Light truck VS passenger Tire

[stang5]

Would I notice a MPG increase and performance if I replace my 31x10.5/15 LT tires to a 265/75/15 passenger tires on my 91 Nissan pathfinder..TIA

 

[CapriRacer]

Probably. P metric tires will have lower rolling resistance - everything else being equal.

But most of the time everything else, won't be equal. Even then, it is more likely that a P metric tire will have lower RR.

But it will depend on what you are replacing and what you are replacing it with. The more meaty the tire, the more the RR.

BTW, this is not going to transform a gas eating monter into a fuel sipper. You won't see a lot of improvment unless you go pretty drastic.

But let's explore this a little more.

According to Tire Guides, a 1999 Nissan Pathfinder came with P265/70R15's inflated to 26 psi mounted on 7" rim - except for one version (XE) that also came with P235/70r15's on 6.5" rims (Steel?)

P235/70R15: 27.99" diameter 6" to 8" rims
P265/70R15: 29.65" diameter 7 to 9" rims
P265 75R15: 30.67" diameter 7" to 9" rims
31X10.50R15LT: 30.52" 7 to 9" rims

But the other part of your question is performance - well, that's a little more difficult, but generally the ride will be softer and the handling will not be as crisp.

Again it will more depend on what you are taking off and what you are putting on.

 

[1sttruck]

A skinnier tire of a traditional, hard rubber will probably help with mileage, and not help with traction.

 

[Master ACiD]

i would think it depends on the tread pattern of those 31's. if youre runnin super swampers or something then yes you will notice a good mileage increase, as well as a reduction is that wamp wamp sound.

just be sure not to overload the passenger car tyres and you shouldnt have any problems.

 

[Huhwhye]

I agree with above. Also consider the weight of the tires. Certain LT tires made for off road use are heavier. The extra weight could could change economy since it take more to turn them.

It depends on your intended use. If a passenger car tire suits your needs go for it.

 

[obbop]

"Would I notice a MPG increase and performance"

Unable to provide meaningful opinion until the word "performance" is defined.

 

[jmacmaster]

Quote:

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if youre runnin super swampers or something then yes you will notice a good mileage increase.

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I think that you meant to day that you'd have a mileage DECREASE. In my opinion, generally, the more agressive the tread, the lower the mpg that you'll get.

 

[Tempest]

I asked Capri Racer about LT vs P tires a while ago in a PM and this is what he said:

Quote:

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Differences between "P"'s and "LT"'s? Let me explain it this way:

A P235/75R15 SL has a load carrying capacity of 2028 # at 35 psi. However, this is only when the tire is used a Passenger car tire.

This particular size is normally used on pickup trucks and vans. When used in this application, the load carrying capacity has to be reduced 10% - 1844# @ 35 psi.

On the other hand, an LT235/75R15 Load Range has a load carrying capacity of 1985 # at 50 psi (single, as opposed to dual). Since "Light Truck" is its intended application, the load table already takes that into account.

If you were to work backwards, you would find that the LT tire has a load carrying capacity of 1857 # @ 46 psi and 1825# @ 45 psi. So for the same load carrying capacity (1844 #), the pressure has to be about 10 psi higher.

For this reason alone - higher pressure - the tire is built stronger. Many people are not aware of this difference in this load carrying vs pressure relationship and incorrectly think that LT tires are simply stronger because they are "Light Truck" tires and not "Passenger" tires.

What is really going on this that "passenger" tires have, over time, gotten larger. The vehicles they are being put on are heavier.

Trucks, on the other hand, have gotten more and more "car-like".

If you go up a step in tire type to the over-the-road trucks (18 wheeler type), you'll find that cost is an extremely important consideration - both initial cost and operating cost. For this reason, the tires are designed to use a minimum amount of material and to utilize this material to the fullest. The best way to do this is to use very high pressures.

It is typical for these tires to use 95 to 120 psi. This means the plies in the tires are pretty strong - typically steel cable.

It also means the rubber in these tires needs to be able to withstand high unit loads. Normally rubber will "creep" when subjected to high load concentrations, so rubber compounds used in this application are designed to minimize this. Plus the load vs pressure table for this type of tire sizing is designed for a smaller amount of deflection, further improving the "creep" properties.

Remembering that there used to be a clear cut difference between passenger cars and light trucks, I think it is easy to see that these 2 vehicle types have developed such that the loads subjected to the tires are sometimes similar.

Put another way, people are using pickup trucks and SUV's as passenger cars, and the ride characteristics of high pressure LT tires is not conducive to good ride.

So when you ask a question like "what are the differences", it's like comparing a dump truck to one of those 200 ton mining trucks. They are coming from different ends of the spectrum - and in some respects it is an "apples and oranges" type of thing.

Bottom line:

I do not recommend anyone use an "LT" where the original tire was a "P" - and vice versa.

The real danger is that if someone were to use an "LT" with the same pressure as specified for a "P", the tire is designed around a higher pressure and there is a higher risk of a tire failure.

Tire failures are fairly rare - for a lot of reasons - and applications where the vehicle has a low curb weight compared to its gross weight (in other words, a large payload - pickup trucks being a good example) result in tires that fail less often for pure durability and more often due to damage - cuts, impacts, etc.

Nevertheless, a tire with a large load carrying capacity offers a lower risk of failure. And that's one of the reasons why the vehicle manufacturers use tires with large amounts of excess capacity.

BTW, I have been PM'd before, but I think the type of information I just provided above is valuable to all - especially the fairly knowledgeable group at BITOG. So I tend to think it's best if these types of questions are posting so everyone can see them.

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Most informative.