Pirelli Scorpion ATR LT265/75R16 on my new Navara

[mauricio_28]

It's done. I handed over $850 for a five-piece set of Pirelli Scorpion ATR LT265/75R16 on my new Navara. I've got them at 50psi, and could not feel any appreciable increase in noise or roughness. Granted I only rode about 300km on the stock tires (Dunlop Grandtrek 255/70 AT20) so I did not sufficiently get accustomed to them. I think I got just a bit less than one inch in lift. Those LT Scorpions should be able to tackle anything (except mud) that Indonesia can dish out.

 

[LexusAllTerrain]

Congratulations I am interested in their performance, any pictures?

 

[madizell]

It's done. I handed over $850 for a five-piece set of Pirelli Scorpion ATR LT265/75R16 on my new Navara. I've got them at 50psi, and could not feel any appreciable increase in noise or roughness. Granted I only rode about 300km on the stock tires (Dunlop Grandtrek 255/70 AT20) so I did not sufficiently get accustomed to them. I think I got just a bit less than one inch in lift. Those LT Scorpions should be able to tackle anything (except mud) that Indonesia can dish out.

50psi?? My US spec version is placarded at 35psi, and frankly that is too high to allow full tread patch contact. 31 or 32psi is closer in my case. Of course, the OEM tires that came on the Frontier are rated max 44psi so I can't even find out what 50psi would feel like, but you have to be riding on the center tread, and if so, you won't have full braking force, your tires will wear out in the center quite fast, and if it rains, look out.

 

[mauricio_28]

50psi?? My US spec version is placarded at 35psi, and frankly that is too high to allow full tread patch contact. 31 or 32psi is closer in my case. Of course, the OEM tires that came on the Frontier are rated max 44psi so I can't even find out what 50psi would feel like, but you have to be riding on the center tread, and if so, you won't have full braking force, your tires will wear out in the center quite fast, and if it rains, look out.

I got the LT version whose maximum pressure, 80psi, is written on the sidewall. I asked the shop to pump them up to 50psi upon installation, but I may decrease it based on feel and performance. I rode back home from the shop in the rain without a problem, granted, at speeds under 40mph. Here are the specs at the Tire Rack:

http://www.tirerack.com/tires/Spec....&vehicleSearch=false&fromCompare1=yes&place=0

BTW, the Tire Rack does not list an non-LT 265/75R16 size.

 

[madizell]

I am familiar with both the build specs of LT range tires, and with the sidewall stated maximum pressures. The maximum pressure is intended to warn you of how much pressure the tire can withstand without danger, and should not be used to determine how much air a tire needs to carry a given load. D and E range tires are intended for heavy load bearing vehicles. The Navarra or Frontier is not a heavy duty truck, and could never carry enough weight to justify approaching the maximum pressure stated for the tire carcass.

Try this: wipe off the tread surface so it is fairly clean, drive slowly across a dusty but firm surface in a straight line so that the tread picks up tell-tale dust, and look at the dust marking on the tread. If you see clean outer tread blocks, those blocks are not contacting the ground. Reduce your tire pressures until they do.

Once you are in the ballpark with pressures, take the vehicle to a clean flat parking lot and carry along a piece of chalk. Strike a line across the full tread face of each tire and drive forward in a straight line for 20 or 30 meters, and look at the chalk line. You should see uniform wear across the line. If the outer parts of the line are unworn, deflate in half-pound increments until you have full contact. Front tire and rear tire pressures may not be the same due to differing weight on front and rear axle.

The amount of air required depends on load, not on the rated pressure of the tire, so if you find a pressure to use for an empty vehicle, you are going to have to increase pressure by several pounds if you carry a load. In the end, you want to stay close to full tread contact regardless of load. Gross overinflation is at least as dangerous to you as underinflation because it leads to loss of vehicle control, and it also wears out your tires in a way that can't be remedied. It can also play havoc with wheel alignment and wheel shimmy issues because at high pressures you will be riding up on the center of the tread. There is no point to having 9 inch wide tread if you use only 4 or 5 of those inches.

 

[mauricio_28]

The original issue was whether the tires, mine, can take up to 80psi. Tire manufacturers seem to indicate that when replacing P-metric tires with LT, the latter require higher psi than the former, even when the tire dimensions (yyy/xx) are identical, to carry the same load. I'll check the contact patch tomorrow, but I didn't see, hear or feel anything out of the ordinary.

 

[madizell]

The Pirelli Scorpion ATR in 265/75/16 is an E range tire, rated to carry 3,415 pounds at 80psi. Per tire. To demand 80psi, then, your vehicle would have to weigh somewhere in the neighborhood of 13,660 pounds. Of course, it does not. Assuming the Navara is close to the Frontier in weight, it would have a GVWR of 5,600 pounds. That would be loaded to the limit.

