This blog has been defunct for too long, and I’d considered taking it offline. However, it continues to get measurable views everyday, without me posting a single word. During the 19-month hiatus a few new readers even subscribed, apparently looking forward to future posts should any be forthcoming… So instead of killing the blog, here is a small revival effort. Thanks for visiting RoadTraveler.net.
Low Pressure Off-Highway Rollin’
With the travel trailer repairs completed, it was finally time for some off-pavement travel. I dropped the front and rear tires to 25 and 20 psi respectively, which was on the high side for me but low enough for the truck, tires, and terrain. The F-350 carries much weight above the front axle so keeping the pressure slightly higher than on a lighter rig helps insure the beads don’t unseat, and is better for handling, control and safety on the faster sections.
Mud Terrain tires look cool, but I’m old and wise enough that looks alone don’t drive my choices. If I didn’t want a high-void tire for rugged backcountry use I’d pick something else, possibly a tread with less noise and better potential longevity. However, I use this truck for plenty of off-highway travel and in the LT255/85R16 size, tread choices are few and most are aggressive traction tires.
The notably high quality construction and roundness of most Toyo tires allows balancing with relatively little weight, which contributes to their good road manners. With only a few exceptions most Toyo M/Ts are constructed with a 7-ply tread and stout 3-ply sidewalls. Though friends have criticized me in the past for using tires with mere 2-ply sidewalls, my reply has always been; all tires are soft balloons, and are punctured relatively easily. For decades most tires have had 2-ply sidewalls, only in the past few years have 3-ply sidewall enthusiast rubber become both popular and offered in several flavors.
But, when I needed to make a choice between the Maxxis Bighorns or the Toyo M/T, it was this rugged reputation, quality construction, and 3-ply sidewalls that made the Toyos the arguably better choice for an old F-350.
Some of the great load-range (LR) D enthusiast tires are going to be improved to load-range E designs. This is only an improvement if one needs the higher load rating, and can be a negative if you don’t (see Wheels, Tires, and Sidewalls from Jan. 2012). I understand manufacturers’ position, if they make all or most of their heavy-duty light-truck (LT) tires load-range E, the tire can be used for stoutest pickups down to the smaller, lighter rigs. I argue that these stiffer, less flexible tires are not ideal for many lighter 4WDs which are typically daily-drivers that rarely haul or tow maximum loads, and would benefit from the better ride and off-pavement traction that more flexible tires offer. There are many applications where a load-range D or C (remember those) are the best choice. I view the reduction and possible elimination of the LR D tire choices similarly to the needless super-sizing of everything in the USA.
I also see similarities to the slow death of the LT255/85R16 size. There is still a small market for this fantastic 33×10-inch tire, and many 255/85 tires that were all LR D five years ago, have become LR E designs. In support of this 255/85R16 change, I do think most trucks running this size are heavy-duty, full-sized pickups that are used as such, and the added capacity and reduced flex is a positive. Unfortunately narrower tires don’t appeal to the masses (strike 1), few new trucks are made with 16-inch wheels (strike 2), and the perfect 17-inch 255/85 replacement, the 255/80R17, is available in one tire (strike three), the BFGoodrich KM2 mud-terrain.
The Sea Change In Load-Range Continues
Recently I noticed that two of my current favorite mud tires, the Dick Cepek Mud Country and the Mickey Thompson Baja MTZ, are losing their load-range D rating in favor of the LR E in a couple popular sizes.
The Mud Country in 285/75R16 and the MTZ in 285/70R17 are switching to a load-range E rating. Both of these tires/sizes were load-range D, with 3-ply sidewalls, a perfect combination for many enthusiast applications. I currently own a set of each of these treads and love the 3-ply sidewalls combined with a load-range D casing. The new LR E offerings will surely offer less sidewall and/or tread flex (bad off-highway, good for tonnage) and be firmer riding during lightly loaded daily use. How stiff is the question, as not all LR E tires are created equal. Some are pretty flexible like the BFG KM2, while others like the new Cooper S/T MAXX and Toyo M/T are quite stiff.
