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Flywheel Effect

By Jon

Is your ride a US-model XC converted to EC engine specs, a Euro-spec EC, or a standard US XC? The XC has a different flywheel than the EC. Very different. I'm not aware of all the flywheel weights that are available but I just finished trying to install two weights on my '01 XC300 with EC engine conversion. The weights screwed right in but didn't fit because they stuck out too far. A spacer on the cover would be needed for them to fit.

Since I'd gone to all the trouble of borrowing the flywheel weights I decided to borrow an XC flywheel and do some analysis of the polar moment of inertia. It's really the moment of inertia that provides the flywheel effect, not the weight or mass. And flywheel effect comes from all the engine rotating components (crankshaft, pistons, rods, clutch basket, etc.), not just the flywheel. I modeled only the flywheels and weights. Here's what I came up with.

Units are pounds for weight and lb-in2 for moment of inertia. (Sorry for those not in the US or UK.)

Component Weight MOI
XC Flywheel 1.18 1.57
"10 oz" Weight 0.75 0.79
"14 oz" Weight 0.99 1.66
Nut 0.03 0.003 (not used when installing a flywheel weight)
EC Flywheel 1.97 5.13

What you can see is that even though the weight of the XC flywheel with the "10 oz" weight is higher than the EC flywheel, the flywheel effect of the combo is only 65% of the EC flywheel. That XC flywheel is just a tiny little thing.

I personally like a lot of flywheel effect. I can ride a bike with a light flywheel just fine but tend to stall more often when I get fatigued. Even with the EC flywheel my Gas Gas seems to have much less flywheel effect than my old KX250 with a 12oz Steahly weight on it (which I plan to also model when I get the time).

For the time being I'm going to happily ride my XC/EC. If I want more flywheel effect I think it's possible to squeeze in a flywheel weight on the EC flywheel if it's designed just a little differently than the current XC weights. Do any of the European riders put flywheel weights on their bikes? Maybe this issue has been dealt with already.

I've heard that for 2002 GGNA isn't converting the flywheel and lighting coil to EC specs upon request as was done in the past. It's XC flywheel and weight.

'01 XC/EC

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