I'm not even going to bother going and finding it, but there were two posts in this thread that made me mad. Not just wow mad. But upset because we, as cyclists, are suppose to be objective.

"asphalt is not softer than concrete." Really Einstein? Is this your professional opinion, or did you just feel qualified to make this random bull**** assessment from inside the cab of your pickup truck? Because that's the type of logic you've engaged when you made this astute assessment of density-to-mass.

Concrete is an artificial material similar to stone that is used for many different structural purposes. It is made by mixing several different coarse aggregates such as sand and pebbles with water and cement and then allowing it to harden by hydration. Hydration causes crystals to form that interlock and bind together. According to the Brooklyn Public Library, concrete was first made in 500 BC and can last up to 50,000 years. Concrete is one of the most important building materials. From sidewalks to skyscrapers, we see concrete everyday everywhere. There are many different kinds of concrete. Reinforced concrete is strengthened by steel. This is done by casting concrete around steel rods or bars and most large structures such as bridges need this extra strong concrete. Prestressed concrete is made by casting concrete around steel cables stretched by hydraulic jacks. After the concrete hardens the jacks are released and the cables compress the concrete. Concrete when compressed is the strongest. This type of concrete is used for floors and roofs as well as other things. Precast concrete is cast and hardened before being used for construction. Precasting makes it possible to produce a mass number of concrete building materials. Nearly all of prestressed concrete is precast as are concrete blocks. Concrete blocks are made in various weights and sizes and they are used to make about two-thirds of masonry walls in the US. Engineers have designed kinds of concrete for certain uses. Air-entrained concrete is good in harsh weather and is used for roads and airport runways. High-early-strength Concrete is used in hurried jobs and cold weather because it hardens quicker than ordinary concrete. Lightweight concrete weighs less than any other concrete because it is made from pumice: a naturally light mineral.
Katrina Jones -- 1999

Density of concrete: 1750–2400 kg/m3

Significantly more difficult to find any physics info on asphalt. It's usually put down onto compacted dirt at less than 3 inches (20MM according to Wikipedia). It is used because of its ability to absorb energy, specifically sound. Since all energy is waves, it doesn't take a genius (or someone making random uneducated guesses) to figure out that when a foot hits the ground, it generates energy (also known as waves) which are absorbed based on these same principles.

Asphalt, crushed: 721-1000 kg/m3

tl;dr

concrete is upwards of 5-10 inches thicker, and twice the density (m3) of asphalt. It has significantly limited absorb ability; asphalt is used specifically for its ability to absorb energy.


To the gentleman who implied that softer, more cushioned shoes were the answer. Please be prepared for all the doctor's appointments that should be set up at your orthopedic institute.

Telling a runner with a neutral gait and no excessive weight issues to "buy a shoe that can absorb all the shock" is not only misinformation, you're going to cause them permanent, life-altering damage to their joints, their running style and probably cripple them. Good game.

tl;dr

Don't tell people to wear a specific shoe to accommodate your bias, you can't afford the lawsuits based on your misinformation.