How to adjust non-adjustable forks?

chesthing

Joined
Jun 6, 2008
Messages
239
Location
Colorado
Bike
R1200RT
I recently installed Sonic springs on my ST1100. Handling around corners is excellent and the front end takes medium-large bumps well, but the front end reacts to every tiny ripple in the road. What I'm looking for is the smoothest, cushiest ride I can get.
Initially I followed the Sonic's recommended 3/4" of preload, which gave me about 32mm of sag. I reduced preload to 1/2" giving me almost 40mm of sag, which seemed to soften the ride, but the front was still responsive to every little dip and ripple in the road. I then took out about 1 ounce of the 10 wt fork oil that was measured to Honda specifications.
The front is pretty good, but I'm wondering if there is anything else I can do, and if the changes I made are the right ones to get the bike to ride across minor imperfections in the road and not feel them in the handlebars.
Would a lighter weight oil help? Any other suggestions before I call it good? I realize these forks are very basic using old tech - I'm not looking for perfect, just as good as I can get without spending tons.
 
When I put in my Sonics I used a 7.5 wt. I'm not experiencing the following the ripples effect that you are. I'm happy with the ride. Didn't actually do any sag measurements but set them up according to the Sonic instructions. I'm in the ball park until I do measure.

That effect could be a function of your tires.
 
I just replaced tires today, the bike certainly takes curves much better (incredible, actually). The absolute only thing about my suspension I'd like to see improved is how the front end handles the little stuff.
 
Race Tech did my work on my 05 ST1300, and they put in 5 wt oil at the usual level along with the Sonic springs.
But the biggest help in getting a cushy front end was putting in their Gold Valves which flow a lot of oil, thereby eliminating the jolts I used to feel.
Jefro.
 
Bill in NY explained to me that the STs are undersprung and overdamped. So the suggestions of using 7.5W or even 5W oil might help.
It will prevent knowing whether you drove over the heads or tails side of a nickel. :D
 
I just went for another ride and really paid attention to what the suspension was doing. When I hit a medium or large bump the forks moved, but anything small they didn't, it just transfers right to the handlebars. The rear moves with everything.
When I get on the bike the rear squats about an inch, the front just 1/4". That means the static sag in the front is 1 1/2" of the total sag of 1 3/4". What this is telling me is that the front of the bike is much heavier due to the engine placement, and after all the weight of the bike is placed on them the springs are too stiff to absorb minor road imperfections.
This wasn't the case with the stock springs, although handling wasn't nearly as good either. The bike wallowed and wasn't as stable in curves.
Correct me if I'm wrong, but I don't think this has anything to do with damping - the straight rate springs are just too stiff after taking the weight of the bike.
I'm thinking of trying a set of Progressive springs, but aren't they basically the same type spring as stock? I could possibly get used to the front of the bike bobbing up and down oh so slightly down the road, but right now it's pretty irritating because I'm thinking about it.
 
chesthing said:
When I get on the bike the rear squats about an inch, the front just 1/4". That means the static sag in the front is 1 1/2" of the total sag of 1 3/4". What this is telling me is that the front of the bike is much heavier due to the engine placement, and after all the weight of the bike is placed on them the springs are too stiff to absorb minor road imperfections.
Click to expand...
This could also mean your rear preload is too soft or the spring rate is too low back there.

If I understand correctly, you have about 1.75" sag in the front. That is about 30% of travel which is on the low side of a rule of thumb of 28-33% for street bikes. Coupled with your description of a harsh ride I might be inclined to reduce preload still further and see how it felt with 33-35% sag.

When I was messing around with preload to tune my forks I raised the sag from 1.85" to 1.4" or 44% to 33% travel. This is on a ST1300. The sag was good but the ride became similar to what you describe. The forks were harsh and the front wheel was twitchy and skittish over bumps. High speed smooth corners were planted as long as the pavement was smooth. The oil in the forks was new Honda 10w SS8. I drained the 10wt out and I mixed 2 parts Honda 5wt with 1 part 10wt fork oil and reduced the oil level slightly. The effect was magical. The ride became plush again and the forks glided over both small and large bumps. In bumpy corners the ride is compliant yet planted and in high speed corners the bike no longer wallows down on the suspension. The front wheel tracks over bumps like they almost were not there.
 
chesthing said:
<snip>
Correct me if I'm wrong, but I don't think this has anything to do with damping - the straight rate springs are just too stiff after taking the weight of the bike.
<snip>
Click to expand...
chesthing:

Not trying to be confrontational, but I think that if you compared rides of a Race Tech equipped bike to one with stock dampers, you'd find that the stock damping is causing much of the effect that you see and feel. That said, I had a problem similar to what you described. It turned out to be an overly tightened fork brace that was causing my forks to bind. If you have a brace, try taking it off for a trial ride.

Paraphrasing what Jefro said: Sonic Spring plus Gold Valves equals a plush, but controlled ride.

