BD Diesel Performance’s Throttle Sensitivity Booster is a popular, easy to install, plug-and-play product. For folks that like to hot rod around, or do a little racing, it’s easy to understand why a Throttle Sensitivity Booster, or TSB, would be a popular item, but this product’s appeal dives deeper. Few complain about a lack of torque or power from modern turbo-diesels, although not all would judge them responsive.
Many late model Ram owners complain about accelerator pedal lag, a dead pedal. So it’s not surprising that increasing the fuel delivery for a given amount of pedal travel could eliminate a drivability complaint while simultaneously adding a perceived performance enhancement. With an automatic transmission’s fluid-coupling, there is less concern about shock-load, jumpiness, or other potentially negative drivability behaviors emanating from increasing the sensitivity. However, on manual transmission trucks, might boosting the accelerator impact driver finesse and vehicle sympathy?
Skeptic Turned Into A Fan?
Do I want a more sensitive accelerator? My answer had been no. As I have shared in past columns, my additional pedal return springs and take-up slack spacer do much to improve the feel, feedback, and drivability of my rigs. I am extremely satisfied with these home brew modifications. So what spurred me to try the second version of BD’s TSB?
Heavy return springs and spacer add greatly to overall control and feel.
An acquaintance with a 2014 crew cab 3500 with automatic transmission let me drive his Ram, to judge what the 3500 leaf springs feel like unloaded. (I don’t know what some are complaining about, must be car people, it wasn’t too stiff or firm with appropriate tire pressure.) His truck had been deleted before he purchased it used, sported a mild fueling tune, and a BD Throttle Sensitivity Booster. His rig really scooted with little pressure on the go-pedal.
Some of that energetic behavior was from the automatic transmission, which goes and never stops until you release the skinny pedal. There is no loss of momentum during upshifts like occur with a manual, combined with a higher-rated A/T engine and the performance tune. Though it was also clear that the 3500 was really moving with a small dip into the accelerator. This experience made me rethink trying a BD TSB on one of my outfits.
Slow To Start And Occasionally A Jerk
My Fourth Generation 2500 G56 Rams have been great, complaints have been few, but there has been a minor irritation: a light throttle surging or hesitation. This behavior is not uncommon on modern drive-by-wire vehicles (cars, trucks, and motorcycles), particularly if fuel metering is held at the exact spot between some, and none. However, the hesitation my 2500s exhibited didn’t occur only at that sour spot, rather a little deeper into the pedal. Fuel delivery would sometimes pulse with a steady but small accelerator application of approximately 10–20% of total travel. It was also slow to respond to input changes.
The choppiness could be reduced or eliminated with a deeper, more aggressive pedal application, but that is not always desirable or safe. More precise and consistent response from all inputs is better for optimal control, smoothness, and fuel economy.
After some online research I called BD to confirm what I’d read. The second version of the BD TSB has three different positions: stock, 50% increase, and 100% increase. The control module must be opened to select the different sensitivities, and the boxes are typically under or behind the dash.
If the optional button kit is ordered, you get three additional choices: a valet mode that reduces pedal sensitivity substantially, a 75% setting, and a “ludicrous” mode, all of which are easily selected with the press of a dash-mounted button. Ludicrous held no appeal, but I was interested in having the 75% setting, plus the easy ability to revert to stock for bumpy off-road situations. With the exception of the ludicrous position, the BD TSB remains in its current mode after an engine shut-down and restart.
Initial setup involves the using stock position, pressing the pedal learn button, then cycling the accelerator a few times.The optional Button Kit includes a button, mounting plate, and mini harness that goes from the button to the main TSB harness.
Geno’s Garage sold the BD TSB Version 2 for $285, and the optional Push Button Kit was $65. The just introduced TS Booster V3 is even less; $265 at Geno’s for 2007–2020 Rams.
