Technical Tuesday - Setting Your Sag

Oct 12, 2010
by Mike Levy  
Making sure that your bike has the correct spring rate and amount of sag is the first step towards having your suspension set up properly. This Tech Tuesday takes a closer look at how to accomplish this, showing you the steps to go through and the formula that I like to use. Inside you'll find a video guiding you through the entire process!

Read on,If you caught last week's Tech Tuesday you'll know what all of the terms mean, including sag, which is what we are taking a closer look at today. Getting your bike's sag set correctly is the first step to sorting out a suspension setup that works for you and how you ride. Only once the sag and spring rate are dialed in can you start to fine tune the compression and rebound damping settings. Below you'll find a video outlining the steps to take in order to figure out how much sag you are using, as well as some sag amount suggestions.

Watch the video to learn how to set sag:

Views: 35,125    Faves: 237    Comments: 11

There are a number of different calculations that you can use to figure out what percentage of sag you are using, but I like to use the one specified in the video. If you do some searching you will also be able to find some online sag calculators that will do the math for you, although you will still need to know the important numbers. Keep in mind that all numbers should be in millimeters.

To find fork sag:

Sag ÷ total fork stroke × 100 = Your sag in %

To find shock sag:

Un-sagged eye to eye length - sagged eye to eye length = Sag (mm), Sag ÷ total shock stroke × 100 = Your sag in %

Past Tech Tuesdays:

Technical Tuesday #1 - How to change a tube.
Technical Tuesday #2 - How to set up your SRAM rear derailleur
Technical Tuesday #3 - How to remove and install pedals
Technical Tuesday #4 - How To Bleed Your Avid Elixir Brakes
Technical Tuesday #5 - How To Check And Adjust Your Headset
Technical Tuesday #6 - How To Fix A Broken Chain
Technical Tuesday #7 - Tubeless Conversion
Technical Tuesday #8 - Chain Wear
Technical Tuesday #9 - SRAM Shift Cable Replacement
Technical Tuesday #10 - Removing And Installing a Headset
Technical Tuesday #11 - Chain Lube Explained
Technical Tuesday #12 - RockShox Totem and Lyric Mission Control Damper Mod
Technical Tuesday #13 - Shimano XT Crank and Bottom Bracket Installation
Technical Tuesday #14 - Straightening Your Derailleur Hanger
Technical Tuesday #15 - Setting Up Your Front Derailleur
Technical Tuesday #16 - Setting Up Your Cockpit
Technical Tuesday #17 - Suspension Basics

Have you found this tutorial helpful? Share any of your hints or tips below!

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  • 10 0
 Air should not be lost when taking the pump off the shock. The lower ammount of pressure comes from when you are putting the pump on the shock - some air escapes to the pump hose, since there's less pressure at that time. The air you hear when taking the pump off comes again from the trapped pressurized air in the hose.. How else would you be able to determine how much pressure you run in your shock?
  • 2 0
 Was thinking the same thing. Pretty sure that is the case.
  • 5 2
 not at all true. schrader valves allow for air to escape while the pump is being removed. it takes time to unthread the pump from the valve, and air can escape for as long as you take to unscrew it. years and years ago i used to wind up my shock pump nozzle with a "rip cord" of tape, so i could unwind it in 1/10 second and it helped. but, for years now there have been pumps with a "zero bleed" or "zero loss" function to deal with this issue. i'm surprised it wasn;t mentioned here as he seems to be really up to date with everything else. they aren't given away with the fork, you have to get an aftermarket pump.

there is no logic to your explanation about pressure, as air would surely escape from the place with the MOST pressure not the least. think about it more.
  • 2 0
 The air pressure in the shock and in the pump's hose are equivalent. There is more volume in the shock but no more pressure than in the pump's hose. However, you're right on the schrader valve allowing air to escape... for some reason I was thinking back to my tires and the presta valves.
  • 1 1
 still it is not that much air escaping also...
  • 5 0
 This topic comes up often in the Mechanics Forum. So glad we can point to it from now on. I like the emphasis on getting spring rate right before anything else - some people want to not have to buy a new spring when they keep bottoming out and think they can fix it with compression damping or higher weight oil. Mike, I like your straightforward presentation style, clear diction, and planned scripting. No mis-communication possible.
  • 2 1
 im under the understanding that the air lost by removing the pump is from the pumps chamber and not the shock, but the air loss from attaching the pump is true as this enters the pumps chamber and shows the remaining pressure in the shock.
  • 3 0
 I'm setting up my rear shock properly on monday, so this was a really good help! Thanks alot, keep the good stuff comin'! Smile
  • 16 5
 One thing to add if I may...

When setting sag at the rear, the shock sag does not always match up to frame sag, as the leverage ratio is hardly ever perfectly linear. (setting to 30% sag on the shock stroke may correspond to as much as much as 50-60% sag of the frames suspension on a frame with a progressive linkage). So you should talk to your frame manufacturer and ask for leverage ratio curves and sag settings.

