Time for a bit more myth busting here. I’m constantly amazed (but never surprised) at the constant drivel pushed out by today’s bicycle marketers how important it is for you to have one of their frames/bikes. Their favourite reasons are nearly always because their frame is so light and its so aerodynamic.
The aerodynamic thing is largely a joke as very, very few riders go fast enough for this to make any real difference. The vast majority of Ironman type triathletes are the biggest sheep in this category as most, even when racing, don’t go much over a 20 mph average which is barely scratching the need for an aero shape. To make it worse, they put themselves in a position and on a bike that is hopeless for trying to get up hills with.
The other bit of silliness about the aero adverted frame is the fact that the frame is such a small part of the whole windage package anyway. The rider’s presence and rotating legs pretty much mess up most of the air streaming past the frame. Check out the claims in some of Felt’s ads saying their 2% more efficient frame shape adds up to around a minute for every hour…..yeah right…if the bike has gone for a ride on its own. In a recent chat about aerodynamics with Canadian super-fast man Zach Bell, he remarked at how, at one of his trips to the wind tunnel, the technican commented on why cyclists fuss so much with the bike when its the body on the bike creating nearly all the resistance. The other big no no about the real crazy aero shapes we see, is that they can actually lose you time in a cross wind. As the wind crosses over the wider sections of the frame (and wheels) it creates a negative (or low) pressure area on the downwind side of the tube (rim) requiring more power to maintain the speed. For very fast riders (TdF types and real fast triathloners) it has less negative effect as the faster one goes, the wind resistance swings further ahead again because the wind angle now changes forward. Confusing yes, its all about physics and apparent wind angles. Its why an ice boat can sail 100mph in a 40mph wind. Check out the HED website, they have something of a fairly intelligent explanation about apparent wind and yaw angles. Anyway…back to the other important stuff….
Ironically the two most important characteristics a frame can and should have are seldom mentioned those ads.
As those who follow what I’m about know, frame fit should always be the number one thing on your new bike selection list, as you’ll never get max performance out of yourself without sitting on the bike right. The other thing…and its an actual physical property of the frame, is the stiffness. I’m NOT speaking of the stiffness relating to how harsh it feels over bumps, but rather its lateral stiffness (side to side). This is the frame’s ability to transfer your power to the back wheel thus driving the bike forward.
The truth is that we, as human’s, are the most feeble power producing thing ever created for that purpose. Look at the immense power of a monkey or a chimp. They can jump from a tree, fall twenty feet and grab a branch on the way by with one arm…..mine would have been ripped off. A dolphin can swim at over 40 MPH, a common house cat can jump several times its height. Of all God’s creatures, mankind was supposedly given the best brain to help overcome this relatively hopeless power supply. Man has created many forms of motorized power all of which, pound for pound, wipe out man in the power department. I once had a small model airplane motor that weighed about a pound. It produced 2.5 horsepower and would propel the model at an actual 240mph!
So what does this mean for you as a cyclist? It means if you want the best use made of what you’ve got, you have to take care of ALL the details, and the biggest on the bike is seeing that your power is used as efficiently as possible. This is true in all forms of cycling but massively important in climbing any hill.
Every time you apply pressure to the pedals, your energy is dispersed into several areas. Obviously the chain is what is stopping the pedals from spinning freely so that is the main source of resistance. This also the most important resistance because the chain is what drives the back wheel around thus propelling you forward. The more of your power that can go into pulling on that chain, the faster you go. The problem with the bicycle’s design is, that because the cranks and pedals are moved away from the centreline of the bike on either side of the bottom bracket, any pressure on them (applied by you) tends to want to move the frame sideways. This frame deflection means a certain amount of power loss. It is magnified when you are out of the saddle accelerating or sprinting as your body is now moving more side to side increasing lateral loading further. It increased even further when climbing out of the saddle as we tend to rock the bike from side to side which really plays havoc on the whole bottom bracket area, torqueing it about madly.
The ideal frame is one that has a high lateral rigidity to minimize power loss but also is of a type of frame material that when flexed, has a very quick ’snap back’ character. This is when once the effort of your pedal stroke subsides as the cranks revolve to the next position, the snaps back to centre shooting the last bit of energy into the chain and hence the wheel….not unlike a pole vaulter’s pole as he reaches the top of his vault. The pole actually snaps out straight increasing his last bit of gained elevation.
When Reynolds developed their famous 531 tube sets in the ’20’s, they set a new standard for liveliness in frames. Not only were they lighter, but they also gave the bicycle frames much more of the resilience and spring that aids in propelling the rider forward.
Over the last eight decades much has been tried in frame materials to further these desirable traits. The Sixties saw early forays into titanium and aluminum framesets. The aluminum alloy used was generally of a lower quality in comparison with what is available today and were very dead feeling and tended to absorb energy rather than give it back. In fact until the 7500 series type scandium frames came along, the tubes had to be somewhat oversized to make the bike a decent performer…in my opinion of decent performer anyway. The early (first 20 years) Cannondales were stiff but hideously uncomfortable on rough stuff. The titanium, while lighter than the steel was much too springy and was only useful for very light riders, Luis Ocana used a titanium frame in the ‘72 Tour but he was a very light rider. Titanium to this day remains a good material for general use and touring frames because it is very springy, durable and comfortable but for heavier and stronger riders is will sap your energy in comparison to some other materials.
The best three materials for a lively, responsive frame are: a high grade thermo-chrome steel, a real, scandium infused 7500 series aluminum and carbon fibre. All have advantages and all have drawbacks. Steel’s advantages are immense durability, a lively, snappy feel and the ability to create any frame geometry (custom shape for the rider) relatively easily but of course by today standards, it will always be a bit heavier. A good Dedacciai or Easton Scandium alloy frame (both use the old Soviet military technology) is as light or even lighter than need be, has nearly the same snap as a steel frame. Also like steel, custom geometry is easy. Because the tubes are so thin walled, one must be a little more careful not to dent them as it will happen easier than on a steel frame. The ubiquitous full carbon frame can of course be very light too. A good, solid carbon frame also has very good snappiness…equal to anything. Carbon can also dampen road shock quite well. Any shape can be created but because 99% of them come out of a mold, the cost of mold production make custom shaping prohibitively expensive. Its other drawback is its propensity to crack and/or explode when overstressed, catastrophic failure being the technical term. Repair is very difficult at best. Care must also be taken not to get them too hot (ie a hot car trunk in the Arizona sun) as it can effect the bonding epoxies adversely.
While we all love to chase the quest for the super light bike, but if the frame is sapping your energy by excessive flexing under load, your results at the scales may be good for nothing more than post ride, bar talk.
I’ll continue this vein of thinking in another post that discusses useful weight reduction.