trailering

Then fuel weighs 5.8 to 7.3 lbs (per gallon), right?

Wow, this thead just got really complicated for a simple question. Let's assume for all of my previous posts the trailer was balanced correctly (weight on the tounge of the tow vehicle). With a longer distance between the hitch and the axel the trailer will track behind the tow vehicle better.

Since most of us trail with bows forward cat trailer have this "advatage" built in.

I would say that the chagne in weight of fuel in a tow vehicle is not going to make it unstable. It's not like we are flying in a small airplace with a fuel tank aft of the rear baggage compatement that when the fuel is burned completly changes the handling of the airplane.

As far as tire size goes, 8" tires will work fine. I like the larger tires because I feel better with that extra margin given by reduction in angular velocity of the bearings. I also really like the larger tire diameter for handling bumps in the road.

Ditto, Amen and all that. There's a lot of real estate between lakes around here, not so breathtaking that one would want to drive slow to take it in (driven at 75 - 80 mph) and never a problem. Specifically the advantage of having the whole "kit" lower far outweighs the supposed advantage of 12" setup. I've pulled and have both sizes and while pulling I can discern no difference.

Pardon me, maybe this should be a new thread?

With soaring fuel costs and lots of miles slated for this season, I like the lower idea (8" wheels), from the wind resistance standpoint. I'm about to take the old school, overblown cooler style box OFF my 16 trailer (sail tube only). Nothing in it can't be kept in the vehicle. Thinking of doing something to the front of the box on the 20 trailer (along the lines of Thull) to cut down wind resistance. Or is this useless? Engineers? I dunno, maybe I can tape some smoke bombs to my bumper. Will a significant amount of air go under a tow vehicle at 70 mph?

I don't think you will see any increase in fuel economy if you take the tool box off your trailer. Remember how much quieter it gets in your car when you tailgate a tractor trailer. The same thing happens behind your vehicle but on a smaller scale. The increase in drag is mostly (at least for me) due to the boat being wider than my car. So, my car has not moved the air out of the way yet.

I don't think a couple inch difference in height of the trailer will increase your fuel economy either for the same reason. Most of the drag comes from the boat being wider than the tow vehicle. Your best bet would be to dissassemble to the boat so it can fit within the width of your tow vehicle. Then you will have better fuel economy.

My 2 cents

All other things being equal, for an equivalent disturbance, the wider trailer will have larger oscillations in the disturbing, restoring and damping forces due to the longer moment arm from the tow point to the tire contact point. In particular, the component of the tire side force that resolves to a force pointing directly aft and acting on the moment arm, sin(yaw)*(axle length), will have a much larger impact on the system on a wider trailer than on a narrower trailer.

Assume a wind vane with a pivot arm of length 1 ft from the pivot point to the center of lift of the vane. Assume a second wind vane with the mid point of an arbitrarily long cross bar attached to the same 1 ft arm with a vane at each end of the cross bar. Any length cross bar will be less stable than the zero crossbar case and with a long enough cross bar, the wind vane will be unstable.

Looking at it qualitatively, an absurdly long crossbar (axle) will, in effect, result in a very short pivot arm (tongue length).

Please don't make me draw a free body diagram.

So am I right in my totally subjective impression that, in general, a narrower axle will tow better than a wider axle, if the tongue length is the same for both and they are both carrying the same load and with the same tongue weight and same percentage of weight forward of the axle?

Nick says no, I say yes. These guys also say yes, though they don't show equations to prove it.

If you feel like dropping $12, you could most likely find the definitive answer in this ... Analytical Methods and Test Procedures

As far as wheel sizes go I feel confident with 8" tires. True a 12" wheel spins 30% less than an 8". Typically 12" tires are wider than 8" tires, which means more rubber is on the road, which means more traction.

In mechanical design we tend to deal with cyclical loads. Funny things happen when a load occurs over and over again. Think about bending a paper clip, you can do it once or twice but if you do it over and over again eventually it breaks. The goal of mechanical engineering is to design paper clips that don’t break. Bearings are designed to have an “infinite” life (on paper any way). On the box it never says “replace after 1 million revolutions.” Industry standards such as SAE are set up to make sure that machine parts don’t have a finite lifespan.

What is more important than wheel size is that your hubs are well maintained. Well maintained bearings with an 8" wheel will last for years and years and miles and miles. Poorly maintained bearings regardless of wheel size can be extremely dangerous. It is all about lubrication and maintenance.

A friend of mine was towing his Boston whaler from Tiburon (just across the Golden Gate from SF) down to Monterey. He didn’t know about bearings or how to pack his bearing buddies. Just south of San Francisco he noticed his trailer was smoking and pulled over right away. A bearing had seized and when he jacked his trailer up the wheel fell right off. The heat had softened his axel and the seized bearing has sheared the wheel right off. I guess the moral of the story is to check your bearing buddies regularly.

I have brand new springs/bearings/hubs/tires (12) that were installed about 6 months ago and I have maybe trailered 100 miles since. Do I need to do anything to the bearings before a long trip?

I totally agree with Nick here. Your trailer essentially drafts behind your car in NASCAR and bicycle racing. An easy way to tell what is causing an increase in drag is to look at the front of your car dead on and see what sticks out above and on the sides.

As far as designing some type of cowl to increase your fuel efficiency it is extremely difficult and I think you’d end up spending much more building the stupid thing than you’d ever see in fuel savings in a hundred years.

Awhile back there was a group of the best of the best engineers working for Porsche that had supposedly used all of this new cutting edge technology to cut down on drag on some new sports car. When they did the wind tunnel tests they found that they did cut down on the drag. Just for fun they put the car in the wind tunnel backwards and the test results were phenomenally better with the car backwards than forwards. Aerodynamics is difficult for even the best of the best.

