How do you guys measure sag?- Mtbr.com
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  1. #1
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    How do you guys measure sag?

    I know a lot of people suggest measuring sag while in that attack position, but I'm thinking that's more for enduro and downhill. When I measure my 30% rear sag while standing on the bike, it becomes more like 50% when I sit. I figure 'all mountain' riding or trail riding involves a lot of pedaling while sitting so to me, it makes more sense to measure sag while seated. What are you guys doing?
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  2. #2
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    Seated for the rear since it's based on pedaling efficiency. I don't pay much attention to the front sag.

  3. #3
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    I dont. And neither should you.

    https://www.shockcraft.co.nz/technic...spension-setup

    These days, with debonair style cans, there can be a HUGE spring rate change (change in pressure) with very little sag change. Its unreasonable to continue using sag. Ive seen people recommend 30% out back. That would be similar to using a piece of rebar as a shock on a debonair can.

    Further, if you set both ends to 30% and your front end wallows terribly, and your rear is rock hard, doesnt it seem crazy to call that ideal? Both ends should be setup until they're properly sprung for your weight, your riding style, and your preference.

  4. #4
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    Don't worry about sag too much. Use it as a rough starting point, but then adjust accordingly to your comfort and desired results.

    One of my riding buddies called SRAM to ask about sag for something a while back.
    He was told by SRAM, sag is a horrible way to set up suspension. Ironically, who touts their "sag measurements on the tubes"? SRAM.

  5. #5
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    The best thing about the internet is there are no shortage of conflicting comments. LOL

    Love the entertainment value!

    To answer, well I never gave it much thought about seated vs. attack. Good point OP.
    As mentioned earlier in the thread, sag would be considered beneficial for seating riding.

    I'll take that to the next step and ask you where you prefer your suspension to be most valuable. If you want it best as a pedal platform, adjust when seated. If you want it best for downhill chunk, probably adjust for attacking.

    If you are not a rider of average weight, you will have a challenging time adjusting suspension. If you are average weight, setting sag will suit you best so you have proper valving throughout the range.

    For example, I am too light to achieve proper sag on my dirt bike so really my spring rate is always too stiff for me. If I were to loosen sag so drastically that I can achieve sag, the bike will be too soft for taking hits.

  6. #6
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    Quote Originally Posted by Christopher Robin View Post
    I know a lot of people suggest measuring sag while in that attack position, but I'm thinking that's more for enduro and downhill. When I measure my 30% rear sag while standing on the bike, it becomes more like 50% when I sit. I figure 'all mountain' riding or trail riding involves a lot of pedaling while sitting so to me, it makes more sense to measure sag while seated. What are you guys doing?
    This is a good question and not straightforward. Furthermore, how we measure, and how much sag used, has changed over the years.

    Back when, on AM/FR type bikes 35% sag on a fork, seated, was common. Now, we are looking at 20% in the attack position.

    That said, I measure my sag in the attack position, with heavy hands, for both ends. But that is sometimes adjusted on the fork based on the manufacturer's spring chart. I've found those charts to be accurate.


    If you are going by setting with sag, I think it's far better to go from the attack position, with heavy hands. The time when you most depend on your suspension doing it's thing properly is when you are going downhill, not pedaling. That's when you are in the attack position with heavy hands. That's where you need your suspension most. Set it up to work best for that situation.


    I have found air spring charts (on forks) to seem high when checked in the seated position. But when positioned in attack with heavy hands, you'll usually end up with correct sag. Maybe the folks making the forks and spring charts actually know what they are doing.
    Last edited by Miker J; 02-17-2019 at 05:58 PM.

  7. #7
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    I believe it actually is very straight forward. Check out that link I posted. Its really pretty easy once you give it a good few tries, and not to be too cliche... its a game changer. You'll kick yourself for not doing it correctly sooner.

    That link solves the problem of being seated or standing or in attack or not. It erases any variable from user input and not being quite positioned right. It also solves the enormous problem of sag and dimpled/balancing cans (debonair).

