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How to set sag

Old 11-25-2006, 07:47 PM
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How to set sag

For all except the newest generation of Showa and some Kayaba forks that have long top-out springs (CBR1000RR, 600RR), I recommend setting the sag to about 1/4 of the total travel of the fork. Stock VTR forks have 120mm of travel, so setting sag at 30mm is about right. Thus, you will have 90mm of fork travel in the direction of compression. For the rear, I like about 25mm sag.

To do this, first measure between the dust seal and the bottom of the lower triple clamp while the forks are fully extended. The best way to do this is to tilt the bike on it's sidestand until the front wheel comes off the ground. Have someone else measure for you. This is measurement A.

Next, get on the bike fully geared up and get into your normal or aggressive riding position, for street or track respectively. A second person needs to hold the bike balanced at the back end. A third person compresses the forks slightly, slowly release the compression, and takes a measurement. This is measurement B.

Do the same thing except slightly extend the forks, slowly let the bike settle, and take a measurement. This is measurement C.

The reason for extending and compressing the forks is to take into account the stiction in the seals and bushings.

Now calculate: Sag = A - [(B + C) / 2]

Adjust preload as necessary. More preload for less sag, and vice versa.
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Old 11-26-2006, 03:53 PM
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Thanks, Greg! I know I'll have more questions once I tear into this. If anybody sees a set of cheap but solid valves floating around - post it up. That's about the only big ticket item that I'm short. I'm still confused about RaceTech's formula for springs. How is .85 good for 165# and .90 good for guys to 220? Seems like an awfully big spread for only .05. I read the discussion about how the rider is weighed gear on/gear off and what their baselines are - it just doesn't make sense. Is the weight of the rider more addressed by the oil viscosity than the springs? If that's the case why not just change the oil?
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Old 11-26-2006, 04:15 PM
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Spring rate is really determined by comparing static sag (no rider) to rider sag. Static sag should be about 10-15mm. Rider sag around 30mm. If you set static sag at 10mm but find that your rider sag is 45mm then you need stiffer springs. Conversely, if you set rider sag at 30mm but you find that the forks are topped out then you need softer springs. It's also partially dependant on how you ride. Track riders prefer stiffer springs and will make a tradeoff with static sag numbers. Street riders may prefer the softer springs for a more compliant feel, while compromising the static sag..

Oil viscosity will determine the amount of damping you will have for a given valve stack. Oil height should be adjusted just high enough so you don't bottom out the forks on max braking with bumps.

Stock oil weight is Showa 10wt SS-8, which has a cSt of 36.47. Oil viscosity depends on the maker. For example, Silkolene RSF Pro 10wt has a cSt of 34.9 and Maxima 10wt is 32.0. The lower the value of cSt, the thinner the oil. So, if you're going to start tuning your own forks and maybe even play around with valving a little bit you should make sure and use the same oil, or at least oil from the same company. If you do decide to do your own valving, valve for a thinner oil. Thinner oils will have a higher viscosity index (VI). The higher the value of VI, the less the viscosity will change with temperature. Thinner oils generally have a higher VI, but not always. It's best to go with "good oil" from a company like Red Line, Silkolene, or Ohlins.
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Old 11-26-2006, 05:04 PM
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I've read other posts where writers have referred to Silkolene but I read one where the user was running ATF. ? In Central Texas response to changing temperatures is the name of the game. We can, and most do, ride all year long. Today was 73F, Wednesday's low is supposed to be 29F (leave her in garage day) but then warming right back up again. Summer can be brutal with air temps at 105F but when you get out over the asphalt 112 to 118F especially in stop & go traffic. Thanks for the info.
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Old 11-26-2006, 05:20 PM
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You never know what you get with ATF. I have the numbers for most of the fork oils.
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Old 11-26-2006, 05:31 PM
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OK, so I got another really stupid question. Is it better (or is it possible) the do the fork overhaul without removing them from the triples? And if you do them in place, it would seem to me that removing the tank would be wise. Y?N? I would really hate to drop a part or a tool on my tank!
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Old 11-26-2006, 05:37 PM
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Spring replacement can be done if fork oil stays. Anything more and you need to remove the forks from the bike.
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Old 11-26-2006, 05:41 PM
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I got a busted set of forks from a 600rr that one of the morons that used to work for me left behind after I helped him replace the busted ones. I'm going to tear them apart just to see what they're made of I want to be very clear about what I doing before I tackle this. So there's no little drain plug thingy at the bottom of the forks? Aw shucks!
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Old 11-26-2006, 06:16 PM
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Yeah, there is a plug at the bottom of the forks, but in order to get at it you need to have the wheel and axle removed, AND have the bike on either a front stem stand or strapped to the rafters. At that point you may as well have the forks off.

