Travel is the total distance your suspension unit can move, from fully extended to fully compressed. More travel means that your shock unit can absorb larger shocks, stretching out the short, sharp impacts so that you can maintain control over your bike. Longer travel allows people to do stuff on bikes that would never have been possible five years ago – jumping off things and onto things, in ways that would previously have resulted in broken bikes and broken bones.
Longer travel isn’t all good, though. Frames have to be beefier and heavier to maintain stiffness, as well as to withstand abuse. The shape of a long travel frame changes through the travel, making it tiring to ride long distances or to take on steep climbs. Cross-country frames with a medium amount of travel seek to find a compromise between soaking up uneven terrain, maximizing grip by keeping the rear wheel glued to the ground, and providing a comfortable, stable pedalling platform. Microtravel suspension – where the rear triangle moves 5cm (2 inches) or so – will absorb harsh trails, adding a bit of comfort with the minimum of weight penalty. Like front suspension, rear shocks need to be set up so that when you sit on the bike the suspension settles slightly. This is important – it means that your rear wheel can drop down into dips, as well as fold upwards to pass over lumps and obstacles in your path. This keeps you floating in a horizontal straight line, rather than climbing in and out of every irregularity on the trail, saving you energy.
Each manufacturer has their own ideas about how much of your total travel should be taken up by this initial sag, so you’ll need to consult the shock handbook or the manufacturer’s website to find out their recommendations. Since the sag is always given as a proportion of total travel, you’ll need to know the travel as well before you can start setting your sag. If you don’t know it already, use the steps below to measure it.
Step 1: Stand the bike up and measure the distance from centre to centre between the shock eyelets. This is the extended length.
Step 2: Release the spring: for an air shock, take the valve cap off, push down the pin in the middle of the valve, pump the bike up and down a couple of times and push the pin down again to release the rest of the air. For coil shocks, back off the preload-adjuster, as far as it will go, so that the spring dangles loose.
Step 3: Push the bike down to compress the shock and measure the distance between the eyelets again. Then subtract the second measurement from the first, and that’s your total available travel.
“This keeps you floating in a horizontal straight line, rather than climbing in and out of every irregularity on the trail”
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
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