KBO: Kerb Blow Off

New for 2013 – Intense development has been under way on what we call KBO (kerb blow-off), a novel technology to provide flatter high speed compression blow-off. This is a major improvement over every commonly available shock and many higher priced ones as well. We can tune for track, bumpy backroad, even true rally applications with more confidence now. It’s a development that can affect many of our FCM Elite customers, allowing us to improve compliance on rough surfaces whether for racing or street use. Some of you already some similar technology from us as we took a separate path in designing this for our external reservoirs. Now, we can make a single or non-adjustable (non-reservoired) FCM Bilstein behave in this manner.

Attached is a a simplified shock dyno graph showing the compression forces of three shocks. Note that these curves are not representative of any particular application but serve to illustrate various types of compression roll-off / blow-off behavior (how the force reduces above a certain shock velocity). The vertical axis is force in pounds, horizontal axis is shock velocity (inches per second). Each of the three shocks have (somewhat coincidentally!) very similar increase in force from 0 in/sec (not moving) to 1 in / sec (small motions or driver turning the wheel, braking, accelerating, etc.). From there, the behaviors differ.


The black curve is from about 2010, for a fairly heavy vehicle. The shock exhibits a typical digressive blow-off where the compression force decreases strongly after about 5 in/sec but still continues building up. This car does have very good composure in most situations but would handle sharper / higher velocity impacts with more ease if the high speed compression force was a bit lower.

The blue is a test from early 2013 when we finally devoted time to this KBO option instead of dreaming about it. We did see a decrease in compression force at high shock velocity compared to the standard digressive piston but still not as impressive as we envisioned.

We hit it big! The red curve indicates a slightly firmer ramp up to 1 in/sec, then some decrease in force from 2-3, further decrease from 3-5 and very strong (nearly flat for all intents and purposes) blow-off happening above 5 in/sec.

Why is this important? The road can induce quite high shock velocities indeed, which actually requires managing both bump and rebound damping (not just bump as many tuners would like to have you believe). There is a greater cost to too much compression than too much rebound but excessive amounts of each creates problems. Given that we’ll be able to keep high-shock-velocity compression forces low when the application requires it, we can truly maximize grip by keeping the tire tracking a rough surface for a wider range of vehicle speeds. We feel we’ve just scratched the surface in finding nuances to this technique!

We are sure all of you know our motto is ‘if we can find or fit a Bilstein, we can craft an FCM Elite setup for you!’ So ANY vehicle we’re working on can conceivably benefit, which can be of particular benefit to strut cars Combining KBO with intelligently chosen rebound forces, spring rates, bump stops, sway bars, etc. we expect to see improved grip and driver confidence across a wide range of road speeds and surface conditions.

Look for more announcements in the coming weeks (via Facebook, newsletter and our Suspension Truth forum) as we do more dyno and on-vehicle testing. I wanted to share this exciting development with a small group of our core customers. You can show it to friends if you wish – we’d like to get the word out of how innovation continues to drive us!

Visit the Suspension Truth forum thread to see further updates and discussions regarding this recent development.

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