Stock 49mm TAC and PSF II back to back comparison.

49mm Showa TAC and PSFII back to back comparison.

MX-TECH recently purchased a new CRF250 for testing. We just had a chance to test the Showa 49mm. TAC on the Honda CRF250, and draw a comparison on the PSFII that comes on the CRF450 an Air fork shot-out on the same bike on the same day with different riders and controlled track.
The 49mm TAC on the CRF250 features one less volume to pressurize and this is a good thing. The TAC runs a much higher pressure than the PSF and the amount of time it takes to pressure the fork is ridiculous. Showa uses a very small hole to feed the chambers so the pressure spikes and settles even from the low volume (high pressure pump.) I’m pretty sure it’s a safety feature. See funny YouTube video.
The very first thing you notice is the massive stiction created in the seals of the air cartridge. The fork just does not like to move unless you really load it up. On the track it’s not so bad if the dirt is soft but I know from experience that the harder the surface gets the worse the friction impacts things. Yes the fork is harsh under a packing load as the air spring really ramps up, in the 60% + stage of the travel. Overall with the smaller engine displacement and light overall chassis the TAC is better on the CRF250 than it is on the KXF, and RMZ.
I was really curious to actually ride the PSFII on the same bike and day. I’ve done several conversions in house taking the PSF II guts and making an open chamber SFF fork. The performance of the PSFII was horrible compared to the Showa TAC. From bouncy and loose, to very vague in the middle. They did have very nice movement (Low stiction) as we rode parking lot to the track.
I have to say the PSFII as delivered on the CRF450 is the worst fork I can remember riding for a long time. So I think the TAC wins in all categories but friction.

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2015 KTM 450SXFE

We have had a month or so on the new 2015 450SXFE.  We have gotten a lot of questions about spring rates and settings and of course general impressions.

Here are the bullet points.

  • Awesome light feeling / neutral handling.

New Shock is really interesting.

  • 12mm Shims.
  • New MX-TECH low friction piston ring required.
  • New Shock piston design, simliar to PDS piston.
  • New motion Ratio, much higher shaft speeds.
  • Shorter Shock Spring.

New Updated 4CS fork.

  • Air spring is 100% bottoming control. (Dummy hardware no-cup supplied.)
  • Longer fork rods. (Must use updated 4cs asymmetrical system, with shorter bottoming cup.)

I’ve come up with a nice Chart that shows the correct springs for the rider.

2015 KTM450SXF-FE
Rider Weight (in gear) Shock Spring Fork Spring
240 5.0 0.52
220 4.8 0.50
200 4.6 0.48
180 4.4 0.46
160 4.2 0.44
140 4.0 0.42
2015 KTM250SXF-FE
Rider Weight (in gear) Shock Spring Fork Spring
240 4.8 0.50
220 4.6 0.48
200 4.4 0.46
180 4.2 0.44
160 4.0 0.42
160 3.8 .40

Lots more to come.   I did a video review of the shock here.

Jeremy Wilkey Riding the 2015 KTM450SXFE

Jeremy Wilkey Riding the 2015 KTM450SXFE

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2015 KXF450 Showa TAC (Triple Air Chamber) Fork first review.

MX-TECH took delivery of our 2015 KXF450 on Friday last week 2nd Week of July. Like everyone I was eager to get my hands on the parts and see how they were constructed and how the adjustments work. Showa and Kawasaki arranged for some major changes to the damper side, like 12mm shims on the base valve! Additionally the base valve is being fed by a 14mm rod and the midvalve remains the same as previous models. Ok, so yes that’s all a big deal and should make for some good tuning opportunities, the real interest for me was the air side (spring) side of the fork.

