First Impression: 8oz Flywheel on '03


13 replies to this topic
  • yz_for_me

Posted September 16, 2005 - 10:11 PM

#1

I recently put a GYT-R 8 oz flywheel on my '03. I've only had one day at the track since the install, but I already know I like the change. The stock '03 power was manageable, but still a handfull in some situations, especially off road. I figured the 8oz would be a good happy medium, not so heavy as to take all the "fun" out of the power, but heavy enough to make a noticeable difference. so far I'm really happy with this weight. The motor feels a lot more "426ish" which in my opinion is a good thing. In saying this I don't mean it has less power, but it is smoother and more controlable. When you grab a handfull of throttle, the response is more predicable and you are less likely to break the rear end loose in corners. The other benefit I noticed is the smoother power doesn't tire you out as quick. I could ride much longer without getting tired. So far I really haven't found any negative aspect of the new flywheel and would highly recommend it for anyone. :banghead:

  • grayracer513

Posted September 17, 2005 - 08:15 AM

#2

What was the part number of the flywheel you bought? Was it a GYT-5TA97-50-00, or a GYT-5TA97-50-50?

Actually, 8 ounces, when it's added as it is here, in the form of a ring welded entirely on the edge of the flywheel is on the heavy end of the spectrum, and is about the same as using a 12 oz bolt-on in terms of how much effect it has on the overall inertia mass. That's because all of the weight in yours is out on the edge, whereas a good part of the weight of a bolt-on is in the central mounting hub area, where is doesn't add as much force.

Which one of the above did you get?

  • rasta

Posted September 17, 2005 - 10:37 AM

#3

i put a 6oz bolt-on on my 03. it did not make it more managable at all. it made it even more snappier. front end comes up way more easier . just helped out on tight trails and hill climbs with not stalling.

  • grayracer513

Posted September 17, 2005 - 11:21 AM

#4

i put a 6oz bolt-on on my 03. it did not make it more managable at all. it made it even more snappier. front end comes up way more easier .

I would simply point out to you that the tendency to raise the front wheel used to be a tendency to spin the back one. That's the difference. :banghead:

  • yz_for_me

Posted September 23, 2005 - 06:29 PM

#5

What was the part number of the flywheel you bought? Was it a GYT-5TA97-50-00, or a GYT-5TA97-50-50?

Actually, 8 ounces, when it's added as it is here, in the form of a ring welded entirely on the edge of the flywheel is on the heavy end of the spectrum, and is about the same as using a 12 oz bolt-on in terms of how much effect it has on the overall inertia mass. That's because all of the weight in yours is out on the edge, whereas a good part of the weight of a bolt-on is in the central mounting hub area, where is doesn't add as much force.

Which one of the above did you get?


Mine is the GYT-5TA97-50-50. This is the heavier of the GYT flywheels and I'm definately glad this is the one I got. The bike hooks up noticably better than stock but still has PLENTY of hit. I think I would have been dissapointed in the lighter GYT-5TA97-50-00 model. I found this one on Ebay and picked it up on an impulse. I wasn't really looking for a flywheel so I didn't do much research before buying. It was a good deal, so I figured what the heck.

  • matt116

Posted September 23, 2005 - 06:37 PM

#6

I used a Doctor D 4oz on my 03' works perfect.

  • Ducksgoquak

Posted September 23, 2005 - 11:34 PM

#7

I have an 03 yz also but i've never really had a problem with the "hit". Maybe it's because i ride pretty exclusively in the sand but why is it exactly everyone likes adding the heavier flywheels to try and smooth it out? Never really had a problem :banghead:

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  • djo269

Posted September 24, 2005 - 02:18 AM

#8

Ok, after reading all these posts I am definitely going to get one soon for my 03' yz450. But which one is right for me? Ok, what I want out of a heavier flywheel is to stop the stalling in tight corners and when I take a jump slowly and not at race speed I dont want it to stall. I need the hard "hit" because I weigh around 280lbs fully geared. I ride alot of tight outdoor mx tracks with very little woods now and then. I am thinking maybe the Dr. D 4oz or 6oz would be perfect. Which one? I enjoy riding my 450 at lower revs as much as revving it to the limiter as well. So any help is greatly appreciated. :banghead:

  • Ga426owner

Posted September 24, 2005 - 06:59 AM

#9

Ok, after reading all these posts I am definitely going to get one soon for my 03' yz450. But which one is right for me? Ok, what I want out of a heavier flywheel is to stop the stalling in tight corners and when I take a jump slowly and not at race speed I dont want it to stall. I need the hard "hit" because I weigh around 280lbs fully geared. I ride alot of tight outdoor mx tracks with very little woods now and then. I am thinking maybe the Dr. D 4oz or 6oz would be perfect. Which one? I enjoy riding my 450 at lower revs as much as revving it to the limiter as well. So any help is greatly appreciated. :banghead:


Guys some of you are way off base here. The Weight does not take away the hit! The weight allows the rear wheel to hook up in less than ideal situations. Example: on a stock 03 the rear wheel wheel will spin ridiculously on a hardpack surface, causing fishtailing etc...Bottom line you lose time. Through in some rocks and sandy top soil and you will see immediately what I am talking about. The weight corrects the amount of torque to the rear wheel allowing it to hook up. For a more scientific answer ask GreyRacer. (Chime in and correct me)
If I was any of you considering a GYTR Weight. Here is what I would base my decision on:
What is your riding ability and are you going to ride on Tracks or in the woods?
A D rider or beginner will need more weight period - in order to get comfortable on the bike. A woods rider will need more weight on the flywheel also - Do I need to explain why? The woods here in my area are somewhat tight - too much wheelspin makes for too much work to ride!
A B/C rider will need less weight because the heavier weight will detract from the torque that goes to the rear wheel.
I use a 5oz on mine. I ride MX exclusively. I have ridin it in the woods and will tell you that I hated it! I would have to have at least a 8oz for riding in the woods. But I think the 03 YZF is not a good choice for the woods period. That is why I am saving $ for a KTM 300 XC or EXC for my woods bike.
Most A riders I know will use a 4 or 5oz on a 03.

