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?

[Grit_dog]

Higher pressure will make it a little stiffer, also more harsh, especially if the front has any weight off of it with the trailer hooked up.
60 psi is about right for the front of a diesel with that size tires.
You're just driving on taller sidewalls, that's all. It's not going to be quite as crisp as with shorter sidewalls.
That's why I get a laugh at all the guys here saying bigger rims don't have enough sodewall to be a truck tire. 285 60 20s are basically the same size as you have, but drive better.
Nothing wrong with those tires though.

[rsaylor3]

So I have towed about three times since this post. First I lowered the front back to stock height and had it realigned. Still feeling the non-centered feel that needed a lot of input from me, or at least more than I was used to giving.

Then I went through and measured everything again and tried different air pressure. Nothing left to do and I have to blame it on the tires now, it me for putting that size on!! I think I have come to the conclusion that the higher side wall is flexing more than my stock size tires (285/75r17 vs 265/70r17). When not towing these tires are amazing! One of my favorites for sure for highway manners and off road use. But I should have stuck with the stock size!

Well we live and we learn and I won't do that again! I did make it a little better by going back to stock height in the front. I also realized that my first measurements after first installing the taller tires was not correct and I had the front of the trailer 1" higher than the rear. Small difference of course but brought it back down to rule out everything else.

So I have one follow up questions to those still reading this I'm running the rears at 80 when towing and front at 60(which the truck calls for). Would going to higher psi in the front be ok? I'm guessing it would give me less side wall flex, but am afraid I wouldn't have as wide of tire patch hitting the ground at 80 up form and would lose some steering control.

[big_buford]

Alot of manufactures offer 30-90 day customer satisfaction guarantee on tires, may want to check that also.

[big_buford]

One other thing to concider, and I would like to know for sure myself. When shopping for 17" LT tires I emailed cooper tire because I was looking for the highest load cap possible. This was their reply: "Starting in 2019, there was a load cap put on LT tires in the 17" tire line. New testing was done and new molds were manufactured for this."

The only tire I could find with a higher cap was the toyo MT. All others 121 load cap. 31xx lbs per tire. 16" and 18" no problem on higher capacity...

[rsaylor3]

Not at all, I think people are misunderstanding my post about the 1" lift, or not reading back to my original post. I partially leveled it adjusted the front height of my truck. By turning the torsion bars. Before or after that I always have had my front returned to original height of the truck before hitching up the trailer.

I did drop the front back down to stock level and will get an alignment again early next week. Will tow this weekend to see if it makes a difference, but I can tell you it already feels better just driving the truck empty with the front back to stock height. Will be Leaving it stock for sure! Hoping this was the main cause and that the tires are going to work, as I don't plan on buying new tires until these wear out

[mkirsch]

So you're saying the front end was sitting 1" high before you readjusted? Yes that will affect steering. It means weight is being removed from the front tires. Less weight, less traction, less steering effectiveness.

1" is a huge amount. It's no wonder it felt squirrelly.

[Grit_dog]

Good luck moving forward. I'm pretty certain that everything is fine and just a little change that you very astutely noticed that some may not.
Did you check total toe before cranking them back down? That was merely a suggestion by me. I'm not certain that little of lift would have a measurable effect on toe. It shouldn't have had an adverse affect on stability though.

[rsaylor3]

Well I ended up praying the front air pressure back up to 60 PSI during the tow. I think 60 is where I'm going to leave it just like I used to. Now that I'm home I just at the torsion bars and brought it back to stock height in the front. we have another trip plan the short one but will still be plenty of interstate time the middle of May so I look forward to seeing how it does with the front back down. Thanks for everybody's advice!

[Grit_dog]

^ No, he didn’t. RGs are a pretty mellow tire with respect to void ratio.
Currently grossing over 18k gcvw on siped mudders. No squirmy.
Taller new tires WILL be a little more squirmy than old short tires. Cranking Torsion bars will reduce good handling characteristics a bit.
This is not an issue, just a slight net effect of the T bars and more aggressive tires than what likely came off of it.
OP, you’re fine. You’ll get used to it and tires will wear in.
I’d consider an alignment though with the cranked t bars. You might have a little too much toe in now. Makes for stable driving but could be a little harsh on the tires

[Lynnmor]

You simply bought the wrong tires.

