A bicycle fork is an often overlooked item, but it really makes up a bike. Believe it or not, even a rigid fork makes a bike softer, “compliant”, or has a significant effect on how it steers. It changes your bike’s overall character more than the frame itself.
I’m surprised to see most people talking a lot about frames, which generally doesn’t matter, but either get the cheapest fork they can get, or don’t think about it much.
Why forks matter – know your fork
Forks also can be dangerous. I’d worry less about my chipped carbon frame then the carbon fork. If the fork cracks, game over. With a cracked frame, you still have a small chance. And unlike forks, frames do not crack (generally at least) without prior signals.
It’s harder to figure out fork problems because it’s not exposed as the frame. The most critical part, the steerer, is hidden from our eyes and stays within the head tube (hopefully).
Most people buy steel frames and carbon forks to make them lighter, which I don’ t understand, except the cosmetic part. Steel frames look cool, but if you’re after its looks, why not build a frame out of carbon fiber tubes, like old Giant Cadex bikes? And that carbon fiber fork looks awful. Not to mention they’ re ruining a perfectly dependable bike. I’d rather buy a carbon fiber frame and put a springy, old school steel fork to it, and not just it comes cheaper, it’s also lighter and more dependable, too.
Suspension forks, especially air shocks doubles your problems, but they do not cause problems by themselves. I’ve seen too many people discussing about suspension forks causing shakes. Well, I generally don’t like suspension forks, they cause lots of headaches, but fork shake is not one of them.
What causes fork shakes?
Reasons of fork shakes are not that much, and the most common one is headset related ones. This is also the one which can cause the most furious shakes.
Other common reasons for a fork shake are hub and axle problems, rims, and brakes.
Headset problems causing fork shakes
Headsets are simple, and you don’t have to scratch your head too much about it. If you have excess noise on front end when riding on rough surface, and violent shaking when braking, it’s generally a headset issue.
Headset issues stems from either a loose headset, or excessively worn or damaged bearings. Latter is more common. I generally don’t get premium headsets. Why? Because I’m not touring the world, and I take apart bikes every year for full service. I also change headset bearings without waiting them to fail. They’re cheap.
Don’t use premium bearings with a cheap headset, because most probably sealing is not good enough, and your 40$ bearings will soak in water. Unless you have bearings made out of ruby, every bearing will die very soon when water enters into races.
The most common reason for headset bearing failure is water, and bad roads with skinny tires, which describes my routine.
Headset problems are very easy to pinpoint: apply front brakes, and rock your bike front and back. They’ll make an ugly sound, and in extremes cases, it feels loose. Take the fork and stem out, remove headset bearings, and inspect them. If they’ re ok, you need to tighten that preload bolt on your stem a bit more.
Hub and axle related problems that causes fork shakes
Worn hub cup and cones or bearings can cause fork shakes, especially under braking. Play in the hubs will manifest itself as fork shake.
It’s not hard to pinpoint such issues, too: lift the front of your bike, and wiggle the front wheel. Any play? If there is any play, you have to take apart the hub, and see what’s going on inside. But before doing that, remove your axles first…
Axles, especially QR axles, can bend easily, depending on make / model. Lay it on a glass, or some surface that is very even, and roll it. If it’s bent, you can see space between the surface and the axle. If that’s the case, change the axle – do not try to straighten it.
Sometimes, just removing the front wheel and installing back can alleviate or fix the problem.If that’s the case for you, that means wheel is not centered between fork blades. This is quite common in QR axles, but unlikely for thru-axles.
Brake related shakes
Brake related fork shakes happen, because braking is not consistent along the surface. This is quite common in rim brakes, if rims are not straight – or worn excessively.
For disc brakes, generally the contaminated rotors or the brake pads is the culprit. Contaminated pads or rotors manifests itself with noisy brakes.
For rim brakes, diagnosing the problem is much harder, though.
What are the risks of fork shake ?
Fork shake is annoying at any speed. Not it makes you feel unsafe, but also causes excess vibration which causes numbness.
But for speeds above 25-30 km/h, the shake can amplify in huge amounts, which can cause panic in rider, or worse, makes bike uncontrollable. I had such instance on a bike with horribly worn headset bearings, and bike became almost unmanageable in a long decent, above speeds 40 km/h. Bad thing is, sudden or strong braking generally amplifies the problem even more. With careful braking, I saved the day, and go back home to replace the headset bearing.
If you have a suspension fork, this shake can also lead to premature fork bushing, stanchion and seal failure.
Headset bearings are cheap, brakes are easy to fix, and hub / axle problems are too serious to be postponed to fix later.