upgraded TV tires to LT's - less stable?

[tommy_z]

I'm still sticking it out with my Ford Expedition hauling my 2920BH. I've managed to get weights and measurements to acceptable levels, but I know my rear axle is still slightly over. I'm planning to upgrade vehicles eventually, just not right now.

I needed new tires, and thought I'd upgrade from P-metric to LT's. I went with Pathfinder AT's from Discount Tire. They recommended 41psi all around for unloaded driving.

I aired up to 60 front/65 rear for towing. Felt like I was driving on marbles! Never been so scared. Truck wandered constantly. This was way worse than when I had the P-metric tires.

I found a tire inflation conversion chart which shows I don't need to air up that high to meet/exceed the load ratings of the P tires. I dropped to 50F/60R and handling improved greatly. I'd say it's comparable to my P-tires.

So, did I really gain anything? Why would it be so unstable, not enough weight on the tires?

[bsmith0404]

How much weight do you have on each axle? The problem that most people experience with a P tire is sidewall flex under load. The LT tires will have a stiffer sidewall designed to carry more weight, but if you're pumping them up too much you are likely driving only on the center tread patch which could give you the feeling you're experiencing. I typically don't pay much attention to air pressure charts and such for my TV, I found it works better to adjust air pressure for a good contact patch getting consistent wear across the entire face of the tread. That also gives you maximum tread contact with the road. It takes a bit of experimentation to find the right pressure, but isn't that difficult to do.

[sourdough]

Some things that come to mind:

Overinflation; take some chalk and put a thick line across your tire then drive it. See how/where the tire is contacting. Adjust pressure until the wear shows all the way across the tire on the chalk.

Tire tread: what kind of Pathfinder AT tread did you get? Aggressive tread can make a vehicle wander under the right circumstances.

Hitch load: How much weight is on the hitch? If there's too much your vehicle will wander.

LT tires should make towing better. Seems like one of the above things may come into play. Also, many years ago, after going through dozens of hoops because my truck was squirrelly after installing a new set of tires, they found the tread had been cut crooked on one of the tires causing it to go all over the place.

[CWtheMan]

Originally Posted by tommy_z

I'm still sticking it out with my Ford Expedition hauling my 2920BH. I've managed to get weights and measurements to acceptable levels, but I know my rear axle is still slightly over. I'm planning to upgrade vehicles eventually, just not right now.

I needed new tires, and thought I'd upgrade from P-metric to LT's. I went with Pathfinder AT's from Discount Tire. They recommended 41psi all around for unloaded driving.

I aired up to 60 front/65 rear for towing. Felt like I was driving on marbles! Never been so scared. Truck wandered constantly. This was way worse than when I had the P-metric tires.

I found a tire inflation conversion chart which shows I don't need to air up that high to meet/exceed the load ratings of the P tires. I dropped to 50F/60R and handling improved greatly. I'd say it's comparable to my P-tires.

So, did I really gain anything? Why would it be so unstable, not enough weight on the tires?

When changing from P to LT tires on your vehicle you must do the math correctly. First you have to get a load inflation chart for the original tires. Match the tire placard inflation pressures to the load capacity they are providing on the chart. Then divide that number by 1.1. The result is the correct load capacity they will actually support. Get a load inflation chart for your new LT tires and find the inflation pressure needed to match the de-rated load capacity you fond when they were de-rated (above). That will be the new recommended inflation pressures for your LT tires.

Automotive vehicles such as your tow vehicle are fitted differently than trailer axles. They factor in a percentage of load capacity reserve via inflation. So, doing as described above you will already have some reserve load capacity up to the TV’s GVWR, and, of course, over that, your TV would be overweight.

Normally SUV vehicles are registered and tagged as trucks. The above information is provided as it would apply to a vehicle registered as a truck.

p.s. You need to figure out how to keep the rear axle on your TV under its maximum load.

[JRTJH]

Certainly not intended to minimize any of the previous comments, but tires, like engines and rear differentials need to be "broken in" prior to expecting "normal performance"...

Buried away in the "insignificant print" in the Ford Owner's Manual is this comment:

"BREAKING-IN
You need to break in new tires for
approximately 300 miles (480
kilometers). During this time, your vehicle
may exhibit some unusual driving
characteristics.
Avoid driving too fast during the first 1000
miles (1600 kilometers). Vary your speed
frequently and change up through the
gears early. Do not labor the engine.
Do not tow during the first 1000 miles
(1600 kilometers)."

So, depending on your tires and how far you've driven the vehicle since installing them, you may be "chasing rainbows" until they're "broken in".....