If you think I’m some kind of tire nut who likes fetish tires (well…) there has been and likely still is plenty of market and demand for good, load-range D tires. The currently popular, practical, and useful 285/70R17 size has several load-range D offerings. A search on www.trierack.com recently listed twenty-eight 285/70R17 tires; 14 of which were LR D treads, 7 were LR E, and 7 were P-rated tires. These LR D designs were not duds, and included some of the best or most popular off-highway enthusiast tires currently offered, including: Dick Cepek F-C II, BFGoodrich KM2 and All-Terrain, Goodyear MT/R with Kevlar, and Goodyear DuraTrac. For years BFG has offered their ever-popular All-Terrain in both load-range D and E flavors in both the 16-inch and 17-inch 285 mm sizes. I respect BFG for seeing and filling this need, and not forcing everyone who wants a 285 to run a load-range E tire. There is a difference.
Does this mean that I will no longer buy certain niche tires once they’re not available in LR D? Probably not. While I prefer a LR D tire for most of my uses, my primary criteria for light-truck tires is that I like the tread and overall characteristics, they balance well, and the chassis I put them on likes the tire. All of these are equally important, any missing ingredient can make a tire undesirable for the specific application—a deal breaker. After these metrics I prefer and will take a load-range D if I can get it, but will accept a load-range E if it’s not overly stiff.
RoadTraveler, enjoying the tire wear to get there.
A thread on the expeditionportal.com prompted this post. A gentleman asked how much sidewall is enough as he’s planning to use 37-inch tires on 20-inch wheels on a full-size diesel pickup. He asked if it would be worth it to spend money on 17-inch wheels and tires for occasional, recreational use, while using his twenties for daily driving. My answer to his question was no, it’s probably not worth it just for vacations. Though for me, it would be very desirable to run 17-inch tires & wheels everyday. His questions spurred me to expound on this important subject as it relates to overland travel for the first time here on RoadTraveler.net.
A Sidewall Baseline For 4WDs
I’m not an advocate of tall wheels if they are not necessary, of course many trucks these days have a minimum wheel diameter of 17-inches because the brakes are so large, and wheels between 18–20 inches have become fashionable. A tall wheel simply means less tire sidewall with which to perform off-highway duties for a given tire diameter. Taller sidewalls help a truck ride above the rocks and obstacles, all of the truck, including the wheels. Low-profile tires are needlessly vulnerable to trail damage, offer less flex, and are generally less versatile. It’s often forgotten, misunderstood, or unappreciated that tires are part of a vehicle’s suspension.
Using a 16-inch wheel with a 33-inch tire offers a sidewall height of 8.5-inches, (33 –16)/2 = 8.5″, a good baseline. We could get more technical and use the static radius, but it’s easier to simply use the manufacturers’ stated diameter, and it’s close enough for this topic. The lower half is what we drive on, what matters, and it provides more or less flex depending on its height and design. Sidewall flex can be a positive or a negative depending on your truck, the terrain, and your needs and preferences. In theory, a 35-inch tire on an 18-inch wheel, a 37-inch tire on a 20-inch wheel, as well as my thirty-three on a sixteen example, all have a lower sidewall height of approx. 8.5-inches.
If we are interested in the clearance we get from a particular tire size, specific tires need to be researched using the manufacturer’s data to determine the true diameter. Some tires will be very close to their stated height, 35-inches for example, while some are a half-inch short. One half-inch less diameter means 1/4-inch less sidewall on the bottom, a difference that can easily be measured and felt depending on the sensitivity of your butt dyno.
