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Old 03-30-2007, 10:40 AM   #1
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Default Heaver vs. Lighter Flywheel

I was always under the impression that lighter meant better - but that's not necessarily the case! After Artificial-I posted some info in the MTX-4 thread on flywheels, I did some research and came up with this pros and cons chart. Can you guys look it over and share your expertise on this? Thanks!

Heavier Flywheel

Pros:

More torque
Smoother idling
Smoother acceleration

Cons:

May lose some responsiveness

Lighter Flywheel:

Pros:

Improved top speed
Improved throttle response
Accelerate and decelerate quicker

Cons:

May cause engine to idle less smoothly
May cause car to accelerate too quickly (difficult to control)
Requires higher traction
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Old 03-30-2007, 11:02 AM   #2
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I don't really think a heavier flywheel will give more torque.
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Old 03-30-2007, 11:08 AM   #3
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A "lighter" flywheel will allow the car to change directions faster. This is a key reason to watch the rotating mass - defeating the "gyroscope effect":

http://en.wikipedia.org/wiki/Gyroscope
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Old 03-30-2007, 11:39 AM   #4
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Quote:
Originally Posted by Scott Fisher
I don't really think a heavier flywheel will give more torque.
A heavier flywheel doesn't generate more torque as much as it maintains rotation inertia better than a light one creating a effect of more torque. This is especially noticable on two stroke motors which have less effective compression ratio than four strokes. Sometimes, on a track with alot of dead stop corners, a heavy flywheel might get off the corners better than a light one and make the motor more tractable and easier to drive.
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Old 03-30-2007, 12:40 PM   #5
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In drag racing cars are known to add weight to their flywheel to make a more consistent and easier launch.

Essentially a flywheel keeps the motor smooth by storing its weight throughout the duration of a stroke. To reconnect it with the next cylinder fire. This translates into easier and quicker revving.

With a lighter flywheel you will get quicker spool up. So on a high traction track , you will get better acceleration. On a low traction traction a heavier drivetrain is going to slow or calm things down and therefore allow more traction.

It doesnt really change the power of the motor. Allthough there are many and huge debates all across the net on weither or not that it can increase power....and thats normally a lighter flywheel.

Id say that flywheels are a very mis understood and almost black magic tuning. Theres so many theories its pretty much pointless to search on google and hope for true info. Theres many many many conflicting arguements on each side. From some guy doing dynos saying they do such and such to some 30 year old road racer giving his knowledge.

But mostly a lightweight flywheel will allow the wheels to spin up to rpm faster. As well when the clutch is engaged and you let off the gas , the engine rpms will also drop faster. This makes it good for racing on an auto course so you can do some engine braking. This is why youll find drag racers adding weight. To make for an easier and consistent launch.

A lighter flywheel you can find more response and less kick when shifting gears. More weight youll get less response and more kick when shifting gears.

A lot of people will also state that a street car is better of with a heavier flywheel , because of the stop and go motions. Where a race bred car that only sees tracks and only has to launch once or twice out of a hole. Its sometimes better to get a lightweight flywheel. As the revs dont drop down enough to really effect it or traction.

But for tight , small tracks with almost stop and go turns you will probably benefit from a heavier drivetrain. Wide , large , sweeping tracks will do well with a lightweight drivetrain.

Then onto the simplistics of weight loss , yes a lighter flywheel will allow you to turn better. But thats really so marginal its probably unmeasureable.

I know I have a LW 3racing flywheel for my mtx-4 and its only 1 gram lighter. So its pretty much pointless and so small it probably wont make any difference anyone can see.

But the shafts on the car , thats a different thing and thats where 10-20grams can be added or removed. This is where you will see some differences.

Best bet is too swap around and find out for yourself. Id like to see some people trying it and seeing how both setups felt on their car.

Also maybe some karting drivers might be able to shine some light on this one as both hobbies are very similiar and that community is pretty knowledgable on subjects of tuning.

Hope this info helps. Im open to reading any article on the subject from any top member of any of racing community , so feel free to share. Ive had years of experience with using lightweight flywheels on cars and more. But havent really seen anything spoken about in the rc community.

Ill help as I can locate more concrete info. All of this is off the top of my head but should be mostly accurate.

