Help! Larger wheels on smaller axle?

[Tearsthuseist]

Hello, I am a newbie here and I am currently building a little teardrop.

I bought a sturdy 5 by 8 ft. trailer last weekend at a great price. Its more beefy than a Harbor Freight type chassis. It uses heavy welded rectangular tubing and has a Dexter Axle. It has currently 10 inch wheels, the wide ones. I was originally planning on putting 14 or 15 inch tires on the axle. The lugs fit that large of a tire, but the trailer shop tells me that unless I upgrade the ends of the axle... The tires will wear down quickly, much quicker than if I stayed with the 10 inch tires. the lady said the larger tires also put more strain on the axle. She did say If I choose to do so anyway, that 14 inch would be better than the 15 inch.

Does anyone have any experience with this? Does it really matter that much if I put on the larger tires? Is it dangerous to do so?

She showed me that the larger wheels use a stepped end where the bearings are two different sizes as a set for each wheel.... Mine is a straight axle end.... Two bearing of the same size on each wheel.

Does that make sense? Difficult to describe that easily.

Thanks for any advice, I really appreciate it!

By the way, Im really just restoring the trailer first. It has bad lights and wiring, Im grinding off all rust and paint from the whole trailer, refurbishing the bearings, ez lube caps, etc. Then onto the actual teardrop.

[72FJ40]

This is going to be interesting. I own six trailers, from small utility to car hauler, and have not heard this explanation of problems with tire size changes.

First: weight cap of axle? standard 4 bolt or 5 bolt pattern? will a larger wheel bolt to the hub? roller bearings in hub? Changing to a larger wheel/tire is usually an advantage and an improvement. The larger combo spins at a slower rate and turns fewer times to travel each mile, thus it stresses the bearing less than a smaller wheel; should run cooler too. In selecting a wheel, you need to maintain correct backspacing and offset to center the load on the bearings. Properly greased and adjusted, the bearings on your axle will support the load for which they were designed with a larger wheel/tire. Something in the 185, 195, or 205 x 14 or 15 would make a good trailer tire for the weight you are planning. Balance the tires when you have them mounted; it does make a difference on a trailer.

I converted a boat trailer axle --12" wheels ?-- to a larger, car size wheel and tire; never had a problems. It was certainly an improvement; many miles and a few near max loads before selling it.

[48Rob]

Perhaps the tire shop assumes that by placing larger wheels on the axle, you, or a future owner will potentially overload the axle because of the higher weight rating of the larger tires, which can trash the bearings, or bend the axle which will cause the tires to wear unevenly.
If the larger wheel has a different offset, that is, the weight bearing portion of the wheel is further away from the the hub face than the current wheel, it could also place more stress on the spindle/bearings.

Rob

[KCStudly]

The larger combo spins at a slower rate and turns fewer times to travel each mile, thus it stresses the bearing less than a smaller wheel

Careful how you word that. The larger wheel will definitely turn at a relatively slower rpm so will tend not to over speed the bearings, but that is a matter of grease film strength vs. speed vs. weight. "Stress" in the structural sense is an all together different thing.

Stress on the other hand can increase if, like 48Rob said, the leverage on the bearing is increased due to wheel offset, not to mention that full size, or even up size 4x4 wheels and tires weigh a lot more than little trailer tires. Unsprung weight has a much larger effect on stress than sprung weight; like the difference between a hammer with a steel handle (your axle) and one made out of a swimming pool noodle (your springs). The heavier the hammer head on the steel handle, the harder the blow to the axle stub.

For most of the smaller light weight TD's it is probably not a big concern, but if you are building a porker like my TPCE, then you may want to think about a stouter axle.

[Tearsthuseist]

@48Rob ~ yes that also crossed my mind, actually its probably safer for them to tell me that. If I did add bigger tires, and sold it later... I could understand how someone could overload the axle that way.

I have been educating myself more on axles, I was really surprised that you buy the axle ends and weld them into a steel tube... I would have thought the whole axle was made from one solid piece of steel. With all of these unexpected developments, I am just continuing with refurbishing the trailer for now. Both of the leaf springs are ground back to bare metal, almost finished with the axle as well... Unfortunately I already bought new bearings and seals, and U~bolts for this axle, and trailer at about $65.00.

With that said, I did see this... http://www.ebay.com/itm/Build-Your-Own- ... 043wt_1166

Everything needed except for the steel tubing for a heavier axle. I know a licensed welder who could weld it up for almost nothing. But then, what to do with the old axle and 10 inch wheels? Make another utility trailer and try to sell it? Maybe just the axle and 10 inch wheels would sell on Craigs List?? Or, just put on the 15 inch tires anyway and build the teardrop. Im hoping it 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!