  • yz_for_me

Posted September 24, 2005 - 08:03 AM

#10

Guys some of you are way off base here. The Weight does not take away the hit! The weight allows the rear wheel to hook up in less than ideal situations. Example: on a stock 03 the rear wheel wheel will spin ridiculously on a hardpack surface, causing fishtailing etc...Bottom line you lose time. Through in some rocks and sandy top soil and you will see immediately what I am talking about. The weight corrects the amount of torque to the rear wheel allowing it to hook up. For a more scientific answer ask GreyRacer. (Chime in and correct me)
If I was any of you considering a GYTR Weight. Here is what I would base my decision on:
What is your riding ability and are you going to ride on Tracks or in the woods?
A D rider or beginner will need more weight period - in order to get comfortable on the bike. A woods rider will need more weight on the flywheel also - Do I need to explain why? The woods here in my area are somewhat tight - too much wheelspin makes for too much work to ride!
A B/C rider will need less weight because the heavier weight will detract from the torque that goes to the rear wheel.
I use a 5oz on mine. I ride MX exclusively. I have ridin it in the woods and will tell you that I hated it! I would have to have at least a 8oz for riding in the woods. But I think the 03 YZF is not a good choice for the woods period. That is why I am saving $ for a KTM 300 XC or EXC for my woods bike.
Most A riders I know will use a 4 or 5oz on a 03.


In some ways I agree with you but not totally. Let me explain. You are right in that the flywheel does not change the power curve of the motor at all. What I mean by this is the power output of the engine has not been reduced in any way. But it does reduce the "hit" felt by the rider and here's why.

First off lets define what the "hit" we talk about is. The hit is nothing more than a quick increase in linear acceleration as felt by the rider. Now it stands to reason that if the linear acceleration of the bike increases quickly the rotational acceleration of the rear wheel must also be increasing proportionally. Here's where the flywheel comes in. From physics we remember the basic equation F=M*a where F= force, M=mass and a=acceleration . This is for linear force and acceleration. For rotational motion the equivalent equation is T=I*alpha where T=torque, I=rotational inertia and alpha=rotational acceleration. So how does this relate to the hit? Well, in our system, Torque remains the same because the motor produces the same torque whether the flywheel is present or not. However, with a heavier flywheel we have increased I (rotational inertia) in the equation above. So for the equation (T=I*alpha) to remain true, alpha (rotational acceleration) must decrease in proportion to any increase in I (rotational inertia). This translates to a decrease in rotational acceleration of the rear wheel and therefor a decrease in linear acceleration as felt by the rider. This is the reduced "hit" that we feel.

The reason the flywheel doesn't reduce the power is because once spinning, for all practical purposes, the flywheel doesn't require any more torque to keep it spinning. It only takes torque to accelerate the flywheel, not keep it spinning at a constant rate. So for a given rpm, the horsepower rating at the rear wheel is virtually unchanged.

In simpler terms, the torque produced by the motor has not been reduced, but some of the that torque has been "used up" by spinning a heavier flywheel. This leaves less torque available to accelerate the rear wheel and therefore reduces straight line acceleration which is the "hit" we refer to.

  • grayracer513

Posted September 24, 2005 - 09:19 AM

#11

In simpler terms, the torque produced by the motor has not been reduced, but some of the that torque has been "used up" by spinning a heavier flywheel. This leaves less torque available to accelerate the rear wheel and therefore reduces straight line acceleration which is the "hit" we refer to.

substitute "accelerating" for "spinning" above.

It's really a question of reducing the engine's ability to accelerate the rear wheel to a more practical, controllable, and usable level. As it comes, an early 450 has the ability to spin up the rear tire on most surfaces as if it weren't there, or didn't have any knobs on it. The downside is that it sometimes handles as if it didn't have any knobs on it because of that. Quite often , if you take a little of the edge off of the engine, traction is improved very noticeably, while the snap of the motor seems unaffected by it. If I want the back wheel loose, I have no problem making it happen, I just don't have to work quite as hard to avoid it anymore. And the great thing about the 450 is that because I did this with the flywheel, I can change it one way or the other any time.

Keep in mind that a YZ450 with an extra 8 ounces still has less flywheel than a stock 426. With the 8oz Dr.D on the bike Doug Dubach describes the engine as "more like a CRF450", hardly a sluggish engine.

  • revolucien

Posted September 24, 2005 - 09:22 AM

#12

This translates to a decrease in rotational acceleration of the rear wheel and therefor a decrease in linear acceleration as felt by the rider. This is the reduced "hit" that we feel.



The decrease in rotational acceleration of the rear tire will actually cause an increase in linear acceleration because you are removing slippage of the rear tire and are appliying that force to the ground rather than losing it.

  • fast426

Posted September 24, 2005 - 10:38 AM

#13

Bottom line is in a 60 foot race the weighted flywheel would beat the stock one. Puts the power to the ground and hooks up, bottom line. Has anyone put one on a 426. I'm tearing mine down this fall and am wondering whats a good ounce of weight.

  • yz_for_me

Posted September 25, 2005 - 07:57 PM

#14

substitute "accelerating" for "spinning" above.


Good point, better choice of words there.





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