Fork Preload Questions

mlheck

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One thing to add here, is if you are going to add a PVC spacer to the stock metal spacer, be sure to put a metal washer between the two. This will make sure that the edge of the stock metal spacer doesn't chew into the PVC, thus contaminating your fork oil. You can also place a washer between the PVC and fork cap to help with the fit. Be sure to add the thickness of the washers to your overall spacer length though.

Actually if you include a couple of washer in your overall spacer length and place them right under the fork caps, you can then add or subtract washer to help dial in your sag. This is much easier than having to pull the plastic spacer and adjust it's length.
 
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dduelin

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One thing to add here, is if you are going to add a PVC spacer to the stock metal spacer, be sure to put a metal washer between the two. This will make sure that the edge of the stock metal spacer doesn't chew into the PVC, thus contaminating your fork oil. You can also place a washer between the PVC and fork cap to help with the fit. Be sure to add the thickness of the washers to your overall spacer length though.
Just replace the 200 mm stock metal spacer with all PVC cut to desired length. That leaves the stock spring washer at the bottom protecting against the spring and plastic spacer bearing against the fork cap up top.
 

mlheck

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Just replace the 200 mm stock metal spacer with all PVC cut to desired length. That leaves the stock spring washer at the bottom protecting against the spring and plastic spacer bearing against the fork cap up top.
Yep, that works also. Just trying to cover all of the bases.
 
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RobbieAG

RobbieAG

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I found some 1.5 inch PVC in 2 foot sections for spacers at Home Depot so I picked a couple up. Unfortunately the 1.5 inches is inside diameter, not outside. The OD is 48 mm, so definitely won't work. They also had 1.25 inch PVC but in 10 foot. I may have to give that a try. I guess we'll see when I get it apart.

Tires came in yesterday, so it won't be long. I got sidetracked by about 10 inches of snow today.
 

mlheck

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I used 1" schedule 40 rigid PVC conduit. It has a 1 3/8" OD and 1/8" sidewalls.
 
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RobbieAG

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I decided to go ahead and get new springs now. The more I thought about it, the more I wanted to get straight rate springs. I also didn?t want to take it apart again in a few months. I ordered a set from Traxxion Dynamics (Woodstock GA) for $99 including precut spacers. I think that?s a small price to pay for a significant improvement in the suspension.
 
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RobbieAG

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I received the fork spring kit today. I've been looking at the directions and they differentiate between different types of forks - damping rod forks, conventional cartridge and inverted cartridge. What type of forks do our ST1300s have? I know it's not inverted, but wasn't sure if they were damping rod or conventional cartridge. The service manual shows and refers to a fork damper so I'm thinking damping rod forks but wanted to be sure before I tear things apart. Thanks.
 

dduelin

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I received the fork spring kit today. I've been looking at the directions and they differentiate between different types of forks - damping rod forks, conventional cartridge and inverted cartridge. What type of forks do our ST1300s have? I know it's not inverted, but wasn't sure if they were damping rod or conventional cartridge. The service manual shows and refers to a fork damper so I'm thinking damping rod forks but wanted to be sure before I tear things apart. Thanks.
The ST1300 has a 45 mm HMAS Showa cartridge fork design.

http://powersports.honda.com/2012/st1300/specifications.aspx
http://www.fuelarc.com/bikes/honda/model-finder/front-suspension/hmas-cartridge-fork/
http://www.peterverdone.com/archive/highspeed.htm
 
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RobbieAG

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The ST1300 has a 45 mm HMAS Showa cartridge fork design.
Okay, that's good to know. For cartridge forks, it distinguishes between "internal top-out spring" and "external top-out spring" forks and says most conventional cartridge forks are external. It says you determine this like so - "If you pull down on your lower fork leg and you can feel a very stiff spring that will only let you pull down very slightly past full extension, then you have external top-out spring. If not you have internal top-out spring". I'm guessing we have external. Am I wrong?
 

dduelin

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From Peter Verdone Designs High Speed Damping - Dan Kyle regarding Honda HMAS forks:

"Understanding and tuning Honda HMAS valves.

