changing 8" tires to 13" tires.

[Home Cookin']

Re: changing 8" tires to 13" tires.

the reason you need to run trailer tires at higher PSI than seems right is so they won't roll off the rim on a turn. there's a lot of outward centrifugal force going on back there, more than on the car.

 

[steelespike]

Re: changing 8" tires to 13" tires.

the reason you need to run trailer tires at higher PSI than seems right is so they won't roll off the rim on a turn. there's a lot of outward centrifugal force going on back there, more than on the car.

Not really; have you ever looked at the front tires on a car in a hard turn there is much more force there than a trailer has in even the hardest turn at speed.
My Load Star 480 X 12" tires on my 07 Load Rite trailer are written this way; load range B 785 lbs at 60 psi. No indication of must be run at that pressure only that the rating is at 60 psi.
The 8" tires on my 02 Chinese utility trailer are written Load range B 585lbs at 60PSI.
No indication they must be run at 60 psi only the rating is at 60 psi.
I think that implies if you are running lets say half that weight somewhat less pressure may be indicated obviously run enough pressure so as not to stress the tires.
I think changing springs in his case is out of the question.
My Load Rite is rated for 1500 lbs My 18 ft utility is about 800 lbs all up.
In this case I will be running 60 psi. and I don't think i need to be searching for different springs.
Load range for his 13" tires must be about 900 or a 1000 lbs at 60 psi
I think with his about 500lb load a little less pressure may be in order enough to ease the ride yet not stress the tires.

 

[bonz_d]

Re: changing 8" tires to 13" tires.

I had read the 1st few posts when this thread started and the left it only to come back today and check the other responses. What caught my attention was the talk of lowering the pressures to soften the ride. Wrong way to do it. Correct way, change springs! Which it appears no one has mentioned unless I missed it.

My current boat when I bought it was sitting on a trailer that was rated for 2200 lbs. The boat fully loaded is about 1000 lbs. The thing rode like a rock and just the weight of the over sized trailer added more weight to what I was pulling. As soon as I was able to find one I swapped that trailer out for a 1500 lb trailer and it now fits, rides and pulls much better.

The whole idea of springs is that THEY are to match the load so that they compress and absorb the shock of the load, not the tire.

 

[Vintin]

Re: changing 8" tires to 13" tires.

What ever happened to the guideline that if the center of the tread is wearing out first that you are running too high of a pressure for the load being carried?

I've got a vintage Tee Nee trailer with 4.80 X 8 wheels and tires and run at 50 psi. The load is a 330lb boat, a 60lb battery and 130lb motor for a total load of about 650lbs not counting the trailer which probably weight about 350 lbs. The Tee Nee has a coil spring at each wheel and a shock absorber.

At 50 psi I'm getting a lot of center of the tire wear.

I've got another boat trailer with the 5.60 X 8" tires and like the looks of the slightly larger 5.60 that fit the same wheels. The 4.80 are rated at 590lbs per tire and the 5.60 are rated at 760lbs.

 

[steelespike]

Re: changing 8" tires to 13" tires.

yes I wonder if that center wear indicates the tire is bearing more of the weight on a smaller working surface
causing more stress and more rapid tread wear.
When your tires were new I wonder if if a thin putty knife might reveal lighter edge contact with the road.
Now,with the wear it's probably more even.
Another thing we have over looked is about 10% of the outfits weight is carried by the hitch.
A small amount but it does lower an already light load in his case.

 

[limitout]

Re: changing 8" tires to 13" tires.

there are ways to lower tire pressure by changing the tire load ratings so you can switch from a "e" rating @ 80lbs tire pressure to a "d" rating @ 65lbs tire pressure to a "c" rating @ 60lbs tire pressure to a "b" @ 50 lbs tire pressure.

there is some room for under inflating tires by 5% and most tires show a minimum inflation pressure on them in addition to the maximum "recommended" pressure

if you had a load rated "b" tire with recommended pressure of 50 lbs you could run it with around 47-48 lbs pressure and be safe but I wouldn't try running it at 45 lbs.

even a pound or two in pressure can make a big difference in the hardness and bounce in a tire. the main issue with tires is heat and wear and under inflating tires increases the heat that builds up in them and can be an issue at high speeds so if you run interstates with your boat you wouldn't want to be running under the recommended pressures.

another consideration is the weight and tire pressure ratings are done for carrying a specified load in mind and by not having any load on them the recommended tire pressure is no longer accurate and following it actually causes the tire to be overinflated. this is evident when you get a situation such as the question asked by VintageALboatFan when he asked:

