I have been studying the various rear suspension designs found on different quads and I wanted to ask about the linkage that is found on some.

For example, on some quads the rear shock is attached directly to the swingarm but on others the shock is connected indirectly to the swingarm via an additional pivoting link. Exactly what does the linkage do for the rear suspension?

Does the linkage provide more wheel travel? Or does it allow for a lower shock placement on the frame? Also, does it have anything to do with the leverage ratio of the shock?

Is there a real benefit to having linkage on a rear suspension system, or is this really something that is model specific as far as quads go?

 

I will try to answer your question the best I can. With a direct link (such as is on a 300ex) if you move the rear tires upward 3 inches, the shock rod must move 3 inches. The linkage system will only move the rod about 2.5". It is progressive though. That means the next 3 inches of wheel travel will only move the rod approximately 2" and so on. Now I know these measurements aren't exact (due to angles), but I am simply trying to explain it. Since your shock doesn't have to move as far on the link as the direct system, you can have a shorter shock or more travel. As for a great advantage, it is debateable. All new dirtbikes that I know of except KTM's still use the link system. KTM uses a very trick progressive shock that works so smoothly that it doesn't need a linkage. This is good because it reduces moving suspension parts.

 

The linkage affects the speed that the shock is compressed, leverage ratio as you put it. If you take a shock (no spring on it) and compress it slowly, it offers little resistance. Move it fast and you'll get lots of resistance. Try slamming a screen door vs. just closing one easy, you'll see what I mean.

The farther you compress the suspension, the faster it moves the shock. So the farther up the wheel is, the stiffer the suspension gets. Soft over small bumps, stiffer over jumps. Springs by nature get stiffer as they are compressed, although there are also variable rate springs that aren't linear in their resistance. A set of triple rate front springs is another way to have a variable spring rate.

The rising rate suspensions (linkage) were developed when shock technology was behind the chassis technology. With today's tech, it's easy to have a linkless suspension and still have a progressive shock. I believe the main reason you still see links is cost. It's cheaper to use a fair grade shock and a couple pieces of aluminum links than it is to use excellent quality shocks.

Did that help?

 

Thanks for the replies.

Do you have or know of any formulas for figuring the proper leverage ratio for a suspension linkage system?

 

There are hundreds, if not thousands of variables. Shock length, swingarm length, angle, relation to countershaft, quad weight, f/r distribution, etc...

If I were starting from scratch, I'd either copy a great existing design, use a CAD system, or just have the shock custom made after the chassis is developed. I would also use a linkless system, getting a progressive suspension from the shock itself.

 

hey what these guys are talking about is how the shock ramps up. in mtb bikes it is realy important on how the rear end ramps up. what u need to do id go to your local bike shop and check out all of the diff full sup. bikes out there. from cross contry to freeride or down hill. that is the bet way ican see you learning about it is go look at them all at he same time. i know your thinking it is a mtb bike not a atv but it i all the same idea
-santa cruz-single lower foward piviot
-gt i drive- esentrick floating bottem
-rotec- oivots around bottem bracket
-specialized FSR ( most popular)- used by every body ev GT before the i drive. it is a gret idea but would never work on a quad (to much latural play)
-santa cruzz-vpp some new ra i dea that works great
there are more great set up out there but this is all i can think of rite now. bu if u wont more ideas take a good hard look at mtb bikes