LT Tires on 20" OE wheels - pressures, clearance, traction, mileage, ride

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MarineBSP

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Thanks to all the folks who have contributed to the several discussions about changing from P-metric to LT tires. I decided to make the change and to report my observations on before/after. This post is meant to share what I observed for my truck, wheels, and tires when I switched from Stock P275/60R20 Wrangler SRA’s to LT275/65R20 Nokian LT3's. Your experiences could vary based upon different GVW, model, and weather & roads in your area of the country. Also consider that my new LT3 tires on this set of wheels are a Light Truck snow tire. I decided to go with 2 sets for winter and non-winter, and I will save up for the second set of LT tires in the Spring.

I bought a used set of wheels - stock 20” painted alloy wheels from a 2014 RAM 1500, and I installed LT275/65R20 tires with new TPMS sensors. My truck is a 2018 RAM 1500 Laramie CC SB, so it came stock with the famous P275/60R20 Goodyear Wrangler SRA P-metric tires. I’m sure that choice is prioritized by tire cost, rolling resistance (fuel economy), and ride compliance. I know that the tires are adequate for their rated load, but those priorities don’t match mine, which are traction and robustness. My SRA’s have a ‘bounce’ to them over bumps that reminds me of the “boiiiiing” noise of a kids’ kick ball versus the “bounce” of a good basketball.

Load capacity, traction, and clearance: Even though I do not do a lot of towing, I wanted a firm foundation. Nokian LT3’s are E-rated tires (126 Q), only moderately aggressive tread for a truck, and they are relatively light in weight for E-rated tires. They are 34.1 inches in diameter, weigh 50.9 pounds each, and have 18/32 tread. The maximum single tire load is 3750 lb at 80 PSI (design max). They are studdable, but Minnesota outlaws studs, so mine have none. I optimized for wet/snow traction, and it seems excellent in the little bit of wet/snow/ice I've experienced. With stock suspension, these tires have not rubbed under any circumstance in the 400+ miles I have driven them so far.

Tire pressures and ride: I did the math (US Tire Manufacturers Association tables), and starting from the door card of my truck, the 39 / 39 PSI recommended front and rear for my old tires calculates to 47 / 47 PSI for the new tires. I chalk-tested, and that is pretty close to the 46-47 Front and 41-42 Rear which the chalk test suggested for cold and unloaded. I’m running 48 / 48 right now. At those pressures I think that my ride is at least as comfortable as on the 60-series P-metric tires, but with a more stable, planted feel.

What about fuel economy? SRA's appear optimized for mileage, so almost all changes are likely to decrease fuel economy, but by how much? Possible mileage eaters include: 1) Wind resistance at ½ inch increase in ride height; 2) Heavier tires (51 lb vs 39 lb); 3) Winter blended gasoline; and 4) Cold weather with warm-up times up to 15 miles for my truck at highway speeds in 10-to-20 degree F temps. If mileage is your only interest in reading, my short answer is that I seem to be losing about 0.5 to 1 mpg compared to the SRA’s across a variety of conditions – the details follow.

Mileage comparison notes: I made all of my observations on the same tank of 87 octane gas – so all the data is from EVIC. It should be good for comparison even if it is optimistic. First thing I noticed was that the half inch increase in ground clearance changed the wind noise for the truck. Not louder, not disagreeable, but different. Right there I expect to lose some mileage, but how much ? My driving is roughly a 50 / 25 / 25 mix of country highway, freeway, city. The first day of driving I was depressed that I had lost a lot of mpg. BUT I had not yet corrected the BCM with AlfaOBD, AND our first cold snap had hit. I changed the BCM tire circumference, which helped less than one mpg according to EVIC. Then we had one nice 45 degree day to drive all the same routes that had such poor fuel economy before – lo and behold ! Mileage popped back up from the 17.5 average I was seeing to more than 19.5 mpg. Last night was about 0 deg F – and sure enough, the mileage was back down. From the back-to-back on the two sets of tires with one fill of gas, I estimate that I am losing about 0.5 mpg relative to the SRA’s that came on the truck – definitely not more than 1 mpg. I am running the new tires at 48 / 48 PSI cold inflation front and rear, and ‘cold’ is below freezing.

Overall I am very happy that these LT tires don't cost me much in mileage or ride but give the added traction and road feel better suited to how I use my truck. I still have to upgrade my spare . . . and the spare tire winch fixture to match the smaller-than-spare wheel centers.
 

Pull Ya

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Thanks for the write up. Great information. As a side note--IMHO the SRA's are a dangerous tire--they are not even safe enough to use as a child's swing. Others may disagree, but that has been my and many others experience.
Jay
 

Smokey613

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Thanks for the write up. Great information. As a side note--IMHO the SRA's are a dangerous tire--they are not even safe enough to use as a child's swing. Others may disagree, but that has been my and many others experience.
Jay

Can you elaborate on the issues with the Wrangler SRA?
 

Pull Ya

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My particular problem was hydroplaning. On a wet road the front tires would hydroplane constantly. Driving in the rain or on wet streets was dangerous in my opinion and I did not trust them with my families safety. I removed the tires immediately therefore I can not speak to the mileage problems many people complain about.
Jay
 

Smokey613

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We had them on our 2014 and our 2018 Laramie we just purchased has a new set of them. We noticed on our 14 they were not real good in the rain. Replaced them with Bridgestones which were much better. It’s just hard to justify replacing brand new tires.
 

billyw

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I siped my original SRAs and though they didn't last long, they performed well, even in winter conditions. They were great for towing too. Much better than the Cooper AT3s that replaced them.
 

mxer201

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TTT with this thread. Have almost 50k on the OEM tires on my 2016 RAM 1500 v6 4x4. Considering a new set of General Grabber ATX LT275 60 20. One of the SRAs was ruined after running over an unknown object on the interstate and another went flat after a sharp rock sliced the tire. But I take some of the blame for the rock induced flat due to driving too fast on a very rough gravel road hence my decision to go LT. General has a $100 rebate until the end of October. Anyone running these tires? Pros Cons?
 

Sinistre1

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I'm putting in the research time right now trying to pick out new tires, Going with coopers or generals but highway tires. Not much offroading in NYC
 

mxer201

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I'm putting in the research time right now trying to pick out new tires, Going with coopers or generals but highway tires. Not much offroading in NYC

I was seriously considering Cooper Discoverer A/T at Wal-Mart since I just put a set on the wife's 4Runner and the price was hard to beat. And I like tread pattern. But low and behold Wal-Mart jacked the on line price up $50.
 

pt1655

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Great post, thanks for the writeup. I went to Michelin LTX AT2's in the LT size and am very happy with them. But, can you elaborate on the chalk tire method for tire pressure? I run 40-42 psi when not towing or heavy load as Discount Tire recommended, the sticker on the door says 35 psi stock. I am not sure and would welcome the explanation.
 

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One thing not mentioned is that wheels have a maximum rating for load and pressure. Putting 80 psi max tires on a 65 psi rated wheel for example, could lead to unintended consequences. Always be aware of the wheel ratings when considering tire upgrades.
 

Hemi395

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One thing not mentioned is that wheels have a maximum rating for load and pressure. Putting 80 psi max tires on a 65 psi rated wheel for example, could lead to unintended consequences. Always be aware of the wheel ratings when considering tire upgrades.
I was wondering about that with the stock 1500 aluminum wheels.....
 

billyw

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On a 1500 there should really never be a reason to inflate even E rated tires anywhere near 80 PSI. 55 or 60 will provide more than adequate support for any load a 1500 is capable of carrying. But it is wise to always be aware of any hardware limitations before learning about them the hard way.
 
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