In 2019, BD received California Air Resources Board (CARB) Executive Order (EO) approval for their TSB for 2005–2018 heavy-duty Ford diesel applications, and was working on approval for the Dodge/Ram and GM products. That is a big deal!
Install Notes And Tips
According to BD Diesel, if one is going to run their TSB in conjunction with the BD High Idle Kit (which I have on my 2014 crew cab) one needs to put the Sensitivity Booster on the pedal side, and the High Idle on the truck side of the wiring chain. That’s because if the signal coming out of the High Idle Kit is sent through the TSB first, before going to the ECM, the High Idle module will have a harder time controlling the rpm (just like a person might with a more sensitive accelerator pedal). However, stacking them the other way around, letting the High Idle Kit communicate directly with the ECM, does not adversely affect operation of either accessory.
Initial test in my 2014, before mounting the module or button.
The installation is a very simple. If one chooses the optional Button Kit, it must be connected to the main TSB wiring harness. The short and adequate instructions tell how, and my closeup images show some details. After following a brief pedal-learning procedure, one simply needs to mount the control box and button where desired and continue motoring.
To add the Button Kit, first remove the blue plugs on the TSB main harness.Instructions tell which color wire goes into each numbered port.This orange plastic block is removed from the front of the main harness connector before inserting the Button Kit wires.Each wire in the correct position, before fully inserted and clicked into place, and replacing the orange block.
Drivability
Does the lowest, 50% sensitivity increase make the truck feel like it has more power? Absolutely! The perception is that the truck has a higher-power rating, like the maximum fuel delivery has been increased though it has not. Nothing mechanical has changed, the driver is simply getting more juice from the same squeeze. There’s no need to push the skinny pedal unnaturally deep to get moderate or brisk acceleration. If you want more than the 50% setting offers, the optional button puts 75% and 100% at your fingertips. The difference between each position is dramatic. To experience this, one can keep constant pressure on the pedal while toggling from stock up through the higher sensitivity levels; it will make the truck accelerate quicker.
Button was mounted on the bottom right of dash, using and existing screw. Easy to reach but also out of the way.With the key on, BD becomes red. In this image the top center light is also on, indicating the 75% setting.
With the lively 50% boost, smooth and precise application of fuel is not difficult. Even the 75% position is fun and controllable with a manual transmission, though my extra return springs and much firmer pedal are surely helping. I’ve mostly preferred 50% when routinely rowing through the gears. The aforementioned light pedal stutter/hesitation is all but gone.
Initially I connected the BD TSB to Clessie the Carryall Crew Cab. After a few days of testing, I moved it to the Pack Mule regular cab camper outfit. I liked it on both, maybe a bit more in the ‘Mule because of the full-time GVWR load. It really helps the truck accelerate as if it has more toque and power. After the first weeklong road, hunting and camping trip to Eastern Nevada, I knew the BD Throttle Sensitivity Booster was a winner; I ordered a second for Clessie the Carryall. That was several months ago, and I’m still pleased with the modification on both Rams.
Recent photoshoot (June 2020) with Cooper Discoverer STT PRO, 35.4″-tall, 295/65R20 tires. My 2014 Ram crew cab with Cummins Diesel and stock-height suspension was the model. Pressures were 27 in front, 17 in the rear.
Disclaimer: As with all things, proceed at your own risk, only you can decide what is appropriate given your training, experience, knowledge, the conditions, etc.
Mount and balance, and first look at the 35.4-inch tall, LT295/65R20 Cooper Discoverer STT PRO tires I’m running on my diesel truck(s). There will be more in the weeks and months ahead, here, and also @RoadTraveler on Instagram (typically extra content in Instagram stories).
This video introduces using Centramatic 400-409 balancers designed for DRW trucks with 16-inch wheels, on SRW pickups with 20-inch wheels. These balancers have 16-ounces of balancing media!
