The Ptwins thread.

[xsiliconkid]

...see my note - demand the dyno torque curve :-) HP don't mean squat--

To clarify – this comes up occasionally ….

To compare performance characteristics of two vehicles you must overlay the two torque curves or the delta between the two torque curves -that’s what is important.

Obviously there are three factors involved
Force, work, and Time.
Horsepower is the ability to do work over *time*
A dyno measure torque (expressed as foot pounds) and then you calculate horsepower by converting the twisting force of torque into work units called horsepower.

Formula HP = (torque * RPM)/5252

TORQUE
BUT NB: ***A vehicle will accelerate at a rate that matches its torque curve .***
END OF STORY

The details - This is why the curve is so important. At max torque the bike will be accelerating the hardest. above and below, acceleration will be slower matching the curve. Torque is what you feel, NOT horsepower
Only at 5252 rpm, horsepower and torque come out the same. Want to know why 5252 - that's another story.

A motor that pulls harder earlier and longer will win in acceleration that’s why gearing matching max torque curve is important.

[xsiliconkid]

I wanna know.

shit now I have to figure it out..... SB1

[xsiliconkid]

I wanna know.

you asked for it... I actuall did the analysis and math about three years ago - here is what I said then..... go at it--- this gives me brain cramp - I'm off skiing for a feew days :-)

Question,

Is there a quantifiable advantage to lightening the flywheel of a motorcycle to aid in linear acceleration?

The short answer, negligible in the lower gears… nothing in higher gears.

For the analysis I covereted the rotaing mass to equiv static mass and I used a Ducati 851/888 with a 3.5lb lighter flywheel from stock. The below analysis showd the lightened flywheel only reduces bike's effective overall mass *weight* by 4.5lbs in first gear and 0.5lb in 6th gear

The rule-of-thumb of lightening a flywheel has a dramatic effect of performance due to reduction of rotational inertia comes from the car world. Motorcycles are tricky devices compared to cars. What works for a car does not necessary translated to motorcycles.

Take a small car - an early 70's mini being re-built by a friend, reducing flywheel weight by 11lbs on the stock flywheel (radius of 5.1") provides an effective overall 200lb weight advantage in first gear (on a 1100lb car) - impressive!


Long answer.....................
I sent the following message to my physics mentor, for checking......
----- Original Message -----
From: Graham Pattison
To: Chris B

Sent: Monday, December 19, 2005 5:39 PM
Subject: Re: flywheel effect on overall mass- therefore acceleration

Chris, do me a favor and double check math and logic.
Also what about the lighter rotating mass effect on torque/HP .... work over time?
G
:
Ducati 851 Motorcycle : Impact of reducing Rotational Inertia (weight) of a flywheel and impact on linear acceleration
We have all seen the ads, replace stock flywheel with “___” and gain significant performance. Reducing weight of something that rotates dramatically improves performance seems to be a good rule of thumb. Is this true? If so, how much improvement?

First, I'm invoking the 80/20 rule. Eighty percent accuracy can be gained with 20% effort, while the last 20% accuracy takes 80% of the effort…..We could go into a great detailed analysis- exactly where on the flywheel is weight removed ( as you move toward the center, rotational effect drops – less equiv static weight advantage) or use a formula to derive and determine the exact relationship between weight on the flywheel and weight of motorcycle. All this requires knowing the moment of inertia, and measuring, that's difficult and does not fit in my 80/20 rule..
As a motorcycle's flywheel's rotational energy is directly linked to the forward motion through the drive train the “equivalent static weight” of the flywheel can be calculated with the following formula. Once the "effective" change in mass has been calculated the impact on acceleration can be derived.
WE= (fw*0.5)(ftx*gr*fd)^2
( tr )
fw = change in flywheel overall weight
ft = flywheel radius
gr = gearbox ratio ( which gear selected)
fd = final drive ration
tr = rear tire radius

The flywheel weight saving is 3.5lbs with a radius of 2.953". First gear ratio is 2.953:1, final drive is 2.6:1, tire radius is 11.8 inches. In first gear, the Ducati "feels" 4.5lbs lighter and in 6th gear (0.86:1) less than 1lbs lighter.
Therefore it's not even worthwhile calculating the linear acceleration benefits on a motor cycle. AS the chart below shows – on a car with a larger heavier flywheel is different.
The following is actual real world data.
Graham


flywheel Flywheel gear final tire
e Weight save weight save radius inches ratio drive radius
4.51 3.5 2.953 2.47 2.6 11.8 1ST
2.31 3.5 2.953 1.76 2.6 11.8 2ND
1.35 3.5 2.953 1.35 2.6 11.8 3RD
0.88 3.5 2.953 1.09 2.6 11.8 4TH
0.68 3.5 2.953 0.96 2.6 11.8 5TH
0.54 3.5 2.953 0.86 2.6 11.8 6TH
car
253.39 12.5 5.5 3.67 3.82 12.1 1st




RESPONSE---------------------------------------------------------------------------------------------
-------- Original Message --------
Subject: Re: flywheel effect on overall mass
Date: Mon, 19 Dec 2005 19:04:29 -0500
From: Chris B
To: Graham Pattison <graham@stargraham.com>

References: <43A72230.6090907@stargraham.com> <43A736B2.4010806@stargraham.com>


Actually, with the F=ma it all comes out in the wash when you look at energy.. that's the beauty of looking at problems from an energy perspective instead of from a force perspective.

