Don't forget that some bikes come set up in a way that very few people will actually ride them (no real guards, paper thin tubes, even thin plastics, etc. I always like to set up a bike the way you will actually ride/race it. Then weigh it. You may be a little shocked at that final number. Now get some mud on it and weigh it again.
Your 4 stroke anything can start reading to 300 lbs!
More Weight can be a positive and a negative (positive: more momentum, less deflection. Negative: harder to lift it on the stand, harder to pick up after your 25th crash)
Less weight can be a positive and a negative: positive, easier to put on stand and pick up after the 25th crash, some aspects of handling are better. Negative: more deflection and skittering around on trail junk, often will be more fragile, will not hold it's line as well, also less traction and hook up (think about that one)
MX bikes: I like lighter feel.
Offroad bikes: as long as you have the skills to put the wheels where they need to be, many benefits to a bit heavier bike (within reason of course, no KLR 650 please LOL) also the mid to big bore 4T can be much easier to ride, low end torque finds traction instead of hi rpm hp from the smaller motors that tends to spin, harder to ride in bad terrain.
Final point on weight: lighter bikes can have thinner engine cases, plastics etc to get that weight down (no magic, less weight means less stuff, less stuff means weaker, unless exotic metals are employed). So it can mean a less durable bike that will not last as long and will need more parts replacement from wear and breakage. Just compare an XR to a modern thumper. No one will argue which bike will last longer and require much less maintenance. Nothing is free. We are in the weight wars, we will test how far we can go before the maintenance schedule gets too much for the average guy, and the cost of ownership becomes unbearable for the average guy, the time spent wrenching instead of riding becomes too much etc.
That is another reason for the resurgence of the 300cc 2T motor. Not really light requires more fuel, and when armoured up weights 250 lbs +/- no matter what the mags say. (owned plenty of them, got another one right now). But it has some big motor character of lower rpm torque, not fragile and enough heft to hold their line, but not too heavy to pick up after a bad one.
Edited by stroker, March 16, 2016 - 07:04 AM.