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Fork oil
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lumpc1
Posted 9/14/2005 10:48 AM (#10024)
Subject: Fork oil


I have noticed on solo riding with my m/c that I needed to go lighter fork oil with the progressive springs to keep from being jarred and to keep from bouncing around. has anyone experimented with a heavy bike on a rig? I think I went down to 5w or maybe 10w. should I go up to 15 or 20w? oh ya, light car, velorex 562.
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Hack'n
Posted 9/14/2005 12:00 PM (#10027 - in reply to #10024)
Subject: RE: Fork oil



Expert

Posts: 4833
2000200050010010010025
Location: Boise, Idaho
I have recommended Heavy duty or racing oil for sidecar applications since that is considered Heavy duty motorcycle usage. It slows the suspension rebound down a little and will help stabilize the rig to a small degree.

Lonnie
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Uncle Ernie
Posted 9/14/2005 5:14 PM (#10029 - in reply to #10024)
Subject: RE: Fork oil


Oil weight is one thing, but there is also the amount that you can adjust, as well as the spacer length
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lumpc1
Posted 9/14/2005 7:03 PM (#10033 - in reply to #10024)
Subject: RE: Fork oil


Thank you for the specifics UE
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Uncle Ernie
Posted 9/14/2005 8:53 PM (#10041 - in reply to #10024)
Subject: RE: Fork oil


Sorry Lump- here is my understanding;
Fork oil works by passing through little passages. Thinner oil will cause the forks to react quicker, but too thin and they may seem too bouncy. Spacer length is like pre-load on your rear shocks sortakinda. Puting more oil in will make the forks stiffer. For instance, with the same solo bike I would like the stock manufacturers recommended amount of fork oil. My friend who is 6'4'' and weighs 75lbs more might like 25cc more than stock to compensate.
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claude #3563
Posted 9/14/2005 9:16 PM (#10043 - in reply to #10041)
Subject: RE: Fork oil



Expert

Posts: 2480
2000100100100100252525
Location: Middleburg, Pa
Hey does anyone still use transmission fluid in their forks?
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BrianP
Posted 9/15/2005 6:02 PM (#10064 - in reply to #10024)
Subject: RE: Fork oil


Please explain how putting more fork oil makes forks stiffer??? I thought the stiffness was controlled by the spring and pre-load spacer. The fork oil weight controls the re-bound. Heavier weight oil (thicker) slows the rebound. This is how I understand the process.
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claude #3563
Posted 9/15/2005 6:36 PM (#10065 - in reply to #10064)
Subject: RE: Fork oil



Expert

Posts: 2480
2000100100100100252525
Location: Middleburg, Pa
There is some interesting reading here:
http://motorcycleinfo.calsci.com/Suspension1.html
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Uncle Ernie
Posted 9/15/2005 7:42 PM (#10070 - in reply to #10024)
Subject: RE: Fork oil


Brian, as I've used Earles forks most of my life, this regular front fork stuff I'm just learning myself. I have a very light bike (GB500) and wanted to get rid of the old and put in fresh oil. The guy who helps me with this kind of thing sets up things for himself, often times. He is a behemoth next to me and put too much fork oil in there thinking I would like it. Well- everytime I went over a little bump it was like the front end of the bike was hit by a huge hammer. We took out about 25cc on each side and it's wonderful now.
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Hack'n
Posted 9/16/2005 2:53 PM (#10083 - in reply to #10070)
Subject: RE: Fork oil



Expert

Posts: 4833
2000200050010010010025
Location: Boise, Idaho
I think the first post was in regards to fork oil viscosity, not volume or spacers.
I prefer changing weight of the fluid as opposed to overfilling the front forks.

Claude,
Some still use AT fluid. I have a good friend who is a diesel mechanic (and long rider). He prefers OC 32 turbine oil in in his Harley primary and AT in the forks.

I use Amsoil for everything except frying possum.

Lonnie
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Posted 10/16/2005 7:30 AM (#10806 - in reply to #10024)
Subject: RE: Fork oil


I've always been of the mind that the guys that designed these "any" fork . Figured out what oil and how much to run . In my days I've added oil and had it leak outa seals . I've used heavier oil and had it pump the forks ,on "seamed highways" , or washboard roads .... So hard that no spring or rebound action was observed . Figured out that.... The heavy oil has to pass both ways in the system . I've found the difference between 5 and 10 weight is a LOT more than 5 numbers also . Most of my front ends have slightly less oil than reccomended . Using the reccomended viscosity . Progressive springs are my first "upgrade" , always . All the above pertains to solo MC's . I'm about to mount a hack on an R00RT BMW . I'll be watching this string and my "oil" levels regularly . Ride safe
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normpottruff
Posted 10/18/2005 1:00 AM (#10867 - in reply to #10064)
Subject: RE: Fork oil


Good Day,
The area in the tube above the fork oil is of course full of air. When you screw the fork cap on to the top of the tube it traps this air in a sealed pocket. Now whenever the forks compress they also must compress this air so you have increasing resistance as the fork rises. If you put more oil in the forks you reduce the size of the pocket that the air has to compress in so you get more resistance quicker, i.e stiffer forks. I often play around with fork oil level to tune a suspension and I've found it can make a dramatic difference but you can only increase it by a reasonable amount or you risk blowing fork seals.
Regards,
Norm
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akathetroll
Posted 10/19/2005 7:51 PM (#10936 - in reply to #10024)
Subject: RE: Fork oil


Since I've only been driving a rig since July, this is what I've done.

Fork oil - 30w Why, because the person who set my rig up recommended it.

Amount per tube - 13.4 oz mfg recommended '92 Virago 750. Used 16 oz per tube. Why, stiffer suspension when using a sidecar is recommended. Also, half of a quart no leftover. Have driven over 1,000 miles since change and no leakage by seals.

Have been told Progressive springs are also the way to go. Know a person who got them and Progressive recommended a spacer also (Virago). I'm cheap so decided to use existing springs with a spacer (ended up adding 2.5"). Not easy, took muscle/technique. Not looking forward to changing fork oil someday, some real pressure on them fork caps.

With all these changes, I can still push the front end of the sidecar down and the front forks will move a good 1". The changes I did worked well for my Virago.

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