The Cooper Discoverer STT Pro is a mud-terrain tires, whereas, the Nitto Ridge Grappler is a hybrid which basically comes in between mud and all-terrain. They are also called rugged terrain. So with less bolder design, they tend to stay more comfortable on tar while compromising very little on rugged terrains.
As a tire engineer, I believe that the Nitto Ridge Grappler provides a better on road traction in comparison. The tire’s great in dry, good enough in wet (comparatively, I should add), and shows better fuel and tread economy. The Cooper STT Pro on the other side, yields a superb performance on all types of off-road terrains.
Table of Contents
Must-Know Facts
The Cooper Discoverer STT Pro offers 49 total sizes (15″ to 22″ rim sizes). All its sizes have following specs:
- All have speed rating of Q
- Load Ratings: C to F
- Weight Range: 42 lbs to 94 lbs
- Tread Depth Range: 18 to 22/32″
On the other side, talking about Nitto Ridge Grappler, this tire offers more sizes, 98 (16″ to 24″). They have the following specs.
- Load ratings: SL, XL, D, E and F
- Speed ratings: T and Q only
- Weight range : 36 to 91 lbs
- Tread depth range: 13 to 18/32″
- Warranty: None
- Winter ratings: Only M+S
Tread Design
If you’re in need of a tire that can handle smooth roads with ease, the Cooper Discoverer STT Pro is the perfect choice.
Its three ribs, each equipped with offset edges and reinforced foundations, provide both stability and bite. The blocks there feature siping, which may not be as abundant as its counterpart, it’s full depth and interlocking structure provide good enough wet grip.
The tire also presents a self-cleaning tread thanks to its clear horizontal and vertical grooves on the ribs, as well as aggressive shoulders with elongated lugs featuring sharp notches and interlocking siping for additional grip.
These lateral grooves between the outer lugs also feature bolder stone ejectors adding to the tire’s overall self cleaning abilities.
Towards outer edges, these lugs are staggered, providing thick mud scoops, and on sidewalls you get a lot of biters, though they are still thinner in comparison.
The Nitto Ridge Grappler on the other side, is not so open in comparison.
It has four ribs that are shaped like triangles. Two of them have full-depth notches facing the sides, while the other two are slightly smaller and have similar features except for the notches.
These blocks are connected to shoulders and together create X and Z-shaped grooves in the middle, as well as zigzag longitudinal surrounding grooves, making prominent circumferential channels.
Moreover, all of them have off-set edges, and reinforced foundations underneath and full depth siping.
Same goes for the shoulder lugs, but they still lack in aggressiveness a little (towards their inner sides).
Though towards outer edges, they present very powerful biters as lugs are staggered, and they extend down on the sidewalls and create dual pattern.
(You can choose, which side to show outwards).
Internal Construction
Off-road tires are made tough through their internal construction, where they get most of their strength from the plies.
Nitto Ridge Grappler has 3 ply polyester cover, 2 steel belts and 2 layers of nylon as cap plies.
And although the Cooper STT Pro also features 3 ply polyester + 2 steel belts, there’s only a single nylon cap ply, the tire is not weaker in comparison subjectively.
Dry Capability
When driving on the highways, several factors come into play in determining optimal performance, including dry grip, handling stability, and steering feedback.
Dry Grip
The tire’s aggressiveness is generally negatively proportional to it’s grip on smooth pavements.
Having said that, the Cooper Discoverer STT Pro having such wider grooves eat away the rubber, that’s could have made contact with the road, and provided grip.
That’s why here, Nitto Ridge Grappler is a better tire, as its triangular lugs, besides providing contact patch gets to provide a more streamlined connection with the road, and their reinforced foundations provide the needed stability.
Lateral Traction
The handling of a tire is a measure of how well it is able to navigate turns, with the shoulders of the tire serving as the primary point of contact with the road during these maneuvers.
But why these outer lugs? Well because the tire turning has all it’s weight shifted towards either one of the outer ribs (depending on the turn).
That’s why with such balder design, the Cooper STT Pro is very lacking here.
On the other side, the Nitto Ridge Grappler does better because of three main reasons. It’s lugs there have very little tread features, so they form a smooth connection with the road, thy are closed up more with smaller lateral grooves, allowing for greater surface area of contact patch. And they give out superior steering sensitivity.
Steering Sensitivity
The compound stiffness and tread design of a tire can significantly influence its steering response, that’s why the Nitto Ridge Grappler with smaller tread depth, weight and a relatively harder compound does better.
All these factors basically make the lugs moldable during cornering, braking and accelerating, creating under and over steering as a result, and decreasing the steering sensitivity of the tire.
The Cooper STT Pro with larger tread depth and malleable lugs, on the other side, takes longer to respond to steering inputs.
Wet Performance
How good a tire would be on wet asphalts, depends on it’s water removal capabilities. And both tires here are pretty bald, and are able to channel water out through their wide grooves, though the little left behind isn’t dealt with properly.
This is because of the limited siping seen on both tires.
Nonetheless, the Nitto Ridge Grappler still shows better performance due to it’s relatively superior siping design and slightly more closed up lugs which better create negative pressure throwing water out of the grooves with better efficiency.