'05-06 600RR forks are nothing like the VTR forks. The CBR's fork internals will come out as an assembly, spring and all, just by removing the bottom bolt and the fork cap. The VTR is different. It's hard to describe how, but it's significantly easier since no fork spring compressor is required.
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Old 11-26-2006, 06:23 PM
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They're junk so I'm going to tear them apart just to look at all the parts. I'm used to the rafter thing as we use it to make sure the bikes don't fall over while we're working on them. This is complicated when the fork tubes have to come out because the Canyon Dancer has nothing to anchor to.
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Old 11-26-2006, 06:29 PM
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Frame? Upper triple? Buddy with a good front stand?
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Old 11-26-2006, 06:42 PM
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Yes, I think the frame or the upper triple. I have taken measurements for a beam that will raise the bike straight up. We used the sideways rigging because the ceiling right above our work area has been sheetrocked. The ends of the shop were never rocked so the beams are open. The area is also complicated by the overhead door and an 8' fluor light fixture.
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Old 11-26-2006, 07:00 PM
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this same method is done for the rear too but i forget the settings. I just had my shop do it for me after the install of my fox shock. he set it up and it and the suspension kicks *** now
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Old 07-29-2012, 03:14 PM
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read the thread but didn't see any further adjustment of sag for the rear shock. Is this not necessary for proper set up?
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Old 07-29-2012, 03:53 PM
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Yes it is, but since the stock shock is about as adjustable as a pine 2*4 it's not really going to matter much unless you have an aftermarket one...

You simply cannot get the rear setup properly with the stock shock, since the front and rear are so mismatched that no rider will match both in weight... If you are heavy enough for the shock, you are bottoming out the front... And if you are near to being light enough for the front, you will be bouncing of the saddle when the rear is at it's lightest setting...
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Old 07-29-2012, 06:14 PM
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Originally Posted by Tweety View Post
Yes it is, but since the stock shock is about as adjustable as a pine 2*4 it's not really going to matter much unless you have an aftermarket one...

You simply cannot get the rear setup properly with the stock shock, since the front and rear are so mismatched that no rider will match both in weight... If you are heavy enough for the shock, you are bottoming out the front... And if you are near to being light enough for the front, you will be bouncing of the saddle when the rear is at it's lightest setting...
I see, setting the sag for the front will give the best control and leaving the shock at lightest or next setting will give the best results using the stock shock? No real way to balance the two?
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Old 07-30-2012, 01:42 AM
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What do you weigh?

The rear shock is ballpark correct for a 220-230 pound rider, and while it's complete crap in outright adjustability, it will work decent for that weight... The front is right for a 100 pound rider, and you will not get the sag even close to correct unless you are under 115-120 pounds... So unless you miraculously match both weights at once, you have to compromise... Set the rear as soft as it will possibly go, and crank the front until you get it ballpark right...

And once you have figured out it's not going to get "right", save up for some springs and valves for the front, and a new shock in the rear... Aftermarket are expensive, so I'd look here... Daugherty Motorsports - Motorcycle Suspension Performance and Modification Jamie is on the forum, so he knows his stuff...
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