Wheels & Tires

Notice the difference in tread depth between the tire used for our spring trip and the spare.

November 29, 2023 - After coming back from our spring trip in the southwestern US, we noticed our tread depth was about half of when the tires were new. We should have rotated the tires mid-trip rather than have one “new” spare and four half worn tires. Lesson learned for our next big trip.

With winter coming and knowing we have to go over a icy mountain pass with no guardrail to get to town, we wanted to be prepared for winter driving at home. Colorado has a winter traction law that provides a minimum acceptable traction depth of 3/16” (4.7 mm). In new condition, the tires that came on our Jeep have a tread depth of 12 mm. After our trip, we had about 6 mm remaining, which is where all-terrain tires start to lose traction under icy conditions. We wanted a set of actual winter tires and new wheels to go with them. This will make it easier to switch them seasonally.

You might be asking, why have separate winter and summer tires? Head-to-head studies have shown that stopping distance on snow is significantly improved with winter tires (310 ft) relative to all-season tires (668 ft). This is largely due to the rubber used in the two types of tires. Winter tires are made of a softer rubber that stays pliable at colder temperatures, allowing the tire to provide more traction at cold temperatures and on slippery surfaces. 

OEM Wheels and Tires

The size of the OEM (Original Equipment Manufacture) tires on our Jeep are 315/70R17. This tire size means the width across the tread is 315 mm (about 12.5”). The next number, 70, means the sidewall height is 70% of the tread width (8.75”). The final number 17 means the inner diameter is 17 inches. While researching which tires to get, we discovered that only one manufacturer makes this size winter tire, Nokian. That makes the selection easy. So let’s look at rims to go with our new tires.

Since, in the future we want to have two sets of wheels that we will switch seasonally, we needed a second set of rims. Again staying close to the OEM specifications, we wanted a 17” diameter wheel that would work with our selected tire. If you know you will be driving off road, a major consideration is whether to go with bead-lock rims. Bead-locks do exactly what it sounds like. They physically lock the bead of the tire to the rim, allowing you to lower the pressure of the tire to very low levels. The wheels in the photo above are bead-lock capable. We don’t use them as bead-locks but we could if we wanted to. You can identify them as bead-locks by the 25 bolts around the rim. There are also wheels that have this pattern of bolts that are purely decorative. These are called street-lock.

Rock Crawlers might air down to 5 psi to provide the maximum traction. We generally stay on dirt so only air down to 15 psi. While bead-locks have their place, they can be difficult to mount and most tire shops won’t work with them. They are also illegal on most roads. For this reason, we decided against bead-locks and instead went with bead-grips which are designed to hold the tire bead more tightly than standard wheels but not as aggressively as bead-locks. This allows us to air-down safely but without the hassle of a bead-lock wheel. 

Our new Wheels Showing the Bead Grip

We have mentioned airing-down on previous posts. It has several advantages when traveling on rough or low traction terrain. Airing down increases the tire surface area that is in contact with the road surface giving you increased traction on rock, sand, snow, and mud. On rough roads, airing-down also provides more of a cushion between the vehicle and the road so the ride is a lot smoother, which is better for the passengers and the vehicle. It also prevent much of the shacking that can make you loose control of the vehicle even at very low speeds.

The next item to consider is rim offset. Offset is the distance (in mm) from the center line of the tire to the mounting surface on the vehicle. Offset values can be either positive or negative depending on the offset direction relative to the center line of the tire. 

A zero offset means that the mounting point is at the center line of the wheel, a positive offset means that the mounting location is out from the center line and a negative offset means that the mounting location is in from the center line of the wheel. In effect, the choice of wheel offset moves your tires IN (positive offset) or OUT (negative offset) relative to the center of the vehicle

The offset on our OEM wheels are +12 mm so we wanted something close to that. The wheels we chose have 0 mm offset which means that the outer surface of the tire is now 12 mm out relative to the original tires. That’s not much and we haven’t noticed a difference in the way the vehicle handles. A lot of offset in either direction can adversely alter the handling of the vehicle, thus our desire to stay close to OEM. 

Knowing what we wanted, we went to our local tire shop to place our order. We were told that the tire manufacturer, Nokian, didn’t manufacture any tires our size last year, so none were available. But we still want a new set of tires for winter. After reconsidering our options we decided the tires on the Jeep, last winter, served us well. They were just worn. Since those were available, we ordered a new set for this winter. We don’t drive much in the winter so in the spring, we will switch back to the old tires, which still have around 14,000 miles of useful life on them. That remaining mileage is based on my geeky extrapolation of miles traveled and tread depth used.

Snow Rated Symbol

Many all-terrain and all-season tires are now “snow rated” and can be visually identified by the above symbol on the side-wall of the tire however, this rating is determined based on straight-line traction on packed powder.

Fortunately for us, we often have packed powder road surfaces around here, but we also have our share of ice, and roads are seldom “straight line.” All-terrain tires do a decent job under many conditions and if nothing else is available, they will probably keep you out of a ditch. Dedicated winter tires, on the other hand, are designed strictly for winter driving conditions (i.e. cold, wet, snowy, and icy roads).  

From experience, our BFG all-terrain tires worked great on winter roads when they were new, but everything I’ve read says that dedicated winter tires are even better, so we will keep a lookout for winter tires and hope they become available before next winter.  In the meantime, we have a new set of BFG all-terrain tires mounted on a new set of Method Bead-Grip wheels on our vehicle. That should get us safely through the winter and we’ll be all set for our summer trip later in the year.  

New Wheels with New Tires