from Rookie’s keyboard
Hello, friends
What’s up? I’ve had a pretty busy week. Hence the fewer posts this week. But today, I am coming back with vengeance.
I decided to make a piece that showcases the peculiarities of alloy (aluminum) and steel forks.
Let’s go, fellas.
Endurance Limit and Compliance – Key Features
Steel is an elastic material that can flex endlessly (within certain parameters) without losing its integrity thanks to its high endurance limit.
The endurance limit indicates how much force a material can withstand before structural damage. The other terms for endurance limit are fatigue limit and fatigue strength.
If the applied stress is below the endurance limit, the material can withstand that level of stress forever.
If the applied stress is above the endurance limit, the material will deform eventually.
It’s ultra-important to know that aluminum does not have a real endurance limit. This means that even small stress cycles fatigue aluminum parts.
For that reason,the endurance limit of aluminum is presented as a number of cycles that the material can endure before structural issues.
If the aluminum component is made well, the number of cycles is unbelievably high. Basic aluminum is expected to fail after 500 million cycles.
To keep the endurance limit high, aluminum components are reinforced at the expense of flexibility.
For that reason, aluminum forks are strong but also stiff. They transmit the road irregularities to the rider and stress the joints.
Meanwhile, the high endurance limit of steel allows manufacturers to produce springy forks that flex vertically and reduce the vibrations reaching the rider.
The final product is a compliant fork that gives a lively feel to the bike
The brake system influences compliance too. Rim brakes do not generate as much torque as disc brakes and allow the production of steel forks with thinner and thus more compliant blades.
But disc brakes require forks with stiffer legs. And subsequently, steel forks designed for disc brakes offer a harsher ride.
Lifespan
Theoretically, steel should outlive aluminum when maintained properly thanks to its high fatigue limit. Hence why you see steel bikes from the ’60s, ’70s, and ’80s still functioning as well as new.
In practice, however, a quality aluminum fork will last decades and can outlive the bike that it’s installed on.
Toughness
Steel is tougher than aluminum. Period. A steel fork is more likely to bend than to crack and disintegrate completely.
Aluminum, on the other hand, is fairly brittle and gives fewer warnings before failure.
When it comes to external stress (hits, scratches…etc.) steel wins again because it’s denser.
If you’re looking for the toughest rigid fork, steel will always be the material of choice.
Weight
Steel forks are heavier.
The table below compares the weight of steel and aluminum forks.
| STEEL | WEIGHT | ALUMINUM | WEIGHT |
| Surly Cross-Check Cyclocross Fork | 1000g | XLC BF-A02 – 28″ Rigid Fork – 1 1/8″ | 943g |
| BLB Classic Fork Chrome | 720g | Kinesis CrossWind 470 Disc 28″ | 1016g |
| SPA CYCLES Steel Road Fork | 1005g | BUCKLOS Rigid Fork | 780g |
| TSUNAMI Steel Lugged Fork 700c | 730g | Kinesis CrossWind 455 Disc 28″ | 880g |
| SOMA Lugged 49 Road Fork | 980g | Kinesis Airbow Race Fork | 661g |
| Surly Steamroller Fork | 1000g | MOSSO FK-M6 | 800g |
| Salsa CroMoto Grande 29″ | 1108g | ROSE 28″/700C | 600g |
| Surly Disc Trucker 28″/700C | 1200g | ACCENT 1.5 to 1-1/8 Taper | 764g |
| Average: | 967.8g | Average: | 805.5g |
The aluminum forks in the table are 162.3g lighter on average. The difference is undeniable, but it isn’t substantial and matters only in two scenarios:
- Competing on the highest level
- Trying to build the lightest possible bicycle
It’s also worth mentioning that the extra weight is perceivable mainly when accelerating. Once the bike is up to speed, it becomes increasingly harder to notice additional grams.
Appearance
Steel forks and frames have thinner tubes because steel is denser than aluminum and thus can offer just as much strength in a thinner package.
Steel forks could look out of place when installed on bikes with oversized aluminum frames.
The same applies to aluminum forks. Installing a modern aluminum fork on a retro road bike wouldn’t be the most aesthetic choice.
Aluminum forks can be made in a variety of shapes. Many models have teardrop blades to increase the aerodynamic properties of the bicycle. However, steel forks have round tubing most of the time.
Reparability
Steel forks are easier to customize and repair because the material doesn’t require an exceptionally advanced welding setup.
Of course, it’s still difficult to weld thin tubing, but you’re a lot more likely to find a welder willing to work with steel than aluminum, especially when traveling.
Moreover, it’s possible to customize the fork by brazing eyelets to it.
This is the reason why most independent frame builders with a limited budget always choose steel as their main material. Aluminum and carbon are simply too expensive to work with.
A cracked aluminum fork can be welded too, but the welding setup is pricy and many recreational welders do not have the necessary experience to work with aluminum.
Also, aluminum requires heat treatment after welding to regain its full strength. Normally, the process is done with a specialized oven.
When you add the labor cost of the repair, the bill jumps quite high. One may be able to buy two new aluminum forks for the same amount of money. For that reason, most aluminum frames and forks are recycled rather than repaired after a crack.
Corrosion Resistance
Steel forks and frames are prone to rust because bike tubing is not made of stainless steel. However, if the paint of the component is in good shape and the inner side of the tubes is treated with a rust protector, steel can last for a very long time.
In different, aluminum is much more corrosion resistance. It still reacts to the elements but requires less attention to remain in good shape.
Availability
Aluminum forks are less desirable than steel and carbon models. Steel forks are heavier than aluminum ones, but they’re also more compliant and gain points for that. Meanwhile, carbon forks are not only more compliant than aluminum rivals but also lighter.
Consequently, there’s less demand for aluminum forks resulting in the production of fewer models.
Wide Tires > Fork Flex
No matter how compliant a fork is, it will never offer as much absorption and comfort as a set of wide tires operating at low air pressure.
For that reason, the tire clearance of the fork is crucial to comfort too. A super-stiff aluminum fork running MTB-wide tires will provide more cushioning than a steel fork with clearance for a 25mm tire.
Until next time,
– Rookie
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