[Update 5] Shop installed the wrong tires.. Need some advice

You don't understand either. It isn't the tire, it is the air that gives the load capacity. The tire simply holds the air in place. Don't believe me, mount the same C load range with an E on the opposite side and remove all the air. Which one will support the vehicle? Neither. It is air, not the tire.

You are absolutely wrong on your assertion that an LT needs more air because of stiffer construction. This makes zero sense because it isn't the thickness, it's the material and construction. Typically adding more plies accomplishes that and is an industry standard, but not always true. This is why no one specs their tires on plies. You seem to agree on this fact so not really understanding your confusion.

As for tire standards in terms of plies, load ratings, etc. They are certainly blended and old references still exist as well as the fact that we have DOT ratings here and Europe has their own. Your understanding of P-Metric seems to be confused as well. The term was created when tires sizes were moved from the old alpha numeric sizing to the sizing we are currently using. The P does stand for passenger and the metric refers to the section width. There was a time in the 90s where a P would indicate that a tire had a 35psi max and non Ps could be lower. This didn't mean that tires were not P-metric. It was to meet a requirement from Europe.

 

You are arguing just to argue. Of course it is the air that gives the load capacity, but the tire construction determines HOW MUCH air pressure is needed to give that strength. And that amount of air pressure to achieve the right volume varies drastically from size to size, and load to load. You don't seem to understand how a weaker SL tire can require less air pressure than the same size LT equivalent. It is simply how they are designed. Two tires of the same size, one LT and one SL, the SL will support most of its weight capacity at a much lower psi.....but it will max out in its capacity much sooner in most cases. SL and C are pretty comparable and max out at similar max loads on most tire sizes, often the C is even rated for less. But overall the C will still be a stronger design due to the sidewall.


I understand P-metric and metric perfectly fine. P metric has a P. Metric (also called euro metric) does not. 285/70R17 SL and P285/70R17 SL are not the same. They will support different loads at different pressures. P-rated start at 27 psi, euro start at 22 psi. If there is no P, it is not a P metric, it is a euro metric. That is why you have to specify in the tire pressure calculator or else the recommended psi for the load will be incorrect, because the two are not synonymous.

For example, lets take the stock 265/70R16 sized tire again. In stock form, it is a euro metric 112T with a recommendation of 30 psi. If the stock tire had been a P265/70R16, the sticker on the door would have been 27 psi instead of 30 psi. Because a P265/70R16 only needs 27 psi to support the load that the stock tire supports at 30 psi. Both same size, both SL, only difference is one is p-metric and the other is euro. They have different load index charts.

 

I appreciate the feedback. This is why I made a thread here; I know I'm certainly not an expert down to that level of granularity, so this is the kind of insight that I'm looking for. Glad to hear that the 35psi isn't something that I should be concerned about.

 

Put them to 27 - they will ride much nicer and will be inflated to the exact same capacity as stock if you keep them. If you end up swapping to the C's, put them around 30-32.

 

I give up. You say you know then you try to justify your inaccuracy with more ignorance. It's simple math.

Your assertion on tire sizes and manufacturers suggested minimum cold pressure it not accurate. They don't assign the recommended pressure based off the size of the tire. There are a number of factors that determine what pressure is deemed the best. Things like MPGs, handling characteristics, stopping distance, etc. These are real factors that determine your PSI, not some website calculator. I get you read things on the internet to gain your knowledge. It is painfully obvious, but remember just because it is on the internet, that doesn't make it true. I hope in the future you disclose that before someone takes bad advice.

 

It should be pretty cut and dry. You didn't get the product you asked for. It is close, but not the same. Stick to that line and they should do what is right. The one thing I would stick with if I were you is the difference in tread depth between the two tires. The ones you wanted have deeper tread. In theory more tread means longer life of the tires. In practice they will probably last about the same, but it is a tangible difference between the two tires. I would suggest you measuring the tread yourself to make sure those specs are correct. As I have stated, those specs are nominal and no one actually verifies accuracy. I have seen two tires from different manufacturers that were supposed to be the same size and there was a 1" difference in height between the two.