Article about the possible performance advantages of 20-inch wheels over 18- or 17-inch wheels on heavy outfits: 20-inch vs. 18-inch Wheels and Tires
Backgrounder: I have installed, used, and liked Banks Power products in the past, and I respect the engineering that goes into everything they do. However, I watched Banks’ YouTube videos regarding the purported inferiority of flat-back, high-capacity, aluminum replacement differential covers while they developed their own aftermarket differential cover.
Their target was obviously the original, and arguably still the best with the most features, Mag-Hytec. Obviously Banks needed to offer more than a rounded rear aluminum cover, as Ram already makes one of those for their trucks, and maybe other OEMs do as well.
Cut-away Mag-Hytec and Banks Ram-Air Differential Covers. 2019 SEMA Show.
Banks says their new Ram-Air Differential Cover “…cools 5X better than flat-backs by directing cool air through its break-away ram-air scoops. Increases fuel economy and extends lubrication life by utilizing proper fluid dynamics”.
Smoother, proper fluid dynamics, I won’t argue with. The theoretical fuel economy improvement is understandable, though I’d like to see a real world test and a measurable increase on a truck actually rolling down the road. For the tow-rigs and hot-rodders that never leave the pavement, the Banks cover might be a great accessory. However, what I noticed and what concerned me in the prototype videos on YouTube I confirmed with my own eyes at the 2019 SEMA Show: the low-hanging “break-away ram-air scoops”.
Solid axle differential housings are generally the lowest chassis component on pickups. Dragging them down the center of a rutted track or caking them with slime on a farm or ranch is not uncommon. During more technical off-road driving, getting hung-up on a differential does happen, which must be why the cooling scoops are “break-away”. During on-road winter travel in our part of The West, we often have a snow/slush mix that gets slung everywhere, and can freeze into a solid mass. Maybe the grimy wintery mix will increase cooling?
Forward-facing, wide and low-hanging cooling scoops are potential anchors and debris catchers.
Some don’t care about all-season or off-pavement performance, and this Banks differential cover might be perfect for them. Because I actually use my four-wheel-drives in rough and sometimes sloppy real-world conditions, the wide, low-hanging cooling scoops are a deal breaker, I’d rather run the stock cover. That’s me, and the Banks Ram-Air Differential Cover might be what you need and want. At press time Banks’ site listed a retail price of $439, with a pre-order sale price of $395.
A version of this article was also published in the Turbo Diesel Register magazine, as part of my 2019 SEMA Show coverage.
20-inch vs. 18-inch Cooper Discoverer AT3 XLT heavy-duty application tire evaluation.
Tires As Suspension
In the high-performance car (and even sport-truck) world it’s obvious that tires are a critical part of the suspension setup and the overall dynamics and handling of a vehicle. In the heavy-duty pickup world tires should be regarded with similar importance regarding how they handle loads, although it seems this is frequently ignored or overlooked until a problem arises. Such laissez-faire attitude seems more prevalent with those who infrequently work their trucks.
Unless one is never going to load their rig, generally aftermarket tire-and-wheel combinations should not have less capacity than the originals. However, just because a tire can support a particular load does not mean it is providing optimal performance. There are many potential differences, which include the tire size, load index, maximum psi, construction, tread pattern and compound, etc. Here is a real-world example of how dramatically tires can affect handling?
Surefooted Mule To Wallowing Pig
While driving to the 2019 Overland Expo West show last May, my ‘Mule started handling poorly. What I discovered, arriving in Flagstaff, Arizona, was that I had lost a bolt clamping the anti-roll bar to the rear axle. This rendered the bar useless and explained the sketchy handling I was experiencing.
On a coil-sprung vehicle, particularly one with a maximum and tall load, body-roll bars can be critical for safe handling, particularly during emergency maneuvers. To mitigate the then unexplained sloppy handling, twice I stopped to increase tire pressures. Adding 20 psi and over-inflating the 65-psi-maximum tires made a slight but still noticeable stability improvement. It firmed-up the relatively tall and flexible 35” tire sidewalls on 17” wheels, partially compensating for the looseness of the disconnected rear body-roll bar.
