Fork compression damping question.

[superhawk996]

I've searched and can't find an answer to my question. My forks feel pretty good overall except high speed compression damping feels really stiff; I think it's what causes it to jump pretty hard on things like raised manhole covers and other bumps when cruising. The spring rate and damping feels ok otherwise. Is there an easy way to reduce just the high speed compression damping without affecting the rest of the damping negatively? Should I re-spring and install race-techs or something like that? I'm about 180-185lbs. I want good control, but don't want harshness. I'm very capable of doing the mechanical work and drilling, cutting, modifying; just don't know what to do to them. The rear feels ok, tho I'm thinking about the Ohlins group buy, then I might dislike the front more.

[xrated]

I may be wrong (I'm certainly not a suspension guru kind of guy), but as far as I know, there are no "high" speed compression adjustments on forks in general.

[jcrich]

Yep, that is a higher end rear shock adjustment feature (like Ohlins). Even their normal aftermarket forks do not have a high speed compression adjustment. This is not to say that it does not exist in some super expensive race fork application. Also not sure which bike you are talking about. There are a lot of suspension tutorials on the Intertoobz or find a suspension tuner to help you sort it out.

[superhawk996]

Oh, I stupidly assumed everyone would know I'm speaking of a XX, mine's a '97. I know it doesn't have the adjustment option as there's no adjustments on these, but I assume there's a way to make the changes by taking the forks apart and modifying.

[jcrich]

You never know in this place, so I did not assume. I also had a 97 at one point and had it handling very nicely for the mountains. As you said there is no adjustment available unless you graft adjustable forks from some other bike onto the XX. On mine, proper springs, removed a shim from valve stack and 10 wt oil changed the bike dramatically up front. Greg (G2) did the fork workfor me. He discovered that the valving in the 97-98s had much larger orifices than the subsequent year models. That on top of the Penske Sport Shock made it light years better than it was in stock form.

[superhawk996]

You never know in this place, so I did not assume. I also had a 97 at one point and had it handling very nicely for the mountains. As you said there is no adjustment available unless you graft adjustable forks from some other bike onto the XX. On mine, proper springs, removed a shim from valve stack and 10 wt oil changed the bike dramatically up front. Greg (G2) did the fork workfor me. He discovered that the valving in the 97-98s had much larger orifices than the subsequent year models. That on top of the Penske Sport Shock made it light years better than it was in stock form.

Thanks!

Was that shim removal to soften the compression? Is a straight forward removal of the shim with no other mods needed to take it's place?

[jcrich]

At the time it was beyond my comprehension as to what exactly Greg did. It actually had the effect of firming up the front suspension along with the oil and springs. The front on these are very mushy.He comes around here every so often, give him a ping (G2 is his user name) and see if he recalls what exactly he did. It was a number of years ago so he may or may not.

[superhawk996]

Mine actually feels good except for the harsh compression, the PO may have changed the oil to something heavier tho. I took the caps off and the springs look to be stock, and shorter than I expected, but I don't know what oil it has. I considered changing it just to see but figured it a waste since I know they won't be good without work. I'll hit up G2, thanks again.

Funny, I just realized I bought a set of headers from Greg recently.

[HANKSXXX]

You may also give Rick a call at Cogent Dynamics.

He's very familiar with BB suspension and mentioned he could cut the group guy guys a super deal on Ohlin's fork valves, both compression and rebound. The pair is cheaper than you think and with Rick setting the shim stacks, you'll end up with a professional setup that compliments the Ohlins on the rear.

FWIW, my 97 turbo BB had a great setup, done by Rick, but the icing on the cake was when he put the shock and the forks on his dyno....

[tomek]

Mine actually feels good except for the harsh compression, the PO may have changed the oil to something heavier tho. I took the caps off and the springs look to be stock, and shorter than I expected, but I don't know what oil it has. I considered changing it just to see but figured it a waste since I know they won't be good without work. I'll hit up G2, thanks again.

Funny, I just realized I bought a set of headers from Greg recently.

