The CBR1000RR’s Balance Free Rear Cushion explained

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twinandsingle

So far as a defining mechanical unique selling points go, “balance free rear cushion” isn’t exactly the most evocative description. Not only does it evoke pillows rather than greasy parts, but it just lacks the pizzaz of terms like “EXUP,” “Deltabox,” and “SRAD.” That’s too bad, because the 2012 Honda CBR1000RR’s neat new trick is actually seriously neat. Here’s how it works.

First, here’s what Honda has to say for themselves:

“Unique Balance Free Rear Cushion: The main objectives for further developing the CBR1000RR’s suspension set-up were a smoother suspension action, improved rider feel and increased grip and traction. The rear suspension system uses the Unit Pro-Link configuration and introduces the first Balance Free Rear Cushion on a production motorcycle.”

“Developed in conjunction with world-leading suspension specialists Showa, instead of the conventional single-tube layout, the Balance Free Rear Cushion uses a double-tube design: the damper case and an internal cylinder. The damper piston features no valves. Instead the damping force is generated as displaced oil passes through a separate damping component.”

“In the conventional structure, the compression-side damping force was generated in two places with the main and sub damping valves, but elimination of the sub valve and concentration in one place allows pressure changes within the cushion to be controlled even more smoothly. And because there is no small amount of oil being used at high pressures, damping force response is improved and damping force can function smoothly during load input. Moreover, damping force can be generated smoothly when switching from tension to compression due to smooth pressure changes.”

“The Balance Free Rear Cushion delivers more consistent damping over the duration of a ride, plus improved shock absorption and therefore greater traction since contact is more consistently maintained between the rear tyre and the road or track surface. This technology has been proven in both the prestigious Suzuka 8 Hour race and the MFJ Superbike All Japan Road Race Championship. Indeed a CBR1000RR Fireblade fitted with a Showa Balance Free Rear Cushion won the 2010 Japanese Superbike championship, underlining the advantages of this advanced new suspension solution.”

“Easily accessed rear suspension adjusters: The combination of Honda’s Unit Pro-Link rear suspension and the Showa Balance Free Rear Cushion brings more than simply improved rear suspension performance and increased traction. To allow road and track riders to more easily adjust the rear compression and rebound damping performance, the adjusters have been placed prominently on the top of the shock body, offset to the left. As a result the rear suspension can be more quickly adapted to suit different riding conditions and requirements.”

If you got bored after the first paragraph, the main points are: It’s never been used on a production bike before, it’s good for a measurable improvement over the last generation shock and most importantly, it utilizes a twin-tube design with a solid piston. Damping takes place outside the shock body and since the piston is solid, the kind of cavitation that can occur in single tube shocks that have valves in the piston is a non-issue.

If you know anything about Öhlins TTX shocks, it’s likely that you would’ve had a feeling of deja vu reading that press release. Why? Because this shock technology is nearly identical. The only discernible difference is the adjuster style, accessibility and position, with the edge going to this Showa unit.

Single tube shocks consist of an oil filled tube and a piston on a shaft. The piston moves up and down through the oil and has valves built into it to affect damping. This is a very simplified explanation, but it works well enough. A twin tube shock works similarly, but instead of one tube filled with oil, there is a tube within a tube. The piston is solid and sealed to the walls of the inner tube and damping occurs elsewhere. This is good for two reasons: Cavitation, or bubbles that form in the oil as it passes through the piston (and then immediately implode, often causing damage) can be significantly reduced, and with damping external to the shock body, it is possible to completely separate compression and rebound and offer both a wider and finer range of adjustment.

Things become more complicated from here. Imagine you’re leaned over on a powerful liter-bike, going through a corner on a track. You’re just about at the apex, and you’ve already started to apply power. Things feel pretty good, you’re confident and ready to drive out of the corner, stand the bike up and fly down the straight. As you apply power, the majority of the bike’s weight is shifted to the rear wheel and the suspension compresses. Traction from the rear tire is more important than anything else right now and a slide or any change will likely upset the chassis and ruin your drive. At worst, you could experience a sudden and complete loss of traction, go sideways, and high-side. That’s certainly not the fastest way around the track.

YouTube Preview ImageLacking the outright power of liter bike rivals like the new ZX-10R, Honda instead plans to push handling as the new CBR’s parlor trick. This shock is going to help that. A lot.