So what is in there?
There are 3 pressure regions, all separate from each other.
There is an inner and an outer compression region and then a “balance” spring (region). Note this fork is very similar to the Suzuki RMZ450 TAC, but it is different from the CRF250 TAC. See notes below.
The Inner Cylinder is highest pressure and has an internal oil volume that will control the rate of progression in the pressure.
The outer chamber is the lowest initial charge, and can be adjusted by internal volume and pressure as well.
The Balance chamber adjusted at the lug. This is a pressure region that counteracts the force produced by the 2 pressure regions above it. It can also have its volume adjusted to control the rate at which its pressure drops as the fork compresses.
What does this mean, and with that let me offer the disclaimer, I’m very early in my understanding of the variables. I am getting my head around it and it will take time. As with most of my approaches to problems I will take 2 paths. One being quantify, measure and test the other be observe the performance in the field and cross validate.
So with that here we go on my initial technical review.
The idea is that with different pressures and volumes you can break the stroke into more segments and better tune the force verse displacement arriving at something that looks like a linear spring. That’s the idea that we all assume. I’m not sure, if that’s possible given the construction. So it’s no wonder the verdict is still out, and pro’s with direct support from Showa are still looking for the magic combination of volumes and pressure in each region.
So how did it ride? The track was deeper than normal, but JMX does not develop big breaking bumps like Walnut, Ki, Redbud, Moto Land or Glen Helen. That’s what I’m waiting for. (Thursday) The action is sticky on the floor but seems decent when you ride. The wheel really follows the ground and the bike gets great traction. The front seems to really dive under braking, and seems to be like the PSF lacking spring rate in the middle of the stroke. I read my manual for clues, it has very little tuning info. It also notes that the balance spring is the method by which a stiff or soft setting should be achieved. But what is weird is that soft setting is the low pressure balance chamber setting, and the stiff setting is the higher pressure balance setting. Can’t say that’s what I think it should be and that’s not what we felt when we rode it! Waiting on Kawasaki to offer a correction. Needless to say I started playing the balance spring settings and found softer balance spring and stiffer inner seemed to get more compression, but it did not add much in the middle, more stiffness at the top and bottom but not so much in the middle. This is volume issue.
Based on my first review of the parts and some initial tuning and observation here is my breakdown of each region.
Outer Compression: It has some impact on preload, and it is used to impact the bottom 1/3 of the stroke. More oil makes it come in sooner, less; later, more pressure more preload more overall force in the bottom 1/3. I think Showa wants to keep this low. It makes the fork more reliable. The outer chamber having significant pressure makes the fork a liability. *Note CRF TAC Notes.
Inner Compression: It has impact on preload and over all spring rate. It is the driver in terms of overall spring rate. Its volume has the most linear pressure change, and therefor closest to a spring. Plus by isolating the “Gas Spring” inside the fork is way more reliable! Rock ding or seal nick the fork will not lose spring rate. Maybe the driver for the middle of the stroke. Have not seen it yet.
Balance spring. Changes the top-1/3 the most.
I can see some things I’d like to try already. But initially I am just going to map spring combinations.
Sorry no picture of the Air side piston. I need to make a tool to remove it safely. I need to ride the fork and can’t risk damaging it.
Technical Details:
Fork Seals: SKF Kit49S works awesome and massively reduces stiction.
Fork Bushings:
Inner 50mm x 1mm x 20mm
Outer 52mm x 1.5mm x 15mm
12mm Shims for the base valve.
*No sub valve.
MXT T1009 is perfect for the bottom bolt on the gas side. (22mm end socket.)
**Honda TAC notes for the CRF250**
Honda has an advanced TAC. It uses no external balance tank because it’s on the inside of cylinder, as a tank or bottle attached to the piston rod.
The outer chamber is not charged. It just uses oil to control progression in the last 1/3.

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CARD 35mm WP Fork Kit

The CARD fork contains industry and OEM firsts including MX-TECH (MXT) Smart technology with the integration of a external adjustable SSBCV in one leg and a fully speed sensitive externally adjustable compression and rebound leg. A fully functional midvalve and base subvalve, and a elastomer controlled final bump stop.

This fork will eliminate the marginal ride quality of the Stock WP and Marzocchi forks. Its adjustable set-up allows for precise individual ride adjustment, and is easy to work on and service!

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CARD 37mm A-KIT Fork

Here it is. After a year in the making, the collective Effort of Cobra Motorcycle and MX-TECH’s Jeremy Wilkey has come to fruition. The 2013 CARD 37mm A-Kit fork.


CARD 37mm A-Kit Fork
Key Advantages:
• Kashima Coated Upper fork tubes. (Coated in Japan) Increases lubricity for easier fork movement in high loads and less stiction.
• DLC coated lower fork tubes. Decreased stiction and improved durability.
• Spring Perch rides on special Teflon DU style thrust washer. Decreased friction and smoother fork action.
• Hard coated inner fork cartridge tube for decreased oil contamination and more consistent fork performance.
• Customized valve settings each rider.
The 2013 CARD A-Kit fork is the best front suspension available combing specially engineered parts, coatings and set-up. Engineered to help your rider achieve the highest level of performance, through greater comfort and control.


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2013 KYB PSF updates.

With the ongoing development of the KYB PSF and a lot of really good info coming to the front of the reader’s attention, I’ve been generally silent. (Except for what I put on Face book.) We have been on this Air system for a long time. Early this summer when I read that the PSF was coming I had Kerry Cannon from Cannon Spring making me negative springs ( balance springs) to put in my standard KYB forks so I could do the air conversion myself. I was thinking we could potentially do conversions. And the learning curve was step; the conversion idea was not going to be possible. But I learned a lot. When the real version became available with the Kawasaki KXF450 I got one right away. (Along with the CRF450 that we received in September) The first rides where exciting but then the fork started to present its characteristics and flaws.