Missing bolt and bent Hellwig Big Wig rear stabilizer bracket explained the loose handling.
Thankfully my friends at Factor 55 had a block of titanium on which we pounded the deformed bushing bracket back into a usable shape. Another friend had a spare fastener. Seems losing anti-sway bar bolts on late-model Ram 2500s is not that uncommon. My friend was carrying a spare bolt because he had previously lost one himself; we both have the same Hellwig Big Wig rear bar. Another acquaintance at the event had also found a bolt missing on his factory rear bar while in Death Valley. So owners of newer Rams might want to check their sway-bar hardware, add some Loctite, and torque ‘em.
Air Supports Weight
It’s important to remember that it’s the total amount of air in a tire that supports weight; this includes the physical volume combined with the psi. This is one reason why some of the super-short sidewall tires are not appropriate for heavy-duty pickups; the ratings can be ridiculously low, partially because there is not enough physical space for adequate compressed air.
Unreasonably short sidewalls (think low-rider) will provide a firm, sometimes even jarring ride over small imperfections in the roadway, and in extreme cases potholes might bend a wheel because the thin sidewall does not provide adequate impact absorption. With that visual in mind, it can be helpful to think of tires as the biggest shock absorbers (dampers) on trucks. They can work in our favor or against us. Softer, tall-sidewalls can absorb impacts and improve ride quality for one application, or reduce control and handling on another. Adjusting the pressure or changing the size can increase or decrease overall performance.
Large 37×12.50R17LT Goodyear Wrangler MT/R is only a 50 psi tire, but the tire volume makes the SRW rating 3,525-lb each. I generally prefer the handling attributes of higher psi tires on heavy rigs. This outfit is a good an example of excessive tail-swing and rear overhang, both all too common on many modern flatbed camper builds.
My dislike for huge wheels with silly shortsidewalls on four-wheel-drive pickups emanates from decades of actually using trucks for off-pavement travel instead owning them as a fashion statement. What constitutes a silly short sidewall on a four-wheel-drive depends on the diameters of both the wheel and tire, but historically an aspect ratio below 70-percent might qualify. However, the aspect ratio alone does not tell the whole story, as it is a percentage of the width. A bigger wheel and tire combination with a lower aspect ratio might still have enough sidewall to work well off-pavement, while providing superior control on-road, particularly with a massive load.
Function Over Form
There’s little doubt that the humongous big-wheel craze on pickups (20” and taller) is mostly the result of the street-truck culture, not farmers and ranchers, heavy haulers, or commercial industries. Brakes are much larger on modern vehicles, but it doesn’t take 20” wheels to clear them. My recent interest in bigger wheels with shorter sidewall rubber is for optimal chassis stability and performance with my Hallmark camper; I prefer the traditional look of more tire and less wheel.
Many late-model diesel pickups are delivered with thirty-threes mounted on 18” wheels, and have a 7.5” sidewall. (Overall diameter minus the wheel height divided by two equals sidewall height.) Increasing tire diameter to 35” on an 18” wheel produces an 8.5” sidewall, an almost 14% increase. The same 35” rubber on a 17” wheel produces a 9” sidewall, which is a substantial 20-percent increase over the stock LT275/70R18 size. Using a 20” wheel for a thirty-five brings the sidewall height back down to 7.5”; same as the factory thirty-three on an 18” rim.
People don’t complain about the stock 275/70R18E having a short sidewall. SRW capacity is a respectable 3,640-lb at 80 psi.
If you think a 35” tire is huge, think again. Most new heavy-duty Rams will fit a narrow 35” tire (LT285/75R18) on stock wheels with little or no rubbing, and only minor rubbing on the radius arms at full-steering-lock if a wider, 35×12.50R18 is squeezed onto the factory rims. Running only 35s on my fourth-generation Ram/Cummins 2500s puts me in the smaller tire club; 37s on aftermarket wheels are the popular cool choice for many.
