Fork spring advice please

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I have an ST1300 purchased used. The PO installed racetech .90 with 10wt honda fluid. I find the ride way too harsh. I weigh 165 and rarely carry gear and never a passenger.
I am looking for a much more plush ride for straight line riding rather than firmer for the twisties.
I have been toying with the idea of going with the racetech .85 springs and 5wt fluid, or even just taking the bike back to stock.
I am soliciting advice as to the best solution. I have limited funds available and do no think I can swing a full racetech valve kit right now but would nonetheless entertain it.
Thanks
 

970mike

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Change the oil back to 5wt and it will make a big difference without costing a bunch of money.
 
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Yes, 5 wt oil and Racetech .90 gives a very cush ride.* Check the sag and the stiction while you're at it.
 
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So I should stay with the .90 springs rather than the .85?
What brand of 5wt fluid gives me the closest value to 5wt ?
 

dduelin

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Just stay within brand......try Honda SS-7 which they label as 5wt which as compared to the stock SS-8 which they label as 10wt. The stock springs are .86 so I wouldn't think you would want anything softer. The bike as stock is under sprung for all but the lightest riders.

You can use Race Tech's spring calculator to gauge spring rate:

http://www.racetech.com
 
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You may have to recheck the installation of the springs.
Check rider sag front and rear, are they correct? Maybe too much pre-load?
Is the oil level correct? If every thing is correct then maybe try the next weight oil down. Beware not all fork oil weight callouts are the same . Best to stick with the honda recommended oil.
 

ST Gui

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even just taking the bike back to stock
NO! Er: no. Even at 165lbs I don't think you're the target weight for Honda's under sprung bikes. Keep the springs and change the oil. Cheap fix. Even if it's not perfect it should be a noticeable improvement for very little money and labor.
 
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The spring rate should be for your weight. Check the Race Tech or Sonic spring rate calculator, and I suspect even .90 is the least you'd want to go. First check the sag and see what you've got. Maybe you actually need more preload if you're familiar with suspension tuning...... Change the oil to 5W is the first thing I'd do.
 
OP
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Great advice everyone, thank you.
I am going to do a fork rebuild with new seals and bushings, keeping the .90 springs and changing the oil to ss-7 fluid.
Decided to do this since I am unsure if the PO actually went through the forks properly when he changed the springs.
I will report back when completed and after a test ride. (could be a couple weeks from now)
 

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Tony, you didn't mention it in your 'list'; but, you might really benefit from adjusting the sag, front and back too.

Good luck with the work,
Mark
 

Byron

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Fluid level in the forks will also affect how stiff or soft it feels. Less air space equals harsher ride while more air space will soften things. Don't go to drastic with more air space or you could end up bottoming the folks over even small to medium bumps or pot holes. Seems levels vary from the factory 62 mm setting down to about 135 mm depending on company recommendations and spring rates.
 
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Tony......I have seen a many suggestions on adjusting SAG and or the amt of pressure already put on fork springs when you screw in the fork caps.......Yes the oil change / viscosity will help but if "harsh" means what I think you are trying to say.............then I would use a ole' motocross trick.......change the length of the spacers in the fork tubes....make them slightly shorter using PVC piping that has the same diameter of the metal tubes inside the fork tubes. Cheap and easily adjustable with a ruler and a hacksaw. I do it all the time for my machines and friends bikes....sometimes stiffer (harsher) sometimes softer (less preload on spring rate)
 

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make them slightly shorter using PVC piping that has the same diameter of the metal tubes
Yup. This is how the sag is adjusted.
You just might want to be sure to use schedule 40 PVC (the thicker type of PVC pipe).
 

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Tony......I have seen a many suggestions on adjusting SAG and or the amt of pressure already put on fork springs when you screw in the fork caps.......Yes the oil change / viscosity will help but if "harsh" means what I think you are trying to say.............then I would use a ole' motocross trick.......change the length of the spacers in the fork tubes....make them slightly shorter using PVC piping that has the same diameter of the metal tubes inside the fork tubes. Cheap and easily adjustable with a ruler and a hacksaw. I do it all the time for my machines and friends bikes....sometimes stiffer (harsher) sometimes softer (less preload on spring rate)
This may work well on other bikes but not so much on the ST1300. The bike is undersprung to begin with and from experience with my bike and other ST1300s at tech days is with OEM springs the rider sag will be far too great to even consider shortening spacer length and reducing preload. For example I weigh 150-152 lbs in street clothes, about 175 in gear and stock fork sag was 47 mm or 44%. 30 to 36 mm is optimal. Because I am so light I was able to increase spacer length (preload)by 16 mm and get the sag to 36 mm but heavier riders would not be able to do that without excessive preload. The solution for riders heavier than 155 lbs is to increase spring rate over the .86 of OEM to get to what is considered an acceptable range of sag.
 

