Preface to the preface: This is a long one. I’m not apologizing for using my words, but I will say that not every entry in this series is going to cover this much stuff. But if you know me, you know that I gotta get in the relevant background, so here it comes.

Let me preface everything that follows – the rest of this post, and all other posts which may involve discussion of the technical aspects of automobiles – by saying: I am not a Car Guy.

Even as a teen, when I should have been at my most Car Guy, I was not a Car Guy. I did want a car, of course, but that was just because I lived in a small town in a rural part of a mostly-rural state, and in order to hang out with friends someone had to have a car. I did not lust over engines or (automotive) bodylines. I did memorize endless specifications, but for CPUs and hard drives rather than engine displacements and horsepower. I did not bond with my father(s) by sharing their love of cars and/or by doing maintenance on family vehicles.

I have never once wanted to have a conversation centered around automobiles. I don’t know how to reply when other people assume that because I’m a guy that I will be capable of, or interested in, having such a conversation. I understand how an internal combustion engine works from the perspective of physics and engineering, but rather than having positive feelings of any sort about them, I find them to be monstrously complex and ecologically horrendous.

I was married to a Car Guy for over a decade, and in all that time I never found anything about her love of/obsession with cars engaging or interesting. But that is a story for another time and a very different blog.

And I tell you all of that, so that you can understand how confusing it has been for me to find myself interested, and in fact at times actually excited, to think about various aspects of the operation of motor vehicles over the past few years.

This has happened because I have always loved the outdoors (even though I did not prioritize this for a big chunk of my life), and that since moving west with MJ, we have put a not-inconsiderable amount of effort and expense into spending more time outdoors, and in being in increasingly remote outdoors spaces.

In the western US, where we are, this means that you need a capable vehicle. Capable in ways that I did not really understand or appreciate until we moved to Colorado.

A primer: tires

The thing I have learned the most about, and still nearly the only thing that I have any opinions about regarding cars, is tires. There are two reasons for that:

  • I knew almost nothing about them, so I had a long way to go when I started figuring things out
  • If you’re going to have a good time and be safe off-pavement, your tires are probably the biggest determining factor of that outcome

If you already know how tire sizing works, feel free to skip to the next section. But if you’re in the place where I was when this all got started, and have no idea what 225/60R17 means, then let me fill you in right quick.

That, by the way, is the stock wheel size for the model of Subaru Forester that I own, which makes it a good example now and very relevant shortly. But for now let’s just break it down. Like a lot of things, it’s easy to understand once you have a few pieces of information under your belt.

A simple thing to know that makes this much easier to understand is that only three pieces of information are being encoded in a tire size, and they’re all numbers. The / and R are acting as separators (I think the R stands for “ratio”, but it is invariant and can be ignored). The data in the tire size are, in order:

  • 225 is the section width, in millimeters. That is to say, the measurement from the outer sidewall to the inner sidewall on a cross-section of the tire
    • I originally thought this represented “tread width” – and it will be close to that number, but they’re not the same thing
  • 60 is the aspect ratio or profile. This number, when given a leading zero (e.g. 0.60) and multiplied by the section width, will give you the measurement from the inner rim of the tire to the edge of the tread
    • To put it another way, section width × profile = sidewall height
    • You may recognize this as a percentage. A tire with a profile of 50 will have a sidewall height that is half the tire width
    • The smaller the aspect ratio, the “thinner” the tire will appear when mounted on the vehicle. This is where “low profile” tires get their name
  • 17 is the wheel diameter, in inches

So yeah. A width in SI, a unitless dimension, and a diameter in Imperial units. Just a fantastic design all around. Hope that helped!

Adventuremobile 0

I didn’t think about it this way at the time, but looking back it’s easy to see that my first car – a 1974 VW Beetle – was my zeroth adventuremobile.

It never went off-road, but it spent a lot of time off-pavement, and I learned a lot by driving it at higher-than-recommended speeds down the dirt, clay, sand, and gravel roads that cris-crossed the county I grew up in.

