Rear Suspension Preload

[teh_engr]

Hi Everyone,

I've almost gotten my '81 GS550T on the road (within the next week, certainly) and am currently making some minor adjustments. I believe that the rear suspension preload needs to be increased, and have two questions:

1) What is the reccomended setting for a 300lb rider?

2) Can someone describe the process for adjusting preload? Do I need a special tool to compress the coil springs?

Thank you all for your help.

-Jack

[Steve]

The recommended setting is the one that will let the suspension settle about (only) ONE INCH with you on the bike, ready to ride.

Have a friend help you with the measurements, but start with the preload cranked up all the way. I have been known to use large Channel-Lock pliers to do this if the correct tool is not available. Stand the bike up, straddle it without putting any weight on it. Have your friend measure something like the distance from the bottom of the license plate to the ground. Sit on the bike, put as much weight on it as you can, just barely tippy-toeing for balance. Measure again at the rear. If it dropped more than one inch (1.5 is OK), you need new shocks with heavier springs. If it moved less, reduce the preload and try again.

The principle here (and for the front forks) is to have no more than about 1/4 of the available travel used up with you sitting on the bike. The forks typically have about 6 inches of travel, the rear shocks about 4 inches.


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[chef1366]

Get a set of Progressive with double (two) HD springs. I'm a big guy too and this works great even with a passenger.

[Billy Ricks]

Steve's got the sag setup procedure outlined pretty well. About the only thing I would add to his directions is to have the wheel at each end off the ground so the suspension is fully extended when you take the first measurement. If you want a firm ride that will handle corners well shoot for an inch of sag. If you want it more plush go for a bit more sag. You should do both ends so you have balanced suspension. Either use more air in the fork or spacers above the springs to get the sag right up front.

[Steve]

About the only thing I would add to his directions is to have the wheel at each end off the ground so the suspension is fully extended when you take the first measurement.

True. I forgot that little tidbit.

If you want a firm ride that will handle corners well shoot for an inch of sag. If you want it more plush go for a bit more sag.

Here, I will have to disagree.
Actually, the more suspension travel you have available, the more plush the ride can be. You will have more travel to absorb bumps, so less energy is transmitted to you. Since the only way to adjust the spring rate on our bikes is to replace the springs/shocks, the preload adjustment only adjusts your ride height, not your ride quality. With your admitted enhanced gravitational attraction, higher-rate springs will certainly be in order, too.

One other thing that can affect the ride quality, especially at the front end, is changing the viscosity of the fork oil. Many on the board recommend 15w fork oil for the enhanced damping characteristics. I have found that 10w fork oil in my wife's 850L rides better wile still retaining good control. Since many sets of forks get neglected far too long, there is a rather dramatic improvement when switching to 15w oil that most of the guys like. I think that if they had used 10w instead of 15w, they would have noticed an improvement, too.

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[Nessism]

No disrespect to the technical guys suggesting measuring sag, but for a 300 lbs rider you had better just go straight to the highest setting. Even at that, the rear is going to bottom out easily over bumps.

The $75 Midi/Emgo shocks sold around the net have stiff springs and would be suitable for someone your size. Hopefully someone will chime in with a recommended source.

Good luck.

Edit: found this source... http://www.crc2onlinecatalog.com/Index_Main_Frame.htm