Technical Tuesday - Setting Your Sag

Oct 8, 2010 at 17:02

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:

You need to upgrade your Flash Player
Click here to install it

Views:18154 Faves:167 Comments:11 Add to my Favorites

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 %

Must Read This Week

1. Why No Y? 51976 reads
2. At Home With Sam Hill 35103 reads
3. Fabien Barel presents #1 - At home and on dirt with Cam Zink 29694 reads
4. "In Good Company" - A film about the importance of mountain biking to a community 28990 reads
5. Movies for Your Monday 28049 reads
6. Graham Agassiz's New Zealand Adventure 25982 reads
7. Ian Morrison, meet Steve Smith - Video 23707 reads
8. Anticipation Pt. 2 - Early season shredding in the Whistler Bike Park - Video 22030 reads

48 Comments

Score Time

tidli (Oct 12, 2010 at 1:39)

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?

collin7 (Oct 12, 2010 at 8:35)

Was thinking the same thing. Pretty sure that is the case.

reallybigmantis (Oct 12, 2010 at 13:51)

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.

collin7 (Oct 12, 2010 at 19:21)

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.

Caiokv (Oct 13, 2010 at 12:48)

still it is not that much air escaping also...

[Reply]

iamamodel (Oct 12, 2010 at 5:23)

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.

[Reply]

SwitchbakLtd (Oct 13, 2010 at 14:18)

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.

[Reply]

staike (Oct 9, 2010 at 15:36)

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

+ 11

builttoride (Oct 12, 2010 at 2:00)

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.
http://bansheebikes.blogspot.com/2010/06/set-your-sag.html

- 26

pperini (Oct 12, 2010 at 3:44) (Below Threshold) show comment

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...

- 27

undercoverfreak (Oct 12, 2010 at 4:02) (Below Threshold) show comment

@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.

+ 24

iamamodel (Oct 12, 2010 at 4:57)

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.

builttoride (Oct 12, 2010 at 6:06)

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.

smike (Oct 12, 2010 at 7:25)

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.

builttoride (Oct 12, 2010 at 7:43)

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.

D-Owen (Oct 12, 2010 at 9:16)

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.

D-Owen (Oct 12, 2010 at 9:21)

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

builttoride (Oct 12, 2010 at 10:28)

D-Owen,
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).

agill135 (Oct 12, 2010 at 15:41)

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

iamamodel (Oct 12, 2010 at 16:06)

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.

BEN-G (Oct 12, 2010 at 23:35)

NERD RAGE

[Reply]

builttoride (Oct 12, 2010 at 1:58)

Pinkbike once again there to help people ride faster and have more fun... keep it up!

[Reply]

ninjea (Oct 12, 2010 at 1:10)

yeah, another useful tech Tuesday! Keep em coming!

[Reply]

A123crash (Oct 12, 2010 at 13:25)

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.

seraph (Oct 12, 2010 at 14:01)

Heh, "times it." You mean "multiply it?"

jessman123 (Oct 12, 2010 at 15:09)

thats what multiplying it by a hundred is: moving the decimal two places.

[Reply]

bikejunkie88 (Oct 12, 2010 at 18:14)

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.

[Reply]

mtberforlife (Oct 14, 2010 at 20:03)

forget all the numbers go by feel
great video if you like to use the numbers tho

lochussie (Oct 15, 2010 at 10:55)

well, you've got to start somewhere

[Reply]

fantaman (Oct 12, 2010 at 2:57)

That was a very usefull information,thanks pinkbike Smile

rstwosix (Oct 12, 2010 at 4:34)

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.

[Reply]

timyoo (Oct 12, 2010 at 2:01)

what kind of fork is that?

pperini (Oct 12, 2010 at 3:44)

X-Fusion Vengance

seraph (Oct 12, 2010 at 14:01)

Vengeance HLR to be exact.

pperini (Oct 21, 2010 at 6:58)

thx!

[Reply]

nikoniko (Oct 13, 2010 at 15:56)

Awesome video!!
Lots of helpful info!!
RideOn!!

[Reply]

kyphoto (Oct 17, 2010 at 13:51)

Great job Mike & PinkBike. Keep 'em coming!

[Reply]

theskidkid (Oct 12, 2010 at 4:19)

why is there a tube on his fork

Stoked-Commencal (Oct 12, 2010 at 4:40)

To stop spray.

[Reply]

mickeydesadist2 (Oct 12, 2010 at 22:38)

This is a great column!

[Reply]

SessionNH (Oct 12, 2010 at 8:54)

thanks mike. good info

[Reply]

pinnr2010 (Oct 12, 2010 at 17:53)

i love tuesdays

[Reply]

Sharonb (Oct 12, 2010 at 20:46)

great tech tuesday mike!

[Reply]

haro-x6 (Oct 13, 2010 at 20:33)

mine is at 70% sag

[Reply]

Below threshold threads are hidden