Ridge Grapplers PSI? I have a bit of wiggle now

[rsaylor3]

So I had put 285/75/17 Nitto Ridge Grapplers on my Chevy 2015 2500 HD stock wheels. Nitto said to run 65 psi in the rear and 47 in the front. This would give me the same carrying capacity as the stock Michelins at 60 and 75 like the door sticker says. They carry the same weight at 65 as the Michelins did at 75. I actually keep them lower when not towing, both front and rear.

So I towed my 9,000 travel trailer for the first time since installing the Grapplers and noticed more movement in the trailer than normal. Before it was pretty well locked down with the Blue Ox Sway Pro and 1,500 lb bars. Been using this setup, same truck and trailer for 3 years. Not sway to scare me, but just needed a lot more steering correction for passing trucks and a windy day. My tongue weight is right at 13%. I was wondering if putting the tires to 80 psi was too much and I wasn't getting a full width of tread patch on the ground? Could this have been the case and why I felt that difference in tow? I have over 6,000 miles on the new tires, so I think they are worn in enough. I always ran the Michelins at 80 when towing so I did the same here, but am second guessing myself now. Heck, I think maybe I need to run the fronts lower as they suggested as well.

Appreciate your thoughts?

[wireman]

fj12ryder wrote:
Considering the off-road type tread for those tires, it's very possible you're just experiencing tread squirm. Those might be the wrong type of tire for towing a heavy trailer.

X2 May be just enough wiggle in the tread pattern to make a difference towing.

Maybe try readjusting your WDH and see if that helps.

Sidewalls should be good considering they are E rated.

[twodownzero]

Just run the factory recommended pressure for the stock sized tires and you'll be fine.

I have Ridge Grapplers on my SUV and they are great, but I probably would not have put them on a tow rig. Mine are 37x12.50R17s on a Chevy Blazer that I use for some pretty serious off road use. My truck has the Terra Grapplers. I would have wanted more siping for a tow rig just due to the possibility of bad weather. On my Blazer (5500 pounds or so), I run them at 25-30 psi on the road and anywhere from 8-14 off road.

It's okay to set pressures based on loading for a single vehicle, but once you get into a combination vehicle, the dynamics of weight shift come into play, and you're going to see that you have more control with a higher tire pressure.

I would probably run something like 60 and 80 psi. I actually run my front tires at 70-75 psi when loaded and rears at 80 always, but I'm also loaded closer to GVWR. Empty pressures are 50 and 40, if I recall correctly.

There's nothing wrong with lower tires pressures when empty, but especially in the rear, more pressure is going to be safer and you'll have more control when loaded.

If you notice more center wear, run lower pressure, but I doubt you will, especially if your rims are wide enough for your tires. I run a 285/70R17 on my Ram on 8" wheels and they have been wearing just fine for years.

I understand the argument about tread squirm, but I'm also not sure the Ridge Grappler is aggressive enough for it to come into play. The Ridge Grapplers don't have the void ratio like a mud tire.

[BenK]

IMHO....

Did you go up in tire size?

If so, did you also increase the rim width to match that upsizing?

Too much sidewall bend-back will have the exact same tire behave differently on a narrow vs wide rim

That increased sidewall bend-back will increase the slip angle and pull the outer tread away from the pavement and bulge the center ribs (not a lot, but enough to make the tire behave differently)

As others have mentioned...a highway tread pattern vs large lugged also behaves differently. On very aggressive lugged treads...there are patents covering several ways to keep those lugs from bending over. Yokohama has steps from the root up to about 1/3 the way up. Some have webs....etc. All to manage allowance of how much those lugs will bend or move around when the tread is new

Guessing the biggest issue with this OP's quest is that the rim width is on the narrow end of that new tire's spec. The OEM tire was better suited for that rim width

[blt2ski]

It's probably the tread itself. A heavy duty traction can get squirmy sooner than an AT which is sooner than an HT.
Even if the new tires were a D rated tire, that should not effect hanging, if the tire was rated for the load. I've referred towing with an 8ply D rated 265-75-16 vs a 10 ply E rated 245-75 or 235-85 16" tire. All three sizes have a max carry load of 3000 lbs.
Another potential issue, is the tire wider than previous, if so, your rim may be to narrow, or on the narrowest it can go on, this will will cause squirm too, in heavier load or trailer tow conditions.

Marty

[rsaylor3]

That's what I was hoping to hear! I think as important as having the tires aired up properly to as not get them overheated, we also want a good contact patch as well for control. Dual rear wheels get hat stability through more tire contact and I was thinking mine, if over aired and riding on the inner tread only, I am losing the stability if a wider contact patch.

I'm getting new weights before the trip, as I am adding the Jack-It bike rack to the tongue. So I will give your advice a try!

[Cummins12V98]

rsaylor3 wrote:
no, they are load range E. Was hoping someone one here had experience with tire pressure on tires with higher load capacity at lower psi. I'm going to do some rest runs and adjust pressures down to see how it goes.

Get your actual weights and air rear +5 and fronts + 10psi compared to the load/inflation chart for your tires.

[fj12ryder]

Considering the off-road type tread for those tires, it's very possible you're just experiencing tread squirm. Those might be the wrong type of tire for towing a heavy trailer.

[rsaylor3]

no, they are load range E. Was hoping someone one here had experience with tire pressure on tires with higher load capacity at lower psi. I'm going to do some rest runs and adjust pressures down to see how it goes.

[Cummins12V98]

What LOAD range are they??? If they are "D" take them back and get "E".

Lots of places like LesSchwab are famous for selling a lesser load range tire but telling people that the carrying capacity is the same.

[camp-n-family]

New tires tend to be a bit squirrelly until they are broken in after a few miles. Your problem though is probably due to the taller sidewalls. Higher psi may help a bit but won't solve your problem.