Suspension Setup Series #1 – Set Your Sag Properly
At virtually every mountain bike and suspension launch we attend, we’re told to simply sit on the bike while someone slides the “fun-o-meter” ring to the base of the fork or shock, then we hop off and see where it lies. If it’s in the ballpark, we gear up and head out, fiddling with the settings as we ride.
Recently, I had some time with Rockshox brand ambassador and SRAM MTB marketing manager Duncan Riffle, who also happens to be a 2x U.S. National Downhill Champ and former World Cup DH competitor, so we discussed the finer points of suspension set up. The result is this 6-part series, with additional input from Manitou’s Eric Porter, who’s raced professionally in XC/DH/DS/DJ over the past 11 years, and Mark Fitzsimmons, Fox Racing Shox’s race program manager and pro athlete suspension tuner. As you’ll see throughout the multi-part story, there’s quite an art to getting it all dialed, but when you do, it’s pure magic on the trail.
So, ready to rethink everything about how your suspension is set up? Good. We’ll start with sag, which is the amount of travel your suspension moves through just by adding your own weight (body, clothes, pack, etc.) to the bike. This puts the suspension into an active state, letting it react in both directions, keeping your tire glued to the dirt. To get it right, there are two things to consider: Rider position and amount of sag. We’ll start with properly positioning yourself on the bike so that sag is set based on your actual riding.
But first, make sure your fork and shock both have their compression damping set to their fully Open/Descend positions, then hop on the bike…
“Understand that when you set your sag, it has nothing to do with your body weight (sitting) directly over the BB or shock,” says Riffle. “It has everything to do with how your weight is pressing on the bike in a neutral ride position. So, obviously, you’re going to want to set your sag accordingly.”
These images illustrate the difference rider position makes. With the same air pressure in the shock, it’s showing almost 40% sag when seated…
…and just 28% in an aggressive standing position.
To figure out how you should set it up, Fitzsimmons breaks it out like so:
- Downhill bike: Set sag in a standing attack position.
- Trail/Enduro bike: Set Sag in a seated position for every day riding and standing if you are bike park riding
- Cross Country bike: Set sag in the seated position
It’s very beneficial to have a friend help you balance the bike and move the O-rings for you. With your usual riding gear on, including filled bottles on the bike or hydration pack on your back, climb aboard the bike. Once in position, bounce up and down a few times without holding the brakes, then settle into the desired position. Once there, hold steady while your friend slides the O-rings against the canister/lowers, then slowly lean over and climb off the bike. Don’t hop off – that movement can compress the suspension further and move the rings. If you want to be absolutely sure, have a third friend record the measurements while you’re still on the bike.
HOW MUCH SAG SHOULD I RUN?
Generally speaking, somewhere between 15% and 40%. Riffle’s preferred starting point is between 25% and 30% for his 160mm to 200mm travel bikes. When he was racing downhill, it was more like 30% to 35%, depending on the bike and the course. Cross Country bikes generally have a much shorter stroke to work with and get away with a little less, unless it’s a really rough course.
“Most bikes feel good between 20-30% sag, I like 25-30% most of the time,” says Porter. “If you are doing a ton of climbing you may like it closer to 20%.”
Ultimately, it depends on four things:
1) The bike you’re riding – how much travel does it have? How aggressive is its leverage ratio? If it’s a shorter travel bike, then you’ve got less to work with and should start off on the lower end of the spectrum, around 25%. If your bike has a high leverage ratio, then it can muscle through the travel too easily if you’re running too much sag, too, so start on the low end. Reverse that for longer travel bikes or those with weak leverage ratios.
2) The terrain you’re riding – more aggressive terrain means your shock is going to see a wider variety of impact forces, so you’ll need to experiment more to make sure you’re not bottoming out too frequently but that you’re still…
3) Getting full use of the bike’s travel – This one’s is the most tangible of the four and is easily measured with the little rubber ring around the stanchion or shock shaft. If you’re leaving travel on the table, then you haven’t made the most of your available suspension, and thus your bike’s potential performance.
4) Your preference – Ultimately, the bike should feel right to you while still getting all of its travel on most rides. Setting the sag at the proper point and while in the proper riding position is a good start to achieving this.
Lest you worry about sagging too far into your travel affecting the performance, the suspension’s compression settings are based on speed, not position. So more or less sag won’t affect damping performance. It does play a role in spring curves, though, which is a story for another time.
WHAT ABOUT FORKS?
Setting the sag on your fork can be a little different. You don’t necessarily need the same percentage of sag on the front of the bike, it’s more about finding the right balance from front to back.
Fox’s Fitzsimmons says “If you race or ride at a faster pace, sag should be set up 15-20% on the fork and 20-25% on the shock. If you are a weekend hobby rider, 20% in the fork and 25% in the shock.”
Porter adds: “When checking the fork sag, you are looking for closer to 10-15% if you are sitting on the bike. This is more accurate than ever due to how good the new class of trail forks are (Manitou Mattoc, Rockshox Pike, Fox 36, etc.). When setting up the fork air pressure, I usually start out where the manufacturer recommends, then I set up the rear, then I cruise around in the parking lot bouncing up and down to make sure that the air pressure feels balanced between the front and the back. Having a balanced bike is very important to making a bike feel good on the trail.”
For hardtails, it’s about finding the point where the fork is supple off the top and able to move through it’s full range of travel when it hits the biggest obstacle or drop on the trail.
From my own experience, after talking to Riffle on the trail, I ended up running more sag on the rear -changing from roughly 22% up to 30%- which let my 100mm Niner JET 9 RDO really soak up the little stuff. Mind you, I was happy with the bike’s performance before, but setting the shock up a little softer made a noticeable improvement in its small bump absorption with no discernible downside. Even if you think you’re happy with your current set up, I’d recommend experimenting throughout your next few rides.
COMING UP: In the next installments we’ll discuss the differences between the spring rate and damping tunes, how to tune your compression and rebound damping, and even how to tell if you’re using the right suspension parts and what to do if you’ve tried everything from 15% to 40% sag and things still don’t feel right. Stay tuned!