Condensed Answer: The purpose of disc/solid wheels found on track bikes is to reduce the drag created by standard spoke wheels. The improved aerodynamic properties have a measurable effect on one’s final times.
Since track bikes are used in a controlled environment, they don’t have to be limited to a single solid wheel and sometimes use two.
The Advantages of Disc Wheels
- Less Drag
When speed is the main goal, every bit of drag is an obstacle stopping you from going faster. Hence why manufacturers and professional teams do everything in their power to reduce the drag generated by both the bike and the rider.
An individual spoke creates very little drag. However, the total volume of spokes increases the drag levels to a higher degree than one might expect. To fight this issue, disc wheels with a very slim profile were created.
On a recreational level, the extra boost is inconsequential and many people use disc wheels for the look rather than the effect. On a pro-level, however, the disc wheel is considered a respectable advantage.
- No Need For Wheel Truing
Since the wheel doesn’t have spokes, it’s not necessary to periodically adjust the spokes to keep the rim round.
The Disadvantages of Solid Wheels
1. Extra Weight
Solid wheels are notably heavier than spoke wheels and even the very expensive models often reach above 1000 grams per unit. Meanwhile, a 50% lighter spoke wheel can be had for about 50% less money.
However, the reduced drag is considered worth the weight penalty because additional grams matter the most during climbing which doesn’t happen on the velodrome.
Of course, the lighter the bike is, the easier it is to accelerate it, but the high gearing of track bikes slows down acceleration far more than the extra weight added by a disc wheel.
Or in other words, this particular downside of solid wheels does not affect track cycling to a performance-altering degree.
A solid wheel of good quality can cost thousands. The aero boost that one gets from such a wheel is not worth the money when the rider is competing on a non-professional level. However, when the rider is trying to boost every possible parameter to reach peak performance, the extra money is considered a necessary investment.
4. Susceptible to Crosswinds
Solid wheels aren’t practical for general road cycling because they act as cross-wind stoppers and compromise the balance and steering of the bike.
But since the velodrome is a close environment, with practically no cross-wind, the danger is minimized. Hence why some track bikes have a solid wheel on the front and back.
FAQ: Why are solid wheels so popular?
Solid wheels gained popularity in 1984 when the Italian cyclist Francesco Moser broke the 1972 hour record of Eddy Merckx. The hour record is the record for the longest distance cycled in one hour on a bicycle from a stationary start.
Moser cycled 50.808 kilometers on a bike equipped with two disc wheels. Ever since Moser’s success, disc wheels began to receive a greater degree of attention. Moser’s entire bike is presented in detail in the video below:
FAQ: Why is a solid wheel more common for the rear?
Disc wheels catch a lot of wind compromising the rider’s balance and the steering of the bicycle. For that reason, time trial bikes (TT) use only rear disc wheels because the rear end is less susceptible to crosswind.
That said, disc wheels are fully forbidden in open races because even the slightest off movement can cause a fall and a subsequent group crash. Or in other words, they are too dangerous for such type of racing and the aero gains are not worth the risk.
FAQ: Are there cheaper alternatives to disc wheels?
A cheaper option is to get a wheel cover. As the name suggests, the wheel cover is put over the spokes on a regular deep rim to create a wheel mimicking a solid one. A disc cover has its downsides, but it can be had for about USD 100 and thus save you a lot of money while still offering improved aero properties.
Another option would be to borrow a disc wheel solely for competitions and pre-competition practice.
FAQ: How much time does a disc wheel save?
A disc rear wheel is expected to save up to 1 second per kilometer. Or in other words, a 50km ride will be about 50 seconds faster. Obviously, the improvement is inconsequential to a recreational rider, but it makes a massive difference on a professional level.
Summary: What You Need To Know
1. The only purpose of a disc wheel is to reduce drag.
2. Disc wheels have three major downsides – they’re heavier, expensive, and affected by crosswind.
3. Track bikes are good candidates for disc wheels because they’re used in a closed environment and are therefore less susceptible to the effect of crosswind.
4. The extra weight of disc wheels is problematic only when the bike is used for climbing. Thus, this downside doesn’t affect track bikes either.