    Once you understand how setting up suspension by frequency works and feels, it makes addressing volume changes so, so much easier and more intuitive. Being stationary on a bike and measuring orings with rulers tells you very little about how you need to modify volume for best behavior on the trail (nevermind that you have to restart the silly sag process!).

    If your spring feels like mush, but the oring says youre at the correct percent, do you guys really just ride like that? You'd be missing out on so much from your bike!

  8. #8
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    With a tape measure ;-)

  9. #9
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    Quote Originally Posted by One Pivot View Post
    If your spring feels like mush, but the oring says youre at the correct percent, do you guys really just ride like that?

    You have to keep in mind that there are lots of people out there who LIKE the three "modes" on their damper. With no appetite for a deeper understanding of how their stuff works an easy to follow setup rule is better than uninformed guessing.

  10. #10
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    Sag gets you to an appropriate neutral point in the suspension travel. That's is only what it is. If you need a higher or lower spring rate, add/subtract spacers and find tune it with pressure. If you need different damping, change that. A properly set up suspension will have sag roughly equal to the suggest nominal point.

    Rear is usually measure while seated and front while standing in attack position. Use the specified amount of travel for the fork and shock, not the exposed stanchion length, which can be more than the specified travel.
    Do the math.

  11. #11
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    Quote Originally Posted by PhillipJ View Post
    You have to keep in mind that there are lots of people out there who LIKE the three "modes" on their damper. With no appetite for a deeper understanding of how their stuff works an easy to follow setup rule is better than uninformed guessing.
    Certainly! I understand that, and thats the intended purpose of setting sag at all. Just get people something that works so they can ride their bike.

    But if you care enough to register for a forum and start poking around and asking questions about proper setup... its worth noting that there is a significantly better, more effective way to get dialed in.

    Its just worth a mention.

  12. #12
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    Quote Originally Posted by DethWshBkr View Post
    Don't worry about sag too much. Use it as a rough starting point, but then adjust accordingly to your comfort and desired results.

    This. Sag is a starting point. I adjust pressure every ride for 7 or 8 rides, or until I can't find a reason to make micro-adjustments anymore.

  13. #13
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    Well all good feedback. The reason I ask is because the manufacturer suggests seated sag adjustment while my suspension tuner advises to be in the attack position. In the end, I'll need more on-the-trail-testing... might be a mix of the two!
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  14. #14
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    Perhaps too much science into sag and not enough common sense to understand that it is a starting point. A starting point only.
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  15. #15
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    One video I was watching, made perfect sense when he suggested standing over the frame, hands in the bars, and supporting almost all your weight on the forks (feet were still on ground but not fully weighted). His reasoning which made sense to me, was when you're really asking the fork to work, you're usually descending and much of your (and the bike) weight is forward.

    My fork is pretty supple at the top so when I tried it, wasn't a noticeable difference.

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  16. #16
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    I traditionally set this up via the front/rear balance, using the manufacturer's guidelines for the shock as a base point to setup the fork. For the rear, I measure it seated, but I measure the front 'standing' (as close as I can to make it consistent, which can be tricky). I usually measure it 3 or 4 times to ensure that I'm somewhat consistent with it.

    For the rear, I typically use manufacturer recommendations unless it's off for some reason. So far, I've found I've settled with what most manufacturers recommend in the rear, I think the only bike I really changed it on was my 5010, where I ran 25% instead of 30%. I've found on some bikes that ship with air shocks, running a coil requires a bit less sag than air, so when my coil shock is on my current bike, the sag is a bit lower than my air shock.

    Typically that number will be 30%, but some bikes will want 25% and others will want over 30% (Transition).

    Once I have the rear set up, I set the front up for the appropriate ride height, which I've found is usually around 20%. I then go ride, if I feel like the rear of the bike is constantly pushing me forward or I feel like I'm having to fight the need to stay centered, then I add a bit more air until it feels like the front/rear of the bike are balanced out. If I feel like I'm falling off the back of the bike and struggling to stay centered due to the fork pushing me backwards, I typically let a few PSI out of the fork (or add air to the shock, depending on where I am in the settings).