Load Range and Tire Construction
A taller, higher aspect ratio, more flexible sidewall is helpful for off-highway travel for both ride quality and traction. One exception being that a stiffer (and tall) sidewall may be more resistant to puncture. A shorter and/or stiffer sidewall is generally less desirable off-highway. For heavy hauling and towing, a shorter, stiffer sidewall can be helpful, as less movement and flex generates less heat. However, on several occasions I’ve successfully and safely used relatively flexible, load-range D light-truck tires with 2-ply sidewalls to haul a couple tons (didn’t exceed tire capacity or GAWR), and have also towed several tons. I’ve also traveled many hundreds of miles (if not thousands) off-highway over the last two decades, mostly on load-range D tires. Have I had sidewall cuts? Of course, but only two that immediately come to mind, and one was last year. If you are concerned about sidewall punctures, there are some excellent, flexible load-range D tires with 3-ply sidewalls in some popular sizes. Your application and performance bias will help you choose your tires. There are many excellent, heavy-duty tires to choose from these days, some in load-range C, D, and E.
I acknowledge that load-range D tires are probably a dying breed, the writing has been on the sidewall for a while. The proliferation of heavy-duty pickups, particularly diesels, over the last several years has greatly influenced the tire aftermarket. Unfortunately even half-ton trucks and lightweight Jeeps are sometimes needlessly sold with load-range E tires, my 2005 Jeep Rubicon and 2011 Tundra are perfect examples. My coil-sprung, 103-inch wheelbase, 2005 Unlimited was a nice riding Jeep, with the exception of the needlessly stiff Goodyear Wrangler MT/R in a 245/75R16E (a relatively short sidewall). I liked the way the Jeep rode with only 25-PSI in the tires. After changing to taller load-range D tires, the combination of a taller sidewall and load-range D made the Jeep ride and perform better at all pressures, on- and off-highway.
My point is that as with many things these days, it’s easy to needlessly go to extremes and forget balance. All-steel, load-range F or G, Michelin military tires are not the best choice for your 3,000-pound soft-top YJ Wrangler, or for your heavy-duty pickup.
Not all load-range E tires are created equal, some are designed to flex better than others when pressures are reduced. My experience with both the BF Goodrich KM2 and All-Terrain T/A in load-range E indicates these tires are not overly stiff and flex well.
I recently tested two sets of 33-inch tires, both the same size with reasonable 70% aspect ratios, on the same OE wheels, but with different load ratings and sidewall construction. This latest trial simply reinforced the potential differences in ride quality and overall performance between some tires with different load ranges, sidewall designs, or heights. The difference was enough that I was comfortable running considerably more PSI in the lighter, more flexible tire, but wanted to run minimal PSI in the much firmer tire to improve daily-driving ride quality, just like with the Jeep example above. Increasing PSI on a flexible tire will reduce flex and help it run cooler on-highway if desired.
One advantage to more flexible tires is there’s often less need to reduce pressures as much off-highway as with a stiffer tire. Tires that flex, conform, and ride better at a given pressure, and are sometimes so pleasant that for short drives on easy dirt roads with few rocks, there may be no need or desire to immediately lower pressures. Conversely, tires with very stiff construction can scream dump the pressure, at the first sign of anything bigger than a pebble, particularly on a firmly sprung heavy-duty pickup with no load.
Reinforcing Sidewall Lessons
Another, older example are tests I conducted a few years ago, using two different sizes of the same tire, on two sets of Jeep Rubicon Moab wheels, on the same vehicle, with the same air pressure in both: Toyo Open Country MT LT265/75R16E vs. LT285/75R16E. Both tires have a 7-ply tread and 3-ply sidewall, are load-range E, have similar load capacities, and are very stiff designs. With 0.6″ additional lower sidewall, the taller 285s rode better on/off-road and flexed a little better when aired-down. This was experienced several times as both sets were in my fleet for a while and used on more than one 4WD. The stiff Toyo MT needs substantial deflation to obtain adequate deformation and ride quality off-highway, one of the tradeoffs for the Toyo’s very rugged design. The noticeable lack of flexibility from this otherwise excellent tire is a big negative for my all-around use. If you want a mud tire with less flex for very heavy hauling, or you don’t mind a firmer ride, the Toyo MT can be a great choice.