What is the benefit to adding fly wheel weight

What is the benefit of adding additional weight to the fly wheel, what changes does it do the way the engine power is delevered.

I have big bore RM250 and its been recommended to add weight to the fly wheel?

Basically, the more weight rotating with the flywheel the more torque you will create but this is offset by the power used to start its rotation.

This is why say for an MX bike, in most cases you would not use extra flywheel weight as you want the bike to rev up and down quickly.

On a bike for woods use where you are on/off the throttle over technical terrain, extra weight can be added to the flywheel so that once it is spinning it will retain more kinetic energy creating smoother and more tractable power delivery.

Hope this makes some sense.

Edited by dirtynidge

What is considered the amount the right amount of weight to add.

depends what you want, more weight if you want like 4 stroke power

i have a 8 oz on my 06rm250 and i love it, still has a hit but is smoothed out a bit down low to mid

I agree with the above replies except for one thing - some very good mx'ers use will use a lighter FWW. While there are plenty of voices for a weight for woods riding, I learned directly from an "A" mx rider that a FWW helped him most out of corners and when it got slippery.

You would loose a little KAPOW on a short run before a jump but the right amount of clutch compensates and you gotta pretty much use some clutch anyway. So for a good mx rider that's got their controls skills down the FWW actually gives them an edge. And he knew a few other racers that had them.

I bought the heaviest weight (13 oz) pretty much right after I bought my 250 because I wanted to maximize traction in woods/offroad. I was a little worried that the 13oz might dull the hit too much but, for me, it turned out to be just fine because these 250s have PLENTY of power and the thing STILL lights off . . . but in a controlled fashion.

I should say that I have carburetor and head mods so I'm not stock . . . but that is more like what you've got with a big bore (although I'd like to get a big bore myself, so I'm interested in hearing your thoughts about that)

One more thing . . . if you go for the weight, whatever size you pick remember that you could resell it and get most $ back to move to a different size because there's nothing that wears.

Some very good explanations here, thanks, it was 13 onz recommended.

What the weight look like and how is it attached tot he fly wheel or do you buy a hevier fly wheel.

Edited by motolink

A good way to describe the effect is to check out a merry-go-round:


If you ever had the pleasure of playing on one, you'll remember it took quite a bit of effort to get that thing spinning to max speed. Mostly because they are made out of heavy steel/iron. But when your friend was at the verge of puking due to extreme dizzines....you'll also remember trying to quickly stop it. If you grabbed a bar it nearly ripped your arm out of it's socket and only took it to about half speed. That is because all that weight stores the centrifugal energy. You couldn't spin it fast, but it sure kept going once you got it to speed.

Now imagine a merry-go-round made of plastic. You could zing that thing to top speed pretty quickly....but it would also slow down quickly.

You get the same effect with flywheels. A light flywheel will allow a motor to rev much freer than a heavy one. Good for zinging right up to the HP range of a motor. A heavy flywheel will make a motor rev slower (because it's luggin the weight around), but at low rpm it will feel torquier due to the stored energy.

Some very good explaations here, thnaks, it was 13 onz recommended.

What the weight look like and how is it attached tot he fly wheel or do you buy a hevier fly wheel.

It's attached to the existing flywheel. I don't know if other years' RMs are different, but on mine the flywheel weight was threaded in the mounting hole, so effectively it replaced the stock flywheel weight nut.

When you buy one you should get instructions with it, pretty self-explanatory.

The steel vs. plastic merry-go-round is a very clever analogy. Stored energy is what it's all about.

Well that all makes sence.

Well that all makes sence.

There was a FWW that had a base (6 oz) with two rings (2oz ea). You could have a 6, 8 & 10 oz weight. Took 10 min. to go from a 6 oz to a 10 oz if you needed it for the mud or hill clinbs.....

Good info Guys

After adding weight is it easy to feel and pick the difference.

only problem is....I have the MSR Flywheel Weight 13oz. coming but it has been on back order since mid November. Nobody has them right now. :banghead:

I did see a 13onz weight on the net for sale by SFB for sale, what is around the right price.

How about this company... Its where I got one for my boys RM65.


They only offer a 10 oz. and I'm not a fan of that plastic gasket.

They are cheaper as no billet cover included....but the 13 oz. weight is what I am after.

crfoot, that is a good article, where would I get a full fly wheel for a RM250.

I did see a 13onz weight on the net for sale by SFB for sale, what is around the right price.

It sold for $70.00, looked like good value.

After adding weight is it easy to feel and pick the difference.

Yes ,,that's a good way of putting it...You can feel and pick the difference....I use a 10oz'er..it's just right for moto and the trail's....Dr.D....

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