MarineBSP
Senior Member
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.
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.