Tire size question

[jmcgill]

I have a 1977 Glastron 17' boat with a 115hp outboard. It is presently being towed on an (I'm assuming) original single axle Murray trailer. I need to replace some badly cupped tires, and am not sure which way to go. It has 20.5x8-10 tires on it right now. I need to tow it at highway speeds for about 10 hours in the future, so I need a good highway tire.

Any suggestions?

 

[steelespike]

Re: Tire size question

This is a chance to up grade your tire size.The taller the tire the cooler it will run.Less stress on the tire and the bearings.If there is room I would go to at least a 13inch rim.Check the load range on your tires and go for at least that.Even a 530 X 12 tire will be 2 inches taller than your 20.5.Not sure but I believe the 12 and 13 inch rims are available in 4 and 5 bolt pattern.A narrower tire will run cooler keeping in mind that the taller the tire the cooler it will run.My old trailer has 15 inch rims with 825 X 15 bias ply tires.
With your towing distance you should have bearing buddies.

 

[Silvertip]

Re: Tire size question

You will obviously need to check fender and boat clearances if you intend to go to larger wheels and tires.

 

[jmcgill]

Re: Tire size question

I'm actually going to replace my fenders when I do the wheels, so I will check the clearance.

What's a bearing buddy?

 

[jmcgill]

Re: Tire size question

I have looked at 530 X 12 tires, and they're quite a bit narrower than the tires I have on my boat right now.

 

[Frank Acampora]

Re: Tire size question

I'm confused by your tire terminology. Do you have 480X8 or 530X8 tires? 480X12 will be narrower than 530X8. but you can also buy 530X12.
I used to tow a 15 foot glastron with a 90 hp on the back for about 2 1/2 hours at highway speeds. Tires were 480X8. When they got a little old, they would regularly blow out. It's dramatic when they go! In the time it takes to stop, the tire is almost completely gone. I used to carry at least 2 spares. With your boat, go for as large a tire as possible. Remember, those little 8 inch wheels are turning 3 to 4 times as fast as the tow vehicle wheels. And so are the bearings. For long tows, bigger is always better.

 

[Frank Acampora]

Re: Tire size question

My other question was: Why are the tires cupped? Do you have a bent axle or bent spindles? Perhaps The axle is not squared on the frame? or perhaps the frame is bent? The straight axle on a trailer should always hold the tires and wheels in alignment and no irregular wear should occur.

 

[jmcgill]

Re: Tire size question

I currently have 20.5x8-10 tires on the trailer. The 530 x 12 tires are taller but are narrower, by quite a bit than the tires on the trailer. The tires aren't cupped, that was bad wording. They're just worn out, and pretty much bald.

 

[tommays]

Re: Tire size question

I think a picture would really help i have seen trailers that have the wheel to far under the hull to change anything ?

Tommays

 

[steelespike]

Re: Tire size question

Generally the narrower tires will carry higher pressure.they will tow easier, run cooler and track better.
Just check the load range is as good as your present tires.

 

[jmcgill]

Re: Tire size question

My current load range is C, and if I upgrade to the 12" tires, I can get a C there too. However, the limit is a bit greater on the 10" tires, presumably because of the wider track.

 

[Silvertip]

Re: Tire size question

Wider tires have nothing to do with load rating. The tires you have now were probably chosen because a low profile tire was needed for clearance purposes. The tires you have are perfectly capable of freeway speeds. The disadvantages of a low profile tire such as yours is that their small diameter makes them tow harder than a larger diameter tire. Their low profile does not make them more or less safe than any other tire. If you change tire type you will need to change the rims.

 

[steelespike]

Re: Tire size question

530 X 12 tires and rims are available at Wal Mart about $48 dollars each tire/rim combo.
Those little tires will run hotter than a taller tire just be sure of the load range. Bearing buddies are a spring loaded bearing cover that keeps you bearings packed
with grease and you can top it up with a grease gun.
Run the max recommended pressure.

 

[Silvertip]

Re: Tire size question

5.30 x 12 load range "C" tires have slightly less load capacity than the 20.5x8x10 (1105 vs 1045 pounds).

 

[jmcgill]

Re: Tire size question

Thanks for all the help! I got my tires, and they're being delivered today. Now I just have to figure out how to get them onto the trailer.

Where do you generally lift a trailer? On the axle, or on the frame???

Thanks,

Joe

 

[Silvertip]

Re: Tire size question

Best is by the axle, directly under the spring. NEVER jack a trailer in the center of the axle. Most hydraulic jacks don't have enough stroke to lift by the frame unless blocked up which gets dangerous. If that's the route you take, keep the jack as close to the rear spring shackle as possible. You will also have to jack higher as you will be relieving the weight on the springs whereas thats not the case lifting under the spring.

 

[jmcgill]

Re: Tire size question

I actually may not have to worry about it as I'm taking the trailer to my marina to have the bearings repacked and have bearing buddies installed. I may have them install the new wheels while they're at it.

Thanks for the help, though!