How the Harley-Davidson suspension works: improvements

The suspension is mission to absorb the imperfections of the land allowing the tires to be most of the time in contact with the soil, and at the same time maintain the stability of the chassis in the order of march while optimally transferred the traction and direction.

Components
The first "component" of damping when we go through a pump is the tire, which is deformed to absorb irregularity; Then the force passes through the tire to the fork bars, which are compressed thanks to the docks installed inside, absorbing energy. Once the bump is exceeded, the docks extend again, trying to make the tire maximum contact with the terrain.
With this system without more the dock would begin to oscillate, release and absorb energy continuously, complicating driving. It is therefore that the suspensions (docks) are added some damping system, which by friction diverts part of the accumulated energy softening the route and the compression and extension speeds.

In conventional forks for motorcycle this element is the oil, which is made by a series of valves (holes) both when climbing and lowering the fork bar, allowing to control and soften the movements.

System improvements
Although there are many ways to improve the front suspension of a motorcycle, perhaps the simplest and most economical is to increase the quality of oil and docks of the forks.
The oil degrades over time and absorbs waste and humidity, losing qualities. Depending on our driving style we can change it by Another slightly densest (not too much) and to have better incorporated additives.
The docks "fatigue" with prolonged use becoming less firm. If we replace them with high performance and progressive operation components (soft and "fast" at the beginning and firm and harder with higher compressions) we will enjoy more safety and driving quality.

Practical case
To illustrate the aforementioned we will take advantage of the change of forks oil in a Sportster model (every 32,000 km) must be done and we will install a kit of the Dutch manufacturers Hyperpro, known for their high -tech damping systems for competition.

The kit consists of firmer progressive docks, with the specific length and hardness for each year and model of Harley-Davidson, and oil with greater density and high performance.
We will begin as always following the procedure indicated in the service manual to drain the oil, loosening the lower screws of the fork bottles (these screws have to be replaced by new ones).

When we have already emptied the oil, the front wheel has to be raised with a easel or cat, releasing the compression of the forks. Next we will extract the upper fork caps using a Specific tool.

With the caps outside we can already get the spacers

and the original dock.

If we compare both docks we can see the variation in thickness and "density" between the originals and those of high performance.

After installing the drain plugs again we will proceed to drop the new docks inside the bars (the most out -of -down spinning part) followed by the original spacers. We will fill the forks with the oil supplied in the recommended amount (in this case 342 ml in each bar) and install the upper plugs again, pressing them from 30 to 70 nm.

Final tests
We can already lower the elevator motorcycle to verify that everything is OK.

We will apply the front brake while we sink the forks several times, causing the oil to lubricate the entire system.
We will perform a road test verifying the suspension and braking improvements, listening that there are no strange noises. If after returning we see that there is no excess oil in the upper fork bars, it means that there are no leaks in the fork seals, so we can give the job for finishing.

Frank Burguera

#mecanicaharley