I've run the XDS2 (14 ply) on the drive axle for a couple of years now. Noisy, compared to the stock tire. I run stock Continental HSR's on the steer axle.
The XDS2 has 1,000 sipes and 400 tread blocks. I've never had a tire that came with more factory cut sipes. Speed limit of 75 is about even with the maximum speed of my truck, with 4.88 gears. But since I only drive 65 miles empty, and 55 miles towing (maximum speed limit in my state when towing) I haven't had any issues.
I have had 3 steer tire blowouts on the highway at speed with General 19.5 tires. Survived all of them, didn't hit anyone, but will never, ever, buy a General tire again. Ever.
Sportscraft, you mentioned running 245's, but it is unsafe to do that on stock rims, which are only 6" wide. 245s (in the 19.5 rim diameter size) require at least 6.75" rim width. This is important, because unlike even size rims like 17s, 18s, and 20s which have a steep 5 degree bead retaining taper, the half size rims like 19.5 have a much shallower 15 degree bead taper. And, the 14 ply rated tire is rated all the way up to 110 psi. Mismatching the manufacturer recommended tire to rim size is not something to disregard lightly. Like I said, I SURVIVED three steer axle blowouts, with correctly match OEM tires to OEM rims... and those were not pleasant experiences. No way would I ask for more probability of trouble by ignoring the warnings of both the tire and the wheel manufacturer.
Something else to look out for is dually spacing. The 6" rims do not have the offset to maintain minimum dually spacing for a 245 tire, never mind the shoulder support for the sidewall and bead retention in rim width. If you want to run 245s, be prepared to also change rims... which of course adds substantially to the cost, and for what, when the 225 in LRG has more than enough capacity for any load an F-550 chassis cab is rated for, much less an F-450 pickup.
Hoseclamp, running a 14 ply steel corded sidewall tire at 40% of the rated inflation pressure is a recipe for zipper failure. The manager of your tire shop may not have any concern, but Michelin sure would, as would any other heavy truck tire manufacture, the Tire Industry Safety Council, the Rubber Manufacturer's Association, and the Tire and Rim Association. Ford would have concern also, and I'll bet Ford provides some guidance in this regard in your new Owner's Manual.
When a steel corded sidewall tire is underinflated, the steel sidewall flexes repeatedly, over 640 times per minute, and even more times for you, because you drive faster than I do. With lower inflation, the excursion of steel flex is amplified, leading to metal fatigue. The fatigued metal can separate, like what happens when wiggling a soda can back and forth too many times. When it is time to haul the XLR and you inflate the tire to match the load, the weakened sidewall may no longer be able to withstand the increase in pressure, and can suddenly blow apart at a fully fatigued portion of the sidewall, which near instantly propagates into a zipper failure with catastrophic results.
The increase in pressure doesn't necessarily need to come from the act of inflation. Heat build up in the tire from use can increase the pressure, and this would be compounded by the underinflation, which flexes the sidewalls generating more excess heat. Ford, and all commercial tire manufacturers recommend, that underinflated 19.5" tire and wheel assemblies be removed from the truck and inflated in a safety cage if the underinflation was less than 80% or less of recommended operating pressure. Your tire store manager says it's ok to run 110 psi rated tires at 40 psi. That isn't advice that I would heed. Even if your door plate recommended operating pressures are at 75 psi, 40-50 psi is still substantially less than 80% of even that reduced operating pressure.
For corroborative information, see the very first page of Michelins Truck Tire Data Book, The Rubber Manufacturer's Association's Tire Information Safety Bulletin #33, or simply check out the relevant pages in your new truck's owner's manual. You will find they all agree with each other, and would disagree with your tire shop manager.
Besides the safety aspect... and when they say serious injury or death, they aren't kidding, just check out some you tube videos from Russia and Asia of truck tire reinflation accidents in the shop... there is also the financial cost of underinflation. The following guidelines are from tire manufacturers, who you would think would keep this information a secret so buyers would wear tires out faster:
• 20% underinflation can reduce tire life 30%
• 30% underinflation can reduce tire life 40%
• 40% underinflation can reduce tire life 50%
The XDS2 tires are $400 each. By recommending 50% underinflation, that tire shop manager appears to be attempting to double his business with you, if you are still around to pass him your credit card.
I like the XDS2s, but back when I bought them, the Toyo M920A hadn't been invented yet. If I lived in snow country, I'd be sorely tempted to try them, based on what little I've been able to research since your post first introduced me to them. My principal concern is wet traction, light snow, and black ice. Mostly wet traction. I don't drive in heavy snow pack like you Canadians have to. One thing I do not worry about is tire wear. Thanks for calling attention to another tire choice in this size range.
And congrats on the selection of an F-450. The Dana 130 axle that comes with the F-450 is underrated for the weight that same axle is normally rated to carry, I believe in part to compensate for the fact that the Dana limits the power input to the S130 axle (at it's maximum rated weight carrying capacity) to a level less than what the pickup engine produces. For more information on this, see the Dana Spicer website information on the Dana S130 axle. It is rated for more weight, but less power input. I think that could be why Ford went with the S130 in the 2015 and up F450 pickup, rather than the S110.