setting suspension sag - K-Bikes.com - Excellence in Motion
 
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post #1 of 7 (permalink) Old May 27th, 2008, 8:50 pm Thread Starter
 
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setting suspension sag

Does anyone have any thoughts on how this is done? Does it take two people to do this?
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post #2 of 7 (permalink) Old May 27th, 2008, 9:30 pm
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The procedure is described on the Ohlins site, among other places. You'll need something like a trammel bar, and, for sure, two other people. One to sit on the bike, one to measure, and the third to hold the bike from falling over.

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post #3 of 7 (permalink) Old May 28th, 2008, 8:39 am Thread Starter
 
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ok...the procedure is outlined sure enough...but does anyone know the principle behind the prodedure? As far as the front spring goes......Does a softer front spring raise the front end? Does a firmer front spring lower the front end? What is the purpose for adjusting the suspension sag? The object should be to get the weight distribution as you ride 50/50 front/rear right? Can I make adjustments based on feel to achieve this instead of measurements?

Last edited by BigHausLittleFalsy; May 28th, 2008 at 10:59 am.
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post #4 of 7 (permalink) Old May 28th, 2008, 1:14 pm
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Softer front spring will lower the front (given same weight and distribution fore/aft). Firmer front spring will keep the front higher.

Purpose of adjusting sag is so you don't top or bottom the suspension while riding over the majority of road conditions. The setting changes if you change weight by adding a pillion or luggage (or if you gain/lose weight).

Spring rate / sag (pre-load) / damping settings have nothing to do with fore/aft weight distribution. However, they do have a marked effect on how the bike handles in corners and bumps. You want to adjust these so that 1) you don't top or bottom the suspension, 2) you are comfortable, and 3) the bike corners well (doesn't push or slide out). There is also the affect of packing and jacking that you want to adjust damping for (more of a problem on dirt bikes). Adjusting spring rate / sag / and damping will have an affect on pushing / sliding, and comfort.

Razel has some good posts on setting sag. You might do a search on his posts.

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post #5 of 7 (permalink) Old May 28th, 2008, 5:35 pm Thread Starter
 
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Thanks for clearing up my misconception about raising and lowering the front end. I'm probably going to a pretty firm setting on the front spring at this point. I've given up on nice and plush because it sacrafices too much in the twisties. I've always preferred a more taut set up anyways. After the front spring is set...I guess just dialing in enough rear pre-load to balance the bike and I'm done setting the sag? Wasn't I suppose to measure for sag? Is measuring a more precise way to set spring pre-load/sag?
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post #6 of 7 (permalink) Old May 28th, 2008, 6:29 pm
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Static sag should be set so that the bike sits in the top one/third of its travel. For the K1200RS / GT, there is roughly six inches of travel, so you want to set pre-load so that you have two inches of sag based on your normal riding set-up (based on your writing, you're probably solo without luggage or extraneous gear). You'll crank-up pre-load if you add weight with a passenger and / or luggage. To measure this two inches, you usually need to have someone hold the bike and take a measurement.

Note that there is a difference between spring rate and pre-load settings. Spring rates can only be changed by physically changing the spring on the shock. Pre-load is adjusted by turning a knob or nut on the shock.

Pre-load is used to get the suspension set within its operating range so that it doesn't bottom out or top out. You do this as described above. If you have pre-load adjusted properly, and still bottom out too often, then you need a firmer spring (or softer spring if you find yourself topping out).

Once sag is set, then you'll want to look at compression and rebound damping settings. These need to be adjusted so that you get the right handling for your style: firmer for twisties, softer for cruising. Soft settings can also lead to bottoming. Finally, you want to ensure that compression and rebound and balanced so that you don't get a jacking or compression problem when exercising the suspension over a succession of bumps.

Spring rate = coarse adjustment
Pre-load or sag = medium adjustment
Damping = fine adjustment

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post #7 of 7 (permalink) Old May 28th, 2008, 10:36 pm Thread Starter
 
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Ok...my rear spring pre-load is set at zero....I've got a heavy duty rear spring...it almost seems like it's topping out. I probably need to add 50 lbs of weight to the back for it to sag properly. I'm guessing only..but I think I'm starting to understand this more thouroughly. Thanks again for going into further detail about sag. Hopefully firming up the front spring will raise the front end enough to put more weight on the rear as well.
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