"What ever happened to the guideline that if the center of the tread is wearing out first that you are running too high of a pressure for the load being carried?"

this guideline is accurate and correct as it pertains to trailer tires. what you are seeing is evidence of over inflated tires, this balding in the middle can be from you over inflating them or having no load on the tire so it rides as though its still over inflated even with you using the recommended air pressure. if you see this and your pressure is at the recommended level then you need to switch to lower rated tires. all too often people only look at the number of plys a tire has and ignore the load rating of it. if you still have issues after going down to "b" rated tires then and only then should you think about running lower then recommended pressures.

all that being said, one thing is for sure, you cant go wrong following the recommended tire pressures even if you find wear issues or ride issues with them. for safety sake and for most people who don't know enough to pay attention to signs of how their tires wear are telling them then its best not to try and deviate from the marked pressures you should run.

if you have the need to soften the ride then these things can be addressed by first going to a different load rated tire and only as a last resort should you use less air then recommended. as long as its only a pound or two of air below what is recommended, then there is no real danger of tire damage or failure. no matter what the situation you definitely don't want to ever run more then 5% under the recommended pressure or you do risk tire failure from overheating.

if you are going to under inflate then you need to check your tires regularly and often to see if they are running hot. warm is normal but if they feel hot you need more air in them.

im sure the posting police will cry foul over me saying there are times when its ok to not following government guidelines for tire pressure ratings but as everyone out there had at one time or the other had a tire low on air and they do not just fall apart instantly because they run low on air, they just wear out faster and burn more gas.

 

[smokeonthewater]

Re: changing 8" tires to 13" tires.

the rating of XXX lbs at XX psi does not imply ANYTHING.... contact the manufacturer and ASK

this endless debate is totally silly..... most of the players on the debate have seen it time and again but still keep arguing the point... the manufacturers specifically state that the trailer tires should be run fully inflated to the rated pressure indicated on the sidewall....

If YOU choose to run at a lower pressure you accept all responsibility for that choice and there is no guideline to make the decision other than trial and error....... there is no magic number or percentage allowable... the rating on the tire does not give ANY information whatsoever to indicate a lower pressure for a lighter load.... none

 

[agallant80]

Re: changing 8" tires to 13" tires.

@60mph
8" 7920rpm
13" 4837RM

I would go with the 13 inch which it looks like you have done

 

[lrak]

Re: changing 8" tires to 13" tires.

@60mph
8" 7920rpm
13" 4837RM

I'd love to see the math that got those numbers. I stand by my 1200rpm @65mph on 8" tires comment.

65mph is 1.08 miles per minute. Depending on the profile 8" tires are somewhere between 17" and 19.25" diameter.

63360 inches in a mile / (17 * Pi) * 1.08 miles per minute = 1280rpm
63360 inches in a mile / (19.25 * Pi) * 1.08 miles per minute = 1132rpm

 

[limitout]

Re: changing 8" tires to 13" tires.

the rating of XXX lbs at XX psi does not imply ANYTHING.... contact the manufacturer ans ASK

this is directly from the manufacturer as you requested:

Checking Tire Inflation Pressure


Regardless of its size, every tire's load capacity, durability, traction and handling is dependent on using the right inflation pressure for the application. Since both too little and too much inflation pressure sacrifices some of the tires' performance, maintaining the "right" inflation pressure is very important.

While a wide variety of tire sizes are available to fit the many different vehicles in use today, almost every tire size can be used on more than one vehicle. Therefore it is the vehicle manufacturers that ultimately determine the tire inflation pressures they believe best fine-tune the tires' capabilities to their specific vehicle makes and models.

The pounds per square inch (psi) pressure number branded on the tire's sidewall identifies the maximum cold inflation pressure that specific tire is rated to hold. However, the tire's maximum pressure is not necessarily the correct pressure for every vehicle upon which the tire can be used (almost all vehicle manufacturers' recommended tire inflation pressures are less than the tires' maximum pressure).

Therefore when checking and adjusting tire inflation pressures, the "right" inflation pressures are those provided by the vehicle manufacturer, not the "maximum" inflation pressure branded on the tire's sidewall. The vehicle manufacturer's pressure recommendation can be found on the vehicle's tire information placard label, as well as in the vehicle owner's manual.

