View Full Version : Forks Binding

Terry Hay
16-07-2004, 08:44 AM
Now when most people start thinking about suspension mods they instantly think about springs or revalving. One area that is often overlooked as a modification is friction reduction. Anyone that owns one of the latest KTMs (03-04) can tell you of the troubles they have with deflection and harshness when they hit square edge bumps. Rocks, roots etc. This harsh sensation is directly attributed to binding and is generated from a tube design that has gone slightly wrong. The fix is very simple in the case of the KTMs, but is binding present in all forks?
To a degree, yes!
USD forks have inherant binding as a trade off in their design. As you impact a bump the forks tend to flex. Naturally the same force of impact thats trying to compress the fork is also trying to break it in half. Conventional forks have a huge advantage here as the sliding length does not have to pass through the "fixed" triple clamp area. Anyone that has compared a conventional fork to an USD one will instantly tell you of the additional harshness with the inverted units.
Given that consumer demand forced the "Best" fork I've ever tried (98RM 125-250) on to the scrap heap, I guess we're stuck with the dreaded USDs and will have to do the best we can.
Ways we can reduce the presence of binding can vary from simple to extreme. Some oils have better lubricating qualities than others. A friend of mine (USA) told me of the issues he had with his forks when he used Silkolene oil. He chased his tail for ages and then finally switched brands and the bulk of his troubles were gone.
Simple alignment of the fork is paramount when re-installing the front wheel.
One of the most significant modifications you can make is to recoat the fork tubes with anti-friction coatings in order to reduce the amount of drag that is present with the standard ones.
Factory forks these days almost always come with modified coatings of some discription.
The biggest benefit riders speak of with friction modified forks is the lack of fatigue and increase in confidence. Obviously if everything is moving more freely the forks will react to bumps much better. This should also mean greater traction as naturally the wheel will be back on the ground faster. The methods of choice for coating the tubes are "Hard anodizing" for the alloy tubes and Titanium nitride for the chrome tubes. This process is not cheap generally adding between $800-$900 to the cost of suspension upgrades but if you ever feel like treating yourself this is one decision you won't regret. It's the kind of thing every bike rider should experience at least once in their life.

D.B.Race Susp.
16-07-2004, 08:58 AM
I just wanted to say that i also loved the forks on the 98 rm250. Certainly one of the best forks i've ever ridden with and it's a shame that progress isn't allways an improvement.


16-07-2004, 10:15 AM
Terry, the Lab Manager for that oil brand you mentioned is a DBW member. Look out for a fight!

16-07-2004, 11:16 AM
Terry, Don't forget about overtightening the triple clamps on upside downs which also can contribute to the binding effect. Most clamp bolt torques are pretty low (8-12 ftlbs) and most people over toque them.


Terry Hay
16-07-2004, 07:06 PM
It's not my finding. Simply the outcome of someone elses experience.

Spot on!
The torque is critical on the lower clamp bolts. As we discussed at the seminar the best thing to do with friction is to piss it off. The unfortunate thing is that it is found in so many places.

16-07-2004, 11:06 PM
speaking of that seminar, as a result I had a go at replacing a mates seals (bugger doing my own first go around!!!).

when I got the tubes apart the wear marks could clearly be seen up in the tube and on the chrome slider thingo!

It was a klx and I think they were kayabas. I told him he needed to get them anodised :)!!!!

oh yeah and they don't leak either! thanks terry!

17-07-2004, 09:57 AM
I suspect I may be the one that suffered with Silkolene stiction issues. I have used the RSF fluid for a long time, and never with any issues in the Jap bikes or MTB forks or rear dampers. That was why it took so long to switch fluid brands. After switching I noticed several others on KTMtalk that had run Silkolene in their forks with similar issues. I don't know why it happened only with the WP's.

On a side note I was planning to test the rear damper using Factory Connection GSF fluid (supposed to be Showa), I tried it first in my rear damper on the Cannondale mtb. It was actually very good on the first ride. The second ride several days later the stiction was high. On an attempt to ride it a third time the damper had locked up. I immediately pulled it apart. In order to remove the seal head I had to coax it off with a plastic hammer. I removed the quad ring seal and found the oil side had swelled while the air side of the seal was normal. It definately would never leak.

