Here are some "shocking" insights about the effects of suspension on your biking and your fitness.
Buying a new mountain bike and understanding the particular suspension system that it comes equipped with may sometimes require a degree in quantum mechanics: Force, rebound, damping, millimeters of travel, air vs. oil shocks, fully active, partial lock-out ...
What clicks for me is discovering the simplest levels and save the complexity for later. So here's the long and short of it.
Bikes usually come in three varieties: fully rigid (no suspension), hard tail (front fork suspension only), and full suspension (both front and rear suspension).
It's entirely possible to start mountain biking without the use of any suspension. If the trails or dirt roads that you ride aren't too beat up, or if you're going to be riding your mountain bike on the road, you probably will not notice a huge difference without it -- but if you want to explore out of your realm onto new terrain and trails, suspension may be very helpful.
The kind of trails and riding that you'll be doing will help determine the type of suspension you'll need. For simplicity's sake, let's say that there are three categories of rides/trails:
Cross country riding
Trails will be a mix of terrain and surfaces: smooth spots, some rocks, roots, and water. Double-width and single-track sections, hills and flats. For the majority of novices and seasoned riders, this will be the terrain of choice most of the time, and the hard tail front suspension fork will work.
In choosing a hard tail, you might think about the spring or travel (in inches or millimeters). This is the amount that the fork will compress and rebound when you push directly down on the handlebars. Somewhere in the range of 2.5 to 4.5 inches (or 80+ millimeters) will be ample to absorb most of the bumps hitting your front end.
Many of the front forks now have fine-tuning adjustments that will make the compression a little softer or a bit stiffer. Some forks provide a complete lockout feature, making the front completely rigid -- in some instances, climbing up hills on a rigid fork could be easier and require less energy usage.
Overall weight of most hard tails tend to be lighter then many full-suspension bikes.
Technical trail riding
You'll encounter only a few smooth surfaces, but will discover more and bigger rocks, roots, and potholes, and the overall ride will feel more broken up with lots more obstacles. You can also expect double or single track with hills and/or flats.
Over years of heavy use and riding, lot of pristine single-track trails that were once smooth and flowing have had their ground surfaces worn down, exposing rocks and roots. The potholes between them get deeper and the trail becomes vastly more challenging and now technical.
The bike of preference for a technical ride is a full-suspension with both front and rear shocks. The kind of rider to take on this type of terrain will tend to be more experienced, stronger, aggressive in their style, and have good balancing skills. The rear suspension travel range could be anywhere from couple of inches up to 6, 7, or 8 inches plus.
Often a fully active rear shock -- lots of travel with no or few adjustment options -- will drain much more of your stamina, especially on the uphills. More recently, a lot of R&D has gone into developing a lighter-weight rear suspension system that gives the rider more options and adjustments to control the amount of travel. Bikes with these kind of engineered controls are growing in popularity, as they seem to be very versatile for use on both cross-country and technical trails and give the rider more range of comfort.
Downhill terrain
Usually trails serviced by a lift at a ski area. The bike of preference will be a full suspension and will tend to have considerably more inches of travel in both front and rear shocks and be fully active with little or very few adjustment options.
It's also entirely possible to ride downhill on a cross-country-style full-suspension with just a couple of inches of travel in front and rear as well as on just a hard tail. Taking the time to pick a smoother fall line down the hill will be important.
Your comfort, however, will depend on how rough the terrain and how fast you want to get down the hill. Keep in mind: rougher terrain and higher speeds often require more shock-absorbing capacity (more inches of travel) in order to maintain stability and control.
Full all-out downhill bikes have a completely different frame geometry as well. The front fork appears to be higher than the rear, where your saddle is. Also many of them are considerably heavier than most other mountain bikes, and riding one of these uphill requires great endurance. If you like riding uphill too, you might not want to get one of these babies.
However, the efficiency that may be lost due to its excessive weight and fully active suspension can work to your advantage on shorter, more technical climbs as you're often able to pedal right over big rocks cause due to its great shock-absorbing capacity. And it's this capacity that keeps the wheels down on the trail, making balance easier to maintain over harsher conditions.
These bike are made for high speeds where picking a line isn't as critical as maintaining balance over whatever comes your way. The range of fork travel is great, with some of them having 6+ inches in front and up to 9 or 10 inches in the rear. This kind of travel will make it possible to go over a big rock and barely feel it, or drop off 4-, 5- or even 6-plus-foot ledges and have a good portion of the shock absorbed by the bike itself.
