Cooper Discoverer S/T Maxx
- Thread starter jim65wagon
- Start date
Honestly that is the only "negative" that I see with them. They do ride a bit rough, but I expected that out of a 10 ply tire on this application. It seems that most anything in a 265 or 285/70/17 and up is a 10 ply these days. I would rather have a slightly rougher ride and a tougher sidewall/tire. I'm running the 265/70/17 as I didn't see a big advantage to going with a 285 this time. Running 35psi.
Redline
Likes to Drive and Ride
Yep, it's quickly becoming a 10-ply rating world. I have long been an advocate of load-range D tires, a nice balance of load-range, strength and ride. But 8-ply rated tires are not as common, even though there is a ride penalty with LR E tires, particularly those with a 3-ply sidewall.
Online this evening I did learn that the Cooper STT (mud tire) in a 285/70R17 is a LR D, and has a 3-ply sidewall. Not sure what the ride is like, only one way to tell, and I'm not wild about running a full MT again.
The ST Maxx is still more appealing.
Online this evening I did learn that the Cooper STT (mud tire) in a 285/70R17 is a LR D, and has a 3-ply sidewall. Not sure what the ride is like, only one way to tell, and I'm not wild about running a full MT again.
The ST Maxx is still more appealing.
Hilldweller
SE Expedition Society
I loved the 285 STTs on my Jeep. Surprisingly quiet and smooth; much better than KM2s on wet roads.
My favorite all-around tire for a vehicle in this weight class.
I'm thinking of the Maxx for the next rubber for the Power Wagon though.
Redline
Likes to Drive and Ride
I much prefer a softer riding and more flexible tire, and know the S/T Maxx is going to be firmer that I really want. However, it's still the #1 pick for my next tire as there seems to be few, if any, competition. With this new design Cooper in filling a niche, eliminating some of the old S/T weaknesses, one of which was 'soft' design. We can't have everything. in addition to what appear to be very attractive off-road tire features, it is relatively inexpensive mail-order or with a local price-match.
Redline
Likes to Drive and Ride
I agree with your premiss and joke
However, I'm sometimes still impressed by how well my built 4Runner drives, rides, and 'wheels, compared to some of the previous rigs I've run. And I've often experienced a stiff tire change the ride of my car over that of a softer, more flexible tire (load range E vs. D for example) both on and off-highway. It's all a compromise, the most rugged/stiff sidewall tires don't flex nearly as well as a regular tire at a give PSI, but….
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jim65wagon
Well-known member
Try dropping them down to 30 or 32 for a while. That E range tire can carry the weight of your vehicle easily at a lower pressure. Play around with it a while and you should find a pressure that works well for a good ride, decent mileage and a good wear pattern.
I think paying close attention to your air pressure whether you run a C, D, or E range tire is important. Finding the right combination for your vehicle may take some experimentation but it will pay off in the end.....
Redline
Likes to Drive and Ride
That's right Jim65.
Of course the higher the load-range usually the firmer tires will ride because of their construction, and this can make it more important to avoid over-inflation if you want a softer ride. However, higher load-range tires are not rated to hold more weight at a given PSI. A load-range C, D, or E light-truck (LT) tire of a certain size (265/75R16) will be rated for the same weight at a given PSI, like 35. Increasing the PSI is how the weight-rating and carrying capacity increases. Higher load rated tires ride firmer, but they do not carry more weight unless you increase the PSI. These stouter tires may also flex less, which affects traction and heat generation, but those are different subjects.
Example:
In the common 31.6-31.9" size- LT265/75R16
35 PSI = 1910-lb.
40 PSI = 2100
45 PSI = 2280
50 PSI = 2470 (Load Range C)
55 PSI = 2625
60 PSI = 2790
65 PSI = 3000 (Load Range D)
70 PSI = 3105
75 PSI = 3260
80 PSI = 3415 (Load Range E)
So it's very simple and takes lots of guess work out of deciding what PSI you may want to run for on-highway loads. Simply weigh your vehicle for a particular load(s) and use a chart for your baseline PSI. Baseline. You may need more PSI for other of reasons (speed, unequal side-to-side loads, heat, etc.), that's for you to decide. But this method takes much of the guessing out of establishing a baseline PSI, as it's based on what your truck actually weighs. I'm pretty sure that vehicle manufactures don't use the often suggested chalk method to establish the OEM suggested tire PSI (just a guess). I'm not saying the chalk method is wrong or doesn't work, I don't use it. But I like using math and science to determine on-road pressures.
Looking at the numbers above many would be surprised that a 265/75R16 is rated to carry 4,200-lb per axle at 40-PSI! Larger tires with more air (volume) typically support more weight at a given PSI. The next size up, a 285/75R16, is rated to support 2,130-lb at 35-PSI. More weight with 5-lb PSI less!
I've been using load inflation charts since about 1996. The charts don't seem to be published intended for public consumption, more for commercial applications. But some net searching will locate some charts, and many light-truck sizes will be listed. It's a little more challenging now, as there has been a proliferation of LT tire sizes in recent years with taller wheels, but I found what I wanted for an 18" tire size recently. Your inflation pressure will vary
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Thanks Jim, I'll experiment...
jim65wagon
Well-known member
Well since I know the front of my truck weighs less than 4260 lbs, I'm pretty sure 35psi is overkill. Too bad the charts don't go down to 15 psi, that would be nice.
I need to get somewhere and air down some just to see if and how much flex there is in that sidewall....
Redline
Likes to Drive and Ride
Until you show them the chart specs people have a hard time believing that 35-PSI supports so much weight in a 285/75.
And yes, figuring the correct pressure below the 35 PSI listed on inflation charts is where it gets interesting
jim65wagon
Well-known member
Well, we got back from Cape Lookout 2 days before Irene landed. We were on the beach for 5 days and the ST Maxx's did very well in the sand.
I wish I could compare the to the ST of the same size.
My personal feeling is the 255/85 STs are slightly better than the 285/75 ST Maxx's.
The reason: in real soft sugar sand the Maxx's took more throttle to maintain speed. I do not know if that is from the change in tread pattern or the change in tread width. Regardless, we never got stuck, or even close to getting stuck.
STMaxx = good sand tire:26_7_2:
I wish I could compare the to the ST of the same size.
My personal feeling is the 255/85 STs are slightly better than the 285/75 ST Maxx's.
The reason: in real soft sugar sand the Maxx's took more throttle to maintain speed. I do not know if that is from the change in tread pattern or the change in tread width. Regardless, we never got stuck, or even close to getting stuck.
STMaxx = good sand tire:26_7_2:
Redline
Likes to Drive and Ride
Your impression that the 255/85 S/T was better in sand than the 285 S/T Maxx doesn't surprise me James. You noted the added width, and I think the much heavier tire also makes them harder to turn.
Also, a critical component of traction we often forget is flexibility. At a given pressure, the more flexible (conforming) the tire usually the better the traction, and this is very important in sand (if in doubt, read some of Tom Sheppard's prose on the matter, he knows a little about sand travel). Since we know the 255/85R16D S/T is a much softer and more flexible tire than load-range E S/T Maxx, this surely affects the sand traction.