Funny part is, the WP damper on my KTM uses the same type quad seal...

Terry has very good points about anti friction coatings. They are expensive but will offer a performance gain. For those interested in having it done, for most folks it's more cost effective to have it done with suspension work. I know of several guys (not me) that decided to save a few bucks and send their inner tube assemblies off for ti-nitride. Boy were they PO'd when they got them back and found the process of plating had destroyed the "O"rings at the axle fittings and the forks leaked once reassembled, not to mention the plater plated what was sent, including the axle fitting. There was more gold on those forks than on Mister T's neck.

I have recently looked into several coatings available here in the US beyond the Ti-nitride (gold). If I remember correct there is a carbo-nitride (black) that is less friction than the gold. And also a bisulfide coating with less friction than teflon. The better it gets the more you spend.

The best coated tubes I've ever seen were done on a friends 250 GP roadracer. Somehow they were brought to work by a good friend and were plated with the black carbonitride process and coated with something else. The guy that did them worked for a huge spacecraft maker here in the US. They were sweet.

I suspect that Terry may back me here. Don't be lazy, drop the dust seals and keep some lube on the top side of the dust seals. Nothing is more annoying than someone asking about there suspension and you push down on the front and it lets out a loud SQQQUUEEEEEEEEEEKKKKKKKKK.


17-07-2004, 05:34 PM
Very interesting, I love to hear this stuff.

I am a big fan of cleaning all the assembly grease off the seals and scrapers form the factory and re-assemble with fork oil. The grease holds the dirt in around the seal causing trouble.

Then I put a bit of kitchen sponge in between the two (with a drop of fork oil if you like). The sponge is softer than foam and it's honeycomb shape lets the dirt fall into the holes away from your chrome.

The fork in the picture is my old TY350 trails bike fork, but it works on any fork.

17-07-2004, 10:46 PM
To add to my previous post and my lack of memory in the brain cells. Titanium Nitride is normally the golden color, Titanium Carbonitride is the grayish black color, Titanium Aluminum nitride is a brownish color. Chromium Nitride is like chrome. There are others but I haven't found out the trade names and colors they go with.

While researching this several years ago I talked with several engineers in this area. I was trying to TiNitride aluminum stanchion tubes on the Bomber MTB forks. After a lot of learning, I was amazed at the difference in friction reduction of the coatings compared to chrome. Also some may have noticed the factory guys running the blackish coatings. The gold may be nice to look at with its bling bling effect, but the black carbonitride offers a slightly better friction reduction. Both of these are far better than chrome so the difference between the black and gold is very slight.

Gold seems to be the easiest color to obtain. It is used to coat many items but mainly cutting tools.

As I stated earlier, almost everyone wanting this done should go through a suspension shop like Terry's or another high end facility. This is not something for the inexperienced small guy unless he's willing to pay the tab on new lowers if they get messed up.

The other coating I mentioned but couldn't recall it's official name is Tungsten Disulfide. I've never knowingly seen it but it does have some impressive statistics.

For those wanting more info you can surf to General Magnaplate's site and also a company here in Florida called Brycoat. These guys claim to do Race Tech USA's coatings, and are expensive for the little guy. I was quoted a price to plate the same as RT charges, and they would pull the axle fittings. Other facilities can apply vacum dep coatings so don't think these are an encompassing list.

Terry touched upon coating the upper legs also, in my opinion this is where a big friction reduction can be realized. Also by coating the uppers the fluid will stay cleaner for longer periods and will not absorb the aluminum oxides.

Ironically this applies to both ends of the motorcycle, but usually only the forks see attention. The rear damper body and shaft should also be done.

Regarding the kitchen sponge, sponges come in many colors, it may be out of site and unseen, but that sponge needs to match your brands colors.

Good tip, I've started getting away from dropping the seals and greasing, I use a variation of the sponge/foam method. I've cut synthetic felt strips and installed between the dust seal and oil seal. I'm using Mobil 1 hypoid gear oil to wet the felt. So far so good. To rewet the felts I use a syringe and needle, slide it between the dust seal lip and the chrome and apply 1/2 cc of the oil each couple of rides. Obviously don't pierce any seals or onesself.


