Matris cartridge fork conversion

http://www.eurospares.com/graphics/FF/Honda CTX700/Matris_Showa_CTX_1146.jpg

That photo shows the Matris parts (upper) compared to the OEM Showa components.

I got the F15K kit which they say is for the 12/13 NC700 and 14/15 NC750. I suspect this is a "how many different models can we claim it will fit without being an exact replacement" deal as the travel is not a match for the NC or the CTX. Since they all use the same tube/slider what fits one fits all the rest.

CTX - 107 mm travel per manual (I got 110 measured)
NC700 - 137 mm travel per manual
Matris kit - 225 mm less 83 mm OEM top out spring - 142 mm
GSXR 1000 - 120 mm
SV650 - 130 mm

So if you don't want a 5 mm travel increase over an NC700 a spacer needs to be made to go above the top out spring. I made mine to give 120 mm of travel as is typical for GSXRs. I wanted more than stock CTX but I didn't want to raise the bike very much. It will be a solo rider and no luggage bike so I don't need a lot of extra travel for heavy loads.

The kit did have to be shipped from Italy and it was about 6 weeks after placing the order before I got them. I suspect this is the first one that was requested by the US importer, and they probably only bring in small batches of the "popular" kits (like FZ07/09 Yamaha). The spring that was requested was a rate higher than is in the normal spring range and someone goofed when grabbing a spring of that rate without checking to see that the diameter was slightly larger (there's about a .004" interference fit with the tube ID). But now we know there are alternate springs readily available here (Race Tech and Ohlins) so that is not an issue.

Matthew Patton of Forks by Matt (a sideline for him, not his day job) got the kit for me and put in his own design of compression piston and shim stack. He said that all three of the major conversions -- Ohlins, Matris and Andreani, have a problem in his eyes with their compression control. The new piston requires a different weight fluid than that which is shipped with the kit, though the supplied fluid is fine for using in the rebound leg. The standard Matris compression is said to be improved over the damper rods, Matthew's piston is a refinement added to that, but it seemed a very reasonable thing to do since he charged about $50 for parts/labor.

Figure $550-600 by the time the kit hits your doorstep. It gets shipped to Matt to change the piston, and he also adds a few extra circlip grooves to the body to allow more variation in the position of the lower spring perch. Then you'll need to buy an extra liter of fluid per Matthew's recommendation, which is another $10-20.

Matthew would also need to make the spacers for whatever travel is decided on, but I built a spread sheet to make it easy to figure that out when I made mine so that will probably not be a big additional price.

The Matris kit drops in. I was impressed with the nice machining and finish of the Matris parts.

A set of RT Emulators can be bought for about $120 and a set of fork springs (likely to be needed for many people) are another $100, so the cartridge conversion is more expensive. For about $30 you can get some preload adjuster fork caps from China. But the Matris allows external adjustment of damping and preload where the Emulators need to have parts pulled out of the forks for that (and if you want to change rebound you have to change the fluid). You also get a rebound piston/shim stack that can be modified if needed, the Emulators basically do just compression damping. Once you get everything set the way you like you may never touch the adjustments again, but it is certainly convenient when dialing things in to make a change in less than a minute and go out and see if you like it.

Note: my CTX is a long term project and while the conversion parts are installed it is not close to being ready to ride as I'm doing a lot of other things, so I can't at this time give a ride report on the forks or the Ohlins NC-spec rear damper.

cheers,
Michael
 

ponydrvr

Member
I have thought long and hard about doing the Race-Tech conversion. I just didn't get good feeliings from either the Race-Tech site descriptions nor the conversations as posted in various forums so I held off on doing anything. The drop-in fork cartridge you have described seems to better resolve my concerns.

I have modified the rear suspension by shortening the suspension links to 131mm increasing the ride height ~ 1 1/8". I have cut the shock lower rubber bumper to increase shock stroke length, also added four steel 12 mm washers to the coil-over to restore loaded sag. The rear has been a huge improvement over the stock suspension set-up. As a result the steering response has quickened noticeably.

The front forks are untouched. The front end is the weak link in control and comfort.

The roads I ride are generally paved rural roads with tight turns, switchbacks, long and short sweepers and some pretty rough surfaces on occasional. I do get into deep loose gravel, hard packed dirt/stone but try to limit this exposure since the CTX is not a off-road style bike. On top of all this, I may well ride for days and miles on straight roads with very little excitement. ? It sounds to me like I need a BMW GS, except their COG is higher than I'm comfortable with?

Not sure where to go from here as far as specifications for travel, spacers, and spring rate are concerned. Is one to presume that the proper fork oil is only that sold by Matthew for this upgrade?

What information would I need to supply to get this ball rolling?
 
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Matthew told me what centistoke viscosity range to get for the compression side (rebound and compression are in separate legs) and mentioned what he used so that is what I bought. He buys fork oil in large quantities which is used when he rebuilds a fork and sends it back ready to install and doesn't keep retail sizes on hand. I bought Maxima (59901-5) 85/150 Grade 5WT Zero Drag Formula Racing Fork Fluid for $14/liter. That's the lightest of their range and is 16.2 c/s @ 40C. As long as you buy some reputable brand in the right viscosity range you should be fine.

I've raced bikes with Emulators that had very nice action on the forks. RT is supplying a product to convert a damper rod fork for a modest amount of money and with a minimal amount of tooling needed. If you read some of the threads at the big NC700 forum you'll find people who are quite pleased with their Emulators (or the similar Cogent Dynamics product), but they may have pulled them out several times to make minor adjustments/drill another one or more bleed holes, etc until they got to a point where they declared full success (vs "good enough") on the project.

So you can save several hundred dollars if you are willing to do more fiddling in your garage. I suspect that the cartridge probably has the potential for more tuning than the Emulators, but then you get into knowing what you are doing with changing shim stacks or pistons or paying someone who does to do it for you.

I've not seen anyone who hasn't found a good quality aftermarket damper to be a significant improvement over the OEM Showa NC/CTX rear damper, plus when you go aftermarket it usually comes with a spring that is selected to be appropriate to YOUR weight and not that of some mythical purchaser. The overall length of the NC damper is longer than the CTX (with more stroke) so you end up with more ride height for a given percentage of travel (and with more travel too). If you put the NC damper on you'd probably want to revert to the stock length tie rods.

I had a visit yesterday from a CTX owner who drove out to CA from KY to have Seth Laam modify the seat on his bike. He had a Computrack dealer put Emulators in the forks and install the same NC-spec Ohlins that I have on my bike (along with a hydraulic preload adjuster that he says was well worth the money as it makes it easy to change preload when adding/removing 80 pounds of gear to the back of the bike). He really liked his CTX before the mods, and he says the suspension upgrades made him like it about 70-80% more. It sounds like the rebuilt seat is adding some additional % points.

I can send you Matthew's email address if you'd like to chat with him.

cheers,
Michael
 
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