[Tbos]

I recently moved to LTs on my Silverado 1500. What I noticed right away was the truck seems much more responsive to every little change in steering. No more sidewall flex. I towed with them at max 80PSI this weekend but from what everyone is saying it sounds like I may need to reduce pressure a little. It sure reduced the bounce the old tires introduced on every bump.

[sourdough]

Originally Posted by Tbos

I recently moved to LTs on my Silverado 1500. What I noticed right away was the truck seems much more responsive to every little change in steering. No more sidewall flex. I towed with them at max 80PSI this weekend but from what everyone is saying it sounds like I may need to reduce pressure a little. It sure reduced the bounce the old tires introduced on every bump.

If you aired up to 80 all the way around you probably over did it on the front. I run 80psi in the rear when towing and 65 in the front on my 3/4 HD. Unloaded I run 65 all around - seems to make a lot of difference.

[Tbos]

Originally Posted by sourdough

If you aired up to 80 all the way around you probably over did it on the front. I run 80psi in the rear when towing and 65 in the front on my 3/4 HD. Unloaded I run 65 all around - seems to make a lot of difference.

Sourdough, thanks. I'll adjust before my trip this weekend.

[tech740]

If you are running 41 psi unloaded and are good I can't imagine you are adding much weight to the front axel when you are loaded. You probably shift some weight to the front to get back to normal or maybe slightly over. Adding more air then needed can cause the "marbles" feeling. Defiantly need extra in the rear but probably not much in the front. I didn't see weights so this is just my guess. I towed the same trailer with an F150 and it was great. I ran 50 psi front all the time and took the rears from 40 to 65 when towing.

[Hideout17]

The E rated tires helped my tundra out alot. I run 35 to 40 unloaded and 55 to 60 loaded. Ride is no worse unloaded than loaded. Towing much more stable.

[mfifield01]

I'm trying to get my LT tires at the right PSI. With the trailer connected my front axle is 60lbs heavier than the rear. I'm running load range D tires (65 PSI max). I might try 55 PSI all around.

[Outback 325BH]

Originally Posted by mfifield01

I'm trying to get my LT tires at the right PSI. With the trailer connected my front axle is 60lbs heavier than the rear. I'm running load range D tires (65 PSI max). I might try 55 PSI all around.

With a load (towing, cargo, etc.), I would run max psi, as noted on the TIRE. Also make sure you use a WD system that gets weight back on the front axle. Front axle weight should be the same (or very close to it) as before you hitched up.


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[Desert185]

Originally Posted by bsmith0404

How much weight do you have on each axle? The problem that most people experience with a P tire is sidewall flex under load. The LT tires will have a stiffer sidewall designed to carry more weight, but if you're pumping them up too much you are likely driving only on the center tread patch which could give you the feeling you're experiencing. I typically don't pay much attention to air pressure charts and such for my TV, I found it works better to adjust air pressure for a good contact patch getting consistent wear across the entire face of the tread. That also gives you maximum tread contact with the road. It takes a bit of experimentation to find the right pressure, but isn't that difficult to do.

^^^^^^

With my LT LRE's:

Solo: 65/50
Towing: 65/80

Even wear. One just has to experiment to find their best combo.

[mfifield01]

Originally Posted by Outback 325BH

With a load (towing, cargo, etc.), I would run max psi, as noted on the TIRE. Also make sure you use a WD system that gets weight back on the front axle. Front axle weight should be the same (or very close to it) as before you hitched up.


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My equalizer hitch is set as close as it can be.

Empty
Front Axle: 3400
Rear Axle: 2620

Loaded
Front Axle: 3360
Rear Axle: 3300

I need to find a good area to do the chalk test. From a chart I found, 55 PSI should carry 2400 lbs per tire (4800 lbs on the axle). I towed to a campsite yesterday at 55 PSI and it seemed fine.

[Desert185]

Or you can baby powder the surface ahead of the tire and roll the rig forward aft slightly in your driveway to see what the contact is. Driving around creates side loads that will skew the results.

[Ken / Claudia]

I have to agree with what most have said. For best tire wear, vehicle control, best steering and braking you need the correct PSI. Likely not needing much more in the front tires under a load but, much more in the back. Too much psi in tire or air bags will cause poor braking and turning or like driving on marbles. Best is to bump up psi maybe 5 lbs at a time and see what is the best. Have a compressor with you to change it.
Unless you drive at high speeds and high speeds thru turns on a normal basis you may not realize how important that psi is for proper vehicle handling. But, the same applies to pickups and heavy loads. And yes I had to train high speed pursuit driving in every patrol vehicle I drove yearly for 25 years including 3 different pickups. Over inflated front tires can cause the vehicle to drift right off the road. When the same tire/truck at same speed will stay within the lane at a lower psi. I am talking at driving faster than you might ever go but, same can apply in that turn if you need a quick adjustment due to something in roadway.