Setting up your XC mountain bike suspension doesn’t have to be some black art that only a few people in the world are qualified to do.
You can get your XC mountain bike suspension dialed in on your own thus gaining the confidence to tweak it yourself. Who wants to rely on your local shop, a friend, or some monk that lives at the top of a mountain far away ever time you want make a small adjustment.
First you need to understand some basic principles of how your XC mountain bike suspension actually works.
XC Mountain Bike Suspension Sag
Sag on XC mountain bike suspension applies to both your XC mountain bike’s front fork and the rear shock.
If you have 100mm rear shock, about 4 inches of suspension travel, it isn’t actually all useable travel.
Let me explain by first focusing on your XC mountain bike’s rear shock suspension first.
You might have heard people talking about sag percentages. On XC mountain bikes, it is common to setup your rear shock to 15-25%. Less sag is typically used on racecourse that is less aggressive, i.e. less jumps, less rocky, etc.
Less sag (more shock air pressure) can make the bike accelerate quicker and expend less energy when your shock is in trail mode, but it will create a rougher ride and requires more force to compress the shock and more upper body strength to control it in rougher terrain like a rock garden.
Less sag (more shock air pressure) setup can also help with repeated bottoming out, assuming your compression is setup correctly.
The upside is you gain a little more travel the less sag you use. On a racecourse that is mostly fire roads, 15% would be ideal.
Here is how sag uses up some of your XC mountain bike’s rear suspension.
If you have a 100mm fork and you set up 25% of sag, your actual remaining useable suspension travel is now only 75mm (about 3 inches of travel). This assumes your rear shock has no bottom out system that prevents it from giving you the full remaining 75mm of travel.
In order to set the sag, it takes two people to perform this operation.
First, use a bike stand to raise the rear tire off the ground or having your assistant hold the rear tire off the ground with the saddle. This is done to make sure your suspension is fully extended. Now measure the distance from the center of the top to the bottom eyelet of the XC mountain bikes rear shock.
The eyelet is where the bolt goes through the top and bottom of the rear shock to connect it to the XC mountain bicycle.
When performing this on your front fork, you are measuring full stanchion extension from the top of the leg just below the crown to the bottom just above the fork seal.
Let’s use 6.5″ as our eyelet example of a fully uncompressed XC mountain bike’s rear shock. You can also check your manual or the bike spec to see what the shock eyelet should be.
To adjust the rear shock to 20% sag, here is the simple calculation:
In case your rusty on math: 20% = . 20
Then to get .8 below, 1 -.2 =.8 (You don’t need the zero)
6.5″ x .8 = 5. 2″
Next you should sit on your bike with all the gear you normally wear, keeping the bike upright by holding onto a wall or similar.
Your assistant will now measure the the XC mountain bikes rear shock, from the center of the top to the bottom eyelet.
If the measurement is below 5. 2″ you need to add more air pressure to the main chamber of the rear shock. If it is greater than 5. 2″, the reverse is true, you need to let out a drop of air.
Now you now the secret to setting up your sag. Remember, some people find a sag setting they like, and never adjust it, while others tweak it a bit based on the demands of the racecourse.
Tip – Changing your sag will affect both your rebound and compression settings, so you may want to keep notes on your base settings for various conditions so you can quickly get to the settings that help you win.
Use the same application to set up the sag on your XC mountain bike front fork as well.
On an XC mountain bike try not ever exceed 30%, as the amount of remaining useable suspension is only 70mm (2.75″) and without good bottom out protection you could damage the internals hitting a 3-4 jump based on rider weight.
XC Mountain Bike Suspension Rebound
Almost all entry level XC mountain bike suspension allow for external rebound adjustment, usually in the form of knob / dial. It is often located at the bottom of the fork and many times red on the rear shock.
Like the name “Rebound” implies, this adjustment helps offset how fast the suspension recoils back when it is compressed. If you hit a rock and your XC mountain bike’s front fork compressed 2″, a slower rebound setting will force the fork to return back to its full 100mm of travel slower, than if you have a very fast rebound setting.
Slower rebound can make the fork feel sluggish over consecutive, very closely spaced obstacles like powering through a rock garden. If it is set too slow, after hitting the first rock the fork will still be attempting to return to it maximum suspension position when you hit the next rock and so forth.
Slower rebound does have its advantages. On courses with lots of jumps, slower rebound sometimes feels better on the landing, then being recoiled quicker.
Examining these two examples above, it becomes clear there is a tradeoff in settings based on the terrain, how aggressive you ride, and of course the feel you prefer.
To initially set up your rebound, you should start in the center of your rebound. If you have 10 clicks, start in the middle at 5. Be careful not to force the knob passed the available clicks. Check your manual if you need too.
Pick a trail you ride often, with a variety of terrain. Attempt to slow the fork down at first and see how that works. If that isn’t working, go the other direction faster. You may have to ride the trail several times to get it right.
Also if you have a higher end fork with compression settings, you may want to set these dials to the center position as well.
Complicating the adjustment of rebound is the fact that both different sag settings, and compression settings have a direct effect on rebound.
That’s what keeps XC mountain biking interesting.
XC Mountain Bike Suspension Compression
There are two kinds of compression settings, high speed and low speed. Some XC mountain bike suspension offer neither externally, some offer one adjustment, while others have both adjustments.
The compression system like the name implies, is how fast the suspension compresses. High speed effects compression over very fast bumpy terrain, while low speed compression is the opposite and can effect bottoming on jumps or drop offs.
The same suggestions for settings apply based on rebound as well, but each adjustment can affect the other settings, so it can be a bit tricky.
Tips – if you are on a racecourse with big drops, increasing your low speed compression can help with bottoming out. If you are very aggressive over rock gardens, it can also help to prevent bottoming. You may have a built in or adjustable bottom out system on very high end suspension.
Sometimes high speed compression settings will benefit from slower rebound speeds to counter the forces.
XC Mountain Bike Suspension Lockout
Most XC mountain bike suspension offers a lockout. Either located on your handle bar, or you have to manually flip it at the shock.
I highly recommend a handlebar system for both safety and efficiency. Obviously a lockout on both the XC mountain bike’s front and rear shock are preferable that work simultaneously.
The lockout system on XC mountain bikes has improved dramatically over the years, as the systems now release a little on big hits to avoid suspension damage.
I damaged an older system with my lockout engaged many years ago. I crashed and didn’t realize it flipped the lockout switch to active. I took off on an aggressive part of the course and damaged my internals. A real bummer!
That kind of damage is hopefully a thing of the past, because even with a handlebar system, sometimes you forget to make the switch and hit something aggressive.
If all of this is just too overwhelming, ask a competent riding buddy, or trusted shop mechanic to get you up too speed.
The morale of the story is, you will be a lot better chance to win races when you have the confidence to both understand what your XC mountain bike suspension is reacting to different input, and how to adjust it accordingly for maximum efficiency.
If you are in the market for a new fork, here are some irresistible choices to get you all fired up: