Will a lightweight flywheel damage a starter sprag?

[Langanobob]

IMHO the subsequent failure was attributable to the installation not the effect of the flywheel itself.

And, to take it one step further, I wonder if the reason they stole his Nichols flywheel was to hide the evidence?
I know it's pure conjecture but it just rubs me wrong that they didn't return the flywheel.

[TAftonomos]

I'll put the lightest flywheel I can stand to drive with on anything with a manual box, and continue to reap the benefits.   The small amount of driveability annoyance can easily be "ridden" around with technique (IE, just a smidge more trottle to drive away from a light).  My 900ss liked it, my 999 REALLY like it, and the S4RT seemed to like the mod even more, with respect to the bike feeling a bit more nimble (reduced gyro). 

The more problems I run into with Ducati service/dealerships, and FACTORY manual having bogus/wrong info in it, and reading crap like this.....well lets say I'm not sure my next 15K motorcycle purchase will be with ducati.

The the OP.  Man, I hope you get this sorted out.  You were charged for installing a part, charged for fixing the shop's screw up, and then your part was stolen, and the MFG denied to help you.  F that.

[Norm]

This supports my standard philosophy: buy used - do the work yourself or thru a small independent shop.

[Langanobob]

Shazaam,  Thanks for taking the time to write all this out for us.   I have a few comments.  I should start out by saying that I don't have a lightened flywheel, although it's on my list.  I'm interested in this topic out of personal curiosity.

This is a known problem and an issue that you should consider before you add a lightweight flywheels to a Ducati. Ducati sees a lot of worn-out starter clutches when there is a very light flywheel attached. Why? Often lighter flywheels seem to let the engine kick-back much harder during start-ups and shut-downs, which causes starter clutch damage.

I talked to an independent tech with lots of lightened flywheel experience.  He agrees that he sees a lot of worn out starter clutches with light flywheels.  He also says he sees a lot of worn out starter clutches with stock flywheels.   His opinion is that there is  no correlation whatsoever between flywheel weight and starter sprag failure.   However, he doesn't have any written records or statistics to back this up.   Can you provide any actual numbers for sprag clutch failures with lightened flywheels vs stock flywheels?  Without actual documented numbers what you are presenting as a fact is still just one more subjective personal opinion.

As you ride at lower rpm in traffic, you are constantly changing between acceleration and deceleration. Engine torque levels are still fairly low at these speeds, so slack in the drive train needs to be smoothed-out with a flywheel. Otherwise, on-off throttle transitions have a jerky effect, giving a less comfortable ride and causing you to use smaller throttle inputs (which is not always easy to do.)

This, and some of your other discussion points make perfect sense - on paper.  However, in the real world where most of us live some of the time, everyone I've talked to or read a post from concerning their lightened flywheel have been downright gleeful about the performance, theoretical drawbacks and all.

But only in neutral. In any other gear, there’s little benefit at all. However, the overall weight of the bike and rider completely overwhelms any reduction of rotational inertia produced by a lighter flywheel. A two pound lighter flywheel on a 600 pound bike-plus-rider will accelerate only 0.3% faster. F=ma.

It looks to me like F=ma is being misapplied here.  Also, I think the reduction in weight from stock to Nichols is closer to 4 pounds than 2 pounds.  And it isn't just the amount of weight removed, it's where on the flywheel the weight is removed from and its effect on the moment of inertia that counts.

F=ma generally applies to a non-rotating mass being  accelerated in a linear fashion, a rider's beerbelly being a good example.  For a rotating flywheel, I think the correct equation is something like F= Ia where I is the moment of Inertia and a is the angular acceleration, completely different animal from linear acceleration.  The energy stored in a rotating flywheel (and this energy has been"stolen" from the energy that would be applied to the rear wheel)  is a function of the square of the angular velocity of the wheel.  If you've considered all this in your 0.3% calculation you have my apology in advance.

You’ll also risk sprag clutch wear or damage. Ducati mechanics see a lot of worn-out starter clutches when there is a very light flywheel attached. Why? Often lighter flywheels seem to let the engine kick-back much harder during start-ups and shut-downs, which causes starter clutch damage.