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Before you even start to rebuild the forks get a baseline measurement of your rider sag. The sweet spot for the ST is 36mm, but if you are looking for a softer ride you could set them at 38. I also suspect that the oil level was set at the factory level instead of the 135mm as Racetech recommends with their spring. They also recommend 5wt oil. I would stick with the .90 springs. If you really have a desire to return to the stock springs, I have a set that we could talk about.
 
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Yes , I suspect as well that the fluid level is at what factory recommended, also I believe the po just measured in the volume rather than measuring the level from the top.
Also unsure if po actually got all the old fork fluid out when he replaced the fluid.
 
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>>New Info<<

I was at MMP in Tooele, UT doing an Advanced Rider Training class put on by Utah Sportbike Association (great class by the way) the past weekend. I spent about 30 minutes Saturday evening talking to Lenny Albin, owner of Nitron USA Suspension (he worked 10 yrs at RaceTech, then 5 yrs at Ohlins) and designed the RaceTech ST1300 damping valves).

His advice - if you run straight rate springs, the OEM oil level of 62 mm is way too high. His recommendation was 130-135 mm (set with no springs in, fork tubes and damper rods fully collapsed). Based on this, the first thing to try would be check and properly set the oil level (actually the air space) to 130-135 mm and see where that gets you.

He did not mention specifically about OEM or aftermarket valving - so maybe keep 10 wt since the OEM damping is considered too low to begin with, going to 5 wt would make it even more underdamped - just seems logical). 5 wt is the correct viscosity for using the RaceTech valving.

He also said that on the ST1300 for typical combination use, he would target a front sag (measured by the RaceTech method - see their website) in the range 40-44 mm, thinking 35 mm range is too stiff for typical road AND track conditions.

This guy knows his stuff - he's been doing MC suspension engineering for 20+ yrs (He's also a very nice guy - he was swamped with work, and still took 30 minutes to talk to me about the ST suspension). I'd pretty much use his guidance as a real good starting point, and it will probably be plenty fine right there.

He also mentioned to consider the Nitron rear shock options (5 different versions available). Very high quality, made in UK, and his pricing runs a bit less than the competing aftermarket units for the ST. I'll be talking with him about that this winter.

My 2? - YMMV of course.

Randy
< end New Info >


There seem to be many unknowns concerning your current set-up. I'm 185# and the racetech chart calls for 0.95 kgf/mm springs (what I ordered).

The OEM springs are progressive wound, so that 0.86 value has little direct significance for comparison. At your street clothes weight, I doubt you will want to be under 0.90 kg/mm single rate springs. The OEM springs take up more volume than the RT springs in the fork. If oil was put in by volume (assuming ALL the old was removed), the level will be a bit below the OEM spec. Checking/adjusting oil level height is what you need, since you are actually setting air volume in the forks with this adjustment. Also note - if you are using PVC pipe/tube for spacers instead of the thin aluminum ones, that will use up more air space. Using the same oil level with heavier plastic tubes will have the effect of running higher oil level (less "oil level dimension" which is actually an assessment of air space).

The OEM SS-8 oil is estimated at 10 wt nominal. By most accounts I have read, the ST front is underdamped with the OEM valving and SS-8 oil. Going to 5 wt would make that worse. I think Racetech recommends heavier oil with their springs and OEM damping valves to Add damping, and I believe a larger oil level dimension (lower physical level, more air space, that would yield a more uniform spring rate over a larger range of fork travel).

Racetech recommends their 5 wt oil WHEN USING THEIR VALVING SYSTEM, which is way different than the OEM.

Knowing the rider sag would also be helpful to help assess. The oil level, if very high, could actually affect the sag some, and create ride harshness (like too high spring rate) at even moderate fork compression. The higher the oil, the more progressive the effective spring rate (spring force + air pressure force) becomes. If your sag with those .90 springs, preload set in the 15 mm range, not excessive stiction (worn bushings or bent tubes), and sag is less than 36-38 range, my guess would be fork oil level is too high. That is only a guess based on limited info.

What I would do:

Check your front and rear sag using the RaceTech method (available on their website, takes 3 people to perform) before doing anything else.

Use the rear preload adjuster to set the rear sag at about 34 mm at the axle. Note: Preload adjusters tend to leak oil over time, and reduce their adjusting range substantially. My '08 ST with 21k miles on it when I got it last year only had about ? of its normal adjusting range when I got it. The previous owner was 280, had never moved the rear adjuster from its original "Standard "setting, and was running with zero added preload to the rear. He was probably 80+% of the way to bottoming just sitting on the bike. He had never adjusted the rebound damping, and it was to soft for me at 90# less than him. I guess a good thing he did almost exclusively interstate highway riding (smooth roads and not much cornering).

It is fairly simple to bleed and refill the adjuster if needed. See other posts about doing that if necessary.

See if your front compression sag and rebound sag are more than ~15-20 mm different (excessive stiction - bad oil, worn bushings, scuffing on outside of fork tube, bent fork tube, misaligned fork tube, etc.), and what the average sag value is. The target is about 36 mm. OEM is significantly more - in the 40s for typical American riders 180+ in weight.

Do the checks multiple times to make sure you have good sag numbers. Write them all down ( rebound sag, compression sag, and average sag for both front and rear).

If the front sag is way wrong, and the oil level is found to be correct, consider changing your preload (new spacer tubes, adding spacer washers - can be bought from Racetech, or cutting spacers (if sag is not enough) to get you at least closer to the right range. Note: Changing preload length does not have a one-to-one relationship to sag, since there is progressive air spring effect in addition to the linear physical spring response. As you add preload, the progressive air spring effect is lessened, since you have more weight on the forks before you ever start compressing the trapped air. The lower the oil is in the fork tubes (more air space, larger "oil level" dimension), the progressive air spring effect is also lessened. The standard starting preload recommended by Racetech is 15 mm (about 5/8") top of fork tube to the underside of the cap outside of the threads (where cap contacts top of fork tube). If your sag is off, and your preload is not around that 15 mm amount, that might be a good starting point to shoot for.

>>>> Before doing anything else, try and do a critical ride assessment on differing surfaces and different speeds, threshold braking, various levels of cornering lean, etc. Make notes about your impressions of handling in all those different cases. You will use this as a point of comparison for your testing after you rework the front end.

Pull the front wheel and pull the forks per service manual procedure. Remove the caps from the tubes and damper rods. Rather than dump spacers, springs, and oil into a tray per service manual...

Remove the spacers. Try and let oil on the spacers (if any) drain back into the fork tubes.
You can probably fish the springs out with a piece of wire with a hook on the end. Pull the springs up above the oil level and let as much oil as possible drain back into the fork tubes (so you can assess the oil level you are starting with).

If they are racetech springs, they will be marked with the rate near one end. Confirm they are 0.90 rate springs as you think they are.

Push the fork tubes into the sliders until they bottom. With fork held vertically, check your oil levels. You can make a "dipstick" from a piece of wire. Mark with masking tape about 150-160 mm from the end. Put wire down fork tube until tape edge is even with top of tube. Withdraw and measure the distance of dry wire between tape and where the wire has oil on it. That is your present oil level. If you were able to not drag out too much oil on the springs, the levels should be with a mm or two of the same in both forks. Record this number and compare to OEM and or Racetech recommended level.

If the oil level is much too high (see Racetech recommendation for those springs and your weight) (or too low), at minimum dump out the old oil and replace with new. I would start with the weight and level recommended by Racetech for OEM valving and their springs. Since you are on a budget, the Honda Pro oil, or another recognized brand, should be fine. RaceTech makes a supposedly super slick, full synthetic oil that is supposed to maintain viscosity longer than conventional oils, and provide significantly lower fork friction and stiction. It is, however, $60 for 2 quarts needed for the ST forks. Maybe overkill for typical street rider...

Depending on your mileage, it would probably be a good idea to disassemble the forks and thoroughly clean the all parts per service manual prior to re-assembly. If budget allows, and the bushings have some miles on them or show wear through the teflon coating, all four are less than $40 (from RockMountainATV.com in UT), put in new bushings. I would always suggest new fork seals - ~$20 for pair. Replace dust seals (if they are dried, worn, or cracked especially). Manual says replace the copper seal washers that hold the cartridge to the bottom of the slider (assuming you took them out). Other say reuse once is generally fine, though.

Reassemble using the PROPER assembly and re-tightening order on all aspects of fork clamps and front wheel and axle reinstall. Failure to do so can cause binding in the forks leading to harsh ride characteristic, and front wheel alignment bad due to improper wheel axle mounting and tightening can lead to a number of handling problems.

Repeat your critical ride assessment (as done before starting) on differing surfaces and different speeds, threshold braking, various levels of cornering lean, etc. Make notes about your impressions of handling in all those different cases. You will use this as a point of comparison for your testing after you rework the front end.

There are a lot of subtleties in suspension assessment, and what your suspension use and feel goals are.

Hope that helps. The guys at RaceTech were very good about helping me choose components for my particular circumstance and suspension performance goals. I'm sure they'll take a few minutes to talk to you about it.

Good luck in getting to a good solution for you.
 
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