First Look: HPSD (Honda Progressive Steering Damper)

We've been sneaking peeks of the Honda Progressive Steering Damper for the last few years, as it hid behind the front number plates of their factory race machines. It was always sort of a fun cat-and-mouse game, trying to catch a sneak peek photo of it in the staging area, or during routine maintenance. Earlier this year, it was getting much easier to spot, which sort of gave you the feeling that they weren't as interested in hiding it, and that maybe it was destined for production. You can read Honda's description below on how they developed it, what it does, and how it's been adapted it for production use.

A revolutionary application of steering damper technology creates a new level of agile handling

If you think you already know a lot about steering dampers, get ready to think again. Why is that? With a stroke of fresh engineering insight, the hard-working minds at Honda have created the Honda Progressive Steering Damper (HPSD), a new application of steering damper technology designed specifically to augment more aggressive turning characteristics rather than assist straight-line handling only, as has been the case with steering dampers in past applications.

Here are cutaway and complete versions of the HPSD (Honda Progressive Steering Damper).

By integrating HPSD the 2008 CRF450R and CRF250R both demonstrate a higher level of front-end traction with significantly enhanced steering feel, specifically a more “planted” feel in turns for better front-wheel control, especially under dry, hard-packed track conditions. Net result: greater cornering speed, a higher level of front end confidence and reduced rider fatigue thanks to this newfound ease of turning. Additionally, HPSD improves handling in whoops and fast sections of the track, all of which combine to create faster lap times over the entire course of a race.

The earliest versions of HPSD first saw action aboard the American Honda Racing Team's CRF450R and CRF250R race bikes during the 2004 AMA Supercross series. Initial response from team riders was overwhelmingly successful. Additional testing confirmed just how versatile the system could be under a wide range of tracks and riding conditions. And so the stage was set for the prototype HPSD to see action at the highest levels of Supercross and Motocross racing for the entire 2004 season.

Thus equipped, the CRF450R found plenty of success in Supercross and went on to sweep every moto win during the 2004 outdoor Motocross season, a high-water mark in the history of the sport. Ongoing development work saw HPSD installed on Honda works motocrossers through the 2007 season. This intensive four-year period of testing and development of various damper settings under top-level racing conditions led to a finalized design and integration on the 2008 model year CRF450R and CRF250R.

HPSD has given Honda's engineers the ability to create more aggressive chassis geometry for increased agility without compromising machine stability. Accordingly, the CRF450R and CRF250R both feature revised steering geometry in 2008, thanks to a change in fork offset via new triple clamps. For example, the change from 24mm of offset to 22mm alters the CRF450R's steering trail from 109.4mm on the 2007 model to 111.4mm for 2008, which reflects the front end being tucked in 2mm closer to the engine. This change also shortens the wheelbase 2mm. The result is even quicker turning characteristics and improved front-end traction, thus allowing the rider to hold the line more easily in tight corners. Moreover, while in mid-turn—and virtually everywhere else on the track—HPSD damps out a lot of the jarring that normally tries to deflect the front wheel. Subsequently the rider doesn't need to work as hard to hold a line. In the past, pulling 2mm from steering off-set and shortening wheelbase might have sacrificed handling, but with HPSD, riders get the best of both worlds: quicker steering and better handling, especially at higher speeds.

The addition of the HPSD has allowed the Honda engineers to reduce the fork offset, and increase the trail, for quicker turning, but at the same time, they claim that it provides a more planted feel in corners, and added stability at high speeds.

HPSD consists of a very clever and very compact damper mounted behind the front number plate. Weighing a mere 6.5 ounces, it attaches to the lower triple clamp and the steering head. The damper is rebuildable and offers 15 clicks of adjustability. It tucks behind a newly styled number plate that protects it from flying debris.

To complement the addition of HPSD, the steering head was completely redesigned and re-tuned for correct flex/stiffness properties, and an HPSD mounting lug was incorporated. Likewise, the triple clamps are newly designed to yield the correct degree of stiffness, given the new forces imparted by the steering damper system. Given the interrelated nature of the forces acting on this latest iteration of Honda's highly sophisticated fourth-generation aluminum frame, every force input was carefully calculated and matched so the chassis, suspension (more on that forthcoming) and HPSD all worked in concert as one system. In short, HPSD is not merely a bolt-on damper.

At the risk of making your eyes go slightly crazy, here's an animation of the HPSD unit in action as it works from center to full lock and back.

As the name Progressive Steering Damper infers, the damping action of the unit progresses over the range of travel. From straight-ahead mode to approximately five degrees of movement in either direction (which are very small changes from off-center), HPSD creates minimal damping force, resulting in neutral steering during straight-line running. As handlebar movement increases and the damper rod extends farther, damping force increases smoothly to produce very natural steering characteristics and feel.

To create this natural steering feel, the damping rates differ in the two directions of travel; under extension when the handlebar turns away from center, the damping forces are significantly greater. Under compression as the handlebar returns to the straight-ahead position, HPSD offers less resistance. In addition, at about the one-third point on the extension throw, a position-sensitive damping circuit opens and progression of the damping action lessens. 

This additional passageway, which in cutaway view looks like a small channel machined into the damper body, moderates the damping force under more extreme handlebar angles. In addition, the damping mechanism is speed sensitive, relative to the speed of handlebar movement and wheel deflection; as sharp impacts cause the front end to deflect very rapidly, HPSD provides proportionally greater damping force. Yet when the rider places steering input through the handlebar, the damping action feels negligible and entirely natural.

The location of the HPSD unit also creates what is in effect a rising-rate mechanical stroke for the damper rod travel without the need for a complicated linkage. As the handlebar arcs toward the steering stops, the increased degree of turning produces increasingly larger amounts of travel from the shock on the extension stroke. Hence, a rising rate relationship in shock stroke versus handlebar movement. Net result: a very natural steering feel along with the bonus of added damping assistance as the handlebar moves farther from center.

In addition, Team Honda riders have discovered that use of HPSD allowed front suspension settings that were distinctly stiffer than had been the case without the steering damper. At work once again was the concept of the entire chassis being a highly tuned system, one that must be designed and adjusted as a whole. The addition of HPSD offered riders another opportunity to fine-tune their machines in new ways to match various riding conditions. Subsequent testing for the 2008 CRFs confirmed this for production bikes as well, and, as a result, the new CRF450R and CRF250R both feature slightly stiffer springs and revised compression and rebound damping rates in the fork.

With HPSD, the 2008 CRF450R and CRF250R feel just as stable through fast whoops as the 2007 model did with its more conservative fork offset, yet steering for both bikes is markedly quicker and easier on the rider. When the front end impacts an obstacle off-center and the handlebar begins to kick out, HPSD automatically lends a steadying degree of damping. As a result, the 2008 model feels distinctly easy to ride; not only are these machines confidence-inspiring with precise steering action, but they are also markedly stable, allowing the rider to more easily steer in and out of ruts and take other lines at will.

In short, the Honda Progressive Steering Damper reflects once again the benefits of innovative engineering. By fundamentally moderating the manner in which outside forces affect a bike's steering, HPSD now extends Honda's ability to elevate the sport to the next level.