Before you spend mega bucks on re-valving, springs etc. I urge you to change the fork fluid to maxima racing formula 85-150 5wt.

Not all fork fluids within certain viscosity are the same, I don`t guarantee results if you use different 5wt .

http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

Basically you need to disassemble entire fork, pull out cartridges, disassemble valves, shims, etc. Everything has to be operation room clean-clean, otherwise it is not worth the effort. Record the stock shim stack

You`ll need to lap faces of the valves so they are actually flat , basically start with wet-or-dry 600 on something flat like piece of glass, finish them off with 1000-1200 grade.

I`m within 5-10 pounds of your weight, I`m extremely happy with results, high speed harshness is gone, I absolutely don`t see the need to mess with forks any further. I`m running stock springs.

Just for the record my track bike has Traxxion Dynamics cartridges in the front and their Penske shock in the back. I do know what the high end suspension feels like.

[blackhawkxx]

Funny, I just realized I bought a set of headers from Greg recently.

Did you get it on and if so, results?

[superhawk996]

Mine actually feels good except for the harsh compression, the PO may have changed the oil to something heavier tho. I took the caps off and the springs look to be stock, and shorter than I expected, but I don't know what oil it has. I considered changing it just to see but figured it a waste since I know they won't be good without work. I'll hit up G2, thanks again.

Funny, I just realized I bought a set of headers from Greg recently.

Before you spend mega bucks on re-valving, springs etc. I urge you to change the fork fluid to maxima racing formula 85-150 5wt.

Not all fork fluids within certain viscosity are the same, I don`t guarantee results if you use different 5wt .

http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

Basically you need to disassemble entire fork, pull out cartridges, disassemble valves, shims, etc. Everything has to be operation room clean-clean, otherwise it is not worth the effort. Record the stock shim stack

You`ll need to lap faces of the valves so they are actually flat , basically start with wet-or-dry 600 on something flat like piece of glass, finish them off with 1000-1200 grade.

I`m within 5-10 pounds of your weight, I`m extremely happy with results, high speed harshness is gone, I absolutely don`t see the need to mess with forks any further. I`m running stock springs.

Just for the record my track bike has Traxxion Dynamics cartridges in the front and their Penske shock in the back. I do know what the high end suspension feels like.

The 5 wt. and lapping the valves takes out the harsh without making the damping mushy?.....sounds interesting. My guess would be the 5wt is removing the harsh and the accurate valve finish is restoring control. (?) Thanks!

[superhawk996]

Funny, I just realized I bought a set of headers from Greg recently.

Did you get it on and if so, results?

I haven't. I have a stock '97 and the header I bought is a late model with Jet-Hot coating. I want to do a few temperature and performance tests before swapping and I just haven't gotten around to it. I actually have a list of stuff I want to test before/after for curiosity and to share. The weather and time have conspired to be uncooperative and it'll probably take a few cold start to run cycles to complete the tests I wanna do. I'd like to do a good MPG test as well, but if I hold out for that it'll be forever before I do the swap so it may not happen.

[tomek]

Mine actually feels good except for the harsh compression, the PO may have changed the oil to something heavier tho. I took the caps off and the springs look to be stock, and shorter than I expected, but I don't know what oil it has. I considered changing it just to see but figured it a waste since I know they won't be good without work. I'll hit up G2, thanks again.

Funny, I just realized I bought a set of headers from Greg recently.

Before you spend mega bucks on re-valving, springs etc. I urge you to change the fork fluid to maxima racing formula 85-150 5wt.

Not all fork fluids within certain viscosity are the same, I don`t guarantee results if you use different 5wt .

http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

Basically you need to disassemble entire fork, pull out cartridges, disassemble valves, shims, etc. Everything has to be operation room clean-clean, otherwise it is not worth the effort. Record the stock shim stack

You`ll need to lap faces of the valves so they are actually flat , basically start with wet-or-dry 600 on something flat like piece of glass, finish them off with 1000-1200 grade.

