The Importance Of Weight And Stiffness In Racing Bikes

Last Updated on March 29, 2021

The Importance Of Weight And Stiffness In Racing Bikes

Weight and stiffness in a racing bike are crucial to consider as an all-around racer’s performance is power output to weight ratio.

So why are weight and stiffness so important?

This has been an ongoing debate in the cycling industry for years now; we are still coming to grips with the balance of stiffness and weight to get the most out of our race bike.

Let’s break down why weight and stiffness are so important in racing bikes.

Why do we want a stiff frame?

You may be looking for ways to make your bike frame stiffer, but why do we want a stiff frame on our road bikes?

Well, to put it simply, a bike has two wheels, and a rider would want to keep them in the relatively same place. If the front and rear wheel spin independently, the bike steering stiffness would be all over the place, which would be quite dangerous on descents, and rather than the brakes giving you control, it would cause you to go out of control.

In any road bike, you should be looking for stiffness that is enough to maintain the bike’s integrity without being too stiff. But here are some other top reasons.

Power transfer:

Power transfer prevents you from wasting all your energy bending the frame back and forth while you stand on your pedals.

Springs in a bicycle frame are energy stores, so when you stand on your pedals, some of the energy goes into bending the frame or coming back to you, so you get power in every stroke. You will feel like your riding is more responsive and quicker.

The frame itself will retain integrity much better with a stiffer frame; the frame stiffness is so important as it makes your bike much more stable, especially at the time of maximum stress, such as racing towards that finish line.

Keeping the frame straight:

Stiffness is a brilliant way to keep bicycle frames straight. Fatigue is often found in a bicycle frame that isn’t stiff enough; if the frame stiffness isn’t stiff enough, it will eventually break if you flex the metal back and forth.

It is often a factor that manufacturers don’t talk about because all metal starts to show fatigue over time. Still, if a bike isn’t stiff enough, then the metal will keep springing back and ‘remember’ each bend until it eventually breaks.

Aluminum and other metals have a lifespan, such as in flying; after a certain number of hours, they are discarded. They can break very easily without showing any signs of fatigue.

Steel and titanium, however, will never fail from fatigue; if they move back and forth a little bit, they won’t fatigue, whereas aluminum will remember every bend no matter how small.

If the titanium or steel frame is designed to be never flexed beyond its fatigue, then it will last forever. In contrast, an aluminum frame must be flexed as little as possible to have the same life expectancy you’d expect out of a bicycle.

If you’re buying a race bike, I would recommend opting for the higher quality metal for more resistance to tube fatigue.

If you look at the bike market, especially in race bikes, you will notice that there’s a big change in replacing high-quality steel for cheaper aluminum frames, which are stiffer but don’t last as long.

Steel frames have a very similar stiffness to aluminum, so you’re not really getting the better quality out of the two either; they have a large diameter and tend to follow the same goals.

Important in racing:

The amount of cable pull between the gears has become smaller and more precise in bikes. If a rider stands or pushes hard on the pedals, then the bottom bracket is the most stressed part of the bike and will pull on the cables.

This means that, especially in racing, the bike must be very stiff around the bottom brackets; it has nothing to do with energy transfer but rather the gear changes. The evolution of more gears has made the stiffness of the bike more and more important.

How do you make a bike frame stiffer?

There are ways you can make your bike stiffer; you can do this by making the tube stiffer. You can either increase the tube’s wall thickness or increase the diameter of the tube shaping, so your tubes look ‘fatter.’

You can increase the wall thickness by adding more material and more weight, and add more frame stiffness. You can increase the diameter using the same amount of materials and weight but give it resistance by making the tube walls bigger but thinner.

These thin walls are straightforward to dent, and they may lead to permanent bending. Also, by making the tube oval in the cross-section, you can make the tube stiffer in one direction and less stiff in another.

Engineering stiffness:

So how do you stiffen the frame in the right places? This all lies in the diameter of the cross-section of the tubes and the length and material of the bike used in the construction. For example, carbon bicycles use layers of carbon fiber in their construction.

As a general rule of thumb, the greater the tube’s diameter, the more frame stiffness; this explains why people tend to go towards oversized down tubes, bottom bracket junctions, and chainstays.

Over the years, bike designers have made major advances in carbon fiber have allowed frame manufacturers to reduce tube walls’ thickness, giving them the freedom to create gargantuan-looking tubes without any excess weight.

