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How to choose the correct road bike wheels depth

What road wheel rim depth do I need?  That vital question will take some research to answer, especially in the era of carbon fiber. In the old days of alloy, rims were narrow and shallow, and weight was the prime consideration for all cyclists. But then carbon fiber took over, because the new miracle material was lighter and more rigid than metal.

Easier to shape as well, which meant designers spent many hours in wind tunnels, perfecting the ultimate aerodynamic rim for road cycling. Streamlining was always important on the road, where air resistance and energy demand increase exponentially to sustain a speed above 15 mph.  Average speeds of 50 kilometers per hour (30+ mph) are achieved in competition, to say nothing of breakneck alpine descents at twice that velocity. Aero rims play an important role in such high performance. 

carbon wheels rim depth

   

At first sight, seen from a distance, the modern pro peloton looks as if it’s rolling on fat bike rubber. But these days tires are still skinny – 23 or 30mm. A closer look reveals that deep carbon rims gave the impression of bulky tires. Those broad carbon hoops are the product of intense aerodynamic development, and in overall cross section resemble a tear drop, rounded off at the leading end by the curved profile of a tire. An elongated tear drop section has different wind-cheating properties compared to a shallow rim. The cross section may be V-shaped, with a sharp edge where it meets the spokes, or U shaped, like a wine glass without a stem. There is a hybrid combination of both profiles which is favored by some aerodynamics experts. The deeper the better, they say – and the ultimate depth is found on a rear disc wheel, where one might say the rim profile ends at the hub!    

The pros and cons of deep rims

Let’s take a look at the pros and cons of deep rims. The advantages are obvious. They shave seconds off your personal best time against the clock, or give you an advantage in a solo break. The greater the distance, the greater the saving of energy, the less time taken. They also add stiffness to the wheel, which results in a more efficient transfer of power from the pedals. Sure, they may be heavier than shallow rims, but there’s no denying that they cross the finish line first – in certain competitions, not all.

However, there are prices to be paid for the deep rim advantages. The first is comfort. The extreme stiffness gives a hard ride. At times the rider may feel he’s sitting on a jack hammer, not a saddle. Especially with the aggressive geometry of a time trial machine. This may be tolerable for a solo event lasting an hour or so on level roads – but no professional would be happy to use very deep rims in a one-day classic or national stage race. However, in the cycling leg of a triathlon on a straight level road in calm weather, an 86mm deep rim is a big advantage.

Now for the bad news. An ultra-deep carbon rim on the front wheel turns into a liability in gusty weather. Deep rims work beautifully when the wind is from ahead. But when a crosswind hits them on their broad sides, they respond like windmills, push the bike sideways  and play merry hell with the steering. When a competitor must fight to keep the bike headed in a straight line, performance suffers. The lighter the cyclist, the more dangerous the effect. A petite lady should never use a deep rim in front – unless the day is utterly calm and windless. A strong crosswind gust could blow her off the road.     

Shallow rims       

Shallow rims are lighter, and even in alloy, they are easier to accelerate, having less inertia. Which can give them a 1/100 sec advantage over the final 200 metres of a sprint. On a course such as a major mountain pass, where the peloton climbs at a speed less than 15 mph, aerodynamics is not an issue. A shallow, light rim helps the cyclist in his fight against gravity. But will give no advantage in the high-speed descent that usually follows a stiff climb. For a course that ends at altitude, such as the famous Alpe d’Huez in France, a deep rim profile would be a handicap. But on the level, battling a head wind, it far surpasses a shallow profile, even though it weighs more.

Which size of depth rim is suitable

Like so many other choices in life, the right depth of rim demands a compromise. For the club rider who enjoys Gran Fondo, a rim between 45 mm and 55mm deep is a good choice.

It strikes a happy medium between the extremes in comfort, aerodynamics and stability. Especially  in the midst of a crowded peloton – even when a cross wind strikes. Such a rim will also offer greater durability, for the rider who competes and trains on the same wheel set. The cyclist who lives and competes in a mountainous region could go shallower. If a heavyweight dedicated competitor is looking for the ultimate rim  to be used on a flat course in calm conditions, he can go for 86mm at the rear – and something less adventurous in front if his course happens to cross a side wind.   

How to choose the suitable rim depth wheels from ICAN.  

ICAN has performance wheel sets with a wide range of rim depths. This gamut of quality wheels caters for extremely specialized purposes – and also for more general cycling. No matter  what two-wheeled discipline an enthusiast follows, the ICAN catalog has a wheel set with a rim depth to satisfy every customer. For mountain climbers there’s the Aero 35 disc at $645; plus  50mm and 55mm versions. For the pro time trial competitor, the top class DT Aero 86 costs $1085, and this range is also available for the peloton in depths of 50, 45, and 40 mm. For beginners on a budget, a good all-round choice would be ICAN’s 50mm 700c Standard clincher wheel set at $490.

  • Nov 24, 2021
  • Category: Articles
  • Comments: 0