A new tire guinea pig "Denman" tire.

[FightinIrish]

Add me to the list of upgraded 15" tire guinea pigs. I just purchased three new Denman ExpressST 275-75-R15 trailer tires on 15" x 6" rims. They are D rated with a load capacity of a bit over 2800 lbs. Only drawback, and I am working with Denman is the max psi is 80. In an effort to not "beat the trailmanor to death", Im working with them to see if I can run them at a lesser psi to soften the ride. It is kind of a catch 22. We are all looking for an increased load capacity to aid in the "overloading" of the OEM tires but at the same time, keeping the best ride possible. Since most of my trailering is on good highways, I opted for the load capacity and will hopefully be able to lessen the pressure to aid in the ride.

I do know there was some talk or comments by bill I believe about trying to put the 15" tires on without a lift kit. I tried it last night. Put the tires on, tightened everything down, lowered the scissor jacks and the clearance between the wheel well and the top of the tire was just shy of 1", too close for comfort especially with an empty trailer. Adam is sending me the lift kit so I should be in good shape.

Ill keep you all up to date as to the wear and ride of the Denman's. I will say the tire store owner said if I was looking for a bias ply tire, he would not have suggested the Denmans but with a radial, he has had great success for the past five years. Oh yeah, almost forgot, checked all the dates and they were made in 2907, 3007 and 3107 so they are pretty darn new. Made sure of that.

[FightinIrish]

Update; just put 1500 miles on the new Denmans. Trip went fine. No issues at all with the new lift kit, 15" wheels and 225-75-15 Denmans. I did decrease the psi to 70 to avoid bouncing the TM apart. Worked pretty well. We did have pretty good roads for about 75% of the trip. Everything stayed in place even through the bouncy road coming and going through Macon on the bypass. What a mess.

[wmtire]

They are D rated with a load capacity of a bit over 2800 lbs. Only drawback, and I am working with Denman is the max psi is 80.


Good deal. Please keep us in the loop on how the Denman's perform. Are you sure that they are not E rated in order to have the 80 psi? Most D rated tires have a 65 max psi. I'd sure hate for you to be running your tires overinflated, if they are indeed Load Range D.

On another note. I have still been twisting my friends arm to get us a self-reporting webpage up, where we can keep up with all our experiment on tires. He keeps tellimg me, he'll get it done for us, but doesn't know when. He is the chief engineer for a television station and they are in the process of making all their transmissions HD digital.

[FightinIrish]

I am 100% sure the psi is 80. Only one I am not sure of is the spare but I purchased them all together. Ill still crawl under and double check. It is a bit easier to access with the new lift kit installed. FYI - DW and I are heading to Asheville NC for a vacation the week of Christmas so Ill be putting another 1500 to 2000 miles on them. Will keep you up to date.

[FightinIrish]

Just received a confirmed email back from Denman that if I do decrease the psi to 70 instead of the 80 max, the load capacity will only drop from 2800 to 2600 lbs which leaves plenty of margin for loading. We will be off to Asheville, NC for Christmas so Ill have another 1500 to 2000 miles on them. Will report back after the trip.

Have a safe Holiday everyone.

[Joseph]

Thank you for the info! Looking forward to your reports.

[Denny_A]

FYI: my tires are load range "E"; max load at 80 psi = 3500 lbs.

To determine safe pressure I use a reduced pressure/vs load formula which returns the same result "FI" got from Denman.

Say; N = new max load at reduced pressure
M = max load at max press
Pm = max pressure
Pr = reduced pressure, then

N = M*(Pm +Pr)/2*Pm

Plug in M = 3500, Pr = 70 psi, Pm = 80 psi and :

N = 3500*[(80+70)/2*80] = 3280 Lbs. (I run my tires at 70 psi, cold). With four tires I can carry 13,000 lbs, but am usually under 11,000 lbs.

In the Denman case that's:

N = 2800*[(80+70)/2*80] = 2625 Lbs (close to the 2600 lbs. they advised)

The formula is, I think, ok as long as the pressure reduction doesn't exceed 20%. Beyond that it predicts load capacity above real world. Also one would really not want to reduce pressure that much anyway.

Just my $0.02 worth:).

Denny_A

[FightinIrish]

I know the stiffer tire and higher psi does give a rougher ride, I just weighed that vs overloading a softer tire and for me, it was an easy decision. If it means me retightening screws and taking care when packing things in the TM, that is a pretty simple decision. Id rather do that then have to fix flats roadside.

[Denny_A]

I know the stiffer tire and higher psi does give a rougher ride, I just weighed that vs overloading a softer tire and for me, it was an easy decision. If it means me retightening screws and taking care when packing things in the TM, that is a pretty simple decision. Id rather do that then have to fix flats roadside.Actually, I was trying to say I reduce pressure to improve the ride of my trailer also. I provided the formula as a way to determine approx load carrying capacity when cold px is reduced. 80 psi taken down to 70 psi is only a 12.5% reduction. Any lower than about 65psi (nearly 20%) and tire life is degraded a bunch (around 10-15%, IIRC).

A consistent 10% to 12% px redux only reduces the lifetime of the tire by about 5%. I think it's worth the reduced wear and tear on the trailer.

Denny_A

[FightinIrish]

Just returned from our trip to Asheville, NC for the Holidays. Put a bit over 1500 miles on the new Denmans without any issues. I am running 68psi to soften the ride and to this point, all is well and in line. No problems to report. Hopefully this will remain the case.

[FightinIrish]

Made another short trip putting just a couple hundred miles on the Denmans. All just fine, no issues. Running between 68-70 psi and no issues whatsoever. Sidewalls barely warm upon stopping after a hundred miles, bearings same. Nothing much more to report.

[fcatwo]

FWIW The understanding I gained while researching tires for our TM a year or so back was that we only need to use enough PSI to maintain an acceptable tire profile under load for the tire to give good service. For instance, you can stand the tire in the corner with no weight on it and it will retain an acceptible profile with "0" PSI. Load it to it's max and it may need the full 80 PSI to retain a safe profile. Goodyear has a chart on it's site that shows carrying capacities at various PSIs for their ST tires. I have to admit however that we ran our Marathons at the full 50 PSI even though Goodyear's chart said 40 would be OK.

It would be nice to know if we are the only TM owners who never had a tire problem in five years of ownership or if that is the case with the vast majority of owners. There is no question however that ST trailer tires suffer failures -- which may explain why Michelin and other big names don't make them.