Goodluck.
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Old 03-30-2007, 01:01 PM   #6
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Quote:
Originally Posted by rmdhawaii
I was always under the impression that lighter meant better - but that's not necessarily the case! After Artificial-I posted some info in the MTX-4 thread on flywheels, I did some research and came up with this pros and cons chart. Can you guys look it over and share your expertise on this? Thanks!

Heavier Flywheel

Pros:

More torque
Smoother idling
Smoother acceleration

Cons:

May lose some responsiveness

Lighter Flywheel:

Pros:

Improved top speed
Improved throttle response
Accelerate and decelerate quicker

Cons:

May cause engine to idle less smoothly
May cause car to accelerate too quickly (difficult to control)
Requires higher traction
After reviewing this I concur with all this information. Its all 100% correct and you should place that into one of your KB guides , its easy to read and covers the bases. Perhaps some tweaks here and there or add-ons will help. If you need help , just let me know. Ill fix it up for you. Iam at work right now but will do what I can....when the boss isnt looking. *sneaky* I will slap something similiar into ph.
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Old 03-30-2007, 01:08 PM   #7
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These engines idle between 12,000 and 18,000 rpm so a heavier flywheel doesn't smooth out much.
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Old 03-30-2007, 01:08 PM   #8
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Quote:
Originally Posted by Artificial-I
After reviewing this I concur with all this information. Its all 100% correct and you should place that into one of your KB guides , its easy to read and covers the bases. Perhaps some tweaks here and there or add-ons will help. If you need help , just let me know. Ill fix it up for you. Iam at work right now but will do what I can....when the boss isnt looking. *sneaky* I will slap something similiar into ph.
Feel free to tweak it all you want. I'll post it up in the engine KB once it's done.

Thanks!
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Old 03-30-2007, 01:10 PM   #9
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we are also talking about tw0 - stroke engines which have no torque and very peaky power bands.
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Old 03-30-2007, 01:16 PM   #10
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Quote:
Originally Posted by YBSLOW
we are also talking about tw0 - stroke engines which have no torque and very peaky power bands.
Motocross = 2 stroke and yes they react the same way. All motors produce torque.

As well you can see dynos on nitrodynesystems , that are producing power below 8000rpm. I believe idle is a bit lower.

Also a 2 stroke motor can be built for many purposes. It doesnt have to have the power range that you explain.
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Old 03-30-2007, 01:32 PM   #11
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Quote:
Originally Posted by Artificial-I
Motocross = 2 stroke and yes they react the same way. All motors produce torque.

As well you can see dynos on nitrodynesystems , that are producing power below 8000rpm. I believe idle is a bit lower.

Also a 2 stroke motor can be built for many purposes. It doesnt have to have the power range that you explain.
Just comparing two stoke to four stroke. Almost all motocross is now 4 stoke completely because of the torque advantages. Two stokes do and will always have a more peakt torqoe curve compared to a four stroke and when you talk about an enine that ia 1/5th of a cubic inch they make almost no torque at all. "ALMOST" we know it can be measured on a dyno but we are just talking about practical horsepower which on smething that turns this kind of rpm the horsepower reading is more of a by product of rpm.
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Old 03-30-2007, 01:40 PM   #12
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This would be a very interesting topic
Keen to see what the experts views or experiences are.

From real 1:1 experience we found that lightened flywheels were great on aspirated motors and helped alot with response and from dyno testing between engine dyno and rolling road we saw that there was less drivetrain losses with lightened flywheels but as mentioned a noticeable difference to engine turn over on start up and lumpiness on idle.
For example a engine that made 120hp on engine dyno made 95hp on rolling road with lightened flywheel it would make 98hp.

Sure the rc counterparts are smaller and a gram or two shouldnt to our minds make a difference but im sure that it should be.
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Old 03-30-2007, 02:12 PM   #13
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some engines become impossible to tune with a lightweight flywheel, for example my traxxas 2.5R, I swapped that out for a .18TM and it ran perfect
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Old 03-30-2007, 07:03 PM   #14
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IMO, a flywheel would have the most effect on idle rather than acceleration, top speed, responsiveness etc.
there are always other changes you can make to the car which would counter-act these effects (if any) given by a heavier/lighter flywheel.
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Old 03-30-2007, 07:14 PM   #15
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It's just like a dirt bike... Heavy flywheel will make it idle better, and may take a little away from acceleration (but this would probably be negligible). Lighter flywheel throttle inputs more 'snappy'.
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