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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Shock Absorber Pre-load /cgi-bin/YaBB.pl?num=1198995592 Message started by drharveys on 12/29/07 at 22:19:52 |
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Title: Shock Absorber Pre-load Post by drharveys on 12/29/07 at 22:19:52 It took me a while to get a handle on just how the pre-load works. As I see it now, it adjusts the range of movement of the suspension to match the load. At first I couldn't understand how shortening the spring would make a difference, but then I realized that I was only looking at the situation when the shock was unloaded and so fully extended. When you're sitting on the bike, the suspension sags under the weight of the bike and its load so the shock is not fully extended. Adding pre-load compensates for the sag and lets the shock operate in it's proper range of motion. Concrete example: Let's say a shock is 20 inches from eye to eye. The spring is 18 inches long, fully extended with no pre-load. There is 8 inches of travel from fully extended to bottomed out. (No, these are not from a specific bike, they're just theoretical to see how things work out.) OK, when you sit on your bike, the suspension sags 5 inches. That means the distance between the mounts is now 15 inches, at which point the spring is 13 inches long. At this length, the spring is "pushing back" with the enough force to balance the weight applied to it. 5 of the 8 inches of travel has been used up, and the shock is 3 inches from bottoming out. Let us say the pre-load is set to 3 inches. Unloaded, the shock is still 20 inches, but the spring is at 15. Now when you sit on the bike, the suspension sags until the spring is at 13 inches, when it again is "pushing back" with the proper force. That happens at only 2 inches of sag. That leaves us with 6 inches of travel until bottoming. True, there's less travel until the suspension is fully extended, but that's not what spanks you in the butt. So, in effect, adding pre-load doesn't shorten the spring so much as it extends the shock when it's under load. This allows us to tune the suspension to the load. OK, all you experts -- do I have it right? |
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Title: Re: Shock Absorber Pre-load Post by bill67 on 12/30/07 at 03:39:40 yep thats the way i see it |
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Title: Re: Shock Absorber Pre-load Post by Reelthing on 12/30/07 at 05:39:59 4D5B41485B5F4C505A290 wrote:
That is the idea - and in the case with the multi rate springs like Hagons or Progressives you get into the heaver spring coils much quicker with a little pre-load - likely can measure the unloaded seat height lifting |
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Title: Re: Shock Absorber Pre-load Post by Savage_Greg on 12/30/07 at 07:01:32 You can also think of the preload as setting the shock for the same extension and travel under a heavier load, like with a passenger. Each notch in the cam is for an additional amount of weight. Without the additional weight, the extension is higher and the travel is shorter... ...and of course, with the chrome cover, you have to do that thinking while upside down :P |
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Title: Re: Shock Absorber Pre-load Post by justin_o_guy2 on 12/30/07 at 21:01:00 Talking suspension? I'd just as soon go to the dentist. |
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Title: Re: Shock Absorber Pre-load Post by drharveys on 12/31/07 at 12:26:21 726D6B6C71764777477F6D612A180 wrote:
Then we got the daily double here -- a dentist talking suspension! |
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Title: Re: Shock Absorber Pre-load Post by justin_o_guy2 on 12/31/07 at 20:10:07 Call me on your picture phone. You can check my teeth while we talk suspensions. Sounds fun Huhh? |
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Title: Re: Shock Absorber Pre-load Post by Rockin_John on 01/01/08 at 00:27:57 32243E372420332F25560 wrote:
I've assembled many types of suspensions for different HEAVY vehicles. Spring loaded; stacked rubber; gas over oil (nitrogen); and the pre-load principal is always pretty much the same. Stop thinking of the changing length of the shock, although that is sometimes a byproduct of "pre-load." The important thing is to think of the spring's action as having been "pre-compressed" (interchangeable with "pre-loading"). If a spring's action has been pre-compressed to a weight of 100#; then it will not sag until more than 100# of down-force has been applied. When you change the position of the spring pre-load on a rear shock, or raise the gas pressure in a gas shock, you are simply raising the weight factor which must be applied to the shock before it begins to compress. Then you get into rebound/recovery rates of the internal oil and valving / passages which control the rate at which the shock may move in either direction. That is why some shocks drop easily, but raise hard, or vice versa. It is the interplay between progressive spring rates and the adjustable pre-loads and variable valving; especially in gas over oil shocks, that can make suspension tuning a black art. Addition: I should have mentioned that you ARE getting a grip on the basic principal of suspension theory. I just wanted to explain more and take you farther. |
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Title: Re: Shock Absorber Pre-load Post by Educatedredneck on 01/11/08 at 22:40:28 Ok - Let me see if I have this right, I have '97 Savage, I'm 6'1" and weigh 250 lbs, I currently run my tire pressures between what the spec's read for single rider and with a passenger, and I have the pre-load on "5". My question is, should I consider changing the preload? My previous experience with motorcyles is over 24 years ago when I was a young lad riding dirt bikes. It does seem to ride ok, but a hard bump will knock your teeth out. ;D When I bought the bike last summer, the pre-load was on "2" and the rear end seemed to move around alot in the curves. |
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Title: Re: Shock Absorber Pre-load Post by verslagen1 on 01/11/08 at 23:29:52 6' 240lbs I think my shocks only have 4 settings. Originally on either the 1 or 2nd setting and it was bottoming out. Tried max setting, and it was too stiff. one setting back is ok and it doesn't bottom out. |
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Title: Re: Shock Absorber Pre-load Post by Educatedredneck on 01/18/08 at 21:32:57 Thanks for the tip - I'll move it down to "4" and see how it rides. Gonna have to wait awhile thou - we have snow here in Maryland and it is too cold to ride. :( |
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