Is this a stupid idea?

[Lion hunter]

I am ready to take the boat I have been restoring to the water. Problem is the tire are shot. Right now there are 155 R 12 car tires on the trailer. The boat is a 16' aluminum w/ 60hp johnson. I have another boat and trailer that runs 8" tires, it's a 12' aluminum. Would it be a dumb idea to put the 8" tires on the other boat. Don't plan on keeping it this way, only a couple of trips to the lake until I can buy new tires. Its about a 60 mile round trip. Here are the differences in the tires:

Height:
8" tire is 15" tall
12" tire is 21" tall

When I buy the 12" tires they will be load range B, which is what the 8" tires are as well.

Last question, Whats the size difference between 5.30 x 12 and 4.80 x 12?
Local store sells the 4.80's Carlisle Sport Trac already mounted on the rims for $44.00 (This would leave me with 2 spares). If I go to the 5.30 (They are $38.00) I'll have to get them mounted on the old rims and have to buy a spare.

 

[Thad]

Re: Is this a stupid idea?

Boy, I have not messed with tires in years. But here goes. I believe the 5.3 and 4.8 refer to the width. They will have slightly different load ranges but not enough to matter in the case of your boat.

As for the 8" tires. I think you would be asking for trouble. That 60hp is what would scare me. Too much weight bouncing off the back end for that small rubber.
My advise would be to take the tires to othe shop and them tubed. That should buy you a trip or two to the lake.

 

[Silvertip]

Re: Is this a stupid idea?

Any time there is a change in tire size there is a price difference but you need to look at the sidewall of the tire for the load capacity and ply rating. This also affect tire price. Just looking at diamter means nothing. A larger diameter obviously rotates slower at highway speed but if it is over loaded you are asking for disaster. The difference between the two tires you mention is in cross section and load capacity. When adding up the weight of the boat, motor and stuff you put in it like fuel, gear, adult beverages, etc., don't forget to add the weight of the trailer as it too sits on those tires.

 

[Lion hunter]

Re: Is this a stupid idea?

Both the 8" and the 12" are load range B. To be honest I see people running 8" tires all over the place, but those things for some reason worry me. I've never had a problem with them, but running down the road at 60mph with what looks like lawnmower tires is a little weird.

EDIT: I've convinced myself that it was a stupid idea. Just got light out so I was able to look at the lb rating for load range B. It's 590lbs. That should equate to 1200lbs at max rating. The boat, trailer, and motor has to be pushing a 1000lbs, add in gear and I'll be over rating. Looks like I need to find some load range C tires.

 

[Silvertip]

Re: Is this a stupid idea?

I think you are still missing the connection between Diameter, cross section, load range, and ply rating. Two tires of different diameters can both have load range B ratings but both tires also have different load ratings. If you have 8 inch, load range B tires, you may be able to up the ante by just switching to 12 inch load range B. In some cases, an 8-inch load range "C" will cost more than a 12 inch load range "B". Small diameter tires are not inherently dangerous or unreliable if they have the proper load capacity. My pontoon trailer has 10 inch wheels but the tires are 10 ply rating and carry 90 PSI for a load capacity of a tick over 3000 pounds. Don't make this choice harder than it needs to be.

 

[Lion hunter]

Re: Is this a stupid idea?

Apparently I did miss the connection. I always assumed that load range correlated to a lb rating. After reading this site that is apparently not so.

http://www.dualport.com/bustech/load_tires.html#anchor-load

I guess I never realized that load range is nothing more than a letter that correlates to the number plys that are in the tire. I do realize that diameter and cross section and plys determine the weight capacity of the tire. I was just speaking of load range in terms that are not correct. If I under stand the site correctly load range is the ability of the tire to handle horizontal stresses (sway). Load index is actually the correlation of the LB rating the tire can handle vertically (Weight of the trailer, boat and gear at rest).

 

[j_martin]

Re: Is this a stupid idea?

The weight bearing ability of any tire depends on both size and load range. The point is you need tires rated to carry the load.

a 5 x 12 load range b tire will carry more weight than a 4 x 12 load range b. A 5 x 12 load range c tire will carry more weight than a 5 x 12 load range b.

It isn't as simple as ply count. You could have a load range c tire with a single steel ply, or 6-8 plies of nylon. It is a rating range to facilitate matching the tire to the load.

I would get the right tires mounted, borrow the money from yer kid, and get going. I would not go 60 miles round trip on deficient tires.

I carry a 12 inch spare for my trailer that has 13 inch tires on it. It just barely meets the load capacity, but it's just to get to the next tire shop in an emergency. The 13 inch tires carry 35 lbs of air, and the 12 inch tire is inflated to over 80.

Rims have to match the load rating also. They have maximum load bearing capacity, and especially maximum inflation pressure rating. If you over-inflate them and they fail, they will throw a metal ring right through anything or anybody that's in the way.

hope it helps
John

 

[Lion hunter]

Re: Is this a stupid idea?

Thanks everyone, I have a grasp of the tires now. The way the lb rating is next to the load range on a tire makes you think that there is a correlation when actually there is not. This is also true with the way tires are marketed as they state the load range and the weight rating. The difference being load index (lbs rating for vertical load) and load range ( the number of plys) which correlates to the horizontal stresses the tire can handle. As a tire size changes the load range may stay the same (same number of plys) but the load index can increase or decrease.

 

[Silvertip]

Re: Is this a stupid idea?

Forget all the vertical and horizontal stress stuff. The only numbers you need to look for on tires is 1) the tire size and 2) it's load capacity. If a given tire size does not have the the load capacity with load range "B" you look at a load range "C". If that still doesn't fit the need, you can look at the same size tire in load ranges "D" and "E" but the price goes up accordingly as does tire pressure. You might then look at the next bigger tire size starting again at load range "B" and working up. Whatever you find that fits your wheels that has the proper load capacity +10/15% margin should work fine.

 

[Lion hunter]

Re: Is this a stupid idea?

It all worked out as I went and bought 2 tires 5.30x12 w/1k load rating. Needed a spare but ended up going with a cheaper 4.80x12 with 780lb load rating. Not much for size difference and it would only have to get me a few miles. Big price difference $37 for the rim and tire vs $88 for a 5.80x12 rim and tire.

Silvertip:
I know that I over complicated things and I realized from the beginning that I could just look at the load rating and pick the right tire. But I wasn't going to be satisfied until I completely understand all the rating that a company puts on a tire. I feel now that I understand it. You cant really forget the vertical stress as that is the load rating (Downward pressure on the tire,just different words meaning the same thing). And the load range (B or C) is important as well in that it relates to how well the tire can hadle trailer sway. Probably not a big problem on the boat I need tire for, but I tow other trailers as well that are much heavier and it's good info to have.