Showa twin chamber, big improvement, no cost.

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7/26/2018 6:48 PM

I've been unhappy with the forks on my 2011 RMZ450 since buying it new, now I have retired I have the time to work on all my bikes, I have greatly improved the ride of the RMZ forks, it was so easy, I should have done it years ago!

I always felt the forks were too firm (I'm 90 kg's), beats me why the MXA test said to go to stiffer springs (I now know why), I even tried running RMZ250 (.46kg) fork springs for a while.

Over the last year I tried lowering the oil level/quantity 10cc each time I rode, until I was -100cc (280cc left in each leg), yes the forks were diving further, right up to the hydraulic oil lock stop. The oil lock starts about 35mm before complete bottoming, well with only 280cc of oil in the fork I could not get the cable-tie, on the outside of the tube, past the 35mm point from fully bottomed, when riding. That is 11% of the forks travel that is wasted !

I had been running ISO22 (International Standards Organization) weight oil (equal to most brands 5wt in SAE terms), changing to ISO11 (Belray HVI3) or ISO15 (Ohlins shock oil) improved the situation but reducing the outside diameter of the oil lock collar (see pic) from 28.10mm to 27.80 made all the difference. And I'm back up to 350cc per leg of ISO15 (2.5wt).

Sure I do not want the forks to bottom with a harsh bang, that is why I did not grind the alloy collar down any further.

Aftermarket companies offer a larger diameter, they say "to stop the forks from bottoming"! Maybe different brand motorcycle manufacturers request Showa to offer more clearance and they have 'complete' bottoming issues? But the Showa twin-chamber forks on my RMZ were NEVER going to bottom-out.

It makes sense now why MXA wanted stiffer springs, to keep them off the hydraulic bottoming stopper, 35mm before fully bottomed. If I had not radically reduced the oil level to be able to study the cable-tie not using the last 35mm, I would not have realized.

Photo

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.

7/26/2018 10:31 PM

When you say these forks were never bottoming do you ride strictly MX and at what level do you ride? Have you tested them like this on big hits yet. Good to know I will save this if I ever get TC forks!

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7/26/2018 11:37 PM

I'd say I'm mid-level, I'm an ex pro racer. Around my own track, 1.5 miles around with about 10 jumps, gets pounded quite hard.

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.

7/27/2018 11:54 AM

I ended up with much softer springs and the Factory Connection Bottom Lock collars in most of the twin chambers I used on both CRF / RMZ.

MXA fork settings have always been way too stiff for my liking. I think they set bikes up for pros at Glen Helen - fast, sandy, steep hills. That setup is completely irrelevant to what the other 99 percent of us do.

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7/27/2018 3:23 PM
Edited Date/Time: 7/27/2018 3:25 PM

mark_swart wrote:

I ended up with much softer springs and the Factory Connection Bottom Lock collars in most of the twin chambers I used on both ...more

Hey Mark, thanks for your feedback. l only see larger FC oil lock collars, is that what you fitted, do you remember the OD? The tube that the collars slide into are quite high on my RMZ (the same as other bikes l see from various pics on the internet), this means that oil-lock starts happening at the start of the tube. lf my bike will not use the last 35mm l wonder if yours is?

Do you ever get your cable-tie to show fully bottomed-out? What do you weigh?

Doesn't make sense to reduce suspension travel from 305mm to 270mm?

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.

7/27/2018 3:30 PM

I honestly didn't do anything that scientific, I went with .47 springs on my 09 RMZ 450, along with the oil lock collars. FC put them in, I never actually handled them.

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7/28/2018 5:44 AM

Measure the FC OL collars, the OD difference is minimal and would make stuff all difference in reality.

Where are your clickers at? 280 is low, especially for mx

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7/28/2018 6:29 AM

bowser wrote:

Measure the FC OL collars, the OD difference is minimal and would make stuff all difference in reality.

Where are your ...more

The OD of the oil lock collar, and oil weight are the only things that effect compression resistance in the last 35mm of travel. clickers have no neglegable effect in that range.

The oil height is too low at 280cc for sure, but it was all part of learning by dropping 10cc each test. Generally my comp & rebound are within 1 or 2 clicks of what the manual or MXA quoted, but l have tested all settings from full soft to full hard.

The point l am making is, regardless of clickers or oil height, the forks would NOT travel through the last 35mm of travel, the forks are so plush now, they suck up every bump and smoother landings from jumps.

Another way to improve the forks is to remove the axle clamps from the chrome legs and trim-down / shorten the tube that the oil lock collars slides down (maybe shorten it to about 10mm), that way you definately have bottoming resistance without sacrificing so much useable travel, l didn't want separate those two components for fear of thread damage or oil leak.

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.

7/28/2018 6:39 PM

I understand what you mean regarding clickers don't have an effect in that specific part of the range, the point I was getting to is clickers effect the whole range and the travel used. If they were all the way in they would effect the stroke the fork uses

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8/5/2018 9:48 PM

I have had another day of testing, man I am so happy with my forks now, with oil-lock collars ground down I had to juggle oil level/quantity and compression damping settings, to give both; the right rise in air chamber pressure, and compression resistance to absorb the bumps & yet keep the forks from fully bottoming.

350ml per leg (369ml stk) of ISO 15 (2.5wt) and 15 clicks-out on compression damping. The stock 11 clicks-out were obviously needed to slow the fork to keep it off the early bottoming of the stock bottoming-cone/oil-lock collar?

I am heavy but I do not flat-land after monster table-tops, so I guess my settings could suit a few riders?

My findings may be of interest to some, certainly something to think about I guess.

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.

4/28/2020 9:26 PM
Edited Date/Time: 4/28/2020 9:27 PM

I know this is a old post....

but ....did you remove the oil lock collar ....or grind it on the rod

how much did you grind it ? ....flush with rod ???

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