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Old 12-02-2010, 06:20 AM   #111
Disco Dean
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Joined: Jul 2007
Location: The Great White North
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Quote:
Originally Posted by Dan Căta View Post
I agree that a flywheel takes power from the engine but I was thinking that since the most power would be directed to the rear wheel, the flywheel would not consume that much power.

And, why didn't they design a smaller diameter flywheel and a more powerfull starter engine ? That would have been a big plus in flywheel bottleneck ;)

Dan.
I don't understand the starter connection but as pointed out above - the flywheel weight directly relates to parasitic losses and also most importantly drive ability. Most lower revving higher torque motors incorporate a larger heavier fly wheel to allow for that bottom end grunt as the intertial mass helps that - but the higher revving you get the less that is needed - ie. light 2 stroke motors that rely on super high revs have little or no fly wheel. A modern 2 stroke trials bike that is designed for huge bottom end has a fly wheel that is huge in comparison to a moto crosser. It all translates to the rear wheel. One of the reasons that crank hp and rear wheel hp are so different - ie. a chain uses approx the same amount of hp to move around as an inline straight cut gear set - but the gear set takes up tons more room. If you factor in the ring and pinion of the GS drive shaft and spinning the drive shaft you lose more power in that system. But you gain in other areas. We run a vintage BSA Gold Star and the fly wheel mass is one of the key determining factors of how the bike comes off the turns - when we wanted to sacrifice drive ability for a few more top end hp - among other things - we reduced the fly wheel weight a bit... A big GS that needs to lug around the dirt and be drivable around town - and even keeping momentum up on the highway helping mpg - a heavier fly wheel does it.

It's not a bottleneck of sorts but a basic design element/parameter that contributes to how the bike runs. And you can manipulate that by adding or reducing the weight of it.
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