Cooper Discoverer STT Pro and the BF Goodrich KM3 are both powerful mud terrain tires which although are equipped with powerful lugs, having deep biters, they don’t makes things a lot difficult on pavements. So both are all rounder options, and you can never go wrong with either of these, though there are some key areas where one lags and one excels.
Being a tire engineer, in my opinion, the Cooper Discoverer STT Pro is one of the best M/T for rocks with it’s arbitrary placement of ribs everywhere. The BF Goodrich KM3 on the other hand, keeps things a little more smooth on pavements, providing better steering communication and traction in all weathers. But at the same time, it does compromise at all on muddy terrains.
Table of Contents
Sizes Important Info
Starting form BF Goodrich KM3, this tire gives you a total of 56 total sizes, ranging from 14 to 22 inches.
All tire sizes are branded with speed rating of Q, and the load rating of C, D, E and F, which brings the tire’s weight up to 83 lbs (where the lightest size is 37 lbs).
All of it’s sizes get to have a tread depth of 18/32″, and they don’t offer any kind of warranty.
On the other side, the Cooper Discoverer STT Pro offers (a little less) 49 total sizes (15″ to 22″ rim sizes).
All its sizes speed rating of Q (on all sizes) and load rating of C to F (similar to BFG KM3).
The weight of the tire however, has a slightly larger range, as it goes from 42 lbs to 94 lbs.
And as for tread depth, it stays between 18 and 22/32″, where most of the sizes get to have 21/32″ (again a little more is seen here, one of the reason why it lasts a little longer as well).
A Side Note: I worked with these guys to make the following video:
Tread Looks
Starting with Cooper Discoverer STT Pro, as this one is more interesting, and want to get some things out of the way first.
In the middle, there are 3 unique ribs of somewhat equal proportions and all of them have sharp off set edges and reinforced foundations underneath, so you get the bite needed along-with stability on smooth paved roads.
It’s ribs also carry siping, which are although not a lot, they are still full depth and interlocking (unlike most M/T). So things are also not too poor on wet roads when compared to other mud tires.
Furthermore, all its ribs make a very clear horizontal and vertical grooves, offering a very self cleaning tread, which helps a lot with mud as well as hydroplaning.
On the shoulders the tire’s becomes even more aggressive, where the elongated lug has sharp notches in them (placed longitudinally), while the other carry interlocking siping (as seen in the middle) with foundations supports on the edges.
Here some features to note are its bolder stone ejectors in it’s wide tread voids, and how the ribs are also connected with each other form underneath (with supports). They also help in expelling the dirt out.
The BF Goodrich KM3 on the other hand, although may not seem as cleaning, it’s quite the contrary.
It unique blocks placement allows it to make 3 different kind of channels (the outer two, the slanted longitudinal crossing the middle, and the lateral).
All these channels interconnect with each other and toss around mud and out of the tire with very ease.
And besides conventional ejectors between outer lugs, it’s also equipped with triangular stone ejectors which do the same thing.
KM3 offers flexible tread, so although there aren’t any conventional sipes on the tire either, the thick notches in those ribs still provide efficient water cleaning.
On sideways, all it’s ribs are staggered (a must-have with M/T), and they are optimized for both on and off road handling.
The smooth deign of the tire provides ample traction on pavements, while the huge lateral gaps, serrated sides/sidewall lugs, offer mud scoops.
These flexible lugs also hang on to the rocks like there’s no tomorrow.
Durability
Mud tires need to be very strong, and that is achieved by inner plies.
But too much of these plies also make these tires very heavy which is not preferable for pavement traction (especially handling and fuel economy).
So both these tires don’t offer a lot of cap plies on top, in fact both of them just have a single layer of polyamide on top.
Beneath these layers both M/Ts have 2 wide steel belts running (covering the central area of the tread).
And these belts sit on 3 ply polyester construction where the Cooper Discoverer STT Pro features Armor-Tek3 technology and BFG KM3 presents you with Aramid ply reinforcements.
So although both tires offer 3 ply sidewall construction, they don’t get way too heavier for on road use.
Ride Quality
Ride quality of a tire is contingent on the tread noise it makes and its ability to dampen the bumps.
Here the single cap ply construction of both tires although offers a good capability to dampen the vibrations, the overall performance is still seen better on BF Goodrich M/T.
This is because with higher silica in it’s rubber, the tire is very pulpy and it absorbs the uneven surface bumps in a better way.
The Cooper STT Pro M/T on the other hand, is better with noise as its tread is not as prone to groove resonance, and the tire also offers better pitch sequencing as well, so although you get a humming noise as well, but it’s with less decibels.
For Your Info: It’s best if you rotate these tires after every 3k miles.
Also when it comes to M/T, I believe the Falken M/T offers the top results. Review it here.
Steering Feedback
The steering response is the way in which the vehicle responds to steering input. It is measured by how quickly the vehicle responds to steering input, and how much it oversteers or understeers.
You can expect a mud tire to be less vocal here mainly because of it’s heavier make and softer rubber top.
