Tire Pressure and Ride

[1engineer]

Wow,
I have never had these tires on a new vehicle and I have had plenty of new vehicles. I am running the OEM Bridgestone Duellers and now have 1200 miles on my 2011 SR5 4Runner. I have experienced the "vibration" some of the others have at around 65 mph (only intermittently) and obviously have the same handling and brake dive. This truck really did not feel "right" to me for a few reasons: A) The steering felt really light, meaning it took almost no force to turn the wheel and B) The grip on the road, or road "feel" was nonexistent at speed. I know OEM tires are usually terrible and attributed that fact to the above driving characteristics. Well, I checked the air pressure in the tires the other day and they were at 44 psi. I really did not think much about it as this is the maximum recommended pressure and I have run tires at max pressure before with no real issues. I just got back from a short interstate trip and had made the decision to get new tires, because these tires are causing me all levels of grief. Before getting new tires, I thought I would try airing these down somewhat just to see if changing the pressure changed any driving characteristic.
I aired down to 38 psi and drove it about 5 miles. HUGE DIFFERENCE. All of a sudden it took a little bit of force to turn the wheel and the tire felt like it gripped the road a bit better. The body lean was still there as was the brake dive, but nowhere near as bad.
I then thought "why not try 32?" I aired down to 32 and again, HUGE DIFFERENCE. Only this time, at least for me, I felt it was a little too much. I ended up at 35 psi and while I have only drove 15 or so miles I am liking the results. The tires are still OEM but not as bad as they were.

Conclusion: I can only guess what was happening but here is what I think: Max pressure in these tires was causing them to have a smaller, more centered contact patch which exacerbated the body lean and brake dive. Some tires do not have this problem (max pressure only makes the ride stiffer) but these tires do. The vibration, well, I really don't know at this point as it is intermittent for me. The normal ride is not really smoother but does absorb the bumps better. So, if any of you feel that this vehicle has excessive body lean, too light steering feel and not gripping the road try adjusting the tire pressure. It worked for me, and now maybe I won't have to spend $800.00 yet on new tires.

 

[Mtn.Rush]

Thats where I keep mine too, 35psi.

 

[mtbnole]

isn't that the setting from the factory?

 

[DaveS]

Most vehicles are delivered to the dealer with tires at pressures above factory recommended levels to reduce the risk of them getting flat spots while sitting during transit and on the lot - the dealer should have aired them down as part of the PDI.

 

[homeyclaus]

isn't that the setting from the factory?

The door sticker on my 2011 says 32 psi for all tires.

My Nittos' droning noises on the highway start getting loud once they've been inflated to 35 psi cold, and on the rear the edges don't make ground contact on blacktop.

 

[mtbnole]

yeah, just checked pressure for the first time today as i left the office. 32, 28, 31, 31. As homey said, 32 is what the door says. I'm going to go up to 33 cold, and see how the upcoming roadtrip works out.

 

[Jtraskell]

Just a thought.. You and the rest of the tribe who are keeping OEM tires are running on 4 ply passenger car tires installed on an almost 5K pound true body on frame 4 wheel drive truck. Do you think there might be a problem here? Playing around with air pressure will certainly make a difference, no doubt. But.......

Think about it. Maybe if you step up to a 6 or even 8 ply light truck tire, imagine the difference then..........and the safety issues for you and your family.

Just a thought to ponder.

 

[1engineer]

Just a thought.. You and the rest of the tribe who are keeping OEM tires are running on 4 ply passenger car tires installed on an almost 5K pound true body on frame 4 wheel drive truck. Do you think there might be a problem here? Playing around with air pressure will certainly make a difference, no doubt. But.......

Think about it. Maybe if you step up to a 6 or even 8 ply light truck tire, imagine the difference then..........and the safety issues for you and your family.

Just a thought to ponder.

I have no problems going to a different tire. I was going to anyway but I changed pressures and that helped considerably. I would like to get a few miles out of the OEM tires if they perform OK. I understand the difference in plys and ratings but when do you stop? 6 ply? 8 Ply? Kevlar? There is a happy medium I know, but the stock tire is rated for the loads and could you imagine a 265 on a car? I like 6 ply for their stiffness not so much for weight. As I said, the pressure change helped a lot. Now I will drive it some and see if it is good and if not I will put Michelins on it. With this tire I just found it amazing that the pressure would change the handling so drastically. Never before have I had a pressure change affect the vehicle so much. That is why I wrote about it.

 

[JB.]

Just a thought.. You and the rest of the tribe who are keeping OEM tires are running on 4 ply passenger car tires installed on an almost 5K pound true body on frame 4 wheel drive truck. Do you think there might be a problem here? Playing around with air pressure will certainly make a difference, no doubt. But.......

Think about it. Maybe if you step up to a 6 or even 8 ply light truck tire, imagine the difference then..........and the safety issues for you and your family.

Gotta chime in here.

