8" Wheel and Tires - Replace with 12"?

[barrynfla]

Just bought a 12' Sears Gamefisher with 7.5 hp Johnson. Waiting for the hitch to be put on my '01 Civic. The trailer isn't in the greatest shape but looks pretty good. It has 8" wheels, the tires have good tread but the tires are pretty old and starting to dry rot. Just had a new valve stem put on one of them and the guy would only put in 35 psi. I know I'm gonna need new tires but not sure whether to just replace the 8" or switch to 12". Measured under the fender and I have about 3" or a bit more to play with so I think they would fit. I live in Tampa and the roads are flat and I don't plan on towing very far.......maybe 20-25 miles tops. Speed limits are about 60-65.

Opinions on keeping the 8" or switching to 12"?

Thanks!

Barry

 

[CaseyP]

Bigger is not always better. I would stay with the 8" tires since the trailer was designed for them.

 

[rickybobbybend]

I would be tempted to go to a tire dealer you trust and get their recommendation. But whether you upsize or not, get new rubber on that trailer and be sure to check the bearings while you are at it.

 

[lckstckn2smknbrls]

How steep are the ramps you plan on using? How long is the trailer? Taller tires mean you will have to back farther into the water to launch or retrieve and considering your using a civic as a tow vehicle lower might be better.

 

[turbotodd]

I would not run a 8" tire/rim if I had the option of going to 12". One reason is speed. Those little 8" tires really hum at 65 mph. Seems like they're turning about 80 or better. Reason two, the 12" tires usually have less rolling resistance. Reason 3-the 12's last longer. Reason 4-the 12's ride a LOT better; and they're easier on the towed load (trailer and boat). There's only one reason to go back to an 8" rim and that's if a 12 won't fit.

 

[Hanr3]

8" tires are fine on the highway and they are only going as fast as the tow vehicle. If the tow vehicle is doing 65mph the trailer tires are going 65 mph. The difference is the number of revolutions per mile, not the speed.

I towed my 14' boat over a 1000 miles this summer, 6 hour trip to Kentucky lake and back. Plus a couple of 3-4 hour trips to "semi-local" lakes, and bunch of trips to my local lakes. The main thing is grease, keep the bearings in grease and you wont have any trouble, once you get new tires. Actually the last 3 years I averaged about 1000 miles per year towing the boat, not a lot, but I dont have any reservations about loading up the boat with firewood, tent, dining fly, my backpack, cooler, fishing gear (500 pounds of gear) and hauling it 500 miles to go camping/fishing for the weekend.

Price those 12" tires and compare it to the 8" tires. :mrgreen:
Those 8" tires look better all the time when you start pricing alternatives.

To verify your bearings are well greased, drive for an hour on the interstate, stop and put your hand carefully ont he hub, if its hot you have a problem. If its cool/warm to the touch, your fine.

 

[Bugpac]

The trailer might be going the same speed, and the rubber. The bearings are certainly not!! Your probably turning close to 2x the rpm, just a guess, could do the math but there is no point. Thats 2x the wear. And 1/2 the life span as a bigger wheel.

 

[RiverBottomOutdoors]

With a small boat and limited towing distance there is no need to switch to 12" tires. For your situation, I don't see a good ROI to make the case for switching to 12" tires.

I debated the same thing myself. I stuck with the 8" tires.

 

[bumpyroad]

well I did the math. just guessing that the 8 inch rim has 5 inches of rubber around it for an 18 inch diameter and the 12 inch rim has 6 inches of rubber for an overall diameter of 24 inches both times Pi gives 1.333 times the circumference. of course actual amount of rubber/diameter could affect this ratio.

 

[barrynfla]

Thank you all for your replies. They're greatly appreciated. I'm pretty sure I'll be replacing the present tires with 8" new ones. Many excellent points were made but two stand out.......I don't want to have to back my trailer into salt water any more than I have to......and I'm not going far and will be on level ground at moderate speeds.

Barry

 

[Hanr3]

The tire is still going 65mph doesn't matter if its 33" or 8", its still going 65 mph. Speed has nothing to do with the number of revolutions the tire makes. The tire makes the same number of revolutions per mile no matter the speed, 20 mph or 65mph, speed doesn't matter.

That being said, the tire is designed for the application. If it wasn't intended for the highway (speed rated), it would be rated accordingly.

