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Old 29-06-2017
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New Showa BFRC (Balance Free Rear-Cushion) Shock

So news has broken on the new 2018 Suzuki RM-Z450 motocross bike, and one of the big news items is the new Showa BFRC (Balance Free Rear-Cushion) shock. The shocks layout is different from a standard shock, with all the valving lying behind the adjuster with no shim stack on the piston on the shock shaft. I'm very interested in learning more about it! Nice to see something new out in the shock world as there seems to have been a lot more happening with forks in the recent past.



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Old 29-06-2017
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So...

This is awesome, it doesn't involve a check plate in the piston but instead has an oil-recycling system (twin tube) to spread the damping load over the entire oil volume. This thing will run cool and get great service life I reckon.

It's hardly innovative though, ORV shocks have used this system for yonks.

p.s. WP Trax shocks have had separate HSC/LSC damping circuits/adjusters for many years
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Old 30-06-2017
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I've been mulling this over in my over-active mind. I can see the advantages you're speaking of Nutty, but one thing niggles me. That is a LOT of work being done through the comparatively restricted passage that is the valving behind the adjuster.

Rather than having the compression damping spread across the piston ports in the main shock body (piston and valving attached to the shock shaft) AND the passage between the main shock body and reservoir (i.e. the "valving behind the [compression] adjuster), all of that is not being done in the passage between the main shock body and the reservoir. So in the common shocks we currently have, the only fluid being forced through that passage to provide damping is the fluid that is displaced by the shock shaft... which really isn't that much. Most of the [low speed?] damping is provided by the piston moving through the fluid in the main shock body, with the shims covering the piston ports metering the flow of the fluid through the piston ports. With this design, there is only 1 passage for the fluid to flow through, and so the "opportunity" for a larger pressure differential across the 2 sides of the valving will be greater - right? So cavitation has got to be a pretty major hurdle to overcome with this design - right?

I guess that because the fluid only flows in 1 direction in the chamber (I'm making a big assumption here as I am not sure), the comparatively less viscous fluid (because of the cavitation is will be "frothy") will be pushed into the reservoir (in the compression stroke) where it will have a little more time for the pressure in the chamber to collapse the bubbles and the gas re-absorbed back into the fluid before being forced through the rebound passage to have the rebound valving do its rebound damping. Again, cavitation might be an issue again in that passage, although probably not as bad as through the compression passage.

If cavitation is just "accepted" as something that this shock will need to deal with, I'm guessing in the long term there will be pitting issues in the reservoir. Because they look to be using a bladder rather than a piston in the reservoir, this probably won't be a big issue though.

Still, pretty interesting stuff. I'll be looking out for any other info on the shock, its design, and how it works for sure.
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Old 30-06-2017
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Ohlins has been using twin tube for ages too. Pic below will give you an idea of where the fluid will flow.

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Old 12-07-2017
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Quote:
Originally Posted by Arctra View Post
With this design, there is only 1 passage for the fluid to flow through, and so the "opportunity" for a larger pressure differential across the 2 sides of the valving will be greater - right? So cavitation has got to be a pretty major hurdle to overcome with this design - right?
One of the major hurdles with both forks and shocks, is to limit the cavitation. Of course this is made easier with internal pressurisation.

With a standard shock, we have to make sure that the pressure below the main piston doesn't drop too low during the compression phase, otherwise we can introduce hysteresis or cavitation. So its a balance of damping on the main piston vs damping at the comp adjuster combined with nitrogen pressure.

With Ohlins and now Showa (actually they've been running this design for a few years in the road bike world) removing the damping from the main piston and placing it all at the comp adjuster, they have removed the chance of low pressure areas below the main piston. I guess that's where the name of this shock comes from....there is no need to pressure balance the shock anymore.

