Help with new 275/55R20 tires after towing blowout

Cotay · Jul 4, 2020

We just returned from fetching our travel trailer in California to bring back to North Idaho. Before departing we had routine maintenance performed on both the Expedition EL 4wd (has factory HD tow package) and trailer. Tires (2 year old Nitto Dura Grappler 275/55R20 XL 117S with 40K miles on them) were inspected by a mechanic the day before we departed and inflated cold to 44 psi (front) and 48 psi (rear) and all four had plenty of tread.

Until now the Dura Grapplers have been the best tires we've used for towing with the Expedition and they exhibited very little mush or sway when properly inflated. About 100 miles from home the right rear passenger tire blew at 60 mph. I have no doubt this was a defective tire but I'm not sure it's even worth a warranty claim. The three remaining tires are all still in very good condition. When we got home I checked and found that others have had similar issues with these tires so I'm looking to replace all four tires now.

I narrowed my choice down to two Cooper tires. The Discoverer HTP 275/55R20 XL 117T (in stock locally) and the Cooper AT3 XLT 275/55R20 120/117S E1 (ordered for delivery on Monday). The difference in price isn't a factor here so I went ahead and asked them to order the AT3 XLT. These E rated LT tires may be overkill but my wife wanted them for the slightly better winter driving traction. Discount Tire assured me that the stock factory Ford 20" rims are capable of 80 psi.

So my questions really are, are the stock Ford 20" rims really capable of running a E rated tire at 80 psi (not that I'll ever do this) and what psi should these be set at for everyday driving and for towing? I've looked for load index figures for an E tire inflated to less than max psi but I simply cannot find it. Or should I just stick to the XL tires?

07navi · Jul 4, 2020

Cotay said:
We just returned from fetching our travel trailer in California to bring back to North Idaho. Before departing we had routine maintenance performed on both the Expedition EL 4wd (has factory HD tow package) and trailer. Tires (2 year old Nitto Dura Grappler 275/55R20 XL 117S with 40K miles on them) were inspected by a mechanic the day before we departed and inflated cold to 44 psi (front) and 48 psi (rear) and all four had plenty of tread.

Until now the Dura Grapplers have been the best tires we've used for towing with the Expedition and they exhibited very little mush or sway when properly inflated. About 100 miles from home the right rear passenger tire blew at 60 mph. I have no doubt this was a defective tire but I'm not sure it's even worth a warranty claim. The three remaining tires are all still in very good condition. When we got home I checked and found that others have had similar issues with these tires so I'm looking to replace all four tires now.

I narrowed my choice down to two Cooper tires. The Discoverer HTP 275/55R20 XL 117T (in stock locally) and the Cooper AT3 XLT 275/55R20 120/117S E1 (ordered for delivery on Monday). The difference in price isn't a factor here so I went ahead and asked them to order the AT3 XLT. These E rated LT tires may be overkill but my wife wanted them for the slightly better winter driving traction. Discount Tire assured me that the stock factory Ford 20" rims are capable of 80 psi.

So my questions really are, are the stock Ford 20" rims really capable of running a E rated tire at 80 psi (not that I'll ever do this) and what psi should these be set at for everyday driving and for towing? I've looked for load index figures for an E tire inflated to less than max psi but I simply cannot find it. Or should I just stick to the XL tires?

Your wife is right, E rated is what you NEED for towing. I did a lot of posts on it earlier and passenger tires don't cut it. The E rated is at it's strongest at 80 psi but most people run them at about 60. It's mainly about how rough you like it but they like to have about 60 in them. Your wheels (rims is slang) will EASILY handle those tires., don't worry about that.

Plati · Jul 4, 2020

07navi said:
Your wife is right, E rated is what you NEED for towing. I did a lot of posts on it earlier and passenger tires don't cut it. The E rated is at it's strongest at 80 psi but most people run them at about 60. It's mainly about how rough you like it but they like to have about 60 in them. Your wheels (rims is slang) will EASILY handle those tires., don't worry about that.

I'm far from an expert but I'm skeptical of your comment. I thought it was all about having the right contact patch of tread on the road. Correct me if I'm wrong. I run LT's (multiple brands) on my Expy's and I have had to go to 48 psi to keep them correctly inflated for uniform tire wear, not towing. I've never done a chalk test but I think I might since I have so much free time now. I used charts from the tire industry association to zero in on a target psi. With LT tires, the more weight pressing down - the higher you want to go in pressure and 80 psi is only at max weight load and the beefed up sidewall can handle that if needed. So, I would say psi is mainly about how much load weight there is on the tire and obtaining the correct contact patch. 60 would not be a crazy place to start if the trailer add's significant load weight to rear. Trailer should have no impact on front psi? This is all easily verifiable with Google search's and even Tire Rack application notes.

I have no idea on the 20's but I think those are for show not function and 275/65R18's offer better performance for towing. Am I wrong on that too?

Cotay · Jul 4, 2020

MrSticker said:
I have no idea on the 20's but I think those are for show not function and 275/65R18's offer better performance for towing. Am I wrong on that too?

I've heard this too, but find it curious that Ford included them stock on a vehicle with the HD tow package. I assume Ford considered them sufficient, but perhaps not optimal. The Coopers are the first E rated tire I've seen in a 275/55R20 size (Tire Rack says Bridgestone and Firestone have them now too, but nothing shows up on their respective websites). I've tried three other sets of Euro Metric (non-P) XL rated tires in eight years and only the Dura Grapplers offered decent performance when towing. I'm hoping these Cooper XLTs will do the trick or I'm going to have to switch to 18" wheels.