Now imagine your powerful liter-bike is equipped with the factory single tube shock. You’ve now passed the apex and you’ve increased the throttle opening to 90%. The front wheel is still in contact with the ground, but just barely. Your rear tire runs over a bump in the track, the shock compresses further and everything is fine. Then, as the bump falls away, the suspension must reverse travel to ensure the tire maintains it’s contact with the ground. The spring supplies the force needed to push everything back toward the ground and the shock keeps things under control. Except that in this particular scenario, bubbles (really voids) have formed on the suction side of the piston when the shock is suddenly compressed to deal with the bump. Now that it is reversing travel, the bubbles immediately collapse and the full force of the spring is temporarily allowed to pass through the shock undamped. The tire is overloaded and traction very suddenly goes away. This is exactly what you don’t want your shock to do.

Cavitation can be countered with an external reservoir that contains oil, pressurized gas and a piston or bag to keep them separate, but as more pressure is added, ‘stiction‘ can start to become an issue.

The solid piston on a twin-tube shock is much less likely to encounter the problem of cavitation because it’s compression and rebound valves are located elsewhere. Oil never has to flow through the piston to the suction side; instead it flows through a valve, the outer tube and then finally, into the inner tube where the piston is. Twin-tube shocks can be run at stiction reducing lower pressures and because of this, they are generally smoother. The separation and remote location of compression and rebound damping also means that they can offer a wider and finer range of adjustment.

What does all this mean? Honda isn’t lying, this is the first application of Showa’s Balance Free Rear Cushion on a production motorcycle, but OEMs have been offering TTX shocks on production bikes like the Triumph Daytona 675R ($12,699), the Ducati 1098R ($39,995) and 1198SP ($21,995). These bikes use this shock because they’re some of the most serious sportsbikes ever built and only the best will do. That TTX is the best. While claims of first and all-new may not be 100 percent true, this is shock definitely a step forward and should help the updated CBR to stay competitive in a market where everyone else makes more power.

  • http://www.muthalovin.com the_doctor

    Ohhh, sciency.

  • Ola

    I bet it’s a poor translation from Japanese. “Rear cushion” is obviously “rear suspension”, anyone have a clue what “balance” might be? Reaction?

    Whatever the engineers wrote in proper technical Japanese, the international marketing team needs a bottle of Canadian Club and some overtime.

    But great to see more new stuff in suspension. Next move, put cartridge emulators in all cheap damper rod forks!

    • Artful

      #1 Fresh Cushion Balance is A+ American Joe!

      I’ve always been a handling over power guy, so this sounds like great news to me.

    • ursus

      Balance may refer to properly balancing the restoring force of the spring (no cavitation, etc…).
      I wonder if this design cools itself better due to the fluid motion next to the wall of the cylinder.

  • Aienan

    This brings up a good point for me, I was trying to figure out how to set the suspension on my F800GS (Which I *think* has damping and rebound adjustment), and I realized, I don’t have a damn clue how to set it up.

    Wes, can you please write another one of your wonderful “How-to” articles about suspension and setup? I’ve looked and have not yet found a good article on suspension, and specifically, how to set it up for my bike.

    • Wereweazle

      “For a dual sport bike it should be about 30% of the suspension travel. The suspension travel for the front is 230mm and the rear is 215mm therefore sag target is 69mm front and 65mm rear. Adjust the preload to provide the correct sag. Sadly the front has no adjustment to what you see is what you get. The damping screw should be set initially full CW then back out 1.5 turns. The final adjustment will be determined by test riding the bike. For the methodology just Google “motorcycle suspension sag” read a few before you start work and aim for 30% sag, you wont go far wrong.”

      ^ Copied from a post I found doing a quick search for “suspension adjustment” under the f800gs section of http://www.f800riders.org. Best of luck to you.

      • Aienan

        Thanks! I was not aware of this site. This will help

    • The other Joe

      +1

    • http://hellforleathermagazine.com Wes Siler

      Your best bet is to look up the relevant subforum on AdvRider and see what adjustments others like.

  • Chris

    The balance free rear cushion is almost definitely a poor translation. Many Japanese suspension manufacturers for cars offer “pillow ball” upgrades which are just metal spherical , but the translation = pillow ball.

    That rear shock looks awfully nice, and it’s awesome that it comes from the factory installed on the CBR.

  • Brian

    To answer post 1, balance free means that there is no pressure balance characteristic that needs to be maintained across the piston. In order to properly setup a mono-tube shock, the pressure in the damping area must be balanced with the pressure in the reservoir. This is generally done by adjusting the valivng or needle area on the DF adjuster located between the main tube and the reservoir.