For Banshee frame owners, refer here for sag graphs of all frames.
  • 5 35
flag pperini (Oct 12, 2010 at 3:44) (Below Threshold)
 you dont need to do that...30% of the shock stroke is also 30% of the wheel travel...dont discuss with me, just do the math...
  • 7 37
flag undercoverfreak (Oct 12, 2010 at 4:02) (Below Threshold)
 @builttoride, you're an idiot. No shock will ever have the same stroke length as the frame has rear travel. Even if that was the case, that is not what's called linear.
  • 25 0
 I think what builttoride is saying is that the distance the rear wheel moves in the first 30% of shock stroke may not necessarily be the same distance that it moves in the next 30% of stroke, and the next 30% of stroke may be different again. This is because the leverage ratio changes throughout the stroke/travel on most bikes.

And he'd be right.
  • 6 0
 I think you guys may have misunderstood me... if a bike has a progressive suspension linkage say starting at 3:1 and ending at 2:1. Then...

At start of travel:
1mm of shock compression = 3mm of wheel travel

at end:
1mm of shock compression = 2mm of wheel travel

The ratio changes, so the shock sag does not always equal the wheel sag especially on highly progressive bikes, or bikes with steep changes in leverage curve.

For example, on the Banshee Scythe (exapmle of progressive suspension frame without being extreme) 30%sag at shock = 70mm/100 x 30 = 21mm

But 30% sag at the wheel (60mm of wheel travel being used) happens at 18.5mm of shock compression.
  • 6 2
 builttoride is correct... the first 30% of shock stroke may not be the first 30% of wheel travel due to the spring rate curve. HOWEVER, I don't think that the leverage ratios will change THAT much (like 2:1 all the way to 3:1... more like 2.4:1 to 2.5:1), so I think that using this method of measuring sag is accurate *enough*. You're not measuring the shock stroke THAT accurately anyway (i.e. down to a mm or two). Besides, the 30% "rule" is just a suggestion anyway... your own personal preference may be slightly more or less than this anyway.
  • 6 1
 Actually you'd be surprised how progressive some bikes are... for example the Evil Revolt (one of the more progressive popular designs right now) starts at around 4.2:1 and finishes around 2.5:1.

So to get 30% sag at wheel you actually set the shock to roughly 25% sag. I'm not saying the difference is massive, but if you wan to do thing properly, it is something worth considering.
  • 2 0
 yah, builttoride is dead on the money with that one. if you have ever used any suspention software you would know. For example the evil revolt starts out in the high 3's and ends in the low 2's (approx). and that is just one example. I urge people who do not know anything about suspension to not debate technical facts. I just ends in disaster.
  • 3 0
 hahahaha i didnt read the last post OMG i look like a retard now. someone please get ride of my last comment lol

well at least we were on the same page +/- some values
  • 2 1
Haha, don't worry man, I thought it was about the same as you said until I looked it up. Starts higher than I thought it was (presuming the data was accurate, which it claimed to be).
  • 2 1
 undercoverFREAK! @, hey es-spainya put a sock in it your the one that sound like and idiot. basically all bikes are different so they can have 30% linear or whatever cos it sounds correct, show in the futur you could just shut it cos u really do sound like a freak. scots = correct. spanish = talking pile that has no f*ckin clue
  • 1 0
 FYI, the Intense M6 goes from 3.1 to 2.6 (a range of only 0.5), but the 951 has a goes from 3.6 to 1.4 (a range of 2.2!!).

That means that 30% sag on the M6 is close to 30% of the travel. But if you want to set sag at 30% of the travel on a 951, you are going to need a nerdy chart similar to undercoverfreak's.
Back in the day, we just set dag so that we had a slight bottom out on the hardest hit on the course - if you ain't gonna use it, why have it. On my trail bike though, I do as Mike shows.
  • 5 1
  • 3 0
 yeah, another useful tech Tuesday! Keep em coming!
  • 2 0
 Pinkbike once again there to help people ride faster and have more fun... keep it up!
  • 1 1
 Great Tech Tuesday one thing I would like to add is you don't have to times it by 100. if you just move the decimal point to the left two places it will do the same thing.
  • 2 0
 Heh, "times it." You mean "multiply it?"
  • 3 0
 thats what multiplying it by a hundred is: moving the decimal two places.
  • 1 0
 i have a 2004 manitou axle comp, about how much sag should i have? i only have about 3/4 of an inch of sag.
  • 1 0
 forget all the numbers go by feel great video if you like to use the numbers tho
  • 1 0
 well, you've got to start somewhere
  • 1 0
 what kind of fork is that?
  • 2 1
 X-Fusion Vengance
  • 2 0
 Vengeance HLR to be exact.
  • 1 0
  • 1 0
 That was a very usefull information,thanks pinkbikeSmile
  • 1 0
 The best suspension setup vid I've seen. Excellent! The other good one I've seen is by Tim Fluke on the Fundamentals DVD from Dirt Mag UK.
  • 1 0
 why is there a tube on his fork
  • 2 0
 To stop spray.
  • 1 0
 Awesome video!! Lots of helpful info!! RideOn!!
  • 1 0
 Great job Mike & PinkBike. Keep 'em coming!
  • 1 0
 thanks mike. good info
  • 1 0
 i love tuesdays
  • 1 0
 great tech tuesday mike!
  • 1 0
 This is a great column!
  • 1 1
 mine is at 70% sag
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