Cooper’s AT3 XLT in 285/75R18E (34.84”) with a 129 load index can handle 4,080-lb each at 80 psi.
Are 19.5” Wheels and Medium-Duty Tires The Answer?
Some of the heavy-hauling crowd, particularly those with cab-over campers, found a solution decades ago with 19.5” medium-duty commercial tires when there were fewer tire size options. Rickson Wheel Manufacturing was founded to service this niche. The enthusiast owner started making 19.5” SRW 8-lug wheels to fit heavy-duty pickups because he was burning through sets of 16” rubber on his camper-equipped second generation Dodge Cummins turbo-diesel. This was before the excellent availability of 18” and 20” light-truck tires and wheels, which can offer up to 35% more capacity per tire than the sixteens of the 1990s.
In addition to superior load support and firmer handling provided by the much stiffer 19.5” components, there are theoretical benefits of substantially more longevity. I have yet to find a well-documented, back-to-back comparison proving similar tread design medium-duty rubber lasting much longer than a commercial-grade modern LT tire. I don’t doubt that it is possible, but show me. Medium-duty tires typically cost more, so more miles may be needed to make the modification pencil-out for those wanting to save money. Tread choices are also fewer.
In addition to limited availability of 19.5 inch wheels for pickups, and the possibly too firm load range F, G, or H construction, the biggest negative I see with medium-duty rubber are the lower speed ratings. Up to 245/70R19.5, which is only a 33” tall tire, the speed rating is a reasonable 87 mph. Moving up to a 265/70/19.5 or larger size typically reduces the speed rating to 75 mph.
Are 19.5” tires and wheels the answer for heavy pickups? They are for some heavy haulers.
There’s one area where the folks who favor 19.5″ tires and wheels and my recent interest in modern heavy-duty light-truck 20″ tires align perfectly; it’s about how they work not their appearance.
If one is going to load their SRW chassis with more than 8,160-pounds on the rear axle, the capacity offered by load-index 129 light-truck tires, super-stout and less flexible medium-duty rubber might be necessary and/or beneficial. I have read several comments online, and spoken to others who say 19.5” tires are too stiff over rough roads, both paved and not, even on heavy trucks. On unloaded rigs, the ride is sometimes described as downright jarring. Some are willing to tolerate an extra-firm ride, but is worth remembering that unnecessary roughness will be transmitted to all chassis components, potentially reducing their longevity. Surely some folks love their 19.5” tires and wheels on SRW pickups, but they appear to be a small minority.
If someone wants to lend me a set I’d be happy to bolt them on and give them a spin. My extensive heavy-duty pickup and LT tire knowledge has repeatedly convinced me that I don’t need to spend my time and money on medium-duty rubber for my pickups. Skipping the 19.5” wheels and going straight to modern, readily available twenties made more sense.
Cooper Discoverer AT3 XLT 18” vs. 20”
In typical RoadTraveler James fashion, I did back-to-back evaluation drives to observe differences between almost identical rubber wrapped around different diameter wheels. To limit controllable variables, the same manufacturer and tread design was chosen. Without this approach, carcass construction differences and other factors would unfairly skew impressions. While construction matters (continue reading), sometimes much, the goal was to test what dynamics are affected by simply changing the wheel diameter. With that established, one can then seek tire construction and/or other suspension solutions as needed for their specific application.
18” wheel on the left, 20” wheel on the right, all other specs are very similar.
The good folks at Cooper Tires, one of the few American companies still making tires in the United States, supplied the rubber to facilitate the evaluations. The redesigned Cooper Discoverer AT3 Family of Tires was introduced at the 2018 SEMA Show. It includes three distinct models targeted at specific segments of the all-terrain market. Cooper describes the attributes of these AT3s as:
Discoverer AT34S™ Severe snow rated with improved wet weather performance, snow performance, fuel economy, and with significantly improved tread wear.