 

Everything I have said is based upon the manufacturer recommended pressure and adjusting the new tire to match that weight capacity. Sure, the manufacturers factor in all sorts of factors before putting the number on the door, especially some manufacturers like Jeep and Nissan who lazily just put 35 psi on the sticker for nearly every vehicle and tire size. However, Toyota deliberately puts specifically determined pressure recommendations on every single different Tacoma trim based on what it ships with. 32 for P245/75R16, 30 for 265/70R16, 29 for P265/65R17, etc. The most common-sense approach for determine a new pressure on a different size/load tire is to use a calculator and base it off of the sticker for the stock tire. If it works well on the stock tire, then adjusting appropriately for the new tire will work well on the new tires.

For the record, I did not ever say the manufacturers base it off of the size of a tire nor did I say they base it off a calculator. I said we should use the calculator to base the new pressure on a new tire off of the old. However, I guarantee you the load index of a tire is absolutely factored in when they make that sticker with the pressure recommendation. Some may add to the minimum required pressure for assisting mpg. For handling, keeping the tire where it is not over inflated will always be best...too much air and the contact patch rounds itself making handling squirrely. So no, that is not really a factor.

You should cut that out. The only reason your comment brought attention to itself is because the 3rd and 4th sentences you posted in your first post, were wrong. The SLs are not 9lbs heavier than the LTs, and they don't have 3/32 more tread. That is the LTs. It's difficult to establish credibility in a conversation when our very first bit of input we give is incorrect. Sorry.

 

Not a tire guru but I don't have to be. You did not get what you were there to get and they should make it right as you choose, be it a swap or a partial refund.

 

All i said in my post is that if one has 29 PSI on the door placard, and LT tires are used, more PSI is needed to support same weight safely. Its a fact.

I never talked about an "ideal tire pressure". I gave examples of what I ran/run according to my tire size and weight added to my truck.

If you think the online tire PSI calculator is BS than that's perfectly fine.

 

~35 PSI sounds about right man.

You can play around a bit (+/- couple PSI or and see how you like it)

When taking long road trips or towing, I always increase my tire pressure. When towing, only rear tires obviously. When offroad, I go down to 15-19 PSI depending on the terrain.



EDIT: Wait my bad. I thought they installed C instead of E. Nevermind, 27-29PSI would be just fine.

 

He’s very clearly not sticking to stock, he went with 285/70R17. So the Firestone thing really has no relevance here at all.

 

Ok, I didn't read through the whole thread, I still wouldn't run the tires under inflated at Highway speeds from what the Sticker on the Door Jamb says.

 

I just don’t understand that reasoning when a larger tires supports more load than a smaller one. That’s the point of the calculator, to tell you what’s safe. The sticker is just a number based on load requirements. A larger tire needs less pressure to maintain those requirements, so it’s perfectly logical to drop the pressure accordingly.

Honestly, the Ford Firestone thing was a Firestone problem IMO. The pressure Ford recommended the tires be ran at, based on load index, was more than capable of supporting the weight of those Explorers.

 

Ford was doing the recommending Not Firestone. I would think if a Tire Company Says run Our Tires at this!!! And a Car Company Says run them at this, I would trust the Tire Company.

 

Right, but a specific size and load of tire has to meet a certain carrying capacity. Ford’s pressure recommendation met that for the size of tire they were using. If Firestone can’t build a tire to actually meet that weight capacity, then it’s on them. You shouldn’t have to run the tires at extra high pressure to over compensate.

 

I dont remember how that came out in the end with the Court ruling, I wouldn't run Firestone tires on my vehicles. All I know is on my Tacoma, I went from the 265/70R16 to the LT265/75R16 10 Ply and I run them at 42 psi. It's more then what the Door Jamb called for on the Stock Tires.

 

I posted an update to the original post. Tire shop ordered the LT285s and will be installing them on Friday at no extra charge. W customer service.

Thanks everyone who pitched in with their insight. I'll take some pictures of the standard load tires and of the C load tires once installed. The comparison pictures may be helpful to those who find themselves on the fence between these two tire sizes in the future.

 

Definitely take tread depth measurements of both to see how accurate they are. Also it would be interesting to see the two sitting side by side unmounted to see if they really are identical in size.