The lighter flywheel requires less energy to spool up... period. The energy comes from the motor which gets it from the fuel (with a considerable efficiency hit). Changing the flywheel should not change the efficiency of the combustion, so any argument that suggests you are missing an element of engine torque would be misguided. (Changing the combustion chamber or camshafts on the other hand.....)

So.. to check your equation.. I left off with:
KEf = 1/2 *m(bike total)*V^2 + (sum of all rotating bodies individual kinetic energies..) [ 1/2 * I * w^2 ]

What you are investigating specifically is the *comparable* mass change to linear energy requirements if the flywheel weight changes. So, we will compare the linear kinetic energy of the bike sum, to the kinetic energy of the spinning flywheel:

delta(1/2*mbike*vbike^2) = delta(1/2 * (I) * w^2)

This allows me to calculate the equivalent delta mass of the bike (assuming that the flywheel *didn't* change) when I change the flywheel weight. This is where the nitpickers will say you're introducing error, because your change to the flywheel is also changing the mass of the bike and must be considered. The linear effect of removing 3.5lb weight is, in effect, neglected, so that you can get a seat-of-the-pants feel for the effective weight loss for forward motion.

Moving on...
1/2(comparabledeltamassbike)*vbike^2 = 1/2 * (1/2 * deltamassflywheel * rflywheel^2) * wflywheel ^2
comparabledeltamassbike = (deltamassflywheel*rflywheel^2*wflywheel^2)/( 2 * vbike^2)

Sanity check:
as the change in the mass of the flywheel increases, the comparable bike mass increases.. CHECK
as the radius of the flywheel increases, the comparable bike mass increases..CHECK
as the speed of the flywheel increases, the comparable bike mass increases..CHECK
as the velocity of the bike decreases, the comparable bike mass increases... CHECK

OK..looks good.


The engine will spin to redline or something slightly less in each gear and the bike will reach a certain velocity at the redline in each gear. Those are the numbers you should use...

Again, its the beauty of energy analysis - everything else comes out in the wash. Sure, there are energy losses to heat and friction.. but those don't matter because you're just comparing flywheel weight to bike mass weight.

For what its worth, you could use a similar analysis to show an equivalent 'weight loss' by increasing the aerodynamics of the bike. Develop the equation for the work lost to friction and then compare it to your kinetic energy equation...You could come up with: "A 50% reduction in CEf is the same as a 20lb weight reduction at 40mph"... or something to that effect..You could continue on for all sorts of effects...
I think I now understand why you used the other variables instead of speed and angular velocity...

the concept is sound

-C

[Kurlon]

For those that prefer purty graphs, here you go.

Pay attention to the Duc, on paper, it should be having it's way with the EX's... and yet it isn't?

I ripped the dyno's in 1000 RPM chunks, so I don't get the peaks perfectly. Peaks are noted to the left. One chart is HP, one chart is tooooooorke.

Edit: Holy crap, I'm playing with spreadsheets and we get a sweet math discussion going on while I'm not looking. Holy carp, random math rules!

[xsiliconkid]

For those that prefer purty graphs, here you go.

Pay attention to the Duc, on paper, it should be having it's way with the EX's... and yet it isn't?

I ripped the dyno's in 1000 RPM chunks, so I don't get the peaks perfectly. Peaks are noted to the left. One chart is HP, one chart is tooooooorke.

Edit: Holy crap, I'm playing with spreadsheets and we get a sweet math discussion going on while I'm not looking. Holy carp, random math rules!

I like the chart! COOL. BUT...
why do you say the Duc does not come out on top (in practice)?

Did "A" skilled rider take each bike out for a number of laps and avg the times and then compare - If it's based upon two different riders, then the rider difference delta far outweighs everything!

[Kurlon]

I like the chart! COOL. BUT...
why do you say the Duc does not come out on top (in practice)?

Did "A" skilled rider take each bike out for a number of laps and avg the times and then compare - If it's based upon two different riders then the rider difference delta far outweighs everything!

So far, the few 620s that have been campaigned haven't dominated. Most of the pair ups I've seen occur on the track have the EX's looking like they're out-motoring the Ducs? How much of that is rider, I agree, unknown.

Observation at LRRS has had me speculating that either the Ducs aren't in a good state of tune, or the EXs which I've watched pull on a couple Motards are in DAMN good tune. I have to temper that with the knowledge that I don't know how the gearing on the various bikes compare, ride styles, etc, but it still floors me every time I see it happen. The Duc should have motor, suspension and brakes on the EX, yet so far one has yet to put up a serious threat for the championship?

