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  #71  
Old 11th March 2015
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"Frankenshock", now that right there is catchy, looks good and nice to have all the adjustabilities. Interesting and thanks again this is kind of fun.
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  #72  
Old 11th March 2015
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Neat idea. Be sure to do a write up on finding correct rebound / compression dampening settings. Did you get a chance to ride on stock shocks? How much do you weigh?
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  #73  
Old 12th March 2015
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I will be riding on stock suspension this weekend but not really fun riding per se. It will be to see what kind of loads I'm putting on the bike (front and rear) under what conditions. I'm guessing straight line [hard] braking will produce the highest front fork loading. Hard braking followed by hard acceleration probably greatest loading on rear.

Will do on the damping - after I get the springs sorted out. I have to know the springs are set up for the loads without bottoming out. Then, I can concentrate on the damping.

I weigh 195; probably between 210 and 215 with gear.

Jerry
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  #74  
Old 14th March 2015
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Default Front Suspension

Its going to rain almost all day tomorrow, so I have to just suck it up and finish out the baselining tomorrow so Sunday is the riding day to verify riding envelope.

Tonight, I pull the front right fork to:
- Verify working range
- Set up fork for verifying riding envelope
- Test to determine spring rate
- Determine spacer length for front sag (25% of working range)

Pic 1: Front fork off the bike. I pull the fork cap to let fork tube compress all the way. I add a zip tie pushing it all the way down to the fork lower; then add black electrical tape to mark max working range of fork (3.63")


Pic 2. I drain all the oil because I do not want to have any trapped air acting as another "spring" during the testing, then add the cap back on. I then take the fork downstairs to place it in the gym equipment and start loading up weigh while recording the compressed distance. The spring is another weak one! 225 lbs, and the spring is more than done...


Pic 3. Test results, a spring rate of 45.0 lbs/in!!! By knowing the equation of the line (I use microsoft excel to do a curve fit and tell me the equation of the line) and the observed sag measurement of 1.31", I can figure out the load running through the spring; 110 lbs. I can also figure out the oem spacer length (1.13").


Pic 4. I can see at 1.31", I am using up too much of the fork working range of 3.63". At 0.25% of 3.63" = 0.91". So I need to cut a longer spacer to shift the dotted line to the right. A little math later, I can see I need a spacer of 1.52". Keep in mind the oem spacer is longer than 1.52". That is because the spring does not come up close to the cap; so the oem spacer has to close that gap then add an additional ~1.13" to compress the spring. My new spacer to set a good front preload (at 25%) is going to be 1.52" - 1.13" = 0.4" longer than the current oem spacer. So tomorrow, I will go to HD and get some PVC pipe to cut the new spacers.


I'll also spend some time tomorrow during the rain correcting the rear oem spring data so I'll have the rear suspension ready for ride/testing too.

I suspect I will get the corrections done early enough to experiment a little on the front fork with some water to account for the "air spring". This will help me when riding to not bottom out and figure out what what rate spring to get.... I want to hear from some of you on what I mean by the air spring...

Enjoy
Jerry
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  #75  
Old 14th March 2015
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What do you mean by "water"? Does the straight line graph demonstrate the spring rate is straight rate?

A few guys, myself included, have added schrader valves to the fork caps to have an adjustable air spring. Nobody really knows how much air pressure is too much for safety, generally 3 to 5 psi is considered safe, but that is a guess based on no reported problems.

I usually call it air chamber instead of air spring.
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  #76  
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Quote:
Originally Posted by XLXR View Post
What do you mean by "water"?
I'm going to fill the fork with water to determine the total volume of the fork. Then, I will empty, then refill to spec volume with water to experiment which volume of water gets me additional help with overall spring rate (steel and air spring).

Quote:
Originally Posted by XLXR View Post
Does the straight line graph demonstrate the spring rate is straight rate?
Yes, it looks like the steel oem spring is a linear rate spring. limited data set (3), but has a X squared curve fit of 1. The only way to get a "1" is to have a straight line curve fit.

