zxrcy
Novice Class
Posts: 62
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posted March 05, 2003 08:46 PM
Fork Oil Weight
Has anyone tried changing the oil to a lighter weight to reduce some of the suspension harshness on the stock forks and valves.
  
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zxrcy
Novice Class
Posts: 62
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posted March 06, 2003 12:34 PM
Suspension Oil Weight
Has no one tried changing oil weight on the 12 to improve the ride ????? I talked with a number of people about suspension changes to get rid of the harsh feel over small bumps at high speed and this was one of the first things they mentioned before changing the valving. A number of reviews have faulted the 12 for it's harsh suspension feel. The problem seems to be high speed damping. My understanding is that you can only alter it by changing the valving or the oil weight (viscosity). I have my 2000 suspension set up to the recommendations put out in the British magazines a couple of years ago. Comments?
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redelk
Moderator
Please... speak to the hand.
Posts: 3212
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posted March 06, 2003 05:18 PM
I've tried 15 wt with the OEM spring. Was not a good move. Tried going to 7.5 wt and really didn't see much difference. Ended up going back to 10 wt.
Then I switched to stiffer RaceTech fork springs (S382710), shorten preload spacers 25mm (per their instructions) and switch to 5 wt, even though I did not switch to the RaceTech valve kit. I quickly noticed a MAJOR difference. It seemed to quicken the damping, but not too twitchy. It's kinda hard to tell what exactly caused what improvements for three reasons.
1. changed to stiffer fork springs at the same time
2. recharged the rear shock to 200 psi (spec is 143 & mine had 60 before the recharge)
3. I'm not the world's greatest rider and probably would know the difference anyway.
The most important thing to do when changing the oil, springs or pressure on any part of your suspension is after you do the changes, you MUST completely reset the supension settings. I mean starting of by remeasuring the sag and going from there.
Here a link to Sport Rider's Suspension Tuning Guide. This is the "BIBLE" of suspension tuning.
http://www.sportrider.com/tech/146_0006_susp/
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There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
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Zhooligan
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Post Whore Extraordinaire!
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posted March 07, 2003 08:17 PM
Elk you are awesome with the endless resource of info. I have carried the original sportrider magazine articlein my tool box all over the country. And it is beat to crap! Now I can print out the info at will!!!
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To those who do not count their life in years, but in how life
has touched them in the past and how much it can hold in the
future; -- Youth is forever.
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zxrcy
Novice Class
Posts: 62
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posted March 07, 2003 11:03 PM
Thanks Red I think I will order a set of the Race Tech springs. Did you put them in yourself. I notice from the manual you need a specialized spring compressor to get the shock apart.
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12RPilot
Pro
Posts: 1094
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posted March 08, 2003 07:40 AM
Pray tell, Redelk. Do you have a pic of your spring compressor? J/K
 
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zxrcy
Novice Class
Posts: 62
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posted March 08, 2003 08:00 PM
 Edited By: zxrcy on 8 Mar 2003 20:01
Well I ordered the springs today. How about that spring compressor do you really need one. I replaced the springs on my CBR 900RR track bike a couple of weeks ago and you didn't need to compress the springs, just back off the preload adjustment. Is that good enough for the 12. Do you get enough room to get at the rod nut??
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redelk
Moderator
Please... speak to the hand.
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posted March 08, 2003 09:09 PM
Try looking here...
http://www.bikeland.org/board//viewthread.php?FID=1&TID=2642
____________
There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
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zxrcy
Novice Class
Posts: 62
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posted March 08, 2003 09:45 PM
Thanks Red seeing your picture gives me an idea how to make a little tool to grip the tube and use ratchet tie downs.
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zxrcy
Novice Class
Posts: 62
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posted March 11, 2003 08:22 PM
Edited By: zxrcy on 11 Mar 2003 20:22
Red I got the new springs and Racetech suggests 5W oil over the 10W stock. I don't understand why? The spring is a heavier 1 kg spring so you would think that if anything you would want a heavier oil to provide additional damping. The 12 has been criticized for harsh damping. Does the lighter weight oil help reduce this harshness in high speed damping. Anyone else have experience with a lighter oil.
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redelk
Moderator
Please... speak to the hand.
Posts: 3212
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posted March 11, 2003 09:17 PM
I might have the experience with 5 wt fork oil, but I'm the last person you'd want to ask about REAL high speed riding. Don't forget to check your shock pressure.