Assuming for argument sake that load bearing capacity of the tire is roughly linear in relation to the inflation value, if the Nissan can not weigh more than 5,600 pounds, it should never need more than 5,600/13,660ths of the maximum tire pressure for an E-range tire (0.41 rounded). If this assumptions hold true, you should never need to inflate your E-range tires to more than 80psi x 0.41 = 32.8 pounds in order to carry the gross vehicle weight for which the Nissan is rated.

I doubt that the relationship is linear, but I also doubt that it is all that far from linear. As far as I know, no one has ever tried to establish the relationship across the scale of usable weights and pressures, but lifetime experiences suggest to me that I am not that far off, either.

E-range tires should require less, not more pressure to carry a given weight because of carcass construction. Certainly they can tolerate higher pressures, but that is not so say that they should be inflated to higher pressures unless vehicle loads demand it. After all, E-range tires were developed for use on heavy trucks so that they could carry higher weights. When we use them on light vehicles, lower tire pressures are generally needed as compared to standard load tires.

 

[mauricio_28]

Back in engineerring school (BSEE), we were taught at least two things:
* very little is ever truly linear;
* when making an assumption for the sake of a simplifying a problem, one must always go back to make sure that the result of the assumption makes intuitive sense.

It does not make intuitive sense, to me, that 33psi would be the correct tire pressure for when the Navara is loaded to the hilt at 2,980kg. 33psi is perhaps the minimum pressure under STATIC load. Unfortunately for the math and the assumptions, those tires spin and deform when I press on the gas. I would never run the rig fully loaded with the tires in question at 33psi. Would you?

Again, if you check the web there are several references indicating that dimensions and load being equal, an LT tire requires, from 5 to 20 psi, more pressure than a P tire.

I took the rig out today, and the ride is indeed more taut, nothing out of this world, but the difference is certainly there. The additional tire weight did noticebly increase rotational mass, but again nothing objectionable. The engine will still propel the rig up sharp inclines off idle. I did notice, however, that engine braking is a bit attenuated going down inclines. I may try to go down to 45psi.

 

[madizell]

Intuition and science aren't related to each other. I am aware that the relationship in question is not linear, and also am aware that the relationship between internal pressure and load capacity differs with each tire design. However, the usable pressure range of a tire increases with its load bearing range. Standard tires have a narrow range of usable pressures. HD tires have a greater range. Because you are using a heavy tire on a light vehicle, you need to create your own science to answer the question of whether a tire is adequately inflated. Any time you increase the pressure of a tire to the point of crowning the tread, you defeat the tires ability to perform.

Moreover, tire engineers intend tires to run at not less than about 80% of the target pressure for an intended load, which target is already well below maximum pressure. No one designs tires to run at maximum pressures. The envelope for intended uses and pressures is fairly narrow, even for heavier structured tires. So obviously, the relationship between load and pressure is not a linear one, but because the number of variables involved is enormous and because they tend to change with each tire and carcass construction, stating a single, simple relationship is not possible. Hence, I posed a hypothetical example for no other than discussion purposes.

It is not necessary to know the mathematical relationships of pressure and load for a given tire. All you really need to do is look at it to see if it is meeting the road. With heavy carcass LT's you can and may need to carry slightly higher pressure than would be needed for stretchier lightweight standard tires of the same general dimension, but the difference should be relatively small, not on the order of 50%. All of which is simply my opinion.

 

[bigreen505]

I would never run the rig fully loaded with the tires in question at 33psi. Would you?

A chalk line test is somewhat dynamic. If it says 33 psi I would trust it. If the truck felt unstable I would add pressure a 1-2 psi increments until I reach the desired balance. In my experience if the pressure indicated by the chalk test is lower than what is required to provide stable handling, your tires are too wide or narrow for your rims. For example, with a relatively empty vehicle, a chalk test suggested about 28 psi for a D-rated 285/76r16 tire on a 7" rim.

 

[mauricio_28]

a chalk test tells you nothing about the stress on and the heat generated by the carcass when moving.

Again, no one has addressed the issue that tire manufacturers themselves unequivocally state that an LT tire requires more pressure than a P tire for the same load and tire dimensions. The same tire manufacturers state that LT tires require roughly 5 to 20 psi more than their P counterparts. I suspect that more pressure is required to shape the more rigid carcass into a spinning, road-worthy, load-bearing tire.