    In other words, I use the manufacturer recommendations to set a baseline for the rear, then work with the front until they feel balanced. If I later find that the rear isn't setup right (too much or too little), I'll adjust it based on feel, then apply the same technique to the front. I typically aim to make the bike work to keep me centered and not overly weighted front or rear, although I do start the setup a bit more biased towards the rear (less sag front, firmer compression front, faster rebound front; opposite for the rear).

    All within reason, I typically wouldn't exceed 15-25% on the fork. The main goal I aim for is to ensure that the bike isn't throwing me forward or backwards.

    This all assumes relatively close rebound speeds, as well. I typically determine if I need to open up the rebound more based on how frequently I feel like an imbalance exists. If it occurs during impacts or frequent hits, then it's probably a rebound thing, but if I'm riding a smooth section of trail and feel like I'm imbalanced one way or the other, then I typically assume it's a spring thing.

  17. #17
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    I do ~37mm on my 150mm fork and 15mm on the rear shock for my 140mm trail bike. I do 30mm on my 120mm fork on the XC bike. They're pretty generic settings...but it seems to work well in most conditions. Two volume spacers in both forks.

  18. #18
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    Yeah, setting sag when stationary was just too inaccurate for me, let alone hard to do. So I played around with the air a bit and and have the bike so it bounces evenly under weight and feels good riding. The result is a few pounds under half my riding weight in the front, and 10 lbs over my riding weight in the back. The sag ends up about recommended in the back and short in the front. I imagine not only does riding style make a huge difference, so does the individual bike geometry and components.

  19. #19
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    For my enduro bike i aim for 30% sag front and rear as a starting point. I do standing attack position and seated for sag measuremnts front and back.


    Then look for bottom out on my biggest hit both front and back evenly. For this i have a G out roll over and a huck to semi down that i use as a datum. I adjust pressures and tokens until i get to a even bottom smooth bottom. Not a harsh loud bang.


    Then i look at setting rebound/compression. I want to adjust the harshness out and go for the fastest possible settings without getting bucked off. For this i have another couple of datum tracks i smash down. Adjust and re-smash. Once i reach the holy grail of plush, fast, nice ramp up limited fork dive and eveness front and rear i'm happy.


    Then i set and forget.

  20. #20
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    A lot of methods here, wow. As for me, I followed the quick method shared by GMBN on YouTube to start with and that actually got me a pretty good feeling base setup that stays nicely hooked up to the ground. I had to tweak rebound a little while riding for several rides to properly balance the bike for jumps, and I ended up pulling a token up front, but that's it.

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  21. #21
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    I use a Shockwiz... the world has moved on.... let technology take you to the next level

  22. #22
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    Quote Originally Posted by PhillipJ View Post
    You have to keep in mind that there are lots of people out there who LIKE the three "modes" on their damper. With no appetite for a deeper understanding of how their stuff works an easy to follow setup rule is better than uninformed guessing.

    Yeah, this is the most pathetic excuse for suspension progress in the history of suspension. You have a hydraulic damper unit, with 3 points of adjustment.

    ALL suspension should have fully adjustable compression and rebound, and higher end units with fully adjustable high and low speed.
    NO SUSPENSION should have a 3 position knob. That's a true waste of suspension tech. What's next? No front derailleur because it's too complicated to understand how to shift?!

    Wait......

  23. #23
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    -

    --

    what most are saying


    SAG is a way to get a base setting started. a go-to spot when you are
    starting with something new.

    but SAG often doesn't exactly fit you, the shock/fork/bike combo, and how you ride it

    the most important thing with SAG is not actual SAG, but 'do I have a SAG O-ring mounted I can check for max hittage later on ?'

    1) set sag at home with your base or mfg recommended pressures


    2) then go ride and bring your shock pump and tire pump and play with pressures
    or just remember how that ride went, and play with pressures at home

    [at this point checking sag is almost useless now, it's all in the suspension and tires PSI]



    eventually you will have a knowledge of 'what am I planning to ride today' and 'how fat or light did I or my gear get or did not get lately' and 'how did that last ride go at those pressures?'


    in the case of carrying more or less gear SAG can help you check the effect of 'the weight change on my position' surely
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  24. #24
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    I've never thought about how others might measure their sag (and other subsequent suspension settings), but as suspected, there are as many methods as there are shocks on bikes.

