More advanced question...kinda

[soccersteve]

I don't think I posted tihs on this site, i think it was KP and i don't think i got many responses. But if i did post this on here, then forgive my ignorance.


I know a little bit about cars, enough that i cna probably replace anything that went wrong with mine with a little help. when it comes to cam pulleys and alternator, etc. pulleys, for every pound you lose in the weight of those, you gain about 2.2 horsepower. I'm wondering if that is the same idea on bikes? I haven't had any of my plastics off to look around, but i was thinking that maybe it was something similar? if someone could satisfy my curiosity, that would be great.

[The CyberPoet]

Re: More advanced question...kinda

[CARS...] when it comes to cam pulleys and alternator, etc. pulleys, for every pound you lose in the weight of those, you gain about 2.2 horsepower. I'm wondering if that is the same idea on bikes? I haven't had any of my plastics off to look around, but i was thinking that maybe it was something similar? if someone could satisfy my curiosity, that would be great.

(A) Bikes generally don't use pulleys, but rather take power directly off the shafts via gearing. On the Katana, only belt/chain I know of is the cam chain, which shouldn't be lightened for obvious reasons (it serves a mandatory function in keeping the cams sync'd to the crank). Such accessories as power steering pump, air conditioning compressor, vacuum or secondary air pumps simply don't exist as such and thus aren't bolted onto the engine to be driven by belts & pulleys like they are on cars.

(B) Yes, reductions in rotating masses increases the engine's ability to produce power (mostly by increasing the rate at which the engine can change Rev's). For a typical MC engine, that means lighter (or hollow) cams, lighter-metal piston rods, reduced weight piston crowns, lighter valves & valve springs, lighter crank, removal of balance-weights, and a lighter flywheel (if a flywheel is used at all). But the cost of implimenting such things is usually prohibitive for the amount of power recovered (and require serious engine tweaking usually as a result as well), and it usually makes more sense to simply move to a different engine, a different bike, or a higher-compression set-up (such as the bore-over kits which increase the stock compression to as high as 13.5:1 depending on the kit). The stock masses also are balanced to a high degree by the factory, so removing mass at any one of these components can have adverse reactions in terms of engine smoothness (and except to blue-print it or balance it, such things are best left for race engines, where smoothness is often traded for performance).

(C) The best way to accomplish the same thing is to remove weight at the other end of the equation -- at the wheels. Moving to magnesium or carbon fiber wheels can easily shave 2 to 12 lbs off the rotating masses there, which improves handling radically (far less mass to redirect when steering), improves the suspension (far less mass for the springs to push back down after a bump means faster road re-acquisition by the tires), improves acceleration (less mass to spin up), improves braking (less mass to spin down). The down sides are that this isn't cheap because of the strength required and the cost of the materials + fabrication (a typical pair of magnesium wheels runs $2500 - $4k); and that the bike may cruise less stably (more flighty) because of the reduction in gyroscopic effect at the wheels as a consequence of losing the masses.

Cheers
=-= The CyberPoet

[soccersteve]

makes complete sense. thanks