Terry Hay
17-07-2004, 11:45 PM
You have a range of resources in the States that simply aren't available to us. The carbon process here is not available in lengths exceeding 6 inches. Apparently the process is set up for tooling and the equipment is not capable of handling long pieces such as fork tubes.

17-07-2004, 11:52 PM
Sorry Terry,
I was of the impression that with many companies your way contracting with Boeing more aerospace may be available.

Besides the differences between the gold vs black is only slight,
the big gain is when jumping from chrome to nitrides.

Kind of funny though, this process of tinitriding has it's big boost from the Japanese. apparently they refined it and use it to coat compact disc's and dvd's.


Almost forgot, I may have resources to trick out the bike, but I suspect the way things are headed here I may not have a place to ride the machine. The resources may truly favor you.

Terry Hay
18-07-2004, 12:00 AM
If you ever feel the need to venture Down Under we have a spare YZf250 just waiting for a pilot. If you are feeling really brave you should aim for the Queens Birthday weekend in June next year. We have a nice little desert race you might be interested in.

19-07-2004, 11:48 AM
Don't worry PK, the TY was read and blue so the sponge was colour coded.

Is chrome coating that much cheaper to do from the factory. I see GasGas going to black coatings. Surely the purchase price for abike manufacturer to buy them from the suspension supplier would be cost effective for the result.

410 rider
27-07-2004, 12:59 AM

It is with interest that I read this thread as lately I have been experiencing a bit of harshness with my forks.

They feel fairly harsh in the initial stroke in that they are deflecting over small square edged obstacles and jarring my hands/arms/body. They then really firm up (too) quickly about mid stroke on slightly bigger hits.

I have checked the torque for the triple clamps, ensured that they are fixed evenly in the clamps/axle, ensured that any air is bled, and have played around with comp/reb settings before resetting to standard. A little bit of air escapes which does help the action a bit but not to the degree that I expect.

The above would not usually present me with too much drama except for the fact that they worked like a dream in the first couple of hundred kliks. It now has just under a thousand. The bike is a 04 TE450.

I cant help but think that maybe one of the valves has become blocked from some manufacturing swarf considering that the adjustments I made made little difference. Apart from that maybe worn/damaged bushing? Seems weird.

Thanks for the forthcoming advice.

27-07-2004, 05:39 PM
I don't know if this has been tried by anyone but maybe Terry may know.
Have the bushes in the end of the fork tubes ever been retro fitted with bearings to fix this problem. Not normal bearings but a kind of "reciprecating ball" type of bearing. I know that this was a major break through at HRT and they improved the operation of the McPhearson strut in the touring cars unbelievabley. This led to dominance over all other Holden teams untill they caught on.

Just a thought.I am sure that one of the factory bike mobs would have tried it,but maybe it has other drawbacks for bikes.

Terry Hay
27-07-2004, 11:09 PM
WP have a prototype fork that incorporates cylindrical bearings as opposed to bushings. The bearings provide an exceptional response to impacts but have not made it to full stream production for some reason. The damping has to be increased to handle the fluidity of motion. Perhaps this had a negative result in other areas.

The Husky has an antiquated bushing land design on the chrome tube. This design will in fact promote extra binding compared to that of a modern Jap fork. The extra binding is likely to wear the anodising from the inside of the alloy tube which will in turn, increase the problem. When I modify a Husky fork for performance I always taper the bushing land which will provide a smoother action. When you feel a service is due send your forks to us and we can sort them out for you.

410 rider
27-07-2004, 11:41 PM
What would the dollar damage be Terry?

Terry Hay
28-07-2004, 08:11 AM
The mod simply involves some machining and labour it would probably add around $40 to the price of a service. If the tubes required "Hard anodising" that would be around $290.

29-07-2004, 03:30 PM
Wondering if you have ever seen the Cannondale bicycle headshok, or lefty.

Sometime hop over to cannondale.com and they should have some cut away drawings.

A neat design but like everything it suffers with some faults.