Discoverer AT3LT™ and Discoverer AT3XLT™ Designed to be powerful, shred-resistant all-terrain tires. With the Discoverer A/T3™ well-known for its long-lasting tread wear and dirt road performance, the new Discoverer AT3LT™ and Discoverer AT3XLT™ tires feature Durable-Tread Technology™, enhancing durability, and enabling a best-in-class mileage warranty.
Longevity and durability has much to do with the application and duty-cycle, but Cooper has certainly upgraded and expanded the all-terrain AT3 line to cover all consumers who want this type of five-rib tire. Heavy-duty pickup owners should look at the AT3 XLT version, as it comes in the largest sizes with the highest load ratings.
Similar But Different
Because I prefer taller and narrower sizes for most conditions, I chose the 34.84-inch-tall LT285/75R18, and the 34.57-inch-tall LT285/65R20. There is very little difference in height or width between these two sizes, for all practical purposes they are the same, with the exception of the wheel diameter, which gives the twenty a much shorter sidewall. The 285/75R18 has a 8.42” sidewall, and the 285/65R20 has a 7.28” sidewall. Both sets of tires were mounted on factory Fourth Generation Ram aluminum wheels.
Both tires have a 285mm section width, but look at the tread width difference, which is noted in Cooper’s specifications.
Cooper Discoverer AT3 XLT
LT285/65R20
LT285/75R18
Load Index (SRW)
127 = 3,860-lb
129 = 4,080-lb
Height
34.57”
34.84”
Section Width
11.5”
11.5”
Tread Width
9.69”
8.9”
Weight
62-lb
60-lb
Tread Depth
16/32”
17/32”
Cooper AT3 XLT General Observation
Both sizes track straight and true, as one would expect with a five-rib all-terrain. While driving through dozens of miles in heavy rain, the AT3XLT performed fantastically, evacuating water well, a forte of a ribbed tread pattern. Siping is generous to help with all slippery conditions. Though obviously not a mudder, some light, shallow mud was handled impressively well during a weeklong autumn camping trip in remote northeast Nevada.
Unless one wants a dedicated highway offering like the Cooper HT3, the AT3 XLT is a quiet, efficient design that should yield good fuel economy. The XLT has attractive, aggressive sidewall shoulder tread that looks good and should prevent both off-pavement and curb scrubbing damage.
Sitting at 8,900’ after two days off-pavement and some recent light mud, the Cooper AT3 XLT performed well.
Test Drives
Several back-to-back drives were performed over six months. The first with more off-pavement miles was a 45-mile loop that included 30 miles of freeway, five miles of rural highway, and 10 miles of rocky dirt on the historic Henness Pass Road trans-Sierra route. When the road got rough, I continued for a few miles at full psi, before dramatically lowering the pressure at a specific point to improve the ride and traction.
Shorter 20” sidewalls are a bit less forgiving at full psi on the roughest roads, lowering pressure helps. This Cooper AT3 XLT 285/65R20 was initially tested at 37 psi, but is at 30 psi in this photo. Dropping the extra 7 psi greatly improved the ride.
Both sets of Cooper AT3 XLT tires, and other sets of rubber in our test fleet, were swapped on-and-off our 2017 Ram regular cab flatbed for comparison. Both sets of Coopers also saw some miles on our 2014 Ram crew cab.
The 20s went on a 1,000-mile vacation with my wife and our little Welsh Terrier Elsie. That trip included over 100-miles of unpaved roads, that were occasionally rocky, snow-covered, or rough washboard. I intentionally gave the 20s more time and miles as I have much experience with Cooper 18s, including the previous AT3. As of this penning both sets have seen a combined 5,700 miles.
Remote northeastern Nevada camp, during a weeklong on- and off-pavement camping trip.
