If there’s one component system that really blows my mind every time I try and wrap my head around it, it’s wheels. They are also arguably one of the most important components on your bike, because they define it; “bi”means "two," and “cycle” is a Latinized form of the Greek “kyklos,” which means "circle” or “wheel." - etymonline.com
Mountain bike wheels are special because they not only have to handle huge forces and stressors coming at them from every angle, but since you power them with your legs, they have to be very light. Many of the wheelsets we build weigh around 4 lbs.
On the same note, our tires also have to be light enough to bring up to speed easily, but they need to resist tearing as you hack your way through a sharp rocky trail or case the landing of a jump. This is all while staying clinched securely to our rims and keeping a bunch of compressed air inside of them.
Bicycle wheels are different from what you’ll find on your car, a skateboard, or most other wheeled vehicles because they rely on tensioned spokes to suspend us off the ground. These spokes are the key to what makes bicycle wheels so incredibly light and so incredibly strong.
How does it work?
If you’ve ever handled a spoke, you’ll be familiar with how flimsy they are when you bend or push on them. They are in fact just a piece of stainless steel wire with threads on one end and a hook on the other, and have very little strength under compression.
A spoke’s strength, and the strength of the wheel as a whole, comes about during the wheel building process, when the mechanic goes around and evenly adds pulling force, called tension, to each spoke.
They do this by threading the spoke nipples, a few turns at a time, further on to each spoke. This creates a condition where the hub is being pulled equally from all sides, distributing any forces that are placed on the wheel throughout the whole structure.
A wheel that has the correct tension applied to its spokes in an even manner is a strong wheel. It’s a wheel where the spokes never have so much compression force on them that it overcomes the tension they are already under. That means the spokes are always working in a condition where they can be really strong, instead of really weak.
That’s the quick and dirty of what’s going on in your bike’s wheels. There’s a whole lot of physics that goes into making the right wheel for the job. To do it well, one can consider everything down to whether you’re making a front wheel or rear wheel, because one deals with pedalling forces and one does not. Even variables like whether you’re using rim brakes or disc brakes can change the way you arrange your spokes (called the lacing pattern). It starts to get pretty deep pretty fast, and I’d love to talk about it more in a future blog post. For now, let’s move on to tires.
Tires - What to Consider
Tires play a massive role in dictating what our connection to the ground feels like, which makes them a really important piece of the puzzle. These days, most mountain bikers ditch the inner tube and run their tires tubeless. This is a pretty simple process, although sometimes it can be fairly frustrating to accomplish, especially if you don’t have the right tools for the job.
All you are doing is covering the spoke holes in your rim with tubeless rim tape, inserting a valve stem, and mounting your tires with a few ounces of tubeless sealant to make sure air doesn’t escape.
Aside from a little weight savings, the primary advantage of this is that when you whack a rock hard enough to compress your tire on to your rim, there’s no inner tube to poke a hole in. Although you can still tear a hole in your tire, that is a lot less likely scenario than a pinch flat on your inner tube.
As far as actually choosing the right tire for the job, that can be a little overwhelming. There are tons of different makes, models, and variants out there, and none of the acronyms and names that these companies use are terribly intuitive.
To simplify things, we’ll use Maxxis tires as an example to examine the three things to consider when comparing tires, which you can then transfer from brand to brand. We’ll break down what Maxxis’ acronyms mean, and with a little research you can find out how Schwalbe and other brands do it.
The first item to look at is tire width. This is denoted first by the wheel size (29” in this case) and then by the tire width; in this case 2.3” wide, then 2.5”, then something called 2.5” WT, which I’ll cover in a moment. The width is measured on your average rim (of say 30mm) when fully inflated, and reported in inches.
Typically people will run either two of the same size tires, or a slightly wider tire in the front, as that is the tire that is doing the turning and can benefit from added traction. For the same reason, people tend to run a knobbier tire in the front, and a faster rolling option in the back.
The second part of picking an appropriate tire width is matching it to the rims on your bike. Rim width is measured in millimeters, and is the distance between the two walls of the rim (called “internal width”).
There's no such thing as the "right answer" for matching tire widths to rim widths, but here's a general guide:
- 2.3-2.5" tires // 26-30mm rims
- 2.5-2.6" tires // 30-35mm rims
- 2.6-3" tires // 35-40mm rims
If you're close to those ranges, it'll work fine and is not worth stressing about.
Manufacturers like Maxxis work different types of rubber into their tires to give them different grip and wear characteristics. Softer rubbers are stickier, but roll more slowly and wear out faster; harder compounds the opposite. Rubber hardness is measured in durometers, but it’s not something you’ll frequently encounter on a tire’s packaging. Instead, manufacturers come up with their own, more logical (sometimes) descriptors for their rubbers.
In concert with the idea of running a wider tire in the front for more traction, most folks will run a stickier tire in the front to aid with grip while turning. The rear tire also benefits from a tire that wears less quickly, since they often get skidded and are the tire that puts your pedal power to the ground.
Maxxis offers a few different rubber arrangements. You’ll frequently see “3C” on their tires, which stands for “three compounds.” With these they’ve used three compounds in the tire to create a hard base layer, a faster rolling top layer in the center of the tread, and a softer, grippier compound on the cornering knobs. The rubbers they use to accomplish that depend on whether they’re labeled MaxxGrip, MaxxTerra, or MaxxSpeed. As you might guess, MaxxGrip is the grippiest, fastest wearing option, MaxxSpeed is the fastest, longest wearing option, and MaxxTerra falls in the middle.
Schwalbe has their own nomenclature for rubber compounds, which they call Addix, and range from Speed at one end to Ultra Soft.
The last consideration to make with your tire selection is the casing. Tires are constructed with differing layers of fabric and other puncture-resistant materials molded inside the rubber. Using fabrics with a tighter weave (measured in threads-per-inch) and puncture resistant layers makes for tires that are stiffer, more supportive, and heavier, while using lighter fabrics and materials can make a tire more compliant.
Because most of a rider’s weight is placed over the rear tire, it tends to suffer more abuse than the front. I like to run a heavier-casing tire on the back with a lighter one on the front. This helps me prevent rear-flats while keeping weight down where I don’t need it.
Maxxis uses a few different names for their casings, with EXO being the most common all-around casing. EXO+ adds a layer they call “Silkshield” to add more puncture resistance, and finally Double Down features two high-thread-count layers for a much stiffer tire with more support.
That covers wheels and tires, Part 3 of Understanding Mountain Bikes. With an understanding of a tensioned spoke wheel, you can start to appreciate what a wonder of engineering your bike really is. By learning a little about different types of mountain bike tires, you can better wade through the infinite models and pick one that will work for you!
- Dan at Fanatik