As for the bearings, bet they turn less than 1200 revolutions per mile. For a bearing, thats nothing, hell the pulley bearing attached to your engine runs at 1200-1500 rpm while your cruising the interstate. Never mind the 2,000-3,000 rpm while getting up to speed. There are 63,360" per mile. How many revolutions per mile with a 8" tire and a 29" in tire? 400-500 revolutions per mile difference is my guess.

 

[JMichael]

I knew if I kept reading this thread I'd do something stupid. So here it goes. An 8" tire will make approx 1267 revolutions per mile while a 13" (sorry, don't have a 12" tire to measure) tire will make approx 868 revolutions. That's almost a 50% increase in the number of revs per mile of the bearing if you changed from a 13" to an 8" tire.

While I don't think it's any less safe to tow at highway speeds with 8" tires than with 12" tires, I do agree that the bearings used with 8" tires will make more revs than those used with 12" tires and therefore the bearings with the 8" tires should theoretically wear out sooner if both sets are subjected to the same wear/mileage and maintenance. Is it enough to worry about??? Probably not as long as you lube and check your bearings regularly. I also agree that the larger diameter tires are going to give a smoother ride for the boat/trailer.

 

[New River Rat]

I just feel better knowing there are less revs going on behind me. I'm running 14 and 15 now.

 

[lckstckn2smknbrls]

I'm running 8" wheels with 3/4" bearings. Should I be doing 100 mph?

 

[Hanr3]

Alright, lets talk bearings. By definition a bearing "bears the load". That is the job of a bearing, to support the load applied between mechanical forces. Bearings are relatively new and have been around for about 100 years, not, try like since 40 B.C. Timken has been making bearings tapered roller bearings for over 100 years. This is NOT new technology here. It is a proven design, it works, and it works very well. Only in the last 20 years or so has the automotive industry switched to unit bearings, and trailers still use tapered roller bearings. Tapered roller bearings have been around for a long time, since Henry Timken pattened them in 1898.

Capitalize on the Proven History of Timken Tapered Roller Bearings
For as long as farmers have relied on power equipment, farm equipment manufacturers have relied on Timken® bearings. Used in transmissions, axles, PTO drives, wheel ends and more, dependable Timken bearings help ensure agricultural equipment will be ready for all farming seasons. The reliable tapered roller bearing is ideal for positions that require higher “power density,” the ability to carry a large load with a relatively small bearing. In the final drives, main gear shafts and wheel ends, more severe loads are present and may combine both radial and axial forces. Perfectly suited for these environments, tapered roller bearings are commonly found in such applications. Each Timken bearing offers specific application advantages.
https://www.timken.com/en-us/solutions/agriculture/solutions/Pages/CapitalizeTimkenTRB.aspx

Your boat trailer doesn't have anything on the load Farm equipment, or your truck puts on tappered roller bearings. I don't care if you do 100 mph with 4" tires, properly set and greased bearings are the least of your concerns.

 

[Bugpac]

Ya ok, and how many guys dont have chinese made bearings, and grease them properly, the real concern is the load weight of the tire, a 4.80 x 8 is like 500 lbs, and a 5.80 x 8 is like 750, that gets you a 1000-1500 capacity, if your boat doesnt weigh that then your good. Regardless that your bearing is spinning 2x as fast, generating 2x the heat, as well as added tire heat, which is what causes blowouts to begin with.

 

[bassboy1]

The tire is still going 65mph doesn't matter if its 33" or 8", its still going 65 mph. Speed has nothing to do with the number of revolutions the tire makes. The tire makes the same number of revolutions per mile no matter the speed, 20 mph or 65mph, speed doesn't matter.

The problem with that logic is that the bearing doesn't give a flying flip about miles, but is more concerned about time. That is why revs are always counting in Revs per minute, and NOT revs per mile.

To put it in perspective, lets take the bearings out of the picture, and pretend you have a metal on metal joint. At slow speeds (under 5 revs per minute) that thing can go on, and on, and on. Tens of thousands of revs, and it won't ever warm enough to be noticeable with a bare hand. The heat is dissipated faster than it is created. Speed it up to 1200 RPM, and you're going to seize it in a matter of minutes, and likely cause 3rd degree burns if you went to check it, as the heat will dissipate at the exact same rate, but is created much quicker.

Same goes for tires. You have twice the rubber to dissipate the heat, as well as a greater amount of time between any given segment of the tire coming back in contact with the road.

