Sag is probably the most fundamental and important aspect of setting up your suspension. In case you didn't know, sag is the amount the suspension compresses under the rider's static weight, usually expressed as a percentage of the total travel. The brilliant thing about sag is that it's transferable between riders of any weight and bikes with any amount of travel. Running 30% sag will give a roughly comparable ride feel for a 120kg rider as it would for a 60kg rider, even though the heavier rider will need roughly double the spring rate (spring stiffness or air pressure) to achieve the same sag. Similarly, if you have twice as much travel you'll generally want to run about twice as much sag (half the spring rate), which means the same
percentage sag.
But when it comes to dialling in your particular bike, it's worth being precise with sag measurements because a small change can have a big effect. If you go from 30% to 27% sag, that may sound like a pretty trivial difference but the amount of sag has actually changed not by 3%, but by 10% (3/30). So, the spring is 10% stiffer with 27% sag as it is with 30%; that's a very noticeable change.
There are two ways to measure sag - either seated or in the attack position. Measuring sag in the attack position (standing on the pedals with elbows bent) is more representative of how you actually ride, but it can be hard to measure sag like this on your own without pushing the O-ring past the sag position as you get on your bike. Measuring sag seated is much easier - just slowly sit your weight onto the saddle, lift your feet in the air briefly, then without bouncing, put your feet back on the ground and dismount, then check the O-ring position. If measuring sag seated, you'll typically measure a little more sag than when standing, but so long as you measure it the same way every time, it's a good reference point.
Another caveat is that with a progressive suspension linkage, 30% sag on the shock correlates to slightly more than 30% of the wheel travel. This is because, with a progressive linkage, the wheel moves further for every millimetre of shock stroke early in the travel than it does later in the travel. It's not worth getting too hung up about this though because, for a moderately progressive bike, the discrepancy between shock sag and wheel sag is only around 2% (30% shock sag correlates to about 32% wheel sag). Also, if you have a more progressive linkage, you might
want to run a bit more wheel sag than with a linear one, so setting them up with the same shock sag isn't a terrible starting point.
Something which is more significant but more rarely discussed is friction. When you apply your weight to the bike, the suspension compresses until the force from the spring plus the friction in the shock and linkage is enough to hold up your weight. So if there's more friction, you'll measure a smaller amount of sag with the same spring rate. You can test this by measuring sag in the normal way, then have someone push down on you to compress the suspension beyond the sag point, then have them slowly release that downward force so the suspension extends until the downward force is removed. You'll find that you measure more sag when the shock extends than when it compresses - sometimes a lot more. The difference is due to friction, so this test can be a useful way to compare friction between bikes or identify sticky shock bushes or seals. Friction is even more significant in the fork, which makes measuring fork sag almost useless in my view.
Traditionally, it was often said that you should run about 25% sag for cross-country and about 30% for everything else. But modern bikes generally have more progressive linkages and radically better air shocks with volume spacers to control bottom-out. On the other hand, people are riding shorter-travel bikes much harder than they used to. So, are these basic guidelines still in the right ballpark, or are they way off?
I ride my hardtail most of the time so I don't really care. But my full suspension bike is a Cannondale Prophet with a Magura MX shock. Which is air sprung and air damped. And you can't measure sag (unless someone else looks at how far the rolling lobe rolls over the cone but it still wouldn't be sufficiently precise for this poll).
Run coil in the back, but it's too damn finicky to measure on my own, and with the huge increments between spring rates, I simply use the one that feels best.
I did measure it and ran 30% when I used an air shock, and with my mystery number sag coil set up it feels better, and I ride faster according to the clock.
hardtails are what feels scary.
i have an issue with a too thin oil in the shock on the dh bike, high speed rebound is what makes it scary. once i've sorted that out the bike should really monstertruck, the only part that will make it scary is my lack of skill on undulating terrain
like i said, if it's scary you're bottoming out
also depends on the shock (tune), right?
Most importantly, though, she's running a coil.
Like when i started riding a bike? When I thought this was the sport for me? When I thought this was how I wanted to structure my whole entire life? or when I first sacrificed the blood of a virgin to the forest and mountain presence?
Is your suspension linear, straight progressive, progressive/linear/progressive, digressive/progressive, progressive/digressive? How progressive/digressive is it and in which part of the travel? Do you over pressure to prevent bottom out? Do you run a lot or a little little fork sag that you have to balance by adjusting the rear? Do you run really heady or really light damping? Are you boosting big jumps on smooth trails or staying on the ground on rough trails?
Do you get my point? Every bike and rider is different. 30% is often a good starting point for tuning, but a specific sag percentage rule is a little silly. Do some back to back runs and figure out what works best then write down your PSI.
I'm not in the window of "average rider" (100 kg and I ride heavy: I'll plow at speed thru a janky section in order to keep the bike loaded up to then pop over the even jankier section that follows. Wheels and shocks hate me.) that most base tunes are made to fit. So just popping X spring onto a shock with out some damper tuning is just going to end with parts flying everywhere.
You’d need to poll people to see what frame they’re on, what shock they’re running, and other setup parameters (spring stiffness, shock tune, tokens in air shock etc. ) for this to be meaningful.
Im lucky enough to weigh pretty close to what Kazimer and Levy weigh, so their setups are usually pretty close to what I end up running.
When i ride XC and mashing pedals, i want my ride height to be 25% and hold there.
Got to say, that, I just upgrade my DH full sus unycicle with front and rear discs breaks, 190 AXS dropper for steeper STA, rear light and 13 speed automatic gearbox, almost forgot a Big S sticker on down tub.
Probably going to get a custom tuned Fox X2 or something of similar ilk with a resonable amount of adjustability so it can be dialed into my liking
Less than recommended
Exactly as recommended
More than recommended
I just add air when my pedals start digging new trail.
If "works fine" is all you care to give yourself as a rider, that's too bad.
And the reason it reads lower the next time you attach is because the hose has to fill again. Only the pressure reading right before you detach is accurate.
Why?
I get what it is. But if 25mm of sag is sufficient for the suspension to absorb small bumps etc,, on my 100mm Trail
Bike, why am I giving up another 25mm on my DH bike in order to achieve 50mm?
SENDIT
i could never get it any less no matter what pressure or bands in the pos and neg chambers
East Coast: they get pulled up higher as the years pass
West Coast: they ride lower and lower as the years pass
Basically set and forget
Ok - so set up your bike to hit jumps and it's going to work good everywhere else....got it.
I hear ya man. I'm pushing' 70 here, I gotta say I'm saggin' way more than my bike.............
30-35% dh/bike park
This poll is biased
If yours doesn't it probably means you have too much pressure. I've got my 2020 Factory 36 dialed to use 95% travel most days, never bottomed unless I almost died, and still super plush of the top: it moves if I just push straight down on only the seat. Sure, I could get on the seat and not move the fork, but it's the most convoluted movement and so far from a normal riding position to be silly to even think about.
Your argument is as useless as using sag as the one number and being done. It's a starting point, that's all, and it can be better than the psi numbers on the fork (also just a starting point) because those numbers don't take into account differing head 5ube angles
couldn't be more wrong. Sag is just right height. Couldn't even tell you what sag I run.
See you on Friday
However, I do use sag rather than having to remember what pressure is right. It's also a quick way of seeing what effect changes in pressure are having. But you're right, it's not really telling you a whole lot. Obviously if you have too much or too little pressure you're going to know pretty quick without having to check your sag.
"I've never even measured his sag"
www.youtube.com/watch?v=DcsbLgceUMg