Again, before this can be accepted as fact rather than personal opinion we need documented numbers on the sprag failures on light flywheels vs stock flywheels, please.  I'm not saying that it's not true, I just want to see data.

Lightweight Wheels Instead

Lightweight wheels don't have the stalling and drivability drawbacks of a lighter flywheel. Also, since the wheels have a much greater rotational inertia than a flywheel, weight reduction here results in a much greater improvement in acceleration (and braking) with an added benefit of reduced gyroscopic forces for improved handling. Lighter front rotors have a similar benefit. There’s even a significant difference in tire weights between brands to consider.

Since as mentioned above, the momentum is a function of the angular velocity squared, I'd like to see the difference in energy stored in a stock flywheel rotating at say 6,000 RPM vs a stock wheel/tire at say 1400 RPM at 100mph or so (also need to consider that we have two sets of wheels/tires).   Not saying it would be greater but it would be interesting to see actual numbers.  

I think that most of my  point of my above comments is that without either documented empirical test results and/or valid numbers punched into Mr.  Newton's equations, this  discussion, mine included, is all just personal opinion without a base in facts.  Again, thanks for taking the time and effort to write your long post and I hope none of this comes across as personal criticism. 

[kuhlka]

+1 on the above post with regard to rotational mass.  If you've ever done the 'spinning bicycle wheel on an axle' twist in a physics experiment, you know increased speed and/or weight makes the wheel harder to turn (centrifugal force stabilizes the wheel?  I think centripetal force was the theoretical 'pushing back' force, right?).

Granted, installing lightweight wheels is a lot safer, but lightweight wheels also cost around $2000+ and I wouldn't go with anything less than BST's carbon fiber street wheels on my 1098.  That won't be happening anytime soon, and I'll DEFINITELY be buying a No-Mar tire changer before buying those wheels so I can be damn sure no one screws up my wheels but me (and thats pretty hard to do with a No-Mar).

On the other hand, while installing a lightweight flywheel might be cheaper, it could actually end up costing a ton more if you misplace your trust in a shop to do the work and something goes wrong.  Lesson learned.

[mitt]

I didn't read 100% of Shazzam's post, but I noticed some contradictions with literature I have read as well.

Lightened rotating parts should equal faster lap times all other things equal - note the latest crop of 800cc gp bikes - faster corners in part due to less gyroscopic effects of the engine.

Also, the big bang traction theory has been challenged by the concept of power feedback.  If the engine is controlling the speed of the bike mainly due to throttle inputs, then the rider has a better feel, more confidence and control.  If the speed of the bike is being controlled to a greater extent with the inertia of rotating engine parts and not throttle input (like a balanced I4 engine), then the rider has less feel, slower times.  Note the newest Yamaha M1 and R1, not to mention the V4 bikes in gp have out of balance cranks.

I will likely never even try a light flywheel, so I have no FHE, but I am a mechanical engineer, and the idea of lower mass = faster is the only logic that lines up with physics.

mitt

[Langanobob]

This supports my standard philosophy: buy used - do the work yourself or thru a small independent shop.

Norm, I'm with you 100% on this and that's exactly what I do.  None of my bikes have ever seen the inside of a dealership or shop of any kind.   The problem seems to be that there are riders out there who like to buy new (which is absolutely fine) and don't have the interest or time to do their own work (which is also absolutelly fine).   They "should" be able to take their bikes to their dealer and get quality work done at a fair price. Unfortunately in many cases they end up getting screwed.

In my biased opinion part of this problem is the decline of the local bike dealer who became  a dealer because he was a rider  and loved the sport.  He sold and worked on bikes all week and then went racing on weekends.  Almost all of the dealers I see today are based on the Home Depot style of marketing and seem to be owned by investors who just want to suck money off the top.

[Capo]

Absolutly, there is a large Yamaha delaer near me, salesmen were suits and none of them know how to ride a motorcycle. My conversation with them lasted 60 seconds.