Check out this link to see the difference in heat emission between 30psi and 50psi under the same load for an LT tire.
http://www.nittotire.com/assets/safety/Replacing Tires on Light Trucks.pdf

 

[greybrick]

To add something to tire pressure choices here are some fairly good threads from Gassavers about pressure vs fuel economy. A search on the site gives some additional information about running higher than door jam pressures, tire wear, safety, etc.

http://www.gassavers.org/showthread.php?t=6597&highlight=tire+pressure

http://www.gassavers.org/showthread.php?t=2345&highlight=tire+pressure

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[madizell]

The following is an excerpt from "Guidelines for the Application of Load and Inflation Tables" provided by Toyo Tires as a .pdf document through the following link:

http://www.toyo.com/docs/tires/loadinflationtables.asp

LT265/75/16:

35psi/1910lbs -- 40psi/2100lbs -- 45psi/2280lbs -- 50psi/2470lbs -- 55psi/2625lbs -- 60psi/2790lbs -- 65psi/3000lbs -- 70psi/3105lbs -- 75psi/3260lbs -- 80psi/3415lbs

The GVWR on my Nissan Frontier is 5,600. The front/rear weight distribution is not known but the difference would not change the result. Assuming a 50/50 distribution suggests that at maximum load capacity, no one tire needs to support more than 1/4 times 5,600, or 1,400 pounds.

Using LT265/75/16 tires inflated to 35psi, each tire will support 1,910 according to Toyo, which is 510 pounds more than the truck can weigh completely loaded with a 50/50 weight distribution.

Assuming that the truck is actually weight biased 65/45 front to rear, the maximum load on either front tire at gross weight would be 1,820 pounds, which is still 90 pounds under the capacity rating for the tire at 35psi. The result is identical whether the front or the rear is the heavier.

Even though the LT tire is capable of carrying more weight, and may require more air to carry the same load when compared to a P-metric tire of the same dimension, an E rated tire is nevertheless so far overmatched to the light duty truck that it does not require more than 35psi to carry the gross weight stated by the manufacturer. Coincidentally, 35psi is exactly the pressure stated on the B-pillar placard. Go figure. If the Navarra weighs a bit more or less, adjust the computations accordingly, but the results will be the same because the E-range tire is so far overmatched for the load you carry. At 1,910 pounds per tire, the load is at the bottom end of the C-range capacity for 35psi.

There is certainly no reason not to use an E-range tire on the Frontier/Navarra, but in doing so, it is not necessary to inflate the tire beyond the manufacturers placard pressure simply because the tire itself is rated to carry more weight.

BTW, the diffrences in load bearing capacity versus pressure required to carry the load is very close to linear as demonstrated by the data provided by Toyo, ranging from .04 to .05 measured variance from pressure range to pressure range.

 

[greybrick]

Given what happen a few years ago with the Ford Firestone tire recall do you think that you are getting acurate light truck tire usage information or just something to keep you safe plus a huge safety margin from the suppliers. My understanding of the whole Firestone tire recall debacle was that everyone was running their tires at too low a pressure to be safe but that was what was specified on the vehicle side door plates. Like most good truck drivers do you have a temperature monitor or guage and do you know at what temperature your tires run at any given pressure. How might a heavier bumper and winch affect what tire pressure you run on the front and will that be the same for offroad as on highway.

.

 

[madizell]

Given what happen a few years ago with the Ford Firestone tire recall do you think that you are getting acurate light truck tire usage information or just something to keep you safe plus a huge safety margin from the suppliers. My understanding of the whole Firestone tire recall debacle was that everyone was running their tires at too low a pressure to be safe but that was what was specified on the vehicle side door plates. Like most good truck drivers do you have a temperature monitor or guage and do you know at what temperature your tires run at any given pressure. How might a heavier bumper and winch affect what tire pressure you run on the front and will that be the same for offroad as on highway.

.

The tire pressure charts are not related to a given vehicle or even a given tire, but relate to all tires manufactured today for cars and light trucks. It has nothing to do with "safety margins."

The Firestone problem was not due to someone running posted but too low pressures. They were simply ignoring their tires, as most of the great unwashed do every day. Now as a result of knee-jerk reactionism on the part of our legislation, we all must deal with tire pressure monitoring systems on our new vehicles, none of which systems work or offer useful information. Nor was the Firestone problem related to the use of LT tires on light trucks or SUV's in place of OEM equipment, but rather because of the use of P-metric light duty tires too close to the limits of their useful load capacity as OEM equipment, combined with the fact that Firestone makes one of the lowest quality tires on the planet. Ford bought them for a song, then would not own up to the problems inherent in their own decision. Again, that placard pressure has nothing to do with safety margins per se.

Yes, I use an IR temperature sensor to determine relationships between pressures and temperature, but since pressure rise as a function of temperature is a known, not a variable, it really isn't all that important. After six months of experimenting and observations on the 265/75/16 tires that came on the Frontier, I know that the 35psi placard pressure is too high for a normally loaded Frontier, and after reading the regulatory white papers on the TPMS legislation arising from the Firestone tire problems, I know why Nissan settled on 35psi as the single stated pressure, rather than stating a load-related range of pressures as all manufacturers used to do only a few years ago.