This shock also meets the trend of the last few years by making the clickers more easily accessible. I just hope the clickers are more effective than the triple adjuster on the KYB shocks. Will be interesting to get my hands on one in the future.
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Old 3 Weeks Ago
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I just read the 2018 Vital MX 450 Shootout article over on VitalMX - http://www.vitalmx.com/features/2018...-Shootout,5510

This excerpt from the section on the 2018 RM-Z450 on the BFRC shock isn't so promising...
Quote:
...
While the chassis feedback is good, that doesn't quite mean the handling is completely on point as the shock is my source of concern for 2018. As I mentioned in my First Impression on the RM-Z at JGR's facility, the BFRC (Balance Free Rear-Cushion) shock has a very free feel. The tighter the tracks we rode, it wasn't as big of a issue. Tracks that go "turn, jump, land, brake, turn, repeat" it worked out pretty decently, as you can keep the shock constantly loaded. Now on wider, sweeping tracks with fewer obstacles and more constant chop, the shock's free feel becomes irritating. Why? It never stays settled. As soon as you have to chop the throttle, or the rate of momentum slows (say once you've been in third gear for a bit) the shock doesn't have enough load to keep it down and it climbs high in the stroke. This unsettles the chassis, and without the rear squatted, it tends to wallow around and step out when you hit anything. Then when braking, the combination of the unloaded shock and taller rear area of the seat ends with me getting kicked in the butt and throwing my weight forward, putting too much load on the forks.

My quick fix was to run a few millimeters less sag to add squat, and slow down the rebound to keep things down but then stiffen it with compression as the shock is a bit on the soft side (there's only compression on this shock, no high and low-speed adjusters). This made things work more "normally" and get the bike to drive forward again, but in turn it lost a lot of its comfort and beat my back up a bit. I've been spoiled enough to ride some "works" version of the BFRC and they work pretty decently and don't feel quite as active, and I feel this production version has a lot of room for improvement. Sadly, this problem overshadows the improvements up front. In my opinion the new Showa spring fork is better than what Honda brought last year with the same Showa unit, but the unbalance of the bike puts too much work on the forks at times.
...
So could this be the "4CS" of shocks that will make a lot of tuners a lot of money? On the face of it the tech seems good, but I thought the same about the 4CS's and look at how much of a bad bet they were! I guess we'll just have to see how it progresses?
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Old 2 Weeks Ago
Rjhug1 Rjhug1 is offline
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Quote:
Originally Posted by Arctra View Post
I just read the 2018 Vital MX 450 Shootout article over on VitalMX - http://www.vitalmx.com/features/2018...-Shootout,5510

This excerpt from the section on the 2018 RM-Z450 on the BFRC shock isn't so promising...


So could this be the "4CS" of shocks that will make a lot of tuners a lot of money? On the face of it the tech seems good, but I thought the same about the 4CS's and look at how much of a bad bet they were! I guess we'll just have to see how it progresses?
Yep we would hope not thats for sure.

FYI, I have both the 4CS forks on my 2015 ktm (worst suspension component of any bike Ive ever owned with a full revalve having minimal effect) and I just bough the new rmz.

The BFRC shock I can say with all certainly aint the disaster the 4cs was. From my initial ride, straight out of the box with no playing with race sag, is that its super plush on a rough tracks and whoops. You could almost sit down over this terrain and not get bucked off like you would on a normal shock.
It does feel though that it doesnt track as well as some other setups, but race sag and more hours might settle that down.
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Old 2 Weeks Ago
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Cool! Thanks for your first hand feedback/opinion

It sure will be interesting to hear your longer term opinions on it. Are you planning on having a tuner try and do anything on it?
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Old 1 Week Ago
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Quote:
Originally Posted by Arctra View Post
Cool! Thanks for your first hand feedback/opinion

It sure will be interesting to hear your longer term opinions on it. Are you planning on having a tuner try and do anything on it?
Yep, will get kroozetune to get stuck into it fairly soon. I think the spring rates are very good so at least that side is ok.
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