They use a round tube and machine four sides to accept flat races and internally machine the upper tube to accept it's races. Then 4 bearing cages each with like 22, 2mm diameter rollers allow the suspension to telescope. They've had some form of this for public use since like 1993.

Being friends with a cannondale rep and talking about some of their skunk works projects always makes me wonder if they may have just tried this setup on their own design motorcycle fork. Cannondale had some great ideas, sadly the advertising and public relations boys got their fingers into the pie before it was done being cooked. Just like so many bicycle things they had great ideas and prototypes but not enough real world testing.

Ironically, the fork they promote now called the "Lefty", a single legged telescopic fork, done right and strengthened, could work as a motorcycle fork.


Flying Fossil
30-07-2004, 05:57 PM
You mention :PMK

Terry touched upon coating the upper legs also, in my opinion this is where a big friction reduction can be realized. Also by coating the uppers the fluid will stay cleaner for longer periods and will not absorb the aluminum oxides.

Do you mean Nitrate coating the uppers inside and out ?

Also you said :

Besides the differences between the gold vs black is only slight,

how much diference is there ..can the average rider tell the diference ? or its so slight that it does not make that much diference unless you are a gun rider ? ..

And Terry you mentioned the upper Hard Anodising :

You mean the outside right ??

Sorry if these questions sound silly but i need to ask them :D

So i can get an idea whats involved before i decide to do this ..
Thanx guys

Terry Hay
30-07-2004, 08:03 PM
The anodic reaction creates an increase in the surface hardness factor providing similar properties to that of hard chrome. The inner and outer surfaces are coated at the same time. By increasing the hardness of the alloy you dramatically reduce friction. Obviously with reduced friction comes reduced wear and contamination. When you were here you would have noticed that my forks were black and gold. The black was the anodising.

30-07-2004, 11:52 PM
Flying Fossil
Sorry to not be fully clear in the post.

The upper or outer tubes in a current style upside down fork are made from aluminum. The majority of the time aluminum is processed by anodizing, there are three main types of anodize process. Here in the US for aerospace they use, Type 1 which is chromic acid process to help prevent corrosion, Type 2 which is sulfuric acid process and then dyed to produce all the pretty colors you see on billet parts and such, Type 3 is Hard anodize which provides a wear surface on the aluminum almost as hard as chrome. This is the type used for fork tubes and shock bodies. It can also have other processes applied into the anodize (like teflon) to provide a more slippery surface.

Anodize is a bath type process where the part is connected to a power supply and immersed in solution, the plating tank is lined with plates that connect also to the power supply. With voltage applied the coating is drawn from the solution and absorbed into the aluminum. Anodize is not a build up type coating like gold or paint(bad example).

The titanium nitriding process is a vacum deposition process. I have never seen this done but have had it explained to me. The part is placed in a vacum chamber and if I remember correct the the deposition gun sprays the part and because of electric charge and the vacum the part is coated. Ti nitrides are extremely hard and long wearing, plus are very smooth. Ti nitride involves heat in the process this is why removing the axle fittings is a must or the Orings will burn.

In regards to the black carbo nitride vs gold ti nitride, I can't locate my data paks with the comparing tests. In the lab there is a difference between the nitrides but when comparing to chrome the jump from chrome to ti nitride (gold) is huge with the carbo nitride (black) only slightly better than gold.

Terry and I have spoke about the nitrides and he has stated that the gold is possible to have done in Austrailia but the carbo process is limited to smaller parts. Even here in the US it is difficult to locate resonably priced platers that can handle the fork tubes and plate using carbo nitride.

FWIW my personal forks are still chrome. I contacted the outfit about coating with carbo nitride but there vacum chamber is being updated. They weren't certain if the updates were going to include a larger chamber. If they can't fit the KTM tubes for black I'll have them done with the gold.

In summary
aluminum is annodized and steel is nitrided or chromed.

Sorry for the long techno weenie post, I just thought some of the details might help.

Terry deals with this and unless you have an uncle doing it for free, let the ones that know handle it. It's not something for most home mechanics trying to remove the axle fittings.


For more info you can look at the brycoat.com website.