divided by 10 = 40 pounds that will transfer to the rear. So, your added load on the rear axle is 240 lb. and your front axle load is reduced by 40 lb.
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Old 02-07-2016, 03:03 PM   #11
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As Carol suggested, just look in the manual that came with the vehicle. There is probably a page or two giving the specs for the tires for your vehicle.
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Old 02-07-2016, 03:06 PM   #12
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Cool, thanks.

I know my max tongue weight is 500#. I'll have to look into the rest of it. My truck came with load range C tires. With the trailer I get, I don't expect to have a ton of extra capacity, but I don't expect to be right at the limit, either.
Don't get too uptight about this issue. Engineers most always design machines with a "safety factor" that lets you overload it without imminent disaster.
How many times have you seen some pickup loaded such that the rear end is dragging and the tires are all squished down?
Get your self a load-inflation chart for your tires. WEIGH the axles, and adjust air pressure accordingly.
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Old 02-07-2016, 03:13 PM   #13
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Yeah, I once saw a early Tacoma (probably a 96) pulling a full-size airstream, with the bed completely loaded down, down I-15. Not to say that's a good idea, but...I'm not pushing things to their limit no matter what 17' trailer I get.

But I do like to be well within the safety zone. With any luck, I'll be home with my new camper mid-week, then I can look into getting things weighed.

Thanks.
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Old 02-07-2016, 03:59 PM   #14
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I went to a grain store that sells feed and fertilizer by the pound to farmers. They have scales that work with smaller amounts. I went to a CAT scale here and he said I didnt weigh enough to tip the scales. ( I just think he didnt want to mess with a small trailer).
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