____________
There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
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zxrcy
Novice Class
Posts: 62
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posted March 11, 2003 09:40 PM
Any idea what changing the pressure in the rear does.
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Zhooligan
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Post Whore Extraordinaire!
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posted March 11, 2003 10:05 PM
Let me understand your question zxrcy? Racetech i.e. One of the very best the suspension gurus, the guys with shock and fork dynos, the guys who don't rely on theory alone, their motto is put it on the shock dyno or put on the bike and test it? They said put in 5 wt and you wonder if it is ok?
I am running 5 wt. and it works great.
Your question about more pressure in the rear shock is a good one. The reason the shock is charged with Nitrogen is essentially to prevent the shock from cavitating. Esentially any air however minute is forced into solution and does not cause or allow cavitation. Guys who rebuild their shocks usually go to great extremes getting all of the air out when they fill them with fluid. It is kind of fun to watch all of the creativity used to do this. But with all of the best intentions, hard work etc., let the shock set for a little while and magically a few air bubbles eventually appear. Pressurize the shock and boom no bubbles! A few years ago the magic number to charge your rear shock too was about 154 pounds, these days its around 172 to 174 pounds.
If you have the time and the money, the Race Tech Suspension certification school is a heck of a school. In my opinion worth the time and money. Helps to seperate a lot of the myths and superstitions about suspension from facts and reality.
____________
To those who do not count their life in years, but in how life
has touched them in the past and how much it can hold in the
future; -- Youth is forever.
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zxrcy
Novice Class
Posts: 62
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posted March 12, 2003 07:30 PM
Thanks Z, wish I lived closer to Racetech I'd take their course. (3000mi) The problem is all the conflicting comments you get in the magazines about the 12's shocks. Some of the magazines were talking about slowing the damping movement down by going to heavier oil (Two Magazine - Nick Jeffries) I was also not clear on the web site whether the fork oil they recommend is based on using their Gold Valves. It does make sense that to reduce the harshness you use a lighter weight oil. I bought the 5W so that's what is going in. Racetech also recommends 200 psi in the rear shock. So the reservoir pressurizing is just to control foaming of the oil?
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Zhooligan
Moderator
Post Whore Extraordinaire!
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posted March 12, 2003 09:05 PM
That is really all it is doing. So put the 200 they are reccomending but don't fret if your at 198 or 201 and have a problem hitting 200 on the nose.
____________
To those who do not count their life in years, but in how life
has touched them in the past and how much it can hold in the
future; -- Youth is forever.
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zxrcy
Novice Class
Posts: 62
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posted March 16, 2003 12:58 PM
Well I re-pressurized the rear shock and put in the new 1kg springs. Racetech instructions say to cut 25mm off the spacer tube. This gave a tube length of 84mm. I did this put everything back together and couldn't get the static sag with rider load to be less than 38mm before I ran out of preload adjustment.
I went back and read Racetech's comments on the setup guide from the spring selection chart. It says that the 12's fork requires 40-45mm preload because of the top out spring. I understand that this means the first part of the travel is actually assisted by the top out spring load so the first part of the travel settles further with less load. I found the static sag with just the weight of the bike was giving 30mm of sag by itself.
I pulled the fork apart again and put in 4 preload washers at the top of the tube. With full preload adjustment this at least puts the static sag with rider at 33mm which is within the range for street setup. This is with full preload adjustment. It would seem that the spacer tube could have been left without cutting it. If I want less sag now I will have to add more washers.
Has anyone had these problems? I don't have a record of the sag from the stock springs. Is the 12 set up to run with more sag than other bikes. Or did I not get the spring rate I ordered from Racetech. The box showed a 1kg spring. Z , Red can you help out here with any ideas or experience.
Thanks
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zxrcy
Novice Class
Posts: 62
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posted March 17, 2003 01:17 PM
Edited By: zxrcy on 17 Mar 2003 13:19
Red & Z Anyone? what sag are you running. I called RaceTech today and they said the website instruction to cut 25mm off the spacer tube was just a guide and may not apply to all bikes. It would appear mine did not need to be cut to give me the proper preload adjustment range. So much for the instructions. The RaceTech tech said he has never even seen the preprinted instructions.
Anyone had a similar experience setting up their forks with RaceTech springs.
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