NOTE: Therefore when checking and adjusting tire inflation pressures, the "right" inflation pressures are those provided by the vehicle manufacturer, not the "maximum" inflation pressure branded on the tire's sidewall.

so there you go, end of discusion

 

[limitout]

Re: changing 8" tires to 13" tires.

duplicate post

 

[naturelover]

Re: changing 8" tires to 13" tires.

And by " not to derail", what you really mean is "THIS IS A HIJACKING!" lol

they have more "give" than you think... they aren't meant to deflect much... just enough to lessen the impact of a hard hit such as a pot hole enough to prevent damage.

you can do as you choose... the tire manufacturers and I recommend running at the rated pressure

LOL.

Well, if you're gonna go, go big!!!!

Was just wondering, the poor boat seems to take a beating, for longer trips , I usually remove the motor.

I bet boat and trailer don't weigh over 250lbs, I can pick up the rear of the boat with trailer attached and skoot it around if necessary.

I'd say I could run them flat without noticing, can't tell by looking at it.


I think mine is only a single spring, but not sure.

 

[agallant80]

Re: changing 8" tires to 13" tires.

I'd love to see the math that got those numbers. I stand by my 1200rpm @65mph on 8" tires comment.



65mph is 1.08 miles per minute. Depending on the profile 8" tires are somewhere between 17" and 19.25" diameter.

63360 inches in a mile / (17 * Pi) * 1.08 miles per minute = 1280rpm
63360 inches in a mile / (19.25 * Pi) * 1.08 miles per minute = 1132rpm

Yeah ignore me. I was typing in a meeting and got very distracted.

 

[smokeonthewater]

Re: changing 8" tires to 13" tires.

so there you go, end of discusion

Couple things missing... No reference is cited to back it up and more importantly no mention of the word TRAILER.... Trailer tires are constructed differently than passenger tires.

 

[smokeonthewater]

Re: changing 8" tires to 13" tires.

I had a big long post typed up w lots of cool links and then I realized something... we are SERIOUSLY Hijacking Dockrat's thread....

how about we drop this and try to help with the O/P's questions if he has any more of them instead of endlessly debating off topic....

 

[steelespike]

Re: changing 8" tires to 13" tires.

Yeh I'm for moving on.

 

[dockrat100]

Re: changing 8" tires to 13" tires.

Well, my take away from this is that I can do anything I want, and someone will think I am right, and someone else will think I am wrong. I really prefer the outboard motor tinkering forum in that the motor will run if you fix it right, and will not run if you don't. This trailer business is a little too subjective for me.

I have found several retailers of the smaller tires online that sell them at much better prices than I can find locally. I have heard too many bad things about Walmart trailer tires, and would prefer not to go there. I can sell the set of 13 inch tires I have for more than they cost me.

I will likely move back to the original size tires, and deal with boat height by adjusting the bunks.

I would now like to open the floor to discuss politics and religion.

 

[smokeonthewater]

Re: changing 8" tires to 13" tires.

or worse yet oil and ethanol

there are a few topics that tend to get us out of control.... sorry

studying your pictures... it sure looks like the back half of the trailer is MIA.... maybe the axle is just adjusted to the very end of a small trailer.... If that trailer would happen to be better suited to a jetski you might be able to adjust it back to normal and sell it for more than a bigger small boat trailer would cost ya.....

If the back half is actually missing maybe (after VERY closely inspecting the rest of it) you could extend the frame in the back.

 

[limitout]

Re: changing 8" tires to 13" tires.

I will likely move back to the original size tires, and deal with boat height by adjusting the bunks.

I would now like to open the floor to discuss politics and religion.

don't forget to flip the axle position to go under the springs where they are "normally" positioned.

remove the hub on one end, unbolt the axle from the springs, slide it out then back under the springs and bolt it back in place. its a very simple thing to do that only takes a short time and a few tools.

somewhere along the line it was moved and put under the springs in order to lower the trailer to make it easier to launch but as you found out, that puts your motors lower unit in harms way.

 

[smokeonthewater]

Re: changing 8" tires to 13" tires.

..................under the springs where they are "normally" positioned.

........................

somewhere along the line it was moved and put under the springs....................

No such thing as "normal" position... they are installed both over AND under on different trailers.... You can't possibly know that it isn't in the factory original position...

MOST trailer axles have camber built into them and installing them upside down can lead to tire wear problems... to correctly "flip" a trailer axle requires that spring perches be mounted on the top or bottom to allow the axle to mount in it's original attitude.

I just counted... of the 9 trailers here on the property 2 have axles under the springs and 7 have axles over the springs. All are believed to be in factory original positions.