[Kanye West]

A heavier bike will have less transient force moving through the suspension. A 30-35# bike versus a 40-42# bike is a big difference, and that's a 25-35% increase in the mass of the inertial damper that rests between you and the wheels bouncing around.

Take a 200# YZ125 and take it through the same rough section as a 300# Husaberg, with the suspension set up appropriately on either one. One will feed back a lot more than the other. Yes, the lighter bike will move through corners easier and allow you to throw it around with less effort, but there are clear benefits to a heavier machine when it comes to suspension action.

Here's another analogy, and I use this one a lot, especially when it comes to heavier vehicles. When your front triangle and bars and fork upper assembly and cranks get so damn light they may as well not be there, this happens: Imagine a 100# girl holding a 45# barbell in front of her and shaking it back and forth. Her upper body will be moving forward and back like crazy. Now imagine a 250# guy holding the same 45# barball in front of him and shaking it back and forth. In comparison, he'll barely move. That's a lumped parameter model of the sprung weight and un-sprung weight of a vehicle, and how low frequency transient force moves through the system.

The only bike I care about weight on any more is my Enduro, because I have to climb it. For descending serious DH trails, shedding those couple lbs isn't making anyone faster or slower. Get stronger, and take a good dump before your ride

 

[sbabuser]

Imagine a 100# girl holding a 45# barbell in front of her and shaking it back and forth. Her upper body will be moving forward and back like crazy. Now imagine a 250# guy holding the same 45# barball in front of him and shaking it back and forth. In comparison, he'll barely move.

Yeah, I'm still picturing this analogy to different sized riders moving a bike around. Weight is relative. Saying that the lightest any dh bike should be is 35lbs is like telling someone the optimum handlebar width without knowing wide their shoulders are. Oh, wait, that's one of the things we do around here...

 

[Udi]

That's talking purely about suspension performance though, and that's just one factor out of many important ones. Like it or not, DH involves all those other things too - and one distinct difference compared to most motorbike racing is very abrupt direction changes (think tight / technical sections), and a high frequency of them.

A simple way to test your theory would be to literally do what I joked about - strap 3kg to your frame in a location you see fit, changing nothing else on the bike except for correctly optimising damper and spring rates - and do a series of back to back timed runs on different tracks.

 

[Kanye West]

I'd agree. Find the heaviest cranks and pedals you could possibly find, and the lightest, and an ultra heavy steel spring and Ti spring. Those locations will affect the side-to-side handling the least. Would be interesting.