This kind of riding requires excellent balance skills, quick reflexes, lots of nerve, a couple of loose screws, and lots of biking experience.
Suspension fork effects on our body and ride
As the bike encounters a variety of obstacles, a certain amount of shock is absorbed by the bike and by our bodies. The suspension fork is the main shock absorber for the front upper torso and arms. With less wear, tear, and fatigue on the arms and less jarring, it's possible to ride longer and increase the speed at which you can ride a trail safely.
How you grip your handlebar will also play a role in reducing tension and fatigue. Make a locked circle around the bar using your thumb and index finger, and brake using one, two, or three of the other fingers. If you cannot reach the brake levers comfortably you should readjust the set screw to draw the brake lever in closer to the bar, or have your local shop adjust it till it's easy to reach.
Try to remind yourself to have a firm grip but not too hard ... think "relax." It's easy to grab on too hard, and excessive tension will build up in hands, arms, and upper body. Stay loose but firm.
With a completely rigid front end, the wheel may bounce off obstacles and into the air more often, but a front shock will tend to assist the front wheel to track more consistently on the ground during most riding conditions.
Shocks and weight shifting
Riding a bit back and off of the seat while standing and using your pedals as a level platform will vastly improve your stability and maneuverability. When standing level on the pedals, your legs bend quite well at the knee and will become the rear shock-absorbing system.
Front shocks definitely soften the blow to the body and make the ride more comfy, but standing on your legs, shifting your weight to the rear, and bending at the knee will improve the system twofold. If you can see or anticipate the hard hits coming ahead -- bumps, potholes, rocks, or roots -- and increase your speed slightly just prior to hitting them, you may not have to pedal at all and you can just stand and coast.
You'll be able to maintain better balance while your momentum, front shock and legs do most of the work.
Suspension and your fitness
It should also be noted that it's highly unlikely that you'll see a bike with just rear suspension. Rear shocks definitely assist in absorbing the bashing that our rear and lower-body torso take, and without them your only option is to stand up over rough terrain with your weight back while bending your legs at the knee.
This standing and bending at the knee is quite effective; however there will be many instances on a technical trail that you'll not be able to maintain enough forward momentum without pedaling and you'll have to remain seated while going over the bumps. It's under these conditions that you quickly begin to notice just how well that rear shock works. The bumps get much softer, and some you'll not even feel. Your balance immediately improves, and whereas before you may have been bounced off the seat by some bumps, now it's easier to remain seated while still pedaling over them.
You'll also be able to travel over the trails at a higher speed and ride for longer periods while still maintaining that important edge of control.
Rear suspension with enough adjustment options and with a modicum of travel will offer the best riding comfort. It will give you the ability to custom-tune the bike for a variety of trail conditions.
If you just converted over to a full-suspension from a hard tail, you may require a short period of adjustment, as at first the full suspension does appear to require more endurance on the climbs. But the gain received by less bashing and less wear and tear on the body will offer you extra energy and endurance in the short and long runs.
Correct seat height is still important, and be sure that you have full leg extension on your pedal stroke. Often on a full-suspension bike, you'll need to raise your seat a bit more to accommodate for the extra travel.
A word about suspension seatposts
Here's another option that is less costly then investing in a full suspension bike. Some companies make a seatpost that has spring (travel), and although the amount of travel you receive tends to be on the low end it's a viable option that will definitely relieve some of that bashing to your body while improving your biking performance.
It certainly is not a substitute for the high performance that adjustable rear suspension will provide, but it will help and is far better then a rigid post under some conditions.
Just about all the major suspension systems within their perspective component group levels work quite well, and usually come with a good warranty, especially if purchased through a reputable shop.
Cliff Krolick is founder and owner of New England-based Back Country Excursions MTB Touring Lodge and Hostel, one of the first and longest running mountain biking cross country touring facilities in the region. On its 10,000-acre semi-wilderness preserve, BCE offers a wide variety of trails for all skill levels, guided rides, mountain bike getaway vacations, and annual recreational MTB events. BCE also features an extensive skills development program, a highly successful comprehensive teaching approach, and one of the few MTB-instructor certificate programs. If you have any questions about mountain biking, send them to Krolick at bcountry@psouth.net.