My Prototype Air fork. June 2012

In a nut shell the fork works really well on hard-pack, and jump filled tracks that involve rhythm and timing. The lack of friction from the coils of the spring is very noticeable and the fork has a nice fluid feel. However in fast, outdoor tracks with big braking bumps the fork is not so happy and becomes very harsh.  The root cause of the problem is that as the fork reaches the second half of the stroke the natural pressure increase due to volume change becomes very pronounced. In the final third the pressure increase is exponential and the air force is much greater than the valving, spring and air spring of a traditional fork.

We attempted a multitude of fixes and here is what we have found that is useful.  Stiffer midspeed valving (midvalve float) this keeps the bike out of the stroke a little delaying exponential increase in pressure as the fork uses stroke.  We run the Oil as low as possible; this delays the pressure rise until deeper in the stroke. Bottoming tends to start to occur. To better manage the bottoming control we designed and tested a SSBCV (Huck Valve) for the PSF. This makes a huge improvement. We have also been testing a MXT LFPR for the 32mm valve.

This image is the external subtank system we tested. It evolved to be an external volume compensation with dual pressure regions.  This was to precede the following more tiddy internal design,



We have also been testing a MXT LFPR for the 32mm pistons. The steel / Teflon ring seals better, and is more stable and lowers friction significantly.

Where is it going? We tested several types of pressure management systems. Enzo Racing style subtanks etc. The real solution will involve multiple pressure regions that compensate relative to position.   (Pressure) We are working on these designs right now.  If this type of stuff interests you make sure you look at the MX-TECH Face book. I’m always posting models of ideas and projects.

The PSF SSBCV Huck Valve P-types.

If you own a PSF fork now and want to improve it. I would do the following in order of value.

#1: SKF 48KHD seals. They will improve the performance and reliability of the fork.

#2: Lower the oil volume.  This will help the bike work better in braking bumps at the expense of bottoming control.

#3: Change the stock midvalve piston rings to the MXT LFPR. The Low Friction Piston Rings improve the wheels ability to follow the ground which improves comfort and control.

#4: Revalve for more midspeed compression damping, and less high speed. This improves plushness while delaying the pressure increase by reducing use of travel.

#5: Install the MXT SSBCV PSF Huck Valve.

Let me know what you think of this Blog.

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KTM 65SX Fork Solution Update.


For those of you who read my last post on the topic of the 2012 KTM 65SX forks and the design issues, and noted that I was working on a new solution. I have an update. It failed, or rather the design was a great, for a problem that could not be fixed so simply.

All is not lost, I went back to the drawing board and came up with a new plan. A new double cartridge set-up that uses one leg for SSBCV, and the other that is a speed sensitive  compression and rebound adjustable format.

The new design is importantly much different from the Betty 6 Five, as it focuses the quality where it needs to be and reduces manufacturing costs on many of the lesser important surfaces, greatly reducing production costs.

I’ll keep you up-to-date.



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Technix Japan.

I was surfing around my Japanese Partners web site and used the cool Google translator. Its neat to see the translation, If you have a second go take a look at the site. Hiro and I have accomplished quite a bit together over the years and its always fun to see what his creative design staff comes up with. To read about our dealings click here.


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2012 KTM 35mm WP Solution.

The WP 35mm Fork has not been meet with rave reviews, and initially we hoped that our Betty6Five cartridge would do the trick. Unfortunately due to the “big piston design” the fork does not operate well given the zero-rod displacement system. The high volume, system while capable of dealing with the air pockets does not allow for a consistent damping force in compression or rebound. This in combination with stiff over-all damping rates makes for terrible suspension for the little riders.

I set out to design a rod displacement system that will allow for a constant cartridge volume and will allow the big piston design to be relaxed. The riders will be able get a nice smooth speed sensitive fork that will retain compression and rebound adjustability. The system will replace the stock inner seal / guide case with our  speed sensitive system.

I’ll keep you posted!




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Old Find.

Here is a little piece I did for the old site that really interested me.  I recieved a lot of e-mails from the post. Here are the other parts I never told you about.

Simple enough. I did a test to determine what the basis of the e7’s advantage really was.  I wanted to know if it was friction or if it was simply the increase in mechanical advantage due to the designs increase in diameter of the effective piston. The only way to do was to make a gas charged Piston set-up in the e7 tank. It took a lot of engineering  to get it all functioning correctly but we pulled it off.

It was money very well spent as it proved conclusively that friction was the selling point in a case where mechanical advantage is factored out just a few times 10-12 verse 34-36.. (That’s why bladders are such a waste in shock.)

Anyway the other pieces where something I was working on at the same time. Working through the various iterations of the then “Huck Valve”.. This version was in fact what it looks like, a PDS needle / twin piston arrangement. We could never develop a enough volume and length to make this compact internal system work. I also tested a 1.5 version (Piston and Cup.) Same issues, it was at that point where the design went 100% external. I made the first parts on my rickety old Rockwell Lathe a Old-school Bridgeport Mill.  It was good times indeed, as I was rushing to get it built before my first Daughter Izzy B was due to arrive.

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