    In the TTX or “balance free” system, this is not a concern because the damping is not generated at the piston but in 2 separate circuits outside of the chamber that houses the piston. The highest pressure area in a damper is at the piston, due to the rod displacement into the shock. Using 2 tubes to move the damping process away from the piston lowers the pressure at the damping circuits, and eliminates the need to “balance” internal shock pressures. Thus the bad translation to Balance Free Rear Shock.

    The graph shown in the article is somewhat accurate, but it seems more like a Force vs Velocity curve than a Force vs Displacement curve. The flat spot you see in the middle of the curve is some “lost motion” from the change in direction on compression to rebound. I can’t believe that any OEM would accept a rear shock that would have a force vs displacement curve like that, which is why I think it is labeled wrong. Pressure balance is critical in a conventional mono-tube shock to eliminate this flat spot. The graph is really trying to demonstrate that with the new shock design, the damping response is far better, with less DF lag in the system.

    • http://www.faster-faster.com fasterfaster

      Yes, Force vs. Velocity which is the standard for shock dyno charts (at least until you get into position sensitive damping, but that needs to be represented in 3 dimensions). Here’s an example of an actual shock dyno chart: http://www.jeffgoji.org/dyno1.JPG

    • Ola

      Thanks Brian! Your explanation is great flower in life of wheels!

    • Sean Smith

      That chart was supplied by Honda as part of the press kit and is of questionable accuracy and value.

  • rohorn

    We get Big Piston Fork front ends, because those Big Pistons are better, then we get Little Piston Shock rear ends, because those Little Pistons are better?

    I need to see the diagram of Honda’s PR/marketing(propaganda) people showing the increased flow of hot air and the graph of how that effects sales.

    • http://hellforleathermagazine.com Wes Siler

      Eh, it’s not so much a question of big or little or one or two, it’s simply two different components with a superior damping arrangement. Neither is earth shattering, but they do control oil flow better than an equivalent spec/quality alternative.

    • http://www.faster-faster.com fasterfaster

      If it helps, think of both as big VALVE dampers. The BPF achieves that by making more room for an on-piston valve, the twin-tube shock does that by moving the valves off of the piston.

      • doublet

        What about a big piston on top of a rod with holes in it for the oil to meter through? :)

  • Scott-jay

    Simple & mechanical trumps simple & electronic in motorcycling.

  • http://www.postpixel.com.au mugget

    I’ll wait for the test ride reports before I start getting too excited… but if it’s all true, I’d take an even sweeter handling CBR over an S1000RR, ZX-10R etc.

    It’s definitely more fun to be able to go even more fast, more easily in a corner, than just being able to go fast in a straight line or say your bike has 200hp. That’s my take on it at least.

    • Roman

      +1.

      I wonder if the new suspension components can be easily swapped into the 2008-2011 CBRs. I’ve seen lightly used examples go pretty cheap, hmmm….

  • Archer

    Wes’ point elsewhere on this bike, about sheer peak HP numbers selling bikes and a perceived disadvantage for Honda on this point, is well made. But that’s for the uninitiated- perhaps 75 (Europe and Japan) to 95% (USA squiddies)of the given market. People who realize usable power (and longevity) trumps big numbers might be in the minority, but for those of us who value such things, (and who want the slight real-world advantages of this bike over, say, an ’07-12 CBR600RR) the new 1000RR will sell just fine.

    A parallel arises in the niche of compound archery products. The market buzz is always about the fastest bows, but every current world record has been set with bows perceived to be relatively slow- because in archery, things like forgiveness and sheer accuracy always trump raw speed.

    Same here.

    The brilliance of the S1000RR lies in its 600-like handling and enormous power. But, the disadvantages of that bike relative to this one (BMW parts, BMW maintenance, BMW attitude, and about five large) will make this new CBR very attractive to some of us.

  • http://www.faster-faster.com fasterfaster

    Not sure I agree with the tech assessment, but I’ll chalk it up to simplification for the masses. In any case, it’s nice to see a company put some emphasis on the chassis, not just in development but in marketing. Realistically, it does the rider a whole lot more good than another 10hp on a liter bike. Woulda been nice to see the CBR lose some weight while it was at it though…

  • Ola

    Okay, given the hipster demographics of HFL I’m sure there’s some good marketing talent here. Let’s come up with a good name.

    1. Tried and true sexy abbreviation. Öhlins has TTX, I submit GRX. I doesn’t mean anything, just looks good on stickers like a growling animal.

    2. Actual abbrevation. Shock Piston Independent Direction Enhanced Rebound. SPIDER. Yeah it’s pretty shoehorned.

    3. iShock. No, not that.

    • Sean Smith

      I think they should just anodize it gold.