So it makes sense why BF Goodrich KM3 offers better performance here.
The tire although provides you with a mushy rubber layer on top, its lighter cap ply of nylon shows less understeering in comparison.
On the other side, the Cooper STT Pro feel slightly more resistant to turning at first, and with a little more input the tire all of sudden jumps in and things get prone to go over.
So overall there is a slight delay when compared.
Traction on dry roads
On road traction is the tire’s ability to create frictional forces with the ground, and here we judge it by looking at two angles, one, how is it directionally, and the other, how is it on corners?
Let’s talk directional grip first, which is mostly calculated by measuring the stopping distances.
Directional Traction
Here both tires are although very similar, the overall performance is slightly better on BFG T/A KM3.
The Cooper Discoverer STT Pro although offers a solid rib construction (backed by foundation supports under them), the tire lacks with it’s balder design, so it’s not able to meet with the road with enough friction, though it’s sharp lugs hold out a lot of chewing power.
Directional traction is very dependent on the central lugs, and here the BF Goodrich KM3 make more of an impact with it’s closed up central tread voids (in comparison).
So it’s stops quickly when braked to a halt.
Lateral Traction
Lateral traction of the tire is judged by considering the tire’s sidewalls and shoulders, and here although the Cooper STT Pro offers a very decent road contact patch, the tire’s heavier construction and stiffer sides lack overall.
The BFG KM3 again offers a lighter and softer composition, where it’s lugs are also stable with not so aggressive tread depth.
The tire is also stickier and while turning, the lugs don’t want to let go off the road that easily, so you get a better cornering grip overall.
Wet Performance
Wet pavement is very different and here grip is made by sipes and flexibility. Both of these offer traction and resistance to hydroplaning by offering water removal capabilities.
Let’s start with the traction part, before moving towards hydroplaning/aquaplaning.
Wet Grip
Most of the water gets escaped with grooves, while the little bit that’s left is wiped off with the help of sipes.
That’s why siping is very crucial, now here there are two more things going on, one the design of the sipes (how efficient are they) and second, what’s the rubber composition of the tread is (can sipes flex?).
Now here, in terms of siping design, the Cooper STT Pro is taking the lead with it’s interlocking pattern as such design of sipes don’t lock up when a tire corners.
These sipes basically get to open and close at various ends, soaking water in, even when the tire is under pressure.
On the other side, the BF Goodrich KM3 provides an all season rubber with more silica in it’s composition, so it’s rubber stays soaking (while the Kevlar in it’s make up protects its from wear as well).
So although this tire does not provide efficient siping design, the slits and grooves are able to flex more effectively to wipe water away.
Hydroplaning
Hydroplaning is just what you call when a tire floats on water, and here speed is the main cause of it, (that’s why its measured with float speeds).
Here water evacuation is very significant and both tires are pretty bald to provide it.
Th Cooper STT Pro has a prominent outer circumferential grooves which are joined together by straight-forward lateral paths.
But the BF Goodrich Km3 offers 3 main paths, where there is outer longitudinal grooves, lateral grooves and then there is slanted groove joining shoulder lugs
Moreover, the tire’s softer rubber also offers a larger pressure force for water to leave, so overall KM3 is slightly superior.
Snow Performance
Both of these mud tires are a bad idea for ice and hard packed snow but they can still perform on softer terrains (with deeper snow), though both of them are not 3 peak mountain snowflake rated.
Here the Cooper Discoverer STT Pro although offers a dual layer where it’s ribs effectively grab on to the snow, the stiffer make of the tire freezes up more and looses traction.
The BFG KM3 is soft enough and it provides traction by not becoming rigid with negative temperatures.
Rock Climbing
The Cooper Discoverer STT Pro is simply awesome on rocks. The tire holds on to all kinds of rocks like there’s no tomorrow.
It features a soup of circumferential and lateral traction with it’s countless biters everywhere. And it’s sidewalls are although not as flexing, with lowered air pressure, that’s not an issue.
The BFG Km3 on the other side provide amazing lateral traction with it’s sidewall lugs, especially on wet rocks.
The tire’ extended shoulder lugs provide great foot print when pressured down and deep biters here ensure the grip is stayed in tact.
Mud performance
Being M/T mud is not an issue for these tires, so let’s keep it short.
Both tires offer a pretty bald design, as they are both highly voided, so mud get to escape pretty quickly.
Though you can say that the lateral path is better created on BFG KM3, so you can get slightly better cleaning over there.
Performance on Sand
On sand you need a light tire, with a big foot print.
Now here both tires are although heavy (which makes things difficult on slopes), they offer ample footprint, as on sand, you always lower down the air pressure to minimum values.
And both tires with powerful rim locks offer you with that.
To Conclude
Overall I can say both tires are very impressive, but still I would rate the Discoverer STT Pro for better traction on rocks and BF Goodrich KM3 for overall all rounder tire which is great on wet roads even (well compared to M/Ts), the tire is not good overall.
