REPRINT FROM OLD HTT: RKC Fork Oil With Progressive Suspension Springs

[ClassicRider2002]

DISCLAIMER: THIS IS A REPRINT TOPIC FROM "OLD" HTT

I have saved many great topical discussions as "links" over the years and would hate to see these lost, so I am reprinting this TOPIC here, which may "perhaps" help some.

TOPIC: RKC FORK OIL WITH PROGRESSIVE SUSPENSION SPRINGS  02-13-05


   

From: KaritheFinn  (Original Message) Sent: 2/13/2005 1:29 AM   Message 1 of 19 in Discussion
Gentlemen,

I have PS 12" 440 shocks and PS normal length fork springs for my 2004 RKC. Which weight fork oil should be used to have a balanced ride? I noticed that MoCo carries 3 different oils:

99880-73 Type B
99884-80 Type E
99881-87 Screaming Eagle

Are the MoCo fork oils good or is some other brand clearly better? I always ride solo with little luggage. Your advise would be very welcome.

[ClassicRider2002]

 

From: ClassicRider2002 Sent: 2/13/2005 7:56 AM   Message 2 of 9 in Discussion
Good Morning....

Before you actually close up your front forks...if you are going to the trouble of changing the springs in the front.....if you have the time and inclination....you might want to investigate the usage of the Race Tech emulators for your front forks....I have Progressive 440 12" shocks on my 2002 RKC and I also put in the Race Tech emulators plus the Race Tech standard spring as a entire package for the front fork set up....which has turned out to be very nice indeed....

Here is some information about the race tech product:

Gold Valve Cartridge Emulators
Damping rod forks are notorious for being both too harsh and too easy to bottom. This is the nature of damping rod fixed orifice forks. Until now, all you could do is change spring rate, oil viscosity and damping hole size. The best available was a serious compromise.

Emulators make damping rod forks perform like well-tuned cartridge forks. Emulators are tunable valves that sit on top of the damping rods and are held in place with the main springs. This makes them both simple to install and completely tunable for all conditions and rider preferences.

Here are some easy to reference Answers to some of the most common Questions:

Q: I have heard of progressive springs and this concept makes sense to me. Why does Race Tech recommend Straight Rate Springs for forks?  

A: When setting up the spring forces in a bike you want a setup that is progressive enough yet not too progressive. A setup that is not progressive enough will have a tendency to feel too harsh yet when a big hit is encountered bottoming occurs. A setup that is too progressive will either drop through the travel feeling mushy and then feel as though it hits a wall or can feel good until it hits that wall. On front forks there are two forces we consider to be "spring" forces. First is the coil (mechanical) spring and second is the force due to air pressure and oil level. Even if you run zero air pressure the oil level causes the pressure to increase as the forks are compressed. By its very nature this increase in pressure is very progressive. We have found that in combination with a straight wound spring we have a good level of progressiveness. If we want more progressiveness we simply raise the oil level.

Q: What is the difference between raising the oil level and changing the viscosity?

A: Raising the oil level increases the compression ratio in the front fork and therefore changes the progressiveness of the spring forces. This has nothing to do with the damping (key point). Changing the oil viscosity changes the damping. Both the compression and the rebound. The spring forces are sensitive to position in other words where it is in the travel while damping forces only care how fast the damper is moving.


Race Tech's Website:
http://www.racetech.com

Ok so you did not actually ask about the springs.....I just put the above information in for you to ponder another solution...you did ask about fork oil....for my 2002RKC I have used Belray 20 weight Fork Oil....

I wish you could ride mine to see how it handles....I think you would be impressed.....it's so impressive that another buddy of mine is going to be going to the same exact set up for his 1998 RK.

The Race Tech emulators and srpings go for around $270.00 for a kit.  Others on this board have had varing degrees of success with Race Tech's support, personally mine has been the best support you can ask for....they were always helpful with me....it took a bit of time to connect with them but when accomplished very helpful....

It took my independent mechanic nearly 5 hours to tear down and reinstall the new set up on my forks....as I was also at the time putting chrome lowers on....I did all of this together....He only charged me for 4 hours so the entire cost was around $500.00 for the front suspension inclusive of parts......

I realized you basically only asked about HD fork oil...and I have taken it beyond...but since we have similar bikes (mine being a 2002 RKC) I thought perhaps this might be helpful as well....and if not perhaps it will be for someone who might open it....

For me I really was feeling like upon braking my bike would really dive from me....and that I was feeling more of a ride similar to like on a cadillac where you feel little road response....and I like more of a ride that gives you more "road feedback" perhaps it allows me to feel more of what the bike is doing....in addition upon braking after all of this was done.....the bike also does not "physically" dive from me anymore.....which is very important to me....

Perhaps you will find this info helpful....

Regards,

"Classic"


From: KaritheFinn Sent: 2/13/2005 11:08 AM   Message 3 of 9 in Discussion
Classic,
thanks for your response. I did earlier give some thought on Race Tech emulators but I've blown my budget way, waay too wide so I decided against them at least at this point. I'm doing chrome lowers so PS springs go in at the same time. I have no idea what weight HD B and E are but I'd guess B is stock so I'll put E in. I don't think my dealer has other stuff than HD in stock. I want get more controlled dive and get more planted feeling on the front.