Lastly, there is one important thing that hasn't been mentioned yet. A boat trailer gets submerged on a regular basis, and it wouldn't be realistic to say that no water ever enters a hub. While water is a fairly decent lubricant on the short term, however it will severely damage the precision parts inside a bearing. Tiny pits on a bearing surface will vastly decrease the bearings efficiency, and you guessed it, cause more heat. Granted, this can and will be an issue on any tire size, but larger tires give a greater margin for error, given the inherently lesser quantity of heat being created in the first place.

On that note, the dust caps on the front bearings in my work truck haven't been removed in well over 300,000 miles. I'm leary of going more than a couple years on any of my boat trailers (in the realm of 10,000 miles), just due to the potential havoc water intrusion can wreak.

 

[bassboy1]

Now, enough of the theoretical.

If you are truly going 30 miles or so at a time (probably at lower speeds, with more stop and go, given the difference), the concern is much lesser than if you're taking longer trips, so in your case, I might be inclined to stick with the 8" tires. This will be nice on shallow ramps, especially considering the tow vehicle. If you see longer trips in the future, I'd absolutely upgrade to the 12s.

 

[PSG-1]

I concur with bassboy on this one. For short trips, 8" tires are fine, as long as the weight load isn't exceeded.

But for long interstate trips, where the speeds are higher for extended periods, the 12 or 13 is a better choice.

 

[Hanr3]

The tire is still going 65mph doesn't matter if its 33" or 8", its still going 65 mph. Speed has nothing to do with the number of revolutions the tire makes. The tire makes the same number of revolutions per mile no matter the speed, 20 mph or 65mph, speed doesn't matter.

The problem with that logic is that the bearing doesn't give a flying flip about miles, but is more concerned about time. That is why revs are always counting in Revs per minute, and NOT revs per mile. A tire is rated by revolutions per mile, not revolutions per minute. Your confusing tire ratings with bearing ratings. Tires are rated in Revolutions per mile. The OP asked about 8" tires.

To put it in perspective, lets take the bearings out of the picture, and pretend you have a metal on metal joint. At slow speeds (under 5 revs per minute) that thing can go on, and on, and on. Tens of thousands of revs, and it won't ever warm enough to be noticeable with a bare hand. The heat is dissipated faster than it is created. Speed it up to 1200 RPM, and you're going to seize it in a matter of minutes, and likely cause 3rd degree burns if you went to check it, as the heat will dissipate at the exact same rate, but is created much quicker. Lets take lubrication out of the picture and have metal on metal bearing contact. Look at the surface of the bearings, even polished bearings. It looks like mountains trying to engage mountains. That resistance IS the reason bearings fail. So NO, they can not go on and on forever while under load, even at slow speeds. They MUST have a lubricant.

Same goes for tires. You have twice the rubber to dissipate the heat, as well as a greater amount of time between any given segment of the tire coming back in contact with the road. Tires are designed to disapate heat, even small tires disapate heat up to thier ratings. Tires serve a ton of functions, heat disapation is only one aspect. Besides the heat generated by the tire never makes it to the wheel bearings. It would first have to travel through the wheel and bearing hub. Realistically your tire would have to be on fire before it had an effect on the bearings. :mrgreen:

Lastly, there is one important thing that hasn't been mentioned yet. A boat trailer gets submerged on a regular basis, and it wouldn't be realistic to say that no water ever enters a hub. While water is a fairly decent lubricant on the short term, however it will severely damage the precision parts inside a bearing. Tiny pits on a bearing surface will vastly decrease the bearings efficiency, and you guessed it, cause more heat. Granted, this can and will be an issue on any tire size, but larger tires give a greater margin for error, given the inherently lesser quantity of heat being created in the first place. Water is a horrible lubricant. It does not adhear to the surfaces, it boils off when heated leaving the mountains to grind against each other eventually welding solid, and is extremely corrosive leading to pits/rust. Water is the reason for Bearing Buddies, Dust Caps, Bearing Seals, and marine grease; which is TEMPERATURE and WATER resistant.

On that note, the dust caps on the front bearings in my work truck haven't been removed in well over 300,000 miles. I'm leary of going more than a couple years on any of my boat trailers (in the realm of 10,000 miles), just due to the potential havoc water intrusion can wreak.

The key to bearing longevity is the grease. Failure to keep your bearings properly lubricated is the number one reason they fail. They fail becuase the grease disapates the heat, no grease, no heat disapation.
No grease, water gets to the bearings and leads to rust, or welded bearings. Again, failure due to improper grease.

More interesting reading.
https://www.machinerylubrication.com/Read/24100/lubrication-basics
https://www.applied.com/base.cfm?page_id=3704

Not picking on any one person here, these are the common misperceptions about how bearings work.