I`m within 5-10 pounds of your weight, I`m extremely happy with results, high speed harshness is gone, I absolutely don`t see the need to mess with forks any further. I`m running stock springs.

Just for the record my track bike has Traxxion Dynamics cartridges in the front and their Penske shock in the back. I do know what the high end suspension feels like.

The 5 wt. and lapping the valves takes out the harsh without making the damping mushy?.....sounds interesting. My guess would be the 5wt is removing the harsh and the accurate valve finish is restoring control. (?) Thanks!

Not at all, slow speed dumping is fine. If you take a look at that suspension fluid data even though there is none for factory fill ss8 you can kind of guesstimate it by comparing ss7 and ss15. SS8 is somewhere in between those two. Maxima 85-150 is about 10-15% less viscous if you look at actually viscosity of those fluids. Just what the doctor ordered.

The other thing is factory fresh fork gets quickly contaminated with all kinds of junk during break in period. If you ever disassemble cartridge fork you quickly realize simple drain and refill are utter waste of time. There is crap everywhere, especially at the bottom of the cartridge and in valves themselves.

Here is what you need http://www.maximausa.com/shopping/index.php?main_page=product_info&products_id=44

1 liter bottle is enough to do both legs, 483 +/- 2.5 cubic cm per leg.

Suspension shops what to sell you complete valves because they make more money that way but HMAS valves are comparable with aftermarket, ohlins, etc. They have large high flow ports and can work very well with some massaging and tweaking.

[superhawk996]

I found a great chart on suspension oils http://www.peterverdone.com/archive/lowspeed.htm It shows how far the labeled viscosities can be from actual viscosity. Interestingly, standard Maxima 5wt. has the same specs as Maxima Racing 85-150 5wt. at probably a lower price. They're also lighter than Showa SS-7 and Honda Pro 5wt. None of those have an impressive viscosity index, tho it's probably not a big deal for a street machine, I'd choose something in the right viscosity with a higher VI if I could.

My confusion with your recommendation of a lighter than stock oil comes from many here saying that the stock forks are mushy, and a lighter oil would make them more mushy--wouldn't it? Also, our forks are said to be cartridge forks and not damper rod forks, but they have a rod...WTF?

[HANKSXXX]

Blackbird forks are under sprung and over damped. Thinner fork oil and a good cleaning, along with stiffer springs or at least setting the sag front and rear are a step in the right direction.
The rebound damper assy is on the bottom of the rod that is affixed to the fork cap and goes up and down in the cartridge.
The compression damper assy is in the bottom of the cartridge.

[blackhawkxx]

Blackbird forks are under sprung and over damped.

Doesn't that depend on the rider's weight?

[HANKSXXX]

Yes, that's correct, and I guess the stock setup would be just fine if you weighed 150 lbs or so and packed light.
Most complain of the front being soft or mushy and if you want to know how your combo is, check the sag, front and rear.

[superhawk996]

I always assumed the "mushy" complaint was the damping, not springs. I'll try an oil change and go from there.

[HANKSXXX]

I always assumed the "mushy" complaint was the damping, not springs. I'll try an oil change and go from there.

While sitting on the bike in riding gear, have someone measure from the top of the front fender to the bottom of the fairing. If it's much less than 4", consider setting the sag..

[superhawk996]

I found the spec for Honda/Showa SS-8. It's a 10w oil with a cSt of 35.48 @ 40c. compared to the Maxima you use which is 15.90 @ 40; quite a difference.

35 cSt is ATF territory like what was used in old damper rod forks and not deemed suitable for a cartridge by any professional.

[superhawk996]

I syphoned out what I could (just over 6oz each tube) and replaced it with Maxima 5wt. and the harshness was reduced. I'm not ready to tear down and disable the bike so I just did a partial change to get a taste of what can be done. Now the shortcomings of the soft springs and rear shock became more obvious. I'm probably gonna have to do the ohlins shock group buy and fully rework the forks. THANK YOU FUCKERS!

And a sincere thanks too :-)