PTP,

You're probably fine. Just look at your bearing buddies, if they're sunk into the hub a bit then add some grease, if they're popped out all the way then you're fine.

I don't know if it's bad or not, but before a long trip I always give mine a shot of grease till it oozes out a bit, then I wipe the excess off. I also always have some type of grease gun with me for long trips, my bearings are older and the seals tend to leak a bit. You can get a whole tube of marine grade grease at the big orange home improvement store for about 2 bucks and a grease gun for less than $10. With all the money we dump into our boats, this is one of the cheapest and most important investments we can all make.

Depending on whether is gas, gas/alcohol or diesel.

So far from this thread I have gleaned that a narrower axle will tow better than a wider axle, if the tongue length is the same for both and they are both carrying the same load and with the same tongue weight and same percentage of weight forward of the axle.

So, it sounds like the wider the axle, the longer the tongue you need to maintain the same towing stability, as far as tracking straight behind the tow vehicle.

AND, it also sounds like you are better off with a narrower axle because it is easier on your bearings if most of the weight is distributed to the outside of the wheels rather between the wheels and directly over the axle.

Am I getting this image correctly? This is really interesting stuff .

Steve,

I never said a narrow axel will tow better or worse than a wider one. I said that a longer tounge length will have more effect that a change of a few feet in the axel width.

I think you and I are on the same page here:

Longer tounge = more stable trailer.

Mary, It doesn't matter how wide or narrow your axel is. The wheel are cantilevered (supported on only one end) no matter what. You need to have an axel/bearing/wheel combo that is designed for the appropriate weight.

That is correct. And as Steve's formula confrimed the longer the tounge the better it will track. In real work application a few foot change in the width of the axel will not have an appreciable effect on the stability of a trailer with a 16' tounge length.

I took stance to mean width. If you meant camber, well, having the tires cambered inward helps stability, too. So does toe-in.

PTP:

Its not so much the mileage (minimal in your case), but how many times have they been SUBMERGED IN WATER at the boat ramp, DEEP puddles, etc. during those 6 months? Axle grease is water RESISTANT, to a point, but if water STAYS in there, the churning at 80MPH will eventually cause the soap-base of the grease to "mayonnaise" and break-down... then, the "bad thing" happens... almost always at a very inconvenient--and even dangerous--time and place.

You're probably fine, but hey, pump some MORE grease in there and CHECK closely if the overflow that oozes out is grease... or WATER? Even if they have NOT been dunked during that period, if you live in a humid climate, there's condensation too...

Is it just me, or am I seeing more and more bearing buddy type hubs withOUT the rubber slip caps on them? No, they don't keep out water, but they do keep out SAND, which is important, given the sliding piston, the need to keep grease nipple clean, etc.

longer tongue makes it easier to back it up.

Ever tried to back up a short little trailer? very hard if you're used to a long tongue.

So that's why the boxster looks the same which ever end you're looking at...

Paul

I have noticed that cars are starting to resemble jelly beans. What is with that body style? The next time you drive down the street look at them. Jelly beans...Mine is Kiwi.

Aerodynamics. Less drag means lower fuel usage. Vans have the same aerodynamic characteristics as a sheet of plywood.

The further apart your wheels are, the more stable you are on the road. As somebody else mentioned, draw bar length (how far back the wheels are relative to your car) will reduce any tendancy for the trailer to weave all over the road.

Furthermore, larger diameter wheels are better than the smaller ones as the bearings are not working anywhere near as hard. I use 15" car rims on mine. Went to a wrecker and found 3 mag wheels with good tyres for $25 the lot The negative is your boat is higher off the ground but then if you match the trailer wheels to your car, you can use the car spare if you ever get a flat

Tiger Mike

I did mean width, but I as said in a later post the 2-4 foot difference in width is not going to make any appreciable difference on a trail with a 16 foot plus tounge length. On a much shorter (5-6 feet) utility trailer, yes the width will have a profound difference.

An easy was to exaggerate the effect of axel width and tounge length is to back the trailer up. The easier it is (removing practice and skill at backing trailers up from the variables) the more stable it will be behind your tow vehicle.

just heard from Trey last night on his way down to spring fever. One of the TheMightyHobie18 trailer axles blew up. Not the bearings, he said the axle just folded in three places.

"I use 15" car rims on mine. Went to a wrecker and found 3 mag wheels with good tyres for $25 the lot"

I don't know with a light weight cat trailer if it makes much difference...but for trailers in general you are not suppose to use car tires because the sidewalls are too flexible in comparison to trailer tires.

Regards,
Bob

The average car tyre will have a working load of approx 1200 lbs and my trailer weight is around 1000 lbs per wheel so the loadings will be similar. (I usually have 2 boats and all my stuff in the trailer). You should use a tyre designed for whatever load you are putting on it.

Tiger Mike

"The average car tyre will have a working load of approx 1200 lbs and my trailer weight is around 1000 lbs per wheel so the loadings will be similar. (I usually have 2 boats and all my stuff in the trailer). You should use a tyre designed for whatever load you are putting on it."

Hi Mike
It's not so much the load, as the flex of the sidewall...from what I have read on the subject, the sidewalls are much stiffer on dedicated trailer tires which helps to keep trailer sway to a minimum...granted this is a much bigger issue with a heavy utility or power boat trailers.

Regards,
Bob

So here's a little twist: How many people tow a train, as in a camper and the boat or a fifth wheel and the boat. A few of our fleet members do this successfully with the fifth-wheel types having better luck. Also, how many people use a sway brace. Reese makes a really good one that I'm thinking of installing.