Marshal
 
I'm looking for insight/advice so I can attain the best ride for the least money, please disagree if you think it will help. I will buy some 5 wt and mix with what's left of my 10 wt and give it a try.
No fork brace. I don't think the rear is the problem. I installed a brand new Hyperpro shock spring at the correct rate for my weight just a few weeks ago. The rear actually feels really good, I can tell pretty easily that all the harshness I'm getting from minor bump is all felt up front. If that doesn't help I'll look at the Race tech setup, but I'm not really in the mood to spend $.
 
I think you can do a lot on the cheap tuning with different weight oils and varying the fork oil height. All it takes is labor.
 
IMHO, the large picture answer to your original post is...

Not Easily!!

No matters what you experiment with, it won't be easy. The front will have to come apart, the oil, spacers, springs, valves, amount of oil, size of spacers... etc etc.

again, not easily. First and foremost, mama Honda needs to make these things adjustable for pre load and dampening, that could save some an awful lot of work. I know of no other sport touring bike that has No, nada, zip, for front end adjustments. That's just not right.

imho... best wishes to all.
 
I agree, it's inexcusable that Honda didn't upgrade the ST1300 with adjustable forks - I get why they didn't on the ST1100, hell it came out in 1991.
Anyhoo, I tried some Bellray 7 wt oil and it was worse. The front end just reacted more and faster to the small bumps. I put the 10 wt back in and called it good. I can get used to it, the bike sure corners well with the Sonic springs - it's a decent trade off from the stockers. I decided years ago I wasn't going to sink $$$ into motorcycle suspension after buying an $800 Penske for my VFR (which of course I sold a year later).
 
I've taken an ounce out of each fork from Honda's oil level spec, and it improved things. I emailed Sonic asking for their recommendation, thanks for the suggestion.
 
chesthing....I believe it's more oil for the sonic setup...not less. If you go to the Sonic web site...I believe the setup is online.

Here's the general recommendation from Sonic....

NOTE B: Oil level

Oil level is difficult to give blanket advice on. Some bikes work best with the stock level, some benefit from less, others are better with more. A general rule is to set it fairly close to the amount of travel that the forks have. Most street bikes have 4.5 - 5 inches of travel, (about 115 - 130mm) so an oil level in that range works for most bikes. Some are different though; For example, the Kawasaki Concours uses a level of 150mm with our springs. If you have a question about your specific application, please e-mail us.


Forest
 
uptoblackwood said:
chesthing....I believe it's more oil for the sonic setup...not less. If you go to the Sonic web site...I believe the setup is online.

Here's the general recommendation from Sonic....

NOTE B: Oil level

Oil level is difficult to give blanket advice on. Some bikes work best with the stock level, some benefit from less, others are better with more. A general rule is to set it fairly close to the amount of travel that the forks have. Most street bikes have 4.5 - 5 inches of travel, (about 115 - 130mm) so an oil level in that range works for most bikes. Some are different though; For example, the Kawasaki Concours uses a level of 150mm with our springs. If you have a question about your specific application, please e-mail us.


Forest
Click to expand...
The measurement for the fork oil is from the top of the fork, down to the oil level. The larger the number, the lower the oil level. Sonics' recommended level is less than stock. Apparently, Honda raised its oil height spec to trap a smaller volume of air, which then acts as an infinitely variable spring. Sonic Springs use steel springs in lieu of the air, so less oil level is required.

Marshal
 
I'll post Sonic's reply, but from what I've seen I'd have to agree with Marshal. Higher oil level produced the same bobbing up and down, only harder. Lower weight oil actually magnified the bouncing. At this point I'm inclined to agree with Jefro and Marshal, if I'm going to use Sonic springs nothing is going to help unless I spend bucks on valving (which ain't going to happen).
If it gets really annoying I'll probably try a set of Progressive springs, although I expect I'll lose in the handling dept. Without spending $$$ it's a trade off.
 
Here's their response:
"That does sound like too much oil, but 7.5" is generally not too much. At
least if we are on the same page as to how the measurement is done.
How exactly did you get the 7.5" number? The "standand" way to measure is
with the spring and spacer removed, and the fork fully collapsed. What you
measure is the distance from the top of the fork tube down to the surface
of the oil, so what you're really measuring is the air gap. A smaller
number means more oil. Was that how you did it?"
Sounds like they go by the same quantity as Honda specs, although the bike did respond well to removing an ounce from each fork.

I looked at Race tech's website, they show fork valve kit FMGV S2054C for my bike for $249. Not terrible, but paying to install them would probably double that.
 
chesthing said:
<snip>
I looked at Race tech's website, they show fork valve kit FMGV S2054C for my bike for $249. Not terrible, but paying to install them would probably double that.
Click to expand...
chesthing:

FMGV S2054C has compression valves only; not what you want/need. You want kit FMGV S2052C. That kit is about $400, unless you can get in on a "group buy" for $300, and includes the very important rebound valves. Installation for that kit is $138 at Race Tech's shop. Admittedly, lots-o-cash, but worth it to me.

See attached PDF from Race Tech for more info on this kit.

Marshal
 

Attachments

  • IP FMGV S2052C.pdf
    58.5 KB · Views: 37
You must log in or register to reply here.
Back
Top Bottom