Large down tubes and bottom brackets are used to channel every watt of rider power on the road, and then the same stiffness design has been implemented in the top tube and head tube for steering stiffness.

When you go around a corner, gravity (which pulls you downwards), kinetic energy (keeps you moving forward), and centripetal forces (pushing you outwards) converge.

These forces push the wheels and head tube out of alignment to imprecise steering, which is why steering stiffness is crucial.

If you’re heading towards a corner that you’ve ridden a thousand times, then you will more confident in carrying a lot of speed. But one day, there may be a pothole where your usual line can throw you off. But this is when steering stiffness comes into play. If your bike is too stiff, the front end becomes difficult to lean.

For example, Specialized bikes developed a new bike that would use a 56cm frame size, a benchmark for new targets such as stiffness, and only once these targets were hit would the frame be scaled with smaller tubes for smaller frames and larger tubes for larger frames.

Smaller bikes tend to be proportionally stiffer than larger bikes, which is the opposite of what a rider would need. With a longer seat post and higher center of gravity, a taller rider would require a bike that will do a lot more work. They need a stiffer frame to prevent the rider from faller and regain traction as the rider turns.

But in road racing, bicycle manufacturers can’t just make the whole bike as stiff as possible; this is because other factors have to come into play, such as comfort or compliance, which is the ability of the frame to contend with imperfections of the road surface by absorbing vibrations and bumps.

You want as little vertical stiffness as possible to ensure that you get the most comfort and compliance out of your bike. Comfort can improve ride quality, but too much comfort will compromise stiffness. This can be quite tricky when you enlarge the tube to improve stiffness; it becomes bigger vertically.

This means that to get a stiffer frame, you will have to compromise comfort; the most comfortable bikes are almost unrideable as they’re too flexible in all directions. The same goes for the stiffest bike as it is too stiff and won’t bend easily; it also makes it slower.

Tires make some difference in terms of the frame stiffness, but some engineers have introduced a degree of flex into the frame, especially in the saddle tube or in seatstays which helps dissipate road and tarmac road shocks while you ride.

Vertical compliance can be divorced in the bottom bracket area and head tube stiffness allowing the start tube to flex in a way that is almost independent of the frame without compromising stiffness.

Frames of the future:

As years go on, our bikes’ design and stiffness have become stiffer, lighter, more comfortable, and show no signs of abating, as engineers are on a continual quest to explore new materials and technology.

Dassi, for example, is investigating the possibilities of graphene in a frame, which offers amazing potential if engineers can find a way to control its capabilities.

Graphene exhibits properties which exceed traditional carbon or aluminum frames and have so many benefits. Their frame can weigh as little as 300g as graphene is much lighter yet stronger than most carbon and any other frame.

It can replace areas like the bottom bracket with a material that is 100 times lighter and 1/1000th the thickness. Cycling, however, is very individual, and buying a bike is very individual to the person purchasing it.

It is not like buying a racing car; a race bike ranges in lots of different benefits and differs from each other. Major races haven’t been won using one or two rob brands of race bikes. There are won with different bikes.

The performance comes out of the rider, not objectively the bike; there’s no set stiffness. It’s just the stiffness that is right for you personally.

That being said, here are the top 10 stiffest bikes- stiffness to weight:

Cervelo Rca Stiffness to Weight: 142Nm/°/kg

Specialized Tarmac SL4 Stiffness to Weight: 141.2Nm/°/kg3.

Cannondale SuperSix Evo Ultimate Stiffness to Weight: 139.2Nm/°/kg4.

Canyon Ultimate CF SLX Stiffness to Weight: 131.5Nm/°/kg5.

Trek Emonda Stiffness to weight: 131.3Nm/°/kg6.

Focus Izalco Max Stiffness to Weight: 127.1Nm/°/kg7.

Felt F1 Stiffness to Weight: 125.3Nm/°/kg8.

AX Lightness Vial Evo: 125.1Nm/°/kg9.

Storck Aernario: 123.9Nm/°/kg10.

Rose X-Lite Team 8000: 123.7Nm/°/kg

Summary:

Stiffness in a race bike is actually more important than you may think, but it is not just down to one bike. Stiffness all depends on the individual comfort of the rider, different riders will require different stiffness.

As a general rule of thumb, you should look for a good balance between comfort and stiffness, this will allow you to ride with ease but allow you to turn efficiency into energy while you ride.

Stiffness is an important factor in racing bicycles but there isn’t a certain bike that is designed for racing, hundreds of bikes win races every year, so it is down to personal preference.

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