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Flywheel weight questions

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I’m looking to buy a steady flywheel weight to help my bike have more low end for the woods and single track riding that I mostly do. I have 2 cr125’s, one a 96, and the other a 97. The 97 is the one I’ve been riding and love. It is the bike that I’m gradually starting convert to be better on the woods. The 96 I just finished rebuilding and just got though the first heat cycle yesterday. It’s the bike that I want to be more for the track suspension wise. Anyways, back to my question, I see 2 different weights for the flywheel, 10 oz and 12oz. Just wanted to see if there is shive difference between the 2, besides the obvious 2 oz, and get some opinions on my thoughts. Thanks.

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Keep in mind a flywheel won't add any 'low end' power, it simply stores energy making the engine less prone to stall and, mellows out the throttle response a bit.

Versus an actual heavier flywheel, a bolt-on disc type flywheel weight (FWW) is a bit less effective

as most of it's extra mass isn't located on the very outer circumference of the flywheel.

 

For a long time I had a 9oz FWW on a motocross track ridden YZ125 and while it's effects were noticeable, it wasn't drastic at all.

(most would have ridden it without noticing anything)

 

For the usage you've described, especially if technical terrain is anticipated

without a doubt I'd say go straight for the +12oz FWW if no motocross track riding is planned.

 

By the way, don't 'heat cycle' a new top end by idling/riding at low speeds as you risk glazing over the piston ring which

will reward you with combustion blow-by for the rest of that top end's lifespan, just ride it 'normally'.

Edited by mlatour
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Keep in mind a flywheel won't add any 'low end' power, it simply stores energy making the engine less prone to stall and mellow out the throttle response a bit.
Versus an actual heavier flywheel, a bolt-on disc type flywheel weight (FWW) is a bit less effective
as most of it's extra mass isn't located on the very outer circumference of the flywheel.
 
For a long time I had a 9oz FWW on a motocross track ridden YZ125 and while it's effects were noticeable, it wasn't drastic at all.
(most would have ridden it without noticing anything)
 
For the usage you've described, especially if technical terrain is anticipated
without a doubt I'd say go straight for the +12oz FWW if no motocross track riding is planned.
 
By the way, don't 'heat cycle' a new top end by idling/riding at low speeds as you risk glazing over the piston ring which
will reward you with combustion blow-by for the rest of that top end's lifespan, just ride it 'normally'.

Thanks for the info regarding the FWW. I think I’ll go with the 10 oz because I do plan on riding it on the track, just not nearly as much as single track.
The only reason I did hear cycles was because it was a complete engine rebuild, not just the top end. New bearings, gaskets, crank,and all. I don’t just let it idle either, I 1/4 to 1/2 throttle it and ride it around the backyard so everything can settle in.
Thanks for the help!
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I was under the impression you were building one bike up for woods/single track and keeping the other bike for motocross.

 

You might have a hard time finding a compromise (tires, gearing, suspension & engine mods) that will be suitable for both types of riding

while never having an 'ideal' setup for each specific usage.

 

Wanting a light and nimble bike, after riding a KDX for many years a very experienced riding buddy of mine 'enduroed' a 2002 or so CR125R,

despite all of his efforts it was always a handful in technical terrain and wore him out each ride/race.

A few years later he switched back to an off-road specific bike (BETA X-Trainer) and never looked back.

Edited by mlatour

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