Ever watched track cycling in the Olympics and wondered why they have those peculiar-looking disc wheels?
Well, you’ve come to the right place!
To get you up to speed on disc wheels, we’ll be covering:
- What Is A disc wheel?
- What’s The Difference Between Disc Wheels And Road Bike Wheels?
- How much faster are disc wheels?
- The Pros And Cons of Disc Wheels
- What Scenarios should you use disc wheels For?
Ready for the full rundown on disc wheels?
Let’s get into it!
What Is A Disc Wheel?
Disc wheels are solid or covered wheels designed to improve airflow and aerodynamics and reduce drag around the rear end of a bike.
You’ll see these on time-trial bikes which are built to slice through the wind with as little resistance as possible. Although they can be used on road bikes, it’s rare that you’d ever need to pop a disc wheel between the chainstays.
These are not to be confused with disc brake wheels. This term refers to any wheel that is compatible with disc brakes – though you can also get disc wheels that are compatible with disc brakes as well (disc brake disc wheels, which is a bit of a mouthful).
Disc wheels typically have no spokes, unlike standard wheels on road bikes. But disc wheels can also just be a fairing that attaches to a traditional spoke wheel, to reduce the drag created by the spokes.
For solid disc wheels, the disc is integral to the wheel and has no spokes inside it. These are often built using carbon fiber for a thinner, lighter wheel.
Disc wheels rose to prominence in competitive time trial cycling in the early 1980s when Italian legend Francesco Moser broke the Cycling World Hour Record using front and rear disc wheels.
Since then, disc wheels have become increasingly popular and are the standard for most time-trial bikes – though often only for the rear wheel.
What’s The Difference Between Disc Wheels And Road Bike Wheels?
Other than the obvious difference using “discs” instead of spokes, the main difference between disc wheels found on a time-trial bike and standard road bike wheels is the rim depth.
Rim depth is the radial distance between the outermost and innermost surfaces of the rim.
But what does that mean in practice?
For road bikes, it’s rare to see wheels that have a rim depth greater than 65 mm. Whereas for disc wheels on TT bikes, 80 mm rims are commonplace.
Simply put, the greater the depth of the wheel, the better the aerodynamics and the faster you’ll go – but the heavier the wheel will be.
How Much Faster Is A Disc Wheel?
Clearly, aerodynamics are key to racing faster. But how important is aerodynamics, and how much faster are disc wheels compared to other wheelsets?
It’s estimated that 85% of your power when riding is used to overcome air resistance. 10% is used to overcome rolling resistance, and another 5% is used to overcome friction within the drivetrain.
Whilst aerodynamics is key to overcoming air resistance, it’s not all about the wheels. There are a number of other factors you have to take into consideration, including positioning, weight, and physiological traits of the rider.
Plus, you’ll need to factor in the aerodynamic benefits of other pieces of cycling equipment such as aero bars, helmets, time-trial suits, and frame design.
The Pros And Cons of Disc Wheels
Riding with disc wheels, you’ll cut through the air more effectively than with spoked wheels. That’s all thanks to the aerodynamic design of disc wheels which minimizes the drag and turbulence created by spokes.
This is pivotal, especially for competitive time-trial cyclists where every second counts.
#2. Flat terrain
Cycling long, flat distances? Disc wheels will always be a winner.
The solid design of the disc smooths airflow around the rear of the bike, enabling cyclists to increase their speed compared to deep-section or spoked wheels.
The aerodynamics of disc wheels provide cyclists with a huge advantage when competing on flat, smooth roads with no gradient.
Though disc wheels can weigh you down when climbing, they provide a massive advantage on descents. The importance of aerodynamics is multiplied at the higher speeds achieved on downhill sections.
So, even over a course with rolling terrain, it could work out faster to use a disc wheel as you regain the time sacrificed on the climbs by taking off down the descents.
#4. Aesthetic (They look awesome!)
Disc wheels look futuristic, sleek, and fast.
Of course, this is subjective. But there’s no denying that disc wheels stand out from the rest of the crowd!
Road bikes and standard spoked wheels are the norms. So why not break from the mold and unlock a whole new world of cycling with some shiny new disc wheels?
Once you’re comfortable, locked into aerodynamic positioning, and zooming along seamless, flat roads, you’ll feel like a true cycling pro.
First and foremost, weight is a factor when considering disc wheels. The very nature of their design means they are heavier than spoked wheels.
This is more than made up for on the flats by the aerodynamic gains of disc wheels, but additional weight is a major disadvantage on uphill sections. Furthermore, the lower speeds achieved while climbing reduces the impact of aerodynamics, tipping the balance further against disc wheels.
Having said all that, Chris Boardman once won the National Hill Climbing Championships using a rear disc wheel – so it’s clearly not all bad news! As with almost all things cycling tech-related, there’s a hefty element of personal preference involved.
High-end disc wheels are also getting lighter every year – but expect your wallet to take extra punishment for every gram that’s shaved off!
Because of the solid design of disc wheels, they have a tendency to act like a sail in windy conditions.
Strong crosswinds can cause unstable handling and reduce the rider’s speed, or even cause an accident. With the potential danger this creates, some time-trial cycling contests (such as Ironman Hawaii) have gone so far as to ban disc wheels entirely.
That said, this effect can have its benefits too. If crosswinds hit the bike at an angle lower than 45 degrees, the ‘sail’ can act in the rider’s favor by propelling them forward.
Because of the “sail” effect, double-disc wheel setups are more common in the controlled conditions of the track than on the road. For outdoor riding, a common compromise is to use a disc wheel at the rear (which is more stable in windy conditions), paired with a conventional wheel at the front.
Most disc wheels are made from carbon fiber with a foam-type inner and struggle with rigorous terrain. Hitting a pothole can spell disaster for a disc wheel.
Dents, bends, and cracks are common for disc wheels, especially on poorly maintained roads. Repairs are another issue, as it’s close to impossible to straighten a damaged or bent disc wheel again.
There is a price to pay for the aerodynamic advantages. Entry-level disc wheelsets start around a few hundred dollars, but you can quite easily spend thousands on mid to high-end disc wheels.
It’s a slippery slope – but if you’ve got the budget, why not consider investing in speed!
When Should You Use Disc Wheels?
Disc wheels are built for time trial bikes and naturally are paired with each other for optimal aerodynamics.
If you’re looking to get competitive and delve into the world of time trial cycling or triathlons, then disc wheels are absolutely something you should be taking full advantage of!
The short answer is disc wheels are performance boosters: get a pair and you’ll go faster.
However, if you’re embarking on a long slog of a climb, without a matching downhill section to make up the difference, you might be better off sticking with conventional wheels.
Disc wheels are also unsuitable for mass-start racing (i.e. most events other than a time-trial). They’re dangerous when used in the peloton, as they magnify any touches the riders have with each other while jostling for position.
For this reason, they’re specifically banned by the UCI for any of its mass-start races. For example, you won’t see disc wheels at the Tour de France for any of the regular mass-start stages – but they are allowed for the time trials.