Consider go karting. Karting is fun because it feels so fast. You're low to the ground and the karts rarely have suspension, so they make 40 mph feel like 140 mph. Now imagine rolling down to the local BMW dealer and taking a 740 sedan for a test drive. When you open up the V-8 engine on the highway to 100 mph, it probably won't feel much faster than 40 mph in a Toyota.
Our Test
Over the course of 14 days we rode a full-suspension bike and a hardtail bike 28 times over a 3.1-mile test course. Both bikes were built from aluminum, had similar geometry and were ridden with the same gearing, the same wheelset and the same tire pressure.
They were ridden in the same smooth-pedaling manner; riding out of the saddle created power spikes and therefore was avoided. Data was gathered using Garmin's 705 GPS unit and a Saris PowerTap.
We kept power output as similar as possible, with climbing limited to 300 watts, and riding the flats limited to 250 watts. (We were able to keep within +/- 25 watts of these ranges.) Downhills were all ridden at zero watts—coasting.
The test course consisted of just under a mile of rolling, lightly technical terrain, a half-mile climb gaining 50 feet in elevation, 1.2 miles of non-technical but bumpy, flat double track, and a half-mile of twisty, fast descending with three moderately technical sections.
It took roughly 15 minutes to complete each loop; the fastest lap recorded stopped the clock at 13:30 and the longest took 15:48. We averaged each bike's 14 times for a final score.
The Results
The full-suspension bike proved faster in every matched trial. It was 24 seconds faster over an average of all the trials. Of the 28 trials, 10 were carried out back-to-back, meaning at each lap, bikes were switched. For the other 18 trials, the bikes were ridden in three-lap blocks.
One interesting trend appeared when multiple laps were carried out on each bike: lap times for the full-suspension bike were very consistent, but each time the hardtail was ridden on multiple laps, it produced its fastest lap first, then times dropped off successively. This could illustrate the added effort a hardtail requires.
Subjectively speaking, the full-suspension bike was much easier to ride, both physically and mentally. It didn't require the concentration that the hardtail required on all points of our test course.
The full-suspension bike cornered faster and more precisely, and it negotiated the technical sections more smoothly. We felt less cornering and braking control on the hardtail. We didn't flat the tires of either bike, but did frequently bottom out the rim on the hardtail.
What to Take Away
Our test reinforced the opinion that riding a full-suspension bike is faster in variable terrain. A full-suspension bike leaves a rider fresher, even when the course is only moderately bumpy. When the course length or bumpiness increases, the advantage grows.
Whenever the terrain is more technical—up or down—a full-suspension bike makes riding easier on the racer's body and mind, as less concentration is required. This allows a racer to focus on race tactics or running their body more efficiently. Full-suspension can help at slow speeds, too, such as in New England, where the tight courses are often littered with roots and rocks.
Short, smooth courses, such as short track, seem to be the best place for hardtails. But there's also a sound argument that races with long, fire-road climbs would be best suited for a hardtail. The same could be said for super fit racers with strong core musculature who spend most of their time out of the saddle mashing gears.
As manufacturing practices improve, the weight argument carries less, well, weight. Many companies now offer sub-22-pound full-suspension bikes. Sauser's S-Works Epic weighs less than 20 pounds. Plus, suspension platform technologies in both frame and shock design now allow bikes like the Specialized Epic and Santa Cruz Blur XC to be ridden like the Euros—out of the saddle in a huge gear—without bob or any other inefficiencies.
So, whether you're racing for fun or results, it's likely you get more of both on a full-suspension bike.