Also its tires were so narrow that I learned a lot about managing hydroplaning. I don’t encounter that a lot out west, but a loss-of-traction situation is a loss-of-traction situation (excepting hill climbs, which are in fact a different situation).

Adventuremobile 1: I should not have done that

The first vehicle that I ever used to intentionally seek out, shall we say, more remote experiences, was MJ’s 2010 Ford Fusion. Or as we came to affectionately call it, the Adventure Ford.

She had already driven it to an impressive number of places when I met her, and together we would drive it to many more. Several of which we definitely should not have attempted.

Before moving west, we thought of “Forest Service roads” as just another category of dirt/gravel road. Maybe they’re less well-maintained than a county road. Maybe they’re muddier, due to being less frequently travelled.

What we quickly learned in Colorado was that a FS road may be a well-maintained dirt road on par with those back east, but it is likely to involve ungraded sections where lumps of bare rock protrude three or four inches above grade. And it could be something that would, back east, be classified as an advanced 4WD trail.

Explorations into AZ and UT expanded those learnings to include things like:

  • Do not expect any specific quality due to a road having a designation as “FS”, “BLM”, or “County”. Any road can be of any quality, and this cannot be inferred from standard maps, designations, or other roads in the area
  • Google maps is should be considered deeply suspect for route planning outside metro areas, excepting interstate highway travel
  • Even when using a specialized, offroad-oriented GPS package, stop the vehicle and scout on foot if things start to look sketchy. The “road” past this point might actually be a firebreak that showed up on decade old aerial surveys
  • Western “gravel” is a very inclusive concept, and may be composed of things like “sharp hunks of granite the size of your fist” and/or “roughly crushed volcanic rock”
  • In remote areas, do not expect water crossings to involve bridges
  • In remote and arid areas, do not expect paved roads to be engineered to avoid transient watercourses, or for transient flows to have been engineered to avoid the road via culverts

We managed never to get stuck, or to disable the car by holing/tearing off the oil pan (this is not hyperbole; it is a thing that is very likely to happen if you misjudge your clearance over an obstacle in a vehicle without undercarriage protection), but we did end up needing to replace every engine mount and one of the transmission mounts. Even the mechanic was impressed by that last one. That’s when we realized we were really pushing our luck, and needed a more capable vehicle.

Adventuremobile 2: Gettin’ lifty with it

Like 107% of the residents of the Denver area, we decided to solve this problem by purchasing a Subaru (the other 9% drive Jeeps or full-conversion, 4WD Sprinter vans). In August of 2020 – which you may remember was just a super-fun year all around – we found a 2017 Forester that was in pretty good condition and attractively priced. Subarus hold their value like Macbooks, so it felt like a steal to get one that young for $17k. It was the base trim, but that’s was fine with us. We immediately started heading out for roads we had been too chicken and/or too reasonable to attempt in the Ford.

It was a revelation, especially all-wheel drive.

The Fusion, a front-wheel drive sedan which was engineered to cruise along city streets and interstates, had never felt sluggish on hills, and had agreeably gone where-ever we asked it to go. But the Forester, with its short wheelbase, light weight, 2.5L engine, and AWD, sprinted up hills like a happy dog. It was nimble. And its stock ride-height of 8.7" clearance let it go on roads that we could only sadly shake our heads at when driving the Fusion.

Forester in 2020 with original shoes Forester in 2020, stock

This also led to us almost immediately encountering another class of roads/trails which were too rugged for the Forester’s capabilities and/or our skills at driving off pavement.

It didn’t take much poking my vehicular nose into these newer, more rugged spaces to realize it was only through dumb luck that we had taken the Ford so many places and not lost a tire. I was especially surprised that we hadn’t ripped open a sidewall. And that’s when I started learning about tires.

There are two basic factors that determine how much stuff you can drive over in a vehicle: clearance and tire capability. Clearance is straightforward, and there is exactly one way to adjust it: lifting the vehicle. Tire capability has more aspects to it, but for my purposes it can be boiled down to durability and traction.

