Questions about trailer tires

[grampi]

After hauling my motorcycle home on my trailer last night, I noticed both rear turn signals were gone, and only the stalks with a couple wires hanging out remained. I can say with certainty the poor condition of the highways I travel on are the culprits. I-65 between Chicago and Indy has a few bad spots, but I-70 between Indy and Dayton just beats the living snot out of the trailer and consequently, the bike. That highway has a heavy flow of semis and they are very hard on the pavement.

Since this trailer has no suspension, I'm wondering about doing a couple of things to help with this problem. On the sidewall of these 8" tires, it says they can handle a load of 585 lbs (which works out to a max load of 1170 lbs for 2 tires) at a max pressure of 60 lbs. Since the bike and the trailer combined weigh roughly 920 lbs, that leaves me a little room to play with. I'd like to run the tires with a little less air pressure to soften the ride a bit, but how would I know how low I can go before 1) I exceed the weight limit of the tires and 2) the lower pressure is causing excessive wear on the tires. Is there some formula that can be used to determine how low I can safely go with the tire pressure?

The other thing I was thinking about doing is moving up to a 12" tire (they have the same 4" lug pattern as the 8 inchers). This size tire would probably handle the lousy road surfaces better than the 8 inchers. However, the problem with the larger diameter tires and wheels is by raising the height of the trailer axle by 2" (which is what going to 12" tires would do), it's going to transfer more weight to the trailer hitch. The hitch can handle the weight, but the tow vehicle is a Corolla, and it already sags quite a bit in the rear from the weight the trailer puts on it. I don't know if it can handle any more. How much more weight would raising the trailer axle by 2" put on the hitch?

 

[gathermewool]

What's the tow rating of that Corolla? Stopping distance while towing?

 

[tomcat27]

I would not lower the air pressure - it would increase the temperature of the tires - which leads to catastrophic failure. I do like your 12" tire idea.... you can balance the tongue weight by shifting the load back - or moving the axle back.

 

[Stewart Fan]

Originally Posted By: tomcat27
I would not lower the air pressure - it would increase the temperature of the tires - which leads to catastrophic failure. I do like your 12" tire idea.... you can balance the tongue weight by shifting the load back - or moving the axle back.


I agree,don't lower the pressure in the tires. Trailer tires are typically JUNK in the best of conditions. Running them at max pressure is a key to help keep them from blowing out.

With that little trailer and motorcycle,it won't take much to adjust the tongue weight. You need about 10-15% for the trailer to tow nicely. You adjust the tongue weight and measure it on a bathroom scale.

12" tires are easily the way to go IMO.

 

[bullwinkle]

You DON'T want to lower your tire pressure-go to 12" tires and get a taller ball mount for your hitch (which hopefully has a receiver and not a fixed ball?), or I've seen hitch balls which are taller, you want the trailer to be as level as possible. My little fishing boat trailer from years ago originally had 4.80" x 8" tires and I changed to 5.70" x 8" tires to get a little more weight hauling ability-you might be able to do that too.

 

[leeharvey418]

Originally Posted By: tomcat27
...or moving the axle back.


I bet you meant forward, right?

 

[CapriRacer]

First, a few specific would be very helpful:

1) 8" tires - what size 8"?

2) 12" tires - same question.

As it turns out, I can take a reasonable guess: 4.80-8 Load Range B and 4.80-12 (I assume Load Range B)

And, yes, there is a formula, but it is conplex and the way you usually see it is in the form of a table - commonly called a "Load Table" - and I have a copy.

But one of the requisites of this load table (and what is printed on the sidewall) is that the vehicle has to have a suspension of some sort. Also, the speed is restricted to 65 mph. Obviously at least one of those conditions is not being met - so if I do the math and take an educated guess - the tires are properly inflated at 60 psi for the driving conditions.

Yes, yes, that's the long way of saying what everyone else said - move to the 4.80-12's.

OK, so let's explore that for a moment. In order to get the same load carrying capacity a 4.80-8 gets at 60 psi, a 4.80-12 needs to use - 37 psi! That's significant as the spring rate of a tire is pretty much linearly proportional to its inflation pressure.

But I also share everyone's concern about the tow vehicle.

 

[eljefino]

I'm wondering about the bike's suspension. Naturally you'll tie it down tightly which compresses the springs somewhat. As it rebounds from a serious bump it will be suddenliy stopped by the straps. This will be a shock or at least chafe. Nylon has a little "give".

If the tail of the bike has a firmer spring rate, it might do better backed onto the trailer. This way it's resting on the tongue, which will have some shock absorption courtesy of the corolla's rear axle.

I also wonder if it's better to have it on the side stand or service. My gut says side, because you have a wider triangular footprint, and it's already "decided" to lean left, so you can strap it down that way. Service stand would be more top heavy.

 

[grampi]

Let me see if I can answer some of your questions. According to the owner's manual, the max tow weight for the Corolla is 1500 lbs. I have no idea about stopping distance while towing. I can't move the axle on the trailer as it's welded in a fixed position, and I can't shift the position of the bike on the trailer because the front tire sits in a locking wheel chock, which is also why I can't load the bike on the trailer facing backward...that and I have to ride the bike onto the trailer in order to load it. The only thing I can really do to keep the tongue weight from increasing if I decide to go to 12" tires is get a hitch that raises the ball 2" higher. That would keep the tongue weight the same.

 

[Ken2]

The towing weight and stopping distance are subject to the total weight of the loaded car and loaded trailer, and whether Toyota requires trailer brakes for a trailer weight less than that max of 1500#. Consider that a car with a 150# driver and 1500# trailer stops differently than a car with four 200 pounders plus that heavy trailer.

The angle the trailer slopes down to the car has almost nothing to do with the tongue weight. Yes, get the ball mount that holds the trailer level or maybe an inch at most down in front. Keep in mind that too much tongue weight levers the front end high and makes the front tires light on the pavement. This reduces the car's braking traction and changes handling. Be sure to inflate the car rear tires and trailer tires to the max sidewall pressure when loaded and towing this heavy.

 

[grampi]

Originally Posted By: Ken2
The towing weight and stopping distance are subject to the total weight of the loaded car and loaded trailer, and whether Toyota requires trailer brakes for a trailer weight less than that max of 1500#. Consider that a car with a 150# driver and 1500# trailer stops differently than a car with four 200 pounders plus that heavy trailer.

The angle the trailer slopes down to the car has almost nothing to do with the tongue weight. Yes, get the ball mount that holds the trailer level or maybe an inch at most down in front. Keep in mind that too much tongue weight levers the front end high and makes the front tires light on the pavement. This reduces the car's braking traction and changes handling. Be sure to inflate the car rear tires and trailer tires to the max sidewall pressure when loaded and towing this heavy.


Your statement that the angle of the trailer in relation to the trailer hitch is absolutely wrong. A nose-down attitude of the trailer, even if it's only a couple of inches, puts far more weight on the hitch as compared to the same trailer with a slight nose-up attitude.