For tires that see little off road use, a passenger tire is the safer bet (if LTs were safer, can you imagine the PR nightmare from Toyota specifying passenger tires?)

Passenger tires handle better, have higher speed ratings, run cooler, carry more load at the same psi, and are generally less prone to failure at highway speeds.

 

[JB.]

I have no problems going to a different tire. I was going to anyway but I changed pressures and that helped considerably. I understand the difference in plys and ratings but when do you stop? 6 ply? 8 Ply? Kevlar? There is a happy medium I know, but the stock tire is rated for the loads and could you imagine a 265 on a car? I like 6 ply for their stiffness not so much for weight.

When you're talking ply ratings (it's not actual plies any more) that gets into discussion of two distinct tire types, passenger (P) and Light Truck (LT). Passenger are 4 ply rated. Going above that gets into LTs. If you didn't like the high pressure, you probably don't want LTs as they require (to do it right) about 12lbs more pressure to carry the same load as Ps, and there you are, right back at 44psi.

 

[1engineer]

When you're talking ply ratings (it's not actual plies any more) that gets into discussion of two distinct tire types, passenger (P) and Light Truck (LT). Passenger are 4 ply rated. Going above that gets into LTs. If you didn't like the high pressure, you probably don't want LTs as they require (to do it right) about 12lbs more pressure to carry the same load as Ps, and there you are, right back at 44psi.

I have to say that the OEM tire at 44 psi is a possible culprit for me. As I have run several sets of different tires over the years I think that a different tire at 44 psi would be fine. I agree otherwise with everything you said.

 

[homeyclaus]

I have to say that the OEM tire at 44 psi is a possible culprit for me. As I have run several sets of different tires over the years I think that a different tire at 44 psi would be fine. I agree otherwise with everything you said.

Just realize there is actually a formula for tire pressure based on the load it's actually carrying. What the sidewall says is the max for the tire at its specified max load. They are not the same.

Going under increases rolling resistance, and at some point reduces traction as the side wall bulges and the contact patch forms a cup in the middle. The point at which this happens is dependent on vehicle weight. That rolling resistance becomes heat. Overheat the tire, and things start to separate.

Going over deceases rolling resistance, but at some point the center of the tire tread gets pushed out, reducing the contact patch and therefore traction. This is also dependent on the vehicle weight, which is why the formula increases tire pressure based on tire load, and why LT tires support higher pressures.

Going up or down a couple of psi has some noticeable effects, so if you prefer that, that's fine. More than 5 psi either way (without a significant change in the loading of the tire) will be a safety issue, no matter what tire you run.

What an LT-rated tire gives you is a much stiffer sidewall and tire edge, which will change the parameters above - not what will happen, but when. The whole wheel becomes much stiffer in order to carry the higher load, but it comes at a price: weight. This increases rolling resistance, increases unsprung weight, and reduces performance and mileage. The lack of flexibility also costs cornering traction, although most people with vehicles like ours never push cornering all that much until moments before an accident.

Saying "you must run an LT" is, I am sorry, total hogwash. All P-series tires of the sizes we use can support the vehicle weight and then some.

 

[1engineer]

Just realize there is actually a formula for tire pressure based on the load it's actually carrying. What the sidewall says is the max for the tire at its specified max load. They are not the same.

Going under increases rolling resistance, and at some point reduces traction as the side wall bulges and the contact patch forms a cup in the middle. The point at which this happens is dependent on vehicle weight. That rolling resistance becomes heat. Overheat the tire, and things start to separate.

Going over deceases rolling resistance, but at some point the center of the tire tread gets pushed out, reducing the contact patch and therefore traction. This is also dependent on the vehicle weight, which is why the formula increases tire pressure based on tire load, and why LT tires support higher pressures.

Going up or down a couple of psi has some noticeable effects, so if you prefer that, that's fine. More than 5 psi either way (without a significant change in the loading of the tire) will be a safety issue, no matter what tire you run.

What an LT-rated tire gives you is a much stiffer sidewall and tire edge, which will change the parameters above - not what will happen, but when. The whole wheel becomes much stiffer in order to carry the higher load, but it comes at a price: weight. This increases rolling resistance, increases unsprung weight, and reduces performance and mileage. The lack of flexibility also costs cornering traction, although most people with vehicles like ours never push cornering all that much until moments before an accident.

Saying "you must run an LT" is, I am sorry, total hogwash. All P-series tires of the sizes we use can support the vehicle weight and then some.

You are right. I tried to explain it to the other poster by asking "Where do you draw the line meaning 4-6-8 or armored ratings." I am fine with the P ratings and was not cognizant enough to check the tire pressure from the dealer. After running the first 1000 miles at 44 psi (which is 12 psi OVER the recommended pressure according to the door label) I dropped it down to 35 psi and it is a completely different vehicle driving and handling wise. So, shame on me for not checking the air pressure but for now, running at 35 psi, I feel pretty good about it.