From: Dakota Sent: 2/13/2005 12:19 PM   Message 4 of 9 in Discussion
When I put in my progressive fork springs, progressive recommended I use the stock harley fork oil. The local dealer told me to use Type E, which was stock. I did this last fall but only got to ride about 1/2 mile to test and it's been cold ever since. I also added the 440 HD shocks at the same time. I had to set them to their lightest setting when I was the only one on the bike, but I normally ride two up.  Dakota


From: HIPPO_ Sent: 2/13/2005 12:21 PM   Message 5 of 9 in Discussion
Kari, when we had bikes that had damper tubes in both legs we used to try and tune them to some minor degree with fluid viscosity and fill amount.  For my weight 15 weight fluid overfilled by about 1 or 1.5 OZ worked extremely well, for others that were heavier 20 weight at the factory fill level.  I always used BelRay fork oil but any good brand will do. One can mix different weight fluids from the same manufacturer to fine tune if desired but I would strongly recommend against mixing brands of fluid. But I have to agree, as much bling as is on the bike the Race Tech emulators are a drop in the bucket and well worth the money in particular when the legs are going to be apart anyway.


From: KaritheFinn Sent: 2/13/2005 12:42 PM   Message 6 of 9 in Discussion    
Thanks guys. I was reading through 2004 Service manual and read Type E to be stock weight just before I saw Dakota's reply. Any idea what weight Type E and #99881-87 Screaming Eagle fork oils are?

Hippo, I agree with you fully - cost of Race Tech Emulators is pi$$ in the wind compared to whole investment. But Emulators were not in stock in Europe when we asked while the PS springs were readily available in Finland so that was an easy decision for a change. But I still get this feeling of "it might get even better". Oh well, just springs for El Cheapo for now.


From: HIPPO_ Sent: 2/13/2005 12:47 PM   Message 7 of 9 in DiscussionHD has to make everything a mistery, but what comes stock in the touring bikes Showa legs is like a 10W.  


From: KaritheFinn Sent: 2/13/2005 12:55 PM    Message 8 of 9 in Discussion 
So E equalling Belray 20W cannot be valid?
 

From: HIPPO_ Sent: 2/13/2005 1:14 PM    Message 9 of 9 in Discussion
Maybe close, but in my experience the 15W is heavier then the stuff that comes in there from the factory and the E which I guess is what they call "sport fluid" is a lot heavier. Probably close to the 20W.

If you use the E then I would definitely use the exact factory fill recommended amount and no more, they do get pretty stiff in a hurry in particular with better springs.

On the older bikes with the air assist it took 5 minutes to change it so it was easier to make little adjustments until you liked it. If I had one of the new bikes without cartridge I would change the top caps to the old style to have the quick change capability, short air lines are real easy to hide.
 

[ClassicRider2002]

Anything added beyond this point is new information.

Regards,

"Classic"

[ClassicRider2002]

As of November 23rd, 2008, this reflections would more accurately state what I feel about what fork oil should be used with a 2002 RKC when used when either changing simply the fork oil or when using the Race Tech Emulators:

ON MY 2002 RKC I HAVE DONE THE FOLLOWING:

The 2002 Factory Service Manual states that for a 2002 Road King with Conventional “Dampening” forks place 11.1 oz of fork oil in each of the right and left fork legs.

HIPPO~~~02-13-05: 
For my weight 15 weight fluid overfilled by about 1 or 1.5 OZ worked extremely well, for others that were heavier 20 weight at the factory fill level. I always used Bel~Ray fork oil. Referred to as the “HIPPO” Recipe  

I Replaced the fork oil for the 2002 RKC on June 27, 2008.
I replaced with 10 oz of 20w Bel~Ray Fork Oil In Each Fork Leg.

With next fork oil maintenance I will see how much oil comes out….because I precisely put in 10 oz.

Personally, I think I should put in 11 oz next time or 11.5 oz and why I chose to put only 10 oz in, June 27th, 2008 was because I placed back in exactly what came out from when I initially installed the Race Tech emulators and chromed lower forks back in 2004.  SO I wanted to match exactly what was in the bike as I liked how it rode, next time PERHAPS a bit more? Some are putting in .5 oz over the OEM Factory specified amount, which is 11.1 oz.

From: HIPPO_   Sent: 2/28/2002 2:14 PM
The air pressure has no effect on damping. It affects spring rate. By upping the oil level, within reason, you achieve the same thing and avoid having to constantly check the pressure, as it leaks down over the time of a trip. That's all.  The weight of the oil is what affects damping, heavier oil, more damping. It must have been the right idea, because the new setup on the 02 right side FLT forks, and both on the RK's, does basically the same thing. You can see they specify different oil volumes for the cartridge and conventional legs now. 
(additional note by me, 2002 Factory Service Manual for Touring Bikes states that for ALL MODELS (Except for the Road King Models ie: FLHR, FLHRI, FLHRCI) the left side ie: the cartridge side is to be filled to 9.9 oz and the right side FOR ALL MODELS ie: the dampening rod side the Factory OEM Level calls for filling to 11.1 oz.


Race Tech Website:
http://www.racetech.com/articles/CartridgeForks.htm

Regards,

"Classic"

[ClassicRider2002]

This reflection was made in 2007 by Mike52 who owns a 2006 Street Glide and speaks to what he decided to do with his bike when doing a fork oil change:

From:   Mike52 Sent: 10/23/2007 7:43 PM
......if you want to go to a heavier fork oil, I'll highly recommend Bel-Ray 20wt. This was recommended to me by several members on this board. I used the Bel-Ray 20wt with an extra 1/2 oz (as recommended) when I changed to chrome lowers on my '06 Street Glide and really like the way the bike rides and handles. On the first ride after the swap I thought that I made a mistake because the front end felt a little too stiff. It did feel more firm than the stock set-up, but after putting a few more miles on the bike and swapping bikes with a couple of friends with '05 E.G. Classics, we all felt like my bike rode better than the others. I don't think you will be disappointed with the 20wt Bel-Ray.

Mike