MrSticker said:
I have had to go to 48 psi to keep them correctly inflated for uniform tire wear, not towing.

Interestingly, I just ran an online calculator that compared the OEM tires (Pirelli Scorpion STR, a P275/55R20 with a load index of 111), and it said to achieve the equivalent in the same sized LT E tire, the pressure should be 48 psi. If I compare them to my current Euro Metric XL tires at 50 psi (what I used for towing), the equivalent for them in the E tire is 61 psi.

07navi · Jul 4, 2020

MrSticker said:
I'm far from an expert but I'm skeptical of your comment. I thought it was all about having the right contact patch of tread on the road. Correct me if I'm wrong. I run LT's (multiple brands) on my Expy's and I have had to go to 48 psi to keep them correctly inflated for uniform tire wear, not towing. I've never done a chalk test but I think I might since I have so much free time now. I used charts from the tire industry association to zero in on a target psi. With LT tires, the more weight pressing down - the higher you want to go in pressure and 80 psi is only at max weight load weight and the beefed up sidewall can handle that? So, I would say psi is mainly about how much load weight there is on the tire and obtaining the correct contact patch. 60 would not be a crazy place to start if the trailer add's significant load weight to rear. Trailer should have no impact on front psi? This is all easily verifiable with Google search's and even Tire Rack application notes.

I have no idea on the 20's but I think those are for show not function and 275/65R18's offer better performance for towing. Am I wrong on that too?

The 80 lbs is the max pressure and they are strongest at that pressure but almost nobody runs them at that PSI. After 10 years on my Expedition forum I learned that people run them where they like them and where they work the best for them. There is no pressure cut in stone but most ran them at 60 PSI including me. Yes they can handle 80 PSI easily and are actually quite happy there but the owners aren't. Many have gone to the LT's for towing after the thread on it a while back. Of course they are a trade-off ; Cost more, and rougher riding VS cheaper and cushier ride but for towing I would definitely have the LT's. You can run the LT's at maybe 50 when not towing which helps a little.

11lariat · Jul 6, 2020

I run 20" AT3 XLTs on my F150 at 55-60 PSI, seems just about right. 80 will rattle your fillings loose. I run the passenger version of the tire (AT3 4S) on my Expy but don't tow with it.

07navi · Jul 6, 2020

In my last forum they were running LT, E rated tires anywhere from 50 to 80 pounds. They will hold up fine at 80 but ride rough.

chuck s · Jul 11, 2020

Blowouts are 99% overloaded tires. Caused by either too much weight on the axle or too little tire pressure. Trailer tires should always be inflated to their maximum sidewall pressure and truck tires can follow that example to protect the tires -- but that won't change the load capacity of the rear axle which I suspect is highly overloaded due to not enough weight transfer with the WDH.

My hybrid travel trailer isn't that heavy but I run my rear P-metric tires at 40 psi when towing and they run cool (ambient road temperature). Easy to measure tire temperature.

-- Chuck

Cotay · Jul 13, 2020

chuck s said:
Blowouts are 99% overloaded tires. Caused by either too much weight on the axle or too little tire pressure. Trailer tires should always be inflated to their maximum sidewall pressure and truck tires can follow that example to protect the tires -- but that won't change the load capacity of the rear axle which I suspect is highly overloaded due to not enough weight transfer with the WDH.

My hybrid travel trailer isn't that heavy but I run my rear P-metric tires at 40 psi when towing and they run cool (ambient road temperature). Easy to measure tire temperature.

-- Chuck

Tires on both the tow vehicle and the trailer were appropriately set. All calculations for load bearing were made and were within spec with proper weight distribution. GVWR and GAWR (for both axles) for the tow vehicle were not exceeded. We had very little cargo other than small children in the Expedition. Cargo consisted of a single backpack per person and food, all of which was stored in the trailer directly over the trailer axles or behind them. The trailer itself is 5483 lbs/550 pound tongue weight and we pull dry. All people and cargo in the Expy plus the tongue weight did not exceed the maximum weight of cargo for the tow vehicle (1576 pounds) and it was properly distributed over both axles.

Adieu · Jul 13, 2020

07navi said:
The 80 lbs is the max pressure and they are strongest at that pressure but almost nobody runs them at that PSI. After 10 years on my Expedition forum I learned that people run them where they like them and where they work the best for them. There is no pressure cut in stone but most ran them at 60 PSI including me. Yes they can handle 80 PSI easily and are actually quite happy there but the owners aren't. Many have gone to the LT's for towing after the thread on it a while back. Of course they are a trade-off ; Cost more, and rougher riding VS cheaper and cushier ride but for towing I would definitely have the LT's. You can run the LT's at maybe 50 when not towing which helps a little.

You can run LTs at 36-38 on pavement if you want (or half that on sand)

Half the population of BFG KO2 drivers get em for looks and never even thought about psis and are OK for wear and safety both. And lots of shops automatically and mindlessly inflate everything to 32 or 34 unless you yell at them (usually twice), in many places without ever asking or informing you (local regulations often say they HAVE to "check" tire pressures if a car is in their maintenance bay, and many interpret "check" as "change")

Help with new 275/55R20 tires after towing blowout

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