Wheel weight ratings

[TheOtherSean]

Are weight ratings for wheels & tires based upon total weight of the trailer, or based upon the proportion of the trailer weight they will be carrying? In other words, with a 1000# single axle trailer, do I need two tires each rated at 1000#, or two tires each rated at 500#?

[SlyTerry]

2 tires at 500 lbs will do the trick but as you probably noticed that on very few trailers does the tire capacity is the limiting factor...The weakest link in the chain determines the capacity of the trailer. usually its the suspension...

[TheOtherSean]

2 tires at 500 lbs will do the trick but as you probably noticed that on very few trailers does the tire capacity is the limiting factor...The weakest link in the chain determines the capacity of the trailer. usually its the suspension...

Thanks.



That's what I suspected, but I developed a bad case of uncertainty staring at the 990# capacity tires I bought and wondering if I was 10# too low or had a 490# margin.

[wlooper89]

2 tires at 500 lbs will do the trick but as you probably noticed that on very few trailers does the tire capacity is the limiting factor...The weakest link in the chain determines the capacity of the trailer. usually its the suspension...

SlyTerry,

I was wondering about that too having recently inspected my tire size to see if they could accept 10" (25.4 cm) electric brakes. The load rating printed on the tires is 2000 lbs (907 kg), and I did wonder if that was one or both tires together. It is nice to know it is each tire. Either way would be fine in my case. The suspension is rated 2200 lbs (998 kg) and that is well below the tire capability and well above my trailer weight.

Bill

[48Rob]

Sean,

Together, the two equal 1000#...but I'd hesitate to run that close to the limit.

If your trailer weighs 1000 pounds, and the weight is even side to side, you have little to no margin for error.
If your weight is not evenly divided, then you are "over" on one side.

If you hit a good bump the 500 pounds will equal much more slamming down.

A 1350-1500 pound rating would give you a realistic margin.

Rob

[SlyTerry]

Hey Bill your pretty comfortable with the metric system for a southern neighbour... Us being metric babies up here are very comfortable with measurement systems even the US gallon - Imperial gallon- liter conundrum 1 us gallon = 132 imperial ounces 1 Imperial gallon= 140 imperial ounces 1 us gallon= 3.78 liters 1 imperial gallon=4.54 liters....See why I just pump gas until it stops and pay the man

[kennyrayandersen]

Sean,

Together, the two equal 1000#...but I'd hesitate to run that close to the limit.

If your trailer weighs 1000 pounds, and the weight is even side to side, you have little to no margin for error.
If your weight is not evenly divided, then you are "over" on one side.

If you hit a good bump the 500 pounds will equal much more slamming down.

A 1350-1500 pound rating would give you a realistic margin.

Rob

Rob, though I would agree you don’t want to push the limit so close, I’m 99 44/100s percent sure that the tire mfg has taken the dynamic loads into consideration. For instance, big-rig rear axle sets are rated for 34,000 lb, but that is a static weight. The stress analyst will have used a factor on top of that when he did his sizing on it (3g on-road, 5g off-road (slamming down weight as you call it)), but the end user only has to know the static weight.

[Lgboro]

All well and good if the tires weren't manufactured years ago and dry rotted. Many tire sold in the US today were made years ago and have been in storage.

[kennyrayandersen]

All well and good if the tires weren't manufactured years ago and dry rotted. Many tire sold in the US today were made years ago and have been in storage.

Perhaps, I have absolutely no information one way or the other, but I can tell you this, if you have a tire that has dry-rot, it will only be marginally helped with an overrating. I've never had a tire that I bought new fail due to dry rot (35 years of driving and lots of tires). Maybe this is a problem with cheaper inferior tires? I only buy good tires from a reputable manufacturer and it has never been a problem. Trailer tires that are 7-10 yrs old that have been sitting outside are more likely to be a candidate for this problem.

[48Rob]

Rob, though I would agree you don’t want to push the limit so close, I’m 99 44/100s percent sure that the tire mfg has taken the dynamic loads into consideration

Kenny,

You may well be right...

No doubt manufacturers and their lawyers leave a margin for error, but the same lawyers would rake me over the coals if I had an accident that hurt someone because "I" didn't allow a large enough margin on my end...

Of course they can't publish the "real" numbers, or the game would be ruined.

Who'd have thought buying a set of tires for a trailer could be so complicated

Rob

[kennyrayandersen]

Rob, though I would agree you don’t want to push the limit so close, I’m 99 44/100s percent sure that the tire mfg has taken the dynamic loads into consideration

Kenny,

You may well be right...

No doubt manufacturers and their lawyers leave a margin for error, but the same lawyers would rake me over the coals if I had an accident that hurt someone because "I" didn't allow a large enough margin on my end...

Of course they can't publish the "real" numbers, or the game would be ruined.

Who'd have thought buying a set of tires for a trailer could be so complicated

Rob

I only say that because when I calculate margins of safety for aircraft structure it's the way we do it and I did a little work for a buddy of mine who is an OEM trailer manufacturer.

There is a little more to it than lawyers (though there are times when it seems they are definately running the show!). Some of the loads issues are empirically derived based on field data. For instance we use a 6g up gust condition as one of the loads for an airplane. 6g! Emagine being squished into your seat at 6 times your body weight! At that kind of crazy loading, we allow yielding and all sorts of deformation. Anyway, it's not lawyers that make us use those, but you know every so often you hear about people being thrown around the cabin like rag dolls (sorry to those with a flying phobia). It's actually for those rare occasions that we use those big load factors -- it would be really bad form if the wings fell off!

Likewise, 3gs on the road is huge -- personally I'm not sure my fanny has ever experienced that kind of force (though a tire and a pothole might?). Of course no one wants to get sued, but as an engineer I can say I I would feel bad if someone got hurt or maimed or something lawsuit aside. I'd like to think the tire guy has some ethics just like I do when I'm doing my job. Ultimately though that lawyer is carrying a pretty big stick (Wilderness AT anyone? -- yeah I know -- not REALLY the tire's fault).

[TheOtherSean]

Sean,

Together, the two equal 1000#...but I'd hesitate to run that close to the limit.

If your trailer weighs 1000 pounds, and the weight is even side to side, you have little to no margin for error.
If your weight is not evenly divided, then you are "over" on one side.

If you hit a good bump the 500 pounds will equal much more slamming down.

A 1350-1500 pound rating would give you a realistic margin.

Rob

Thanks, Rob. From what you and the others are saying, I feel pretty comfortable with a pair of 990# tires for a trailer I'm aiming for under 1000#.

[Dale M.]

All well and good if the tires weren't manufactured years ago and dry rotted. Many tire sold in the US today were made years ago and have been in storage.

I'm curious to this remark.... Have any documentation to back up that statement or at least a website that offers up proof....

Dale

[Errol]

As a tyre tech for over 30 years, I can tell you that tyres are not stored for a number of years. That is urban legend. The serial number on the sidewall provides all the information about the tyre, ie. date and place of manufacture.
As for the tyre load capacity, this takes into account most loads that the tyre will encounter, eg: under braking, cornering etc where the load on a particular tyre will be well beyond what one might imagine, but then it is only for a relatively short time.
Hitting potholes is not a consideration during manufacture, but should be considered by the purchaser for their particular usage. Therefore you might consider a light truck type tyre that will not deform like a passenger tyre, if you are concerned about potholes for example. As for the cost, remember that without brakes on your trailer, the tyres will outlast the trailer, so it may be worthwhile going for better quality in the first place.
The science behind tyre manufacturing is incredible, although tyres manufactured in some countries, whilst meeting the local legal requirements, are dangerous and you will only discover this when it is too late.
Errol.