    For me, I start with dampening and rebound wide open, and target 30% front, 25% rear, and go from there. I focus more on an even rebound feel between the front and rear than anything else initially. A 5% difference works well on my daily ride, whereas another bike I have likes a wider spread. I usually set sag in a seated position. If setting sag in an attack position, 25%/25% provides a more even feel. From there, I may add or reduce sag (maintaining front/rear ratio), depending on the trail in question, or sometimes ambient air temps.
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  25. #25
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    Quote Originally Posted by One Pivot View Post
    I believe it actually is very straight forward. Check out that link I posted.
    Their use of the term "natural frequency" is pretty confusing as nothing they discuss, other than a reference to walking, has to do with repeated cycles of anything. They seem to be confusing that term with "spring rate" or maybe "rebound damping" - or do those words mean something else in the UK?

  26. #26
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    There are two schools of thought:

    1. Use all your travel all the time
    2. only use all your travel on the hardest hits/trails

    Sag will be a byproduct of whichever you prefer.

  27. #27
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    Quote Originally Posted by weeksy950 View Post
    I use a Shockwiz... the world has moved on.... let technology take you to the next level

    Both my DH and trail rig are coil, both ends. I'm out of luck with the Shockwiz. It is something I would have liked to try, at least for fun.

  28. #28
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    Quote Originally Posted by slimat99 View Post
    There are two schools of thought:

    1. Use all your travel all the time
    2. only use all your travel on the hardest hits/trails

    Sag will be a byproduct of whichever you prefer.
    Yup. I go for the latter.


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  29. #29
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    Quote Originally Posted by dir-T View Post
    Their use of the term "natural frequency" is pretty confusing as nothing they discuss, other than a reference to walking, has to do with repeated cycles of anything. They seem to be confusing that term with "spring rate" or maybe "rebound damping" - or do those words mean something else in the UK?
    Natural frequency means the spring feels equal when compressing and rebounding.

    Too soft and the fork will compress quickly, but rebound slowly. Too stiff and it will compress slowly and rebound quickly.

    When it's set right, it's even. This is checked with your dampers open, and it works incredibly well. I understand it sounds confusing, but if you set out looking for even less, it makes a lot of sense and feels natural when you get there.

    It is a decent sized window, so there is adjustment room.

    Once your spring is set correctly you can finally set sag. It's done via volume change, last!

    It's more work than just measuring the oring, but it works so, so much better. It's also really not that much work anyway.

  30. #30
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    Quote Originally Posted by mtbcat47 View Post
    Yup. I go for the latter.


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    Use all your travel on your hardest normal hit. Ot at the reasonable top end of your riding.


    That should be once or twice a ride on your hard rides.


    If you dont you might as well soften your suspension and getter use out of it. Or if you dont need all that travel then get a lower travel bike that is lighter and faster that you will use all the travel for and be able to go faster more efficiently on.

    I'm regularly at the limit of my travel. Which is a good thing. Because that means i'm hitting the features that i enjoy the most.
    Last edited by plummet; 02-20-2019 at 02:38 AM.

  31. #31
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    Quote Originally Posted by One Pivot View Post
    .

    Too soft and the fork will compress quickly, but rebound slowly. Too stiff and it will compress slowly and rebound quickly.


    Once your spring is set correctly you can finally set sag. It's done via volume change, last!

    It's more work than just measuring the oring, but it works so, so much better. It's also really not that much work anyway.

    Once you have the proper spring (air or coil) the sag should be pretty close (but sag is NOT the do all for settings).

    As you increase spring, you will need to increase rebound damping. That's just the nature of suspension, and the nature of a spring.

    Volume spacers are more of a feel item, not really a suspension setup thing. The only point of volume spacers is to change the nature of the spring (since air is ALWAYS PROGRESSIVE rate, no matter what). You can add or remove spring progressiveness, OR, in my opinion, attempt to compensate for horrible damping/spring setup by lowering the spring rate to an absurdly low number (due to bad design or poor damping characteristics) and still preventing bottom out. Or, you remove spacers to get a more linear feel.

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