|Professional Tweaks, Tips & Reviews By "AJ" Picarello
|I hope you find my Tweaks and Tips section helpful. If there is something you want to know about, send me an email and I will try to add that to one of my upcoming articles.
Fork and shock technology is becoming more sophisticated every year. Many 2002 bikes come stock with "Pro only" suspension. If you're wallet is fat enough, you can buy the same "works" bikes your favorite pro rides. This may sound great for most of us, but you'll need a lesson about tuning your new tricked out machine.
During this tech tip, rebound, compression, preload, damping and spring rate, are just a few words you'll have to deal with. I will explain the terminology as we go along. If you have a puddle of oil under your bike and it feels like a pogo stick, you have a blown shock or fork. If your full suspension bike cost around $300, then stop reading this Tech tip. Your suspension is not tunable, it's not intended for aggressive mountain biking, and it's probably blown.
I make it a point to test people's suspension whenever I get a chance. What I usually notice is an uneven balance between the fork and shock. Usually the front forks are set up too soft on XC bikes. Try adjusting the rear shock to match the front fork. Also adjust the rear shock's rebound slightly slower than the forks rebound. This method helps prevent flipping over the handlebars.
Most likely you've heard the term "suspension sag". This is the amount your shocks sink into their travel when you sit on the bike. Motocross racers have been measuring sag for years to help set up the proper spring rate. Downhill bicycles should use the same methods Motocross racers use. You should use up 1/3 of the bike's suspension while sitting on the seat. Freeride bikes should use around 1/4 the bikes travel. This method works better for rear shocks. XC racers usually run no sag. XC suspension should be set up for harsh impacts only. Small bump compliance is not an issue. Set up properly, you should rarely bottom out your bike.
I notice heavier riders tend to add too much preload on the shocks. By adding more than 2 turns of preload to the coil over spring could cause many problems. Over twisting the rear shocks spring puts pressure on the shock body, sometimes causing the shock body to unthread from the piggyback reservoir. Oil and nitrogen gas will spill from the shock and you'll need a rebuild. Bike shops can't fix the shock. You'll have to send it back to the manufacturer. Mention to them that your spring rate is too soft and you need a stiffer spring. Adding too much preload not only causes your suspension to work improperly, but the shock can coil bind. Coil bind is when the complete coil compresses, but the shocks stroke still has room to travel. Your bike will have less travel with this problem and you'll lose traction with a harsh ride.
Sophisticated rear shocks have many external adjustments: rebound, spring preload, high and low speed compression. The rebound adjuster is located on the small shaft side of the shock. It's sometimes chrome plated. I've seen the knob colored red and gold. It controls how fast the shock returns. The compression adjuster is located on the piggyback reservoir or on a remote mounted reservoir. Most shocks adjust only low speed compression. Newer shocks by Currnutt, Progression and Avalanche have both low speed and high-speed adjusters. Compression is when the shock is forced downwards. Compression damping resists bottom out and can help reduce bobbing when pedaling. Low speed compression is easier to adjust than High speed. You can test low speed compression by riding your bike while forcing the suspension downward with your body weight. For example: If your bike bottoms out at the bottom of a steep roll or while carving through a berm, then you need more low speed compression. High-speed compression kicks in when your suspension encounters a sharp object at a high rate of speed. Extreme drop offs and rock gardens trigger high speed valving. If your bike slams through its travel when you blast through rock sections then add more high-speed compression.
Suspension set up is personal preference. The faster you ride the stiffer your suspension has to be. Most shocks can be tuned for your riding style and weight. You may need a simple fix such as a stiffer spring or heavier weight oil. Some companies even offer custom valving. Most bikes come sprung for 160-190Lb riders. Set your bike up to fit your style. You will ride faster with more confidence. 2002 should be an amazing year for everyone from world cup professionals to first time mountain bikers. Enjoy the technology, I know I will!
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