"Works" linkages - thoughts for a new machining project

[Masterphil]

Jeremy or other more knowledgeable person than myself please feel free to correct any of my mis-thinking, it has been a long time since i have read up on suspension setup, although i did have a good discussion about subtanks a few months ago...

I have been thinking a lot lately about the effects of changing the legnth of the links will have on the handling, and more importantly any adverse effects that might have on making the rate either too progressive, or not progressive enough. The idea was to machine new dogbones that would raise the rear of the bike for better cornering, but what effect would this have on the progressivity (I think that's a new word) of the linkage. It seems like every "works" bike that a magazine tests has some custom shock linkage that makes the suspension have a more progressive rate. Is it possible to make a linkage that raises the overall height of the rear but keeps the rate the same? I remember a company that was recently selling dogbones that were intended to raise the rear on the (i think it was 2003) yzf and crf's too make them turn quicker. I have access to appropriate materieals and tools to make new links, so that is not a real concern of mine. It would be rather dangerous if a shock linkage broke on the landing of a big jump. Another question: since a linkage such as this would raise the rear of the bike when the suspention is in basically an unloaded state, the rear would also be that much higher when the suspension is bottoming too, right? I think that i now need to go out to the garage and rip that linkage apart to get a little bit better understanding of what exactally it is that i want to be changing to achieve my goal. So, supension guru's what changes should i make to the linkage if i want to do this? I have plenty of material, so i can do some testing on various dogbone legnths, unless it is already known what the effects will be.
BTW. The bike that is in question to be modified is a 2002 yz426.

 

[marcusgunby]

I was under the impression the dog link length will only really alter the start point of the progression curve-not the shape.

 

[Masterphil]

My goal is to have the progression curve of stock, but to slightly raise the rear end of the bike to make it turn quicker. Upon a slightly closer inspection of the linkage it appears as though a shorter dogbone would lift the rear of the bike (or lower the swingarm in comparison to the rest of the bike, which is much more correct than raising the rear of the bike). Another thing that i was thinking: doing this will also slightly shorten the wheelbase since the swingarm will be in a lower position and closer to the front wheel, would this in its own be enough of an angle change in the suspension to cause the way the bike takes a hit like the face of a whoop?

 

[russ17]

Changing the length of the link on most linkage systems as little as 10mm will have a 20% effect on the progression rate. From this info I would gather any change to the length one way or the other will change the progression rate from stock.

Interesting topic

Russ

 

[MSracer]

PC and Devol sell links that could give you an idea on length changes. The PC ones I bought for a KX were 2mm differance.

 

[mxneagle]

Before you go thru that trouble, may I suggest the easiest way to raise the rear of the bike, lower the front. Simply slide the forks up in the clamps a few mm's. That will accomplish the change you wish and also lower the center of gravity rather than raise it. If for some reason you don't like that approach, you can simply lengthen the shock by a little bit. How you ask, place the desired amount of shims onto the shaft before you put the top out washer on. Remember, a little goes a long way here since the change will be magnified by the linkage rate so 1mm on the shock may net you 10mm in ride height.