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I've searched the forum and found a great explanation of how LT & XL load ratings compare:
The LT version is built much stronger, less flexible and quite a bit heavier. If you will be carrying lots of weight and cargo in your Defender (including adding hundreds of pounds of rock sliders, winches, etc.) and spend a lot of time on 2 or 3 wheels off-road, the LTs may be a good idea. Their multi-ply construction also makes them less susceptible to cuts and gashes in the sidewalls. The disadvantage will be a harsher ride and less precise handling on pavement (due to the harder and thicker compound, higher inflation figures and heavier unsprung weight) and perhaps a bit more road noise as well. Your gas mileage may also worsen a little versus using the lighter P(assenger) version, and LT tires normally tend to wear out faster, often manufacturers don't offer a treadwear warranty at all, or offer a more limited one vs. the passenger version of the same tire. Finally, LT tires normally have lower speed ratings than regular tires, such as the above example - Q means you need to keep it at or under 99 mph to be safe, with the XL version you can sustain speeds up to 118 mph. And you need to inflate the LTs quite a bit more than regular passenger tires to maintain the same load capacity. So, if the passenger (XL - extra load) tires of our Defender say 36 PSI for example, a Light Truck tire will need 45 - 50 PSI to achieve a matching load.
Based on this, LT is not for me. But is there a construction advantage of extra load over a standard load tire in passenger tires? I'm looking at two tires, the OEM tire classified as a XL with a load index of 114 (2601 lbs / max psi of 50) and the possible replacement tire listed as standard load with an index of 116 (2756 lbs / max psi of 44). It seems that regardless of the passenger tire load range, the tire with the higher load index will be better for a fully loaded vehicle and the occasional rocky off-road adventure. Is my thinking correct on this?
I’m pretty sure the OEM is XL and the vehicle should be given either XL or LT tires. I don’t think standard passenger tires (non-LT) are sufficient for the vehicle. Stick to XL or LT.
Many tire places, the reputable ones at least, will not fit tires that are below the OEM tires' load rating.
I don't know the first thing about load rating tolerance but know I'd not gamble with putting tires on the Defender with anything less than recommended XL rating. Blowouts are less than fun.
Experienced it once, and that was enough for me. Terrifying.
On the mileage warranty. Costco offers a 50 or 60k prorated warranty on its BFG K02.
255/70 R18 are D rated and have a 3 ply wall construction. A little lighter than the E rated 275/65 R18.
275/55 R20 are an OEM size option in the 20" rims with a similar warranty. I think they are also E rated. All are LT tires.
Just some food for thought.
Many tire places, the reputable ones at least, will not fit tires that are below the OEM tires' load rating.
I don't know the first thing about load rating tolerance but know I'd not gamble with putting tires on the Defender with anything less than recommended XL rating. Blowouts are less than fun.
Experienced it once, and that was enough for me. Terrifying.
On the mileage warranty. Costco offers a 50 or 60k prorated warranty on its BFG K02.
255/70 R18 are D rated and have a 3 ply wall construction. A little lighter than the E rated 275/65 R18.
275/55 R20 are an OEM size option in the 20" rims with a similar warranty. I think they are also E rated. All are LT tires.
Just some food for thought.
This is what I'm trying to sort out - the difference between the load range, extra load / standard load, and load index. The standard load tires I'm considering have a load index of 150 lbs greater than the OEM XL tire. It seems the standard load tires can actually carry a greater load. Is there something else other than the load to consider when deciding between extra and standard?
You need to consider whether the tire is designed and proven over time to be used on a vehicle designed to carry the load on only two or three of of its tires (and designed to come down to hit the trail from a height of several feet from the trail surface). There is no way I would consider NOT using at least an XL tire, nor unproven / unapproved rims, nor deviating from what is proven to work for others.
There are several threads on this site which list the all the usual tire suspects suitable for the use on the New Defender which others have found effective and satisfying -- KO2, Nitto, Falken, etc.
SL tire weight ratings are for lower psi than XL. I am going through this same decision process myself because the new Nokian outpost only comes in LT or SL, no XL, and I’m not sure I want to put up with the downsides of L’s if I don’t really need them. Then again I do tow a 4,000 lb camper occasionally off road. Should I just go with LT’s?
SL tire weight ratings are for lower psi than XL. I am going through this same decision process myself because the new Nokian outpost only comes in LT or SL, no XL, and I’m not sure I want to put up with the downsides of L’s if I don’t really need them. Then again I do tow a 4,000 lb camper occasionally off road. Should I just go with LT’s?
Since I've posted my original question, I've leaned quite a bit more. You are correct, when moving to tires with larger diameters and sidewalls the options for XL rated tires is less. SL/XL seems to be more for a low/high psi categorization for passenger cars. For my purposes, the actual load index and construction seems to be the key. I ended up with a set of SL tires that have the same or greater number of plys on both the tread and sidewall as the OEM XL tires and whose load index is greater than OEM XL tires. And while not 50 psi of the OEM XL, the 44 psi max of my tires is a heck of a lot more than the max psi for typical SL tires. I'm satisfied that the construction, load and pressure ratings all comport with the OEM tires and Tire Rack agrees. If you can't find suitable SL tires, then LTs would be the way to go.
Thanks. I’ll have to see what the max psi is on the Nokian SL’s. I run mine at the recommended heavy load psi of 47 so I guess I cant even do that with a typical SL.
I decided against LT’s because once you lower psi to 50 on the LT version of the Outpost for example, you end up with a load capacity of only 1900 lbs, which is 600 lbs below OEM. Only way to get that higher is to drive at much higher psi, and I don’t want to do that. Since my tire place will not mount SL tires on the Defender, the Outpost is out for me. Looks like I’ve narrowed it down to either Falken’s or Mickey Thompson at this point and seem to be good mix of road and dirt capabilities. Both available in XL.
If anyone is interested, I went with Cooper Discoverer Rugged Trek (RT) in 255/70-18. It's also available in 265/65-18, as well as 275/55-20.
The RT is a XL rated tire with a 116T (18") or 117T (20") load rating. I use this as my off-road wheel/tire setup, keeping the 20" OEM Goodyears for street use. I have one long trip out west with a lot of off-roading in the San Juans and was very pleased with the performance. It's louder than the OEM so I keep them for street use (because wife), but compared to what I was used to in my Wrangler before, they are whisper quiet. If you're not familiar with the RT designation it slots in between AT and MT in "ruggedness." A good compromise for this truck, IMO.
XL vs SL Tire Load Rating
