Purpose of suspension linkage

Ask MC what he thinks of that bike

I typed up my best explanation from someone who loves this stuff more than anything but barely passed high school, then I realized someone like Billy from Luxon MX can answer your question in depth without even thinking so I deleted it. 
 

I had an 03 250XC, thought the PDS hate was overhyped. Fuck that thing, most unpredictable and most nervous POS I’ve ever ridden. 

If memory serves me correct the 02 SX had a rocket ship of a motor which made it even more scary. 

PDS bikes can work pretty good, the biggest problem is they have too much travel / sag. Shorten the shock by 6-8mm, run a standard 100-105mm of sag and a PDS bike will handle good. Good valving and spring rate for your weight will give good suspension feel, the only thing I know is that PDS will bottom out easier but mine isn’t a evil feeling bottoming, it’s just a soft, controllable bottoming. 

I currently have an 06 450 with PDS and an 18 450 with linkage. Both have good valving, both are stable, turn good and are totally raceable. The 06 was a mess until I had the shock shortened, I absolutely hated the thing. It was evil under hard braking/corner entry. 

Overall I do like the linkage bike better, but it’s 3 generations newer so it really should be better!

Linkage is a variable lever system that changes the the amount of the shock shaft movement relative to movement of the swingarm. PDS has come a long way since 02 and works well on technical trails. Not good for higher speeds in MX. 

A PDS style bike (no linkage) is super simple and doesn't have the weight or complexity of the linkage, but that comes with some serious limitations. The shock can only be mounted in so many places, which generally results in a long (heavy) shock that moves quite a bi throughout the stroke (hurts packaging) and a fairly linear motion ratio (ratio of wheel movement to shock movement - or vice versa depending on who you're talking to). The motion ratio issue is usually "fixed" with a progressive rate spring. 

A linkage bike is obviously more complex with more moving parts, but it allows for a lot more tunability of the motion ratio, which results in a curve more progressive that better resists bottoming. It also allows for a shorter length shock that doesn't move as much throughout the stroke so everything can be packaged tighter. 

Overall, the linkage bike allows for a better suspension setup at the compromise of a small weight increase, more parts, and more complexity.