*Forgotten giant flaming flaw with my comparison... The data is from different dynos, I don't know the brands/models of them all, so I'm really being inappropriate comparing the numbers like I have. I'll see if I can get a batch of dynos for the various bikes off the local shop dyno so we can better compare 'apples to apples'. I dunno if they've had a Hawk on there, but I know there are a few 620s and GS500s.

[xsiliconkid]

For those that prefer purty graphs, here you go.

Pay attention to the Duc, on paper, it should be having it's way with the EX's... and yet it isn't?

I ripped the dyno's in 1000 RPM chunks, so I don't get the peaks perfectly. Peaks are noted to the left. One chart is HP, one chart is tooooooorke.

Edit: Holy crap, I'm playing with spreadsheets and we get a sweet math discussion going on while I'm not looking. Holy carp, random math rules!

Nerd fight!

[Pittenger5]

Nerd fight!

Phew, its a good thing you two lost me about 3 pages ago.

[xsiliconkid]

So far, the few 620s that have been campaigned haven't dominated. Most of the pair ups I've seen occur on the track have the EX's looking like they're out-motoring the Ducs? How much of that is rider, I agree, unknown..

I know the various racers involved and to protect the guilty will not mention their names and leave it at that.....
The 620 is a bit of a moot point - the Duc in a SS trim version only released for one year...not many around, the Monster version - forget about it the chassis and ground clearance an issue!

Note your point on different dyno's good catch....
BTW even BJ says "stock" Hawk's walk him coming out of the turns - and he knows how to put EX power down early (or more to the point higher corner speed)....

[zx1012r]

Scott Barley's Duc 620 was easily out-pulling BJ's bike and mine. I don't know what's in BJ's motor but I can pull on him slightly on the straight. My engine is stock and the last time I had it apart-3 seasons ago to do a head gasket-the valves are so wobbly my friend and I were laughing hysterically at it. The leak down test was ridiculous that the thing still runs! The lower end on it hasn't been touched since 2001 and it has been raced every year since.

But it runs. And it shifts perfect. So I am not inclined to change it even though I have a 900 mile 2004 motor in the basement. And it is still good enough to keep near the front.

I think with enough time on the bike, the Duc would kill us all easily. Simply the chassis is way more capable, and the brakes-if they stop anywhere near like the SV-no contest. I would be interested to try one out if anyone ever has one to borrow for a practice!

[Doc]

I bet Hobbs would let you borrow his. The bike is the slut of T1a.

[butcher bergs]

That and 3/4 of the replies are from people that don't run PTwins.

And the problem with that is.....?

Maybe some of said replyees are considering running additional classes should those classes be made available.

[pasta-rocket]

I have done the drag race with all the front runners down the straight and my 620 is slower than Dana's, latonas, and vaughns. I have a 5spd and have been playing with gearing all year. Scott barleys pulls on mine as well but he has a 6spd. The 620 looks better on paper, but they are very well matched up at the track. I do not see the hawk having any advantage at all.

[R7]

Hawk = around 37hp. 411.5lbs
GS500E - 39hp @ rear wheel - 397lbs dry (MCreports.com lists wet weight at 416lbs)
EX500 - 50hp @ rear wheel - 388lbs dry (Wet weight of 437lbs for 94 and up)
620SS - 59hp @ rear wheel - 404lbs wet sans gas

Aprilia SXV 450 - around 50hp @ rear wheel, 275lbs

[Kurlon]

I have done the drag race with all the front runners down the straight and my 620 is slower than Dana's, latonas, and vaughns. I have a 5spd and have been playing with gearing all year. Scott barleys pulls on mine as well but he has a 6spd. The 620 looks better on paper, but they are very well matched up at the track. I do not see the hawk having any advantage at all.

What's happening to Rick's old 620? I'd love to drag it up here and see how it compares to some known 620s on the local dyno, and then see what can be found to wake it the fark up. : )

[pasta-rocket]

If you can get dyno time i will drop mine off...please

[Kurlon]

If you can get dyno time i will drop mine off...please

I will see what I can do for ya.

[nt650hawk]

Graham you ruined my plan. I know how everyone related to HP a being the number to live by. They started to take the bait.

back to the flywheel. You did not go into its gyroscopic effect that is reduced.

[SVRACER01]

can you change jetting in a ptwins bike? is that allowed?

[Doc]

Yes I believe it is.

[SVRACER01]

what duc would be eligible at 750cc air cooled? just the monster?

[SVRACER01]

the 696 makes 80hp and only weighs 355lbs...the sv might actually be at a disadvantage.

[Doc]

what duc would be eligible at 750cc air cooled? just the monster?

You mean MW Ptwins... I was confused.

[BLACK SQUIRREL]

the 696 makes 80hp and only weighs 355lbs...the sv might actually be at a disadvantage.

Is that Dyno & Actual Weight or what Ducati claims it is?

[Doc]

what duc would be eligible at 750cc air cooled? just the monster?

Old Supersports...