Quote:
Originally Posted by XLXR View Post
A few guys, myself included, have added schrader valves to the fork caps to have an adjustable air spring. Nobody really knows how much air pressure is too much for safety, generally 3 to 5 psi is considered safe, but that is a guess based on no reported problems.
The fork is a sealed chamber with a number of things inside. All the metal things have a fixed volume. That leaves air and oil volumes as the only things to play with. By adding more oil, thnere is less air and vice versa. Your choice to add air via a schrader valve allows you to make adjustments easier. You can do the same thing by adding more oil. Since I am testing and want to avoid the expense of adding a schrader valve, I'm going to use water as a substitute for oil.

Pic 1. This shows the affect of compressing the air chamber as you call it. If I had a 3" air column (at atmospheric pressure of 14.7 psi) and compressed it in half, the pressure would double to 29.4 psi. If I kept cutting the distance in half (next would be to 0.75"), the pressure keeps doubling. You can see what happens to the pressure. If you add a schrader valve and add 5 more psi, you get the red line on the graph.


Pic 2. A fork example: On the left you see the fork with oil and air chamber. Next pic over is that fork compressed. The air chamber is now 1/2 the volume it was. Third pic is the same fork with some extra oil in it. 4th figure is the compressed fork with the extra oil in it. You can see the air chamber is now only 1/5th the air volume.


Pic 3. The affect of the changing air chamber can be seen in this graph. I am in effect moving up further on the psi curve. The additional air pressure acts as a spring, hence, why I call it the air spring. This air spring affect is additive to the steel oem spring to help me keep from bottoming out. Its the cheap way of finding the spring rate I need for the bike.



I have to get my shop manual I left at another place so I know the spec volume of oil. I'll post back the experimentation with water and what the total volume is later today.


Quote:
Originally Posted by XLXR View Post
I usually call it air chamber instead of air spring.
It is an air chamber, but since it varies as the fork compresses, it really acts like an air spring...
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  #77  
Old 14th March 2015
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Some info I have been posting over the years to help guys understand:

Generally, I recommend guys start with stock oil height. Test ride, if bottoming out, then add oil. Generally, long forks can add up to 2 oz, short fork 1 oz extra oil. Anything more than that tends to cause hydro locking, so it is best to add just enough oil to control bottoming, which may be less then 1 or 2 ozs. Generally, if adding more oil than above to control bottoming, and assuming preload and oil viscosity is correct, the main spring is too light and needs replacing.

How did you come up with the psi scale up to 2,000 psi? Even working range up to 500 psi seems a lot to me, but I have never measured it.
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Generally, I recommend guys start with stock oil height. Test ride, if bottoming out, then add oil. Generally, long forks can add up to 2 oz, short fork 1 oz extra oil. Anything more than that tends to cause hydro locking, so it is best to add just enough oil to control bottoming, which may be less then 1 or 2 ozs. Generally, if adding more oil than above to control bottoming, and assuming preload and oil viscosity is correct, the main spring is too light and needs replacing.
These look to be good rules of thumb; I will be interesting to see what the testing shows.

How did you come up with the psi scale up to 2,000 psi? Even working range up to 500 psi seems a lot to me, but I have never measured it.
What I posted were math extrapolations. I did not set up something, then measured it. I suspect the fork seals would not hold anything close to that pressure. Perhaps a few hundred psi max? If you had too much oil in, I suspect you would see weaping of oil on the fork tubes as well as experiencing the "hydro locking" condition you mentioned above.

Jerry
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Quote:
What I posted were math extrapolations. I did not set up something, then measured it. I suspect the fork seals would not hold anything close to that pressure. Perhaps a few hundred psi max? If you had too much oil in, I suspect you would see weaping of oil on the fork tubes as well as experiencing the "hydro locking" condition you mentioned above.
Just to be clear and for safety reasons, an additional 3 to 5 psi air pressure to the forks is OK. DO NOT TRY ADDING 2,000 psi!!!!!!!!
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Old 14th March 2015
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How does 45 lb/in spring compare with 1.0 kg/mm?
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