Help! Larger wheels on smaller axle?

[High Desert]

Just an FYI, the difference in unsprung weight between an 8" wheel tire combo and a 12" is roughly seven pounds. Now if you go to a big 15" wheel and an off road tire then you're talking 30 pounds or more. Just food for thought.

[KCStudly]

I've heard tell that unsprung weight is equal to 10 times sprung weight. If accurate, your 7 lbs is equal to 70 lbs per wheel. Could make the difference for someone that has no idea what their axle load rating is.

Do your homework. I don't want to be that guy who comes on here and posts photos of my labor of love laying in a ditch because I guesstimated.

Peace.

[CarlLaFong]

So, for the few of us who didn't graduate Magna Cum Laude from MIT, what are you trying to say, or are you just trying to impress us high school grads?

Well, I am no no MIT graduate, and, yes, we all have egos so that is fair. However, I have enough education to know that...

None of what that lady told you makes a bit of sense. First of all, the axle doesn't support the tire and wheel, it's the other way around. The wheel hold the axle and the trailer up. The tires will not wear any differently than they would on any other trailer. They simply go round and round

... could be totally misleading to many people that do not have enough education to know better than to believe anything they read on-line.

Do your research and make your own educated judgments. Every design situation is a compromise. Some succeed and some fail. Depends on the application. If you misjudge the loads and/or application you risk failure (a couple come to mind http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940) and http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse... others http://en.wikipedia.org/wiki/Category:Engineering_failures).

Or you could just get lucky.

I'll crawl back in my hole now.

I'm just busting your chops. Still, you seem to have some insight that some of us may not have,. Why not share the knowledge, rather that befuddle us with technical jargon? Many here have put larger wheels and tires on their existing axles and springs. Are they courting disaster? Will the sky fall?

[KCStudly]

Many here have put larger wheels and tires on their existing axles and springs. Are they courting disaster? Will the sky fall?

No, of course not...maybe. Engineering, like medicine, is not an exact science. To be an engineer is to juggle all of the design criteria; expected conditions, cost, practical issues related to fabrication complexity and cost, risk, unknown conditions and cost.

I know just enough to be dangerous.

We are all engineers in our own way. Do you need a band aid, or a stitch, or major surgery?

I have an associates degree in mechanical engineering (ASME) and a lot more practical experience in both government contract shipbuilding, and production support engineering. Further, I have been an automotive sports enthusiast for many years and have read lots of stuff that is related. For what that is worth, I'm just another backyard engineer living a dream. I claim no expertise except for, in this format, being the progenitor of "TLAR" (that looks about right) engineering.

I consider myself to be well read, and to have lots of practical engineering experience. Sometimes exceeding the more educated and long lived experience of my superior professional "engineers".

I'm not always right, and I am the first to admit when I am wrong.

As far as beating around the bush, I am no more guilty of that than any of us, given the input provided by the OP.

We assume too much, so I wax poetic.

I am but a regular guy that has done too many crossword puzzles (vocabulary) and hath drunk too much bourbon.

But that does not change much of my opinion, nor my education, nor my experience.

Blah blah blah blah blah.

We are brothers, please do not be offended. At least 50% of my post is intended to entertain. The other 50% is intended to promote thoughtful introspective, hopefully resulting in a more favorable outcome.

[48Rob]

What is the outside diameter of your axle tube?

2-3/8" indicates a 3500# axle
1.75" says it is around 2000#

There may be a tag affixed, it will also have the weight rating.

This chart may help as you can use bearing sizes and dust cap sizes too.

[Tearsthuseist]

It looks like about 1.80" holding the tape measure next to it. I have a "Dial Caliper" but it only goes up to 1".

There is a tag.. It has many layers of paint, even after I have removed most of the paint, its still difficult to make out, but I think it says...

Dexter Axle, Elkhart Indiana
8N ID 0018419

Cant tell for sure if that last number is a nine, but it looks like it.

Also my axle is different than the one in that picture... Here, I will post a photo of mine...
http://i412.photobucket.com/albums/pp204/bartonartist/IMG_9951.jpg

After a second look I see it is the same, In my photo you can see the two bearings are the same size on the spindle. It almost looks like bearing ride on that wider diameter near the break plate, but they dont.

[High Desert]

Good job finding that stamp. That part # doesn't want to translate on the Dexter site, but I bet you could call them at 574-295-7888 (0800-1700 EST) and confirm what rating you have. Good luck!

[eamarquardt]

I'm not sure my ego is a problem but I have trouble with folks that don't care to understand how the world really rotates and confuse opinions with facts. I'm not "entirely convinced" that the size of the tires (within reason and a similar offset) will affect the stresses on the axle. As Carl la Fong points out, the weight of the trailer hasn't changed and the trailer is being supported by the axle just as it would be with smaller tires. A larger tire might smooth things out a bit and put less stress on the axle but that's only conjecture. I think it's accepted that cars with larger tires ride smoother than cars with smaller tires as they roll over obstacles easier and there is more tire height to act as a cushion. I just bought a new Chevrolet Traverse and it is well documented that the smaller rims with higher profile tire ride softer than the larger rims and low profile tires. I ensured that I got the smaller rims and high profile tires to so that I got the softest ride.