Tread Longevity
Tread life of a tire is also very closely related to fuel economy, as they are both tied together with rolling resistance. That’s why comparing both tires, the Cooper Discoverer STT Pro burns down faster.
The Nitto Ridge Grappler has a harder compound, and it’s lugs stay more stable as they are not so prone to bending, so you see a better performance here.
Though still both tires don’t offer you with any kind of warranty.
For Your Info: The more aggressive the tire gets, the more it tends to wear, generally speaking, that’s why All-terrain tires wear slower, compared to mud and rugged terrains.
Fuel Consumption
In general, off-road tires with deeper treads and heavier weights can increase fuel consumption compared to tires with shallower treads and lighter weights.
This is because the deep tread blocks and wide gaps between them create more flexing of the lugs, which causes the wastage of the energy.
That’s why the Cooper STT Pro with tread depth reaching up to 22/32″ and a greater weight consumes more fuel in comparison.
The Nitto Ridge Grappler on the other side, features more stable lugs formation, and so less energy is consumed to bending of the lugs, and more is focused upon the movement of the tire as a whole.
Level of Comfort
The level of comfort provided by off-road tires will depend on a variety of factors, including settling of vibrations of road.
And although Cooper STT Pro with a softer compound and larger tread depth would settle down those bumps by cushioning them better, it does not mean the tire is comfortable out of the two here.
This is because it’s pliable tread is less responsive and stable on paved roads, and with a larger void to tread ratio, it would create more noise (which gets generated when air particles collides with the walls of the tread).
Nitto Ridge Grappler in comparison, with a less balder structure, would be slightly quieter in comparison, and on roads, it would account for a much stable ride.
Though I can give you one thing, the STT Pro would provide better comfort off-road.
Check Out:
Are All-Terrain Tires Noisy? : https://tiredriver.com/are-all-terrain-tires-noisy/
Off Road Traction
Off-road tires should be able to handle rougher tracks and be able to shake off debris to perform well on various terrain types, which I discussed below.
On Mud
Self-cleaning tires are ideal for driving on mud, as they can effectively clear muddy debris from the tread.
And here its not surprise, that the Cooper Discoverer STT Pro is a better tire. It’s balder design allows for faster mud removal, and its thick shoulder lugs provide the needed scooping of the thick clay. They throw the mud backwards (without any hurdle), and provide forward momentum with it.
Nitto Ridge Grappler on the other hand, despite having X/Z shaped grooves and sidewall lugs/staggered shoulders is still not able to compete with a “mud-terrain” tire.
Gravely Performance
Although both tires have great voids to tread ratio, and stone ejectors which prevent any sharp dirt particles to get lodged in the tread (to cause damage and traction issues), the Cooper STT Pro still does better mainly because of it’s elongated shoulder lugs.
They handle loose ground much better, and provide greater cornering abilities
Nitto Ridge Grappler on the other hand, lacks mostly due to it’s stiffer compound, which does not let of the trapped dirt particles too easily.
On Rocks
Both tires are pretty durable and equipped with a ton of biters, but overall you’d still see a superior traction on Cooper Discoverer STT Pro.
This is because being a mud terrain tires, it offers a bigger groove mouth which hug on to the rocky surface, and with a clear-cut combination of lateral and longitudinal tread voids, they lugs bite in all directions, providing grip from multiple angles.
Moreover, with elongated shoulder lugs with traction scoops, and more aggressive sidewall lugs, you get much better traction with lowered air pressure.
Nitto Ridge Grappler on the other side, is although not too far off either, with it’s equal durability (3 ply sides), and a lot of biters, combined with dual sidewalls, its still can’t outperform STT Pro simply because of it’s less aggressive design.
Sandy Terrains
On sand, you have to avoid as much digging as possible. That’s why tire’s weight and sharper edges work against the sand traction.
And although both tires are pretty similar in weight, the softer compound of Cooper Discoverer STT Pro, combined with it’s elongated lugs, provide better efficacy overall.
The tire basically provide pretty spread-out sidewall lugs, and they provide ample footprint and with it floating, meanwhile it’s laterally oriented lugs paddle the tire’s way through this soft terrain.
Nitto Ridge Grappler on the other side, lacks with it’s sharper/stiffer sides having two cap plies (which tires to dig), and its joined up lugs don’t allow for as effective paddling as the STT Pro.
(It’s one of the reasons, why paddle tires are used for sand races).
Winter Performance
Both tires are although not so great on snowy terrains, especially when it comes to hard packed snow, the Nitto Ridge Grappler provides better grip.
It features more closed up biters, which trap in the snow particles and make snow to snow contact with it.
Cooper Discoverer STT Pro on the other hand, is too wide to hold on to the snow, so it comes with limited traction.
Winding Up
Cooper Discoverer STT Pro features a superior traction off-road overall. Surprise, surprise. The tire does best on sand, and mud, though on rocks it’s only a little better off the two tires, according to my tests.
Nitto Ridge Grappler on the other hand, features a better on road traction and comfort, combined with fuel economy and tread wear.