Let’s talk about durability first. Not to get tautolopgical, but you make a tire more durable by putting more tire in the tire.

Modern street tires are very lightweight in the name of fuel efficiency. They are made with harder rubber compounds, which give a long lifetime in miles driven with less weight. By comparison, all-terrain tires have:

  • A physically thicker tread, which adds durability, puncture resistance, and traction
  • A tread design that “wraps” around onto the sidewall, rather than being a simple band around the circumference of the tire
  • Multi-layer sidewalls, since the expectation is that they will be scrubbed on obstacles

All of this goes a long way toward making a tire that is somewhat “armored” compared to a street tire. But it will be heavier since there’s more material, and that impacts mileage. The more aggressive tread also makes them louder and rougher-riding than street tires.

The multi-layer sidewall also becomes important in another way, as we move on to talking about traction. The extra strength from having a sidewall with multiple fabric belts and layers of tire compound lets you air down the tire, which is one of the first offroading concepts that I learned about.

(A later post on recovery gear will address the how of airing down, and the reverse.)

On a rugged road, or on any trail, you want to air down your tires, which means running them at less than the rated pressure. This makes for a softer ride, but also allows the tires to wrap around obstacles to a degree, greatly increasing traction. It also also protects the tread of the tire by letting it offer less resistance to sharp obstacles.

Traction also comes from tire compound choice and tread design. In engineering as in life, nothing comes for free, and when designing street tires all the optimization choices are made in the direction of efficiency and on-pavement safety. This is understandable, as most people will never take their cars off-pavement, much less off-road.

AT tires go in the other direction, with “gnarly” tread designs that enhance traction and compounds that offer okay road durability but are much grippier – which impacts not only tire longevity but also fuel efficiency.

It turns out that sidewalls are surprisingly important for making tires that are highly durable and get better traction in off-pavement conditions. And in addition to wanting better sidewalls, you also want bigger sidewalls. But how do you make that happen?

You can lift a vehicle to increase the ground clearance. And that lift will also introduce some additional vertical space in the wheelwells, so do you just cram the bigget possible tire in there? Not if you still want to be able to do things like “change direction”, because you need to be able to swivel the tire within the wheelwell. You also want the suspension to travel, which is what lets it do its job of soaking up bumps, and you want this to happen without tearing up the tire in the process.

So no, you can’t just stuff the biggest tire that will possibly fit while the car is sitting still. Luckily, the internet is full of Car Guys, and some of them have built online tools that will give you all the dimensions of a wheel/tire set just from inputting a tire size. This makes it easy to compare different setups and work out what will be good for your purposes.

There is another approach, but that involves cutting tools and modifying the bodywork – a direction I was not willing to go in. Yes, I wanted to make the Forester far more capable at handling rugged terrain, but I did not want to turn it into a rock crawler or lose its daily-driver-ness.

Where I ended up with the Forester, after lifting it by 2", was moving from the stock 225/60R17 to 235/75R15. This means:

  • The tires are 1cm wider (235mm vs 225mm section width)
  • The sidewall is 41.25mm taller (75% of 235 vs 60% of 225)
    • The extra sidewall height is enabled by the reduction in wheel size from 17" to 15"
    • Thanks again to Car Guys on the internet for verifying that it was possible to put (many) 15" wheels on a 2017 Forester
    • The reason you can’t just arbitrarily downsize wheels is the size of the brake rotors and calipers, something I had never previous considered. Of course, I had never previously considered putting different wheels/tires on a car at all, so…
  • All of this resulted in a less than 1% difference in tire circumference, which is important if you want your odomoeter and speedometer to remain even vaguely accurate
  • Finally, the change to 235/75 moved from the SUV class of tires to the light truck class of tires. Functionally, this means nothing. But if I ever need to buy a new tire in a remote place, I reckon there’s a better chance of a truck-sized AT tire being available nearby

All-terrain adventure jellybean in 2023 Forester at Taos Gorge in 2023, with lift and Goodrich KO2s. You can see the tread wrap-around onto the sidewall clearly here.