There are many potential variables to putting softer or firmer tires, and taller or shorter wheels on a chassis. If your suspension is stiff or the load is light, maybe a softer tire is better, as long as it’s not overly susceptible to punctures. Softer suspension and/or huge loads may benefit from a stouter design. The bullet points below share the pros and cons of using 20” verses 18” Cooper Discoverer AT3 XLT tires for big loads on heavy-duty trucks.
20” Tire & Wheel Positives
-Substantial improvement in lateral stability from reduced body-roll/sway when compared to 17” or 18” tires of similar construction. Feels like the improvement from adding a heavy-duty rear anti-sway bar compared to the factory bar.
-Steering feel is better, tighter, and more responsive with less delay.
-Slow, mountain turns and switchbacks with warning signs are less concerning.
-Freeway hop/bed-bounce caused by concrete freeway expansion joints is reduced.
My 140.5” wheelbase regular cab is stable and controlled over most surfaces, with inherently little freeway hop compared to the 149.5” wheelbase crew cab. Mounting the Cooper AT3 XLT 20” wheels on the crew cab both firmed-up the ride as we’d expect, and noticeably reduced freeway hop.
An important safety consideration is that even if the chassis feels stable and composed enough to increase speed in certain situations, there is only so much available traction. When we use more of the total traction available, we are reducing our safety cushion, and putting more load on the tires, which causes wear and reduces longevity.
Does a 20” tire and wheel work best for your late-model truck? The answer may depend on your needs, preferences, and duty-cycle.…or does an 18” tire and wheel work better for your application? You be the judge.
20” Tire & Wheel Negatives
-Noticeably less forgiving and rougher than the 18” tire over speed-bumps and on rocky roads at full street pressure. However, when the going gets tough, reducing psi benefits all tires and sizes tremendously. To get the same ride over rocky terrain, the 20” tire liked being about five psi lower than the 18”, particularly the fronts.
-Small bumps, cracks, or holes on the roadway are more noticeable, as the tire has less ability to absorb the imperfections. How noticeable depends on the tire construction, pressure, load, and surface. With my heavy Hallmark camper, 20″ Cooper AT3 XLT, which is admittedly a softer design, never felt harsh or uncomfortable on the pavement.
Conclusion?
My 18” vs. 20” test driving quickly convinced me that with heavy loads a shorter and/or firmer sidewall that reduces some of the squishiness of a more flexible design was a positive. The biggest tradeoff is on the roughest, unpaved surfaces, which can be mitigated by adjusting tire psi and/or choosing a taller size.
With a given design like the Cooper AT3 XLT used for this comparison, the shorter 20” sidewall was also firmer and less flexible. However, if you change the tire construction characteristics, you have changed the suspension, and you have a new baseline.
Mounting the stoutly-constructed Cooper Discoverer S/T MAXX (or similar) with 3-ply sidewalls in an 18” size delivered better overall control than the softer 20” AT3 XLT. That is not a dig against the AT3, as it intentionally targets a different audience. Want or need another level of firm performance over an 18” Cooper Discoverer S/T MAXX? You can move up to one of the 20” S/T MAXX sizes. Modifications lead to modifications, and every change can affect something else.
Cooper S/T MAXX is a favorite heavy-duty hybrid/commercial traction design. Even a 1” wheel diameter difference is easy to see and feel. Both about 34” tall, 17” Power Wagon wheel (left), and forged Big Horn 18” wheel (right).
My travels include more off-pavement miles than many, so I am still evaluating where I want to make my long-term compromises, but like everyone, most of my driving is on good, paved roads. Currently I’m preferring 20″ tires for my flatbed camper outfit. My tire and suspension evaluations are continuing, and you can find additional information about these and other subjects here on RoadTraveler.net, or on Instagram, @RoadTraveler.
The sign says, “TRAILERS NOT ADVISED BEYOND HERE”. My camper is frequently off-pavement, but like nearly everyone, most miles are on blacktop.