[48Rob]

Here is a link to help you figure your axle capacity.

http://www.randpcarriages.com/tech/axlechart.html

Having a reasonable cushion between actual weight and rated weight is good.
If your finshed (and loaded for camping) trailer weight is approaching the rated axle/springs weight, it will be very easy to bend the axle or break a spring if you travel rough roads or hit a pothole, etc...

Rob

[Tearsthuseist]

Here are a few pictures of the trailer itself. The frame, after a little work is almost readymade for a teardrop. All the frame tubing is actual tubing except for the last rectangular shape hanging behind the wheels, U~shaped steel there... Maybe a later add on? or??....I paid very little for this 8 x 5 ft trailer.

By the way, I rolled the inside of the axle on a small table, since the axle has break brackets near the ends.... This axle is slightly warped, and is not straight. Not much, but there is a bowing in the middle. Thats probably not good huh?

[KCStudly]

That bowing is absolutely normal and is a good sign that your axle is of a decent weight rating. The bow is for camber (i.e. the tops of the tires are tipped out compared to the contact patch with the road). This is so that when the trailer is loaded the tire contact patch gets closer to optimum. The peak of the bow goes at the top.

You would pick up a lot of useful info if you look back in this part of the forum (Trailer and Chassis) and read through some of the previous posts. It's all here. Be prepared to spend a lot of time learning and planning your build. I absorbed and designed for 2 years before officially starting my build.

[Nobody]

Looking at hour first pic, it appears the 'bow' in your axle is normal. Most all tubular axles have an upward bow in the middle, it's to provide camber in the tires/wheels.Your axle appears to me to be a fairly sturdy small trailer axle, probably rated in the neighborhood of 1500# or so. Looks to be 5 on 4.5 lug pattern with probably 1" spindles(?) I see no reason you can't go to 13" wheels with no problem, maybe even 14" if they're zero offset trailer wheels. Fenders will probably hafta be changed tho for the larger wheels/tires. I'm kinda doubtful that the tire store gave you good, valid information. My 2K Dexter 'Torflex' axle on my Scamp trailer has non-tapered spindles & both inner & outer bearings are the same size, & so is the 1740# HF trailer that my TD is built on.

[CarlLaFong]

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

[High Desert]

What everyone else said. That's a 5 lug hub, and if it has brake mounting flanges then all the better. That's a good indicator of a decent rating. Look real close, there may even be a stamp or small tag on it with the rating. I'd not be worried about a with in reason larger wheel tire combo if it was mine. I think you've got a great start for your TD, congrats on a good find.

[KCStudly]

The energy, or forces, transmitted between the axle and wheel, through the wheel bearings, is a two way street.

In steady state or static situations the weight of the trailer is directed toward gravity and the tire reacts against earth to hold the trailer away from earth.

In dynamic situations, such as a bump in the road, the tire and wheel attempt to shove the axle up, attempting to bend the axle stub, thus transmitting forces beyond gravity into the spring. In the case of a pothole, the wheel is no longer supported by earth and the entire assembly is allowed to fall toward gravity. Upon hitting the rim of the pothole (the proverbial immovable object) the tire is deflected upward transmitting the dynamic load in a vector through the axle stub and into the spring. As the trailer is still attempting to fall down, the reaction against the pothole is trying to heave the "unsprung" mass or weight up. This dynamic shift in energy can greatly exceed any static load. The heavier the tire/wheel/brake/hub combination, the more kinetic energy involved in the process, and the more this dynamic loading is exaggerated.

Er go, it all depends on your point of view and the direction and magnitude of the force being analyzed. That's why engineering calculations all reference positive, negative, clock wise and counter clockwise directions. It is all relative and a standard must be maintained to uphold order.

Do not underestimate or use conjecture. Stick to known conditions or use accepted standards.

My 3500# axle is designed to cope with the dynamic loads of my full size brakes and large tire/wheel combination. However, the static weight of my trailer is considerably lower, so I have derated my springs accordingly.

There are plenty of people here that would argue that my design is overkill, and that they have been successful with lighter axles, heavier tires/wheels, and maybe even heavier gross trailer weights, but have they driven over rough roads?

Relativity is the reason that Einstein was considered a genius.

(Some small batch bourbon was involved in the creation of this post, so forgive me if I have been too frank or insensitive.)

[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?

[KCStudly]

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.

[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.