We got the Sube near the end of our time in Colorado, so most of our experience with it has been in New Mexico (with some additional time in AZ and UT), where we have learned a few more things about driving off-pavement.

  • In addition to not having expectations about road quality/condition based on whether it’s a FS, BLM, or County road, also do not make any assumptions about state highways, especially the further out from towns you go
  • Pay attention to how roads have been used in the past. A section which was a wallowed-out mudhole in spring will become a powdery sandpit in summer
    • People who tear up trails in mud season are assholes
  • Sandy and rocky soils are fine all the time, but keep an eye on the weather when driving on the volcanic clay of the four corners region; when wet it turns into an impassable mess not unlike natural peanut butter
    • When there is a sign advising you of this, believe it
    • Nothing except the biggest, balloon-iest mud tires has traction in those conditions
  • Not getting stuck is best, but having traction boards is a good fallback position (more about this in the recovery gear post to come)
  • Don’t be surprised if something marked as a road (rather than a 4WD trail) has one or more rock benches 6-8" high in it
    • When encountering obstacles like this, do not “run at” them
    • Come up to them gently, and then use engine power, traction, and 4WD/AWD to get over them
  • If something is marked as 4WD though, it may be something that an unmodified pickup could not traverse, but it may also be in surprisingly good condition and have no significant obstacles; there are no standards and you are on your own recognizance

Adventuremobile 3: First drive and plans

With all info internalized and lessons learned, what are the plans for the Highlander? There’s a good bit to write about, but for the purposes of this post I’m only going to talk about tires and wheels. And first, here’s what isn’t planned:

  • We do not intend for it to be a highly-capable off-pavement machine like the Forester, so we will not be lifting it
  • We do intend for it to be a touring/road-tripping machine that gets good mileage, so we will also not be putting ATs on it

Last weekend we took it out on its first cruise, to the southeastern extent of the San Juan mountains, around the state line between Colorado and New Mexico. Specifically up the Rio Conejos valley.

It handled everything about highway travel with aplomb. The Highlander is not an exciting vehicle, but it’s a Toyota and it’s a model that has been evolving since it was introduced in 2000, so it’s a reliable vehicle. Zero surprises there.

Highlander, stock, at campground in 2024 The Highlander, stock, in a campground

The unpaved roads we explored could have been taken at 40MPH in the Forester, but they were still a bit rougher than what I had been planning to do on this trip.

The Highlander has 8" of ground clearance, but it rides on fairly ludicrous 20" wheels. Well, ludicrous for my purposes. The stock tires are 235/55R20s, and if you’ve been paying attention at all, the first thing that should have jumped out at you there is that the sidewalls are proportionally even narrower than the ones that I took off the Forester. Also, being a hybrid with an AWD system that involves a rear-axle motor, the Highlander weighs close to 1100 pounds more than the Forester despite having very similar external dimensions. So I was being careful.

As stated, we have no plans to ever take this vehicle offroad, but we would like to be able to explore decent, unpaved roads without having to be quite so cautious as we were on this trip. So the plan is:

  • Switch to 18" wheels
    • Standard on other trim levels of the same model year, so we know they fit
    • We also know that 17"ers do not fit due to large brake components (thanks one more time, Internet Car Guys)
  • And to 235/65R18s
    • Specifically, to Yokohama Geolandar CV4S tires
    • Still a SUV-class road tire, but one with an ever-so-slightly aggressive tread
    • Tested tops in wet traction against other all-season SUV tires
    • CV4S are actually all-weather rather than all-season, and are 3PMSF rated (like the Forester’s KO2s), making them snow tires as well

The wheels and tires are already ordered and should arrive next week, in time for our first camping trip. I’ll get some pics but a post about the new tires might be on hold until another piece of gear arrives, Therefore, next up will be something I’ve mentioned a few times in this post: recovery gear.