From Nitto:

The Ridge Grappler represents the next generation of the Nitto Grappler family of products which provides the best of both worlds from our mud-terrain and all-terrain product offerings. Featuring a revolutionary dynamic hybrid tread pattern, the Ridge Grappler provides a quiet and comfortable ride while the deep, aggressive sidewall lugs and tread pattern provide capable off-road performance.

[rsaylor3]

I don't have any sway, just a loose feeling in the front of the truck that causes me to give a lot of input to keep straight and I noticed the bow wave of even small vehicles. I think the hitch is completely fine and has been fine for the entire four years I have had it. Must be the tires it slightly raised front end, as they were the only two changes made.

The ten links seemed to make a huge difference so I'm leaning towards the raised front end as being the problem. I am leaving this morning to head home so I dropped the front tire air pressure by 5 psi to give that a shot. Inflation load guides for the ridge Grapplers show that 47psi will give same load carrying ability as 60psi for the stock tires I had before. Trying 55 as I am wondering if this will flatten my tread contact patch and give me more control. We shall see..

[Hannibal]

Between tread squirm and

https://www.etrailer.com/question-116001.html

Might get better once tires are worn in a little.

[JIMNLIN]

I also did 2 sizes up ridge Grapplers(285/75/17 on stock wheels).

Some points I've had issues with when pulling heavy GN trailers and going with large tires.
If your OEM GM stock wheels are the 6 1/2"-7" GM uses then you have too big of a tire and will always have issues with carcass roll/tread squirm when carrying weight and a heavy trailer pushing you even after the tire has ran 3k miles for a good break in. Load carrying tires need a wheels width to match the tires tread width.
Now if were doing some type of racing then we can play with wide or narrow wheels for certain traction or handling requirements.

The Ridge Grapplers show a tire with large lugs and voids which also can lead to tread squirm.
A 285/75 tires can have a 8.5"-9" tread width....now mount them on a narrow wheel with a 6.5"-7" wide wheel will basket ball the tires tread and sidewalls. Pump the tire to high pressures for the load and the tire rides the center of the tread producing a squirrely handling truck. Lower pressures can produce carcass roll and a hot running tire when carrying loads.
Once the tire is broke in then find which tire pressures make the best handling and a cooler running tire.

[rsaylor3]

Ok, I towed the camper for 6 hours the other day. Had the rears at 80 and fronts at 60 as people suggested and as truck door asks for. Still sloppy or just not a tight feeling. Before I would feel the little push when busses and certain semi's passed me. At the beginning of this trip I could feel motorcycles passing me:) really weird, as I needed to give constant input and it just felt unsettled.

I stopped at a rest area and went from 9 free chain links on my blue ox to 10. I had always ran with 9 for the last 4 years. Going to the 10th cleaned and tightened things up to 70+% of what it was before I made the changes. To recap I have a 2015 Chevy 2500hd Duramax 4x4 crew cab regular bed. I did 4 turns of the torsion bars for 1" of front lift. I also did 2 sizes up ridge Grapplers(285/75/17 on stock wheels). Truck is still raked and I have stable loads lowers in the back and have had them the entire time. With the blue ox and the stable loads I never squat before or after the 1" front lift. I just checked my weights again before this trip and I'm at 14% tongue at 1,350lbs. With 9 links I was returning the front to unloaded height.

With taking that extra link of chain and it making such a big difference, I'm wondering if because the front was raised, is that what is causing this unsettled feeling? Is not having the front resting on the jounce bumpers taking some stability from my package??

Would love to hear more thoughts? Thinking I will lower the truck 1/2" in the front, tow again and see how it is. Then drop it back to stock and try again. I love the look of that slight front lift, but won't sacrifice my towing comfort for it.

Thanks and sorry for the long winded post.