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Old 12-16-2013, 03:36 PM   #29
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Now to try to apply some of this to our tow vehicles and travel trailers. I suspect that in my case of Nissan Frontier and SOB camper, the first lateral cornering limit is either lateral traction of the trailer tires, or the tip over limit of the trailer.
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I think the more common reason to use low profile tires is to reduce sway moments, not to increase cornering of the whole rig. Tall, flexible sidewalls make it easier for the trailer to push the rear of the TV around. Low profile makes it more difficult.
Ok, and I get that. In a related way, let me tell you about my setup. The Nissan has BFG Long Trail T/A tires. They are P metrics, max press allowed 44psi. When I first started pulling this trailer from new, it came with Load range C ( 50 psi ) ST tires. The back of the truck seemed to have something of a sideways movement to it. I would not call it sway, because it was not cyclical, but it just felt kind of, let's say wallowy ( tech term there ). I felt like it might be sidewall flex in the P tires on the truck. I pumped them to 44 psi, and it improved the situation, but it still felt like it was moving around, exactly like I would have imagined drive tire sidewall flex to feel like. Anyway, not being a ST tire kinda guy, I took them off the trailer and replaced with load rangd D LT tires ( 65 psi ). Problem solved. So what I had been thinking was drive tire flex turned out to be trailer tire flex. It now pulls so precise and firm, even in crosswinds, the difference is staggering. Even in gusting crosswinds at 55-60mph I can now very easily place this whole rig "exactly" where I want it, like for instance passing through a tight construction zone, etc.
So my point is when trying to diagnose a situation like this, sometimes what may seem to be, is actually something else.
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Old 12-17-2013, 06:44 AM   #30
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I'm going to parse the post a bit to extract an interesting tidbit:

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..... When I first started pulling this trailer from new, it came with Load range C ( 50 psi ) ST tires...... ....I took them off the trailer and replaced with load range D LT tires ( 65 psi ). Problem solved......
So I'm wondering if the idea of using a larger load carrying capacity tire on the trailer has more benefits that just a reduced risk of failure. What would happen if you went up in tire size, but kept the same inflation pressure? My guess is something similar. I think we need to get some more input before we jump to that conclusion.
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Old 12-17-2013, 07:05 AM   #31
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Old 12-17-2013, 09:30 AM   #32
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I'm going to parse the post a bit to extract an interesting tidbit:



So I'm wondering if the idea of using a larger load carrying capacity tire on the trailer has more benefits that just a reduced risk of failure. What would happen if you went up in tire size, but kept the same inflation pressure? My guess is something similar. I think we need to get some more input before we jump to that conclusion.
Could be, but you tire engineers often discuss the importance of minimizing inter-ply shear forces within the tire ( when fitted to multi axle trailers ), so it makes sense to me to run these tires at max ( 65 psi ) if for no other reason than that.
So far they are wearing perfectly even across the width of the tread ( about 12,000 miles ), so at least by that metric, I feel safe in saying I am not over-inflated. And this, at only about 50% of their rated load.
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Old 12-17-2013, 10:40 AM   #33
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Tires. I think it is understood here that the idea is a very stiff sidewall. This is often accomplished by simply reducing the profile of the tire from something like 70 to something like 40. With stiff sidewalls and a short overhang, and a long wb, it will be hard for those lateral forces to affect the path of the car.
Sway also occurs as a result of the rear tires skidding. In a trailer with proper weight distribution, the rear tires of the tow vehicle are the source of sway.

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Which is more crucial, the absolute value of overhang, or the ratio of overhang to WB?
Front tire skidding is proportional to the ratio of overhang to wb.

Rear tire skidding is proportional to the ratio of (overhang+wb)/wb or 1+(overhang/wb).

In both cases, the propensity for skidding is inversely proportional to the weight on the front and rear axle.

There's more to the dynamics than that though. The mass distribution of the trailer matters, which is why a (loaded) boat trailer of the same length and mass, and with the same center of mass point, is less likely to sway than an Airstream. Boat trailers have most of the weight concentrated around the axles. Airstreams have more evenly distributed weight, which means that the moment of inertia around the yaw axis is greater.

Another factor is trailer's overcorrection for sideways displacement of the rear tires of the tow vehicle. The Propride/Hensley hitches attack this portion of the sway dynamics.
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