I also have concerns about folks whose only consideration is cost. Safety and reliability seem to sometimes take back seats, unwisely, to cost.

That said, a 3500# axle with idler hubs is about a hundred bucks. It will have flanges so you can add brakes at a later time should you decide to. With me, if the trailer weighs more than a third of the tow vehicle, it's gonna have brakes. You will probably have to replace your "U" bolts and plates but might be able to reuse the springs.

Sounds like you have a 2000# axle based upon the straight/unstepped stub. Several folks on the forum with reasonably light trailers (Cliffmeister for one) have bent 2000# axles. If it were me, I'd flip a few burgers, mow a few lawns, sell one of my boys (23 and 25), or whatever to buy a 3500# axle and put all worries to bed.

That said, I'm not clear why Carl has a picture of Oliver Hardy. Carl la Fong was a character in a William Claude Dunkenfield movie. Perhaps he can enlighten us.

Cheers,

Gus

[CarlLaFong]

On to the really important stuff.
As far as building stuff, I rely on the TLAR as well as the WAG principle. My education is minimal, I am a self taught Boy Genius™. I also do, too many, crossword puzzles. Sundays are reserved for church, a nap and the NY times puzzle.
I appreciate the work of Mr. Dunkenfield and always thought CLF was a funny name, so I've used it quite a bit on different boards, as well as being my evil alter ego on my blog. However L&H are, to me, the funniest team in history. There are monikers I could have chosen to reflect my love of "The Boys". Perhaps Peter Cucumber, the oil magnate, Ambrose Aloysius Plumtree or Col. Wilberforce Buckshot, to name a few.

[48Rob]

Im hoping it (teardrop) will not be much over 1000 lbs. I have come to think my axle is rated at somewhere around 1500 ~ 2000 lbs. Many decisions to make!

It really sounds like you need to establish a plan, and gather the required information before you, or anyone else can determine if your setup will work, and or be safe.

Axle capacity (which you are currently trying to establish) is pretty important.
The need for brakes?
The finished and loaded for camping weight of your trailer?

In order to answer the first two, you need to know the answer to the third.
Since you don't know/or haven't shared the design, as you suggested you are "hoping" to come in at a particular weight.
While having invested $65.00 in parts to rebuild your existing axle is a lot, it really is just a drop in the bucket compared to the overall project.


I recently bought a small camping trailer that was advertised as having a bent axle.
It weighed around 1600-1700 pounds, and had a 2000 pound axle.
There was a little cushion, but not nearly enough.
I'm not qualified to make the kind of calculations that those with training can, but more was clearly needed.
I tossed the 2000# idea and bought a 3500 pound axle.
While the axle itself is now more than I need, even with a healthy cushion, I no longer need be concerned with bent axles.
I did have to de-rate the spring packs though, to achieve a nice ride.

When I bought it, the trailer bounced like a rubber ball, had a dangerous sway/tracking problem, and was unsafe over about 45mph.
With the new axle, derated springs and correct/lowered tire pressure, the trailer pulls straight, is extremely stable, and is very smooth, no bouncing.
We just returned from a 300 mile camping trip where we pulled the trailer at 70-75mph.

The axle (a 4" drop) cost around $140.00.
I had a good set of brakes from a straight axle, so installed them as well.
Now we can go camping, any distance, at high speed.
If my kids get carried away with bringing more things than they need, I don't have to worry if we are too heavy/too close to the rating.

If Dexter can tell you what you have, and it leaves you a safe cushion, great!
If not, selling a freshly painted and gone over axle to someone on Craigslist, or someone building a trailer with a known final weight shouldn't be a difficult thing to do.

Rob

[Tearsthuseist]

yes, definitely good advice! I have already decided that I will get a heavier axle. Seems like the safe way to go... I knew going into this project that there would be set backs and unexpected things to come up. Id rather pay extra for something like a good axle than say, leave out a cabinet, or some interior item. Makes sense to me.

I will probably buy that kit for the 3500lb axle. Do they even sell pre fabricated axles locally?
That kit from earlier in this thread... http://www.ebay.com/itm/Build-Your-Own-Trailer-Axle-Kit-3500-Camper-ROUND-NoBK-/370511235235?pt=Motors_RV_Trailer_Camper_Parts_Accessories&vxp=mtr&hash=item564430c8a3#ht_4043wt_1166

After just checking again I guess that kit is only rated to 1750 lbs... I bet this same destributer has a 3500 lb. axle.. I have some research to do.

[amelia]

Larger wheel means longer torque arm on the axle, making it easier to overcome any friction in the axle. I don't see any advantage to mixing the sizes either.