Basic MTB Suspension Setup Controls

Basic MTB Suspension Setup Controls

In January we hosted a Suspension Clinic at BikeCo.com.

We had a great turnout for what turned into a couple hours of BikeCo owner / World Cup level mechanic Joe Binatena explaining setup and tune options.

At the clinic we handed out a printed concept sheet to help riders understand the basics (in some cases pretty over simplified basics). We've had a handful of requests for copies of the handout, so here it is for riders and clients worldwide.

SUSPENSION BASICS

Springs

Spring Rate: spring rate is used to set static sag within a range depending on chassis, rider ground speed, riding style, preference, etc.

Coil Springs: considered “linear” feeling. Each inch (or unit) of spring compression requires the addition of another preset unit of weight. There are progressive springs, typically in motorsports. Most MTB coils would be considered single rate.

Air Springs: considered “progressive”. As the air spring is compressed it resists (pushes back) with an increasing rate due to

decreasing volume in the air cylinder. Most modern bikes utilize air springs rather than coil options. They are more easily  adjusted for differing rider weights, and nearly all modern suspension takes advantage of the progressive nature in suspension  design for a more “bottomless” feel.

Volume Spacing

Volume spacers modify the ramp rate (progressiveness) of an air spring. We’ve used some arbitrary sizes and values for this example, but it identifies the concept in MTB application.

Some simplified concepts as you review the graph:

We measure PSI on unloaded shocks (100% of stroke remaining) while setting sag (example 33% sag or 67% remaining).

Sag is supporting a specific weight (same rider = same weight) and thus must have a specific force applied to the air piston. This force equates to the PSI x Piston Surface Area (same shock = same piston). Based on this, PSI at sag should be equal to support the same sag.

However the RAMP RATE is different, meaning you start at a different number to get to the correct sag PSI.

Continuing along the shock stroke these values will differ more substantially deeper into the travel.

Gray Graph represents a 2.5” tall air spring.

100% remaining   =   93psi

67% remaining    =   133psi

33.5% remaining   =   233psi

0% remaining   =   864psi

Black Graph represents a 3” tall air spring.

100% remaining = 100psi

67% remaining = 133psi

33.5% remaining = 200psi

0% remaining = 401psi

Damping - the oversimplifed version

At its most basic, damping is controlling shaft speed by modifying flow of oil.

Greater, or faster volume changes, oil flow means less damping. Slower oil flow provides more damping.

Illustration shows extremely basic shim stack assembly. As shaft speed increases pressure against the shim stack increases. This additional pressure is designed to flex shims to access larger sections of the oil flow porting creating a dynamic tune.

Modern MTB suspension uses shim stacks, gas bladders, bypass valves, etc. This allows complex tunes for a variety of suspension systems, leverage ratios and riding styles.

Rebound

Rebound Damping: opposes and controls a compressed spring’s return to static height “out of” travel.

Without rebound a sprung wheel simply bounces while trying to return to a static position. (think of a car with a blown shock on the freeway.)

Single, typically low speed, or dual low and high speed rebound controls are available depending on model.

Setting rebound speed is based on individual riding speed.

Too fast of a rebound setting results in suspension skipping and loss of traction.

Too slow and suspension will "pack”.  Suspension "packs" when the shock doesn’t return to full travel before the next feature and each bump sits it deeper and deeper into the travel.

Compression

Compression Damping: assists the spring’s resistance to bump input by controlling shaft speed “into” travel.

Too little compression control uses a larger portion of travel than necessary.

Too much compression creates a harsh ride as well as lost traction due to poor small bump compliance.

Single, typically low, or dual low and high speed options available depending on model.

Most stock MTB suspension is set near open compression settings to maximize small bump compliance. Adding compression will help suspension ride higher in the travel, with greater resistance to “dive”. Low Speed Compression on a fork is often used for additional support. This keeps a rider's hands taller riding in steeps, etc.

Many compression setup misconceptions are based on theories from coil sprung motorsports. For instance a motorcycle typically will feature progressive coil springs. A motorcycle also carries much more weight compounding compression forces. 

Fine tuning compression with progressive air springs isn’t the same as tuning compression with a linear coil or air springs.

Rundown on the clinic

It was a fun turnout to the clinic in January. What was estimated to be a 30-45 minute run down ended up with Joe going through details for a bit over two hours!

Joe covered the basics of setting up stock as well as what we look for when tuning custom suspension for riders. Range of sag settings for specific riding styles, how rebound and compression actually modify each other, how to maximize suspension for a range of terrain compared, etc, etc.

Without writing a novel on the suspension clinic here are the a couple quick points reiterated:

• High and Low speed settings should be within a handful of clicks of each other. 1 click high and 12 clicks low is a bizarre setup and may mechanically confuse the system. 4 clicks high and 7 clicks low would be a much more appropriate setting.

• If you have a good base setting, you're working with a reliable resource, changes should be "relatively" minor at a time. Wholesale changes are often a sign of something else going on. If you add ten clicks of rebound to a bike that's close you might bump it well out of setup and start fighting with other issues as well.

•The most important piece of information for riders who were only going to take a single data point was this: Learn to use the fork's low speed compression when riding steeps! After all this is advantageous in situation after situation. It supports your body, keeps the front end from burying, as well as add confidence on trail. If there was one control that riders might use frequently during a ride it is low speed fork compression.

Ready for the new 2019 Fox Racing Shox? We are working to get those uploaded to the website now - in the meantime feel free to reach out to our sales staff to get dialed in!

Hope this blog was insightful for riders. We look forward to seeing as many of you as possible at the next clinic!

See you on the trails - Nate@BikeCo.com