My current take on them is that they initially offer some transitional high speed damping like a high flow valve, but they then begin to behave more like an orifice as the speed reaches peak, in general, progressive high speed damping.

The Ohlins valves are very similar to the Honda valves. What do you do with the ohlins valves? Can you really notice the difference going from Honda to Ohlins?

I also figure that the shim stack may become far more of a factor with these valves when using an ISO 15 fluid rather than the stock ISO 37 fluid. Reducing the oil height to a more realistic height than stock, so that the shock isn't ramping up like crazy regardless of high speed damping, is certainly a necessity.

I'm going to attempt to work with them on my next bike, since I never really worked with them on my current bike before switching to the race tech high flow valves. I'd just hate to feel that i didn't give a good part it's due before changing it."


This is essentially what I did with my forks. I mixed Showa Honda oils to move from a cSt of 36.44 to 22.6 and added preload for my riding weight to achieve a target sag of 36 mm. I am running an oil level slightly below stock. I don't feel I can go lower because threshold braking collapses the forks to within ~10 mm of bottoming thus leaving a margin for heavy braking over bumps or rough pavement.
 
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The top out springs in a cartridge can be either internal (trapped inside the cartridge, the maximum extension is determined by the rebound valve holder hitting the bottom end of the spring, the top of the spring hits the top of the cartridge) or external (where the spring is retained on the outside of the cartridge at its upper end, and the bottom of the fork stanchion engages with the bottom of the spring to limit movement). The external spring system is possibly better as the spring is held in place not free to bounce around, and as soon as the damper rod is installed, fork travel is limited. For the internal spring, the fork travel is only limited by the bushings, which is why on my 1100 I can over-extend the fork and lose oil past the fork seal before the fork cap is installed.

I would expect that the ST1300 uses the Honda-common Showa 20mm cartridge, which means you can interchange parts from other bikes that use that same design.
 
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RobbieAG

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I installed the new springs in the forks this past weekend. The Traxxion Dynamics springs come with an ?Omni Buffer Kit? which is a plastic piece and a couple washers that goes into the top of the spring and supports the spacer on top of it. Also, the springs are quite a bit longer than stock. After I added the fork oil and put everything together, it occurred to me that these extra parts have some volume and that the fork oil level should be adjusted accordingly. I had used the Honda spec of 62 mm and had a bit of trouble getting things back together without spilling some oil. I contacted Traxxion to inquire about it and got the response back to change the oil level to 120mm. Wow, I wasn?t expecting such a big difference! I?m glad I asked. Needless to say, I?ll be adjusting the level to the spec recommended by Traxxion.
 

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I'm not going to derail this thread beyond this point but this I know from experience with the ST1300 and other bikes in my garage. I've set sag on three of my bikes that have progressive springs and one with straight rate springs and the amount of extra preload in mm is not the amount of sag reduction on progressive springs.
+1 I added RaceTech straight rate springs. Every 3 mm washer subtracted a greater sag amount than the one before it, I thought of it as a logarithmic decrease in sag. I had to trial and error three times with by adding one washer/spacer to get mine to 35 mm. Total added length was 9 mm. I really have to apply a lot of force on the cap to seal it with that third washer, with just the spacer I could finger press it in. When I talked to RaceTech about it they confirmed that most of the time they have to add or subtract spacers to get it right. PS setting sag on progressive springs generally turns them into straight rate springs, unless your weight matches closely what the spring is rated at.
 
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RobbieAG

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I got everything back together last weekend. I went for a short test ride (15 miles) and so far I'm pleased with the suspension changes. There's noticibly less dive under braking, but it's not harsh or too stiff. I haven't checked the sag yet, but it "feels good".
Next winter, I'm going to get a spare shock that I picked up off of eBay rebuilt and install that. Or maybe I'll do it mid season if I get impatient!
 

mlheck

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What difference does it make measuring sag with full fuel as oposed to quarter tank ?
Not that much. Sag is the average of upward motion and compressed motion on the forks. It is not a hard and fast number. The fuel load my make a 1mm difference if your are lucky. If you were racing the bike and hanging off in the corners like the GP racers then you might notice. Suspension settings are always a compromise and personal. What works for one person may seem extreme for another. I started with the general settings and went from there.

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