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Court
| | Posted on Tuesday, March 17, 2009 - 06:18 am: | 
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>>>I was just curious if anyone knew how much power is available by losing 5 lbs off the wheel.
If, in fact, you are talking about POWER I'd suggest the answer is none.
A 500# wheel and a 5# wheel should, in theory, record the same horsepower on a dyno.
Wheel weight (actually mass) comes into play only when mass enters equations such as acceleration.
My bet is that Terry or Jim could add some practical knowledge to this. |
Firemanjim
| | Posted on Tuesday, March 17, 2009 - 11:15 am: |
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If I wasn't so lazy I would throw my Triumph on the dyno--have stock rear wheel and a Dymag. Maybe when I finish up the retune with Tuneboy. Made it halfway before customers got in the way. (Race-can, K&N, ported Daytona head--) |
Davegess
| | Posted on Tuesday, March 17, 2009 - 05:22 pm: |
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It will not change the HP of the motor but is will give you faster acceleration. Not only is it less weight but less rotating weight and that has a larger effect than staic weight on acceleration. |
Jlnance
| | Posted on Tuesday, March 17, 2009 - 08:07 pm: |
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It will change the HP reading on an inertial dyno, but it doesn't change the actual HP. I wouldn't think it would change the reading much. |
Froggy
| | Posted on Wednesday, March 18, 2009 - 01:13 am: |
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This sounds perfect for a episode of Mythbusters! Perhaps they can work in Tori crashing and getting thrown over the bars.  |
Court
| | Posted on Wednesday, March 18, 2009 - 05:05 am: |
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>>>It will not change the HP of the motor but is will give you faster acceleration. Not only is it less weight but less rotating weight and that has a larger effect than static weight on acceleration.
Precisely.
And what role, in POWER, does ACCELERATION play?
The answer is zero. Ergo, any difference, higher or lower, would therefore have to be dyno error.
Hehehehe . . the new contact patch! |
Id073897
| | Posted on Wednesday, March 18, 2009 - 06:29 am: |
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It will change the HP reading on an inertial dyno, but it doesn't change the actual HP. I wouldn't think it would change the reading much.
Would agree in this. Inertial dynamometer (in comparison to e.g. Prony brake) measure change of drum position vs. time, which is dependend on acceleration. For that reason drum mass is large compared to that of wheel and transmission and the error gets corrected by driving wheel and transmission to calculate drag power. |
Court
| | Posted on Wednesday, March 18, 2009 - 11:19 am: |
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Would it be fair to say (I'm asking because it seems true mathematically) that a varying dyno indication as a result of wheel mass would be read as dyno error.
There is no change in power.
I believe the bike, with the lighter wheels, would accelerate faster and perhaps handle better, but have no more power as MASS have no impact on power. |
Reepicheep
| | Posted on Wednesday, March 18, 2009 - 12:45 pm: |
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When we calibrated new test cells at (a large aerospace engine company), my understanding was that a key step in the process was to take a known good engine, stand it up on a known good test stand, run it through a comprehensive regression test, then immediately run it over to the new test stand, and run it through the same test, and "caulk to fit and paint to match".
Of course, our goals there were to keep airplanes from falling out of the sky. If our goal was to impress people with Dyno's, we would have used a different (less reliable) approach |
Id073897
| | Posted on Wednesday, March 18, 2009 - 04:02 pm: |
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There is no change in power.
Sure there isn't, that's impossible. The effect would be visible only when comparing the same bike with different wheels and when not taking drag power into account. With the lighter wheel the drum is decelerating faster than with the heavier wheel (when driving wheel and transmission), with exactly the same amount as it had been accelerating faster before. |
Court
| | Posted on Wednesday, March 18, 2009 - 04:24 pm: |
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The weight of the wheels of a motorcycle SHOULD have NO EFFECT on power read on a dynamometer.
If an difference is noted I'd look for a problem with the dyno. |
Id073897
| | Posted on Wednesday, March 18, 2009 - 04:48 pm: |
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An inertial dynamometer is in reality an accelerometer, which is used to calculate torque from acceleration and inertial mass and from that power.
From http://www.rcboat.com/dynotech.htm:
"An Inertial Dynamometer, like ours, measures how quickly a given engine can accelerate a known rotational inertia from one rpm to another. This is enough information to know the average Torque the engine produced during that time, and, since we already know the rpm, the average Power the engine produced during that time. With enough small steps in rpm, say several dozen, this produces a smooth curve of Torque versus rpm and Power versus rpm." |
Pammy
| | Posted on Thursday, March 19, 2009 - 09:56 am: |
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The size and weight of the tire/wheel assembly absolutely do effect the readings of the chassis dyno. ANYTHING adds/subtracts parasitic loss to the hp equation makes a significant difference. Air pressure in the tires makes a difference.
We even use the same operators(due to difference in body weight) when making motor mods.
We just did a motor for a customer that made a peak 201HP. We knew we were down a bit on HP due to the fact he was running a 300 series tire, but figured that 201 would be sufficient for the job at hand. When he got to the shoot out in Daytona, they ran his bike on a dual drum dyno(2 rear wheel drums vs 1) and as a result he made just over 189. Between the ambient temperature difference(we made no jetting changs on site) and the extra weight of the drums, there was a considerable loss of HP.
I know this is tangent ladened, but you get the idea.
Any dynomometer only measures torque. It calculates HP. |
Court
| | Posted on Thursday, March 19, 2009 - 10:25 am: |
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So . . . a lighter wheel makes more horsepower?
I stand corrected.
How much (I've done the calculation but don't work with this stuff everyday) of an increase in horsepower should I expect if I replace the stock wheels on my 111RWHP S2 with Dymag carbon fiber wheels that weigh 2 pounds less?
It looks to me . . . like the increase in power, dealing with the numbers on a motorcycle, are nearly negligble, The question becomes, is it worth spending $5,000 for wheels to get 1/10th HP increase?
I don't know. Right or wrong?
quote:This drop down menu automatically fills in some or all of your vehicle data including:
- Vehicle Name
- Vehicle Weight [Without Driver, you must add your weight to this value]
- Drag Coefficient
- Frontal Area
- Rolling Coefficient
- Speedometer Calibration [Always best to calibrate yourself]
- RPM Calibration [Always best to calibrate yourself]
It, however. appears that the way weight (mass) works into the calculation that the difference between a 5# wheel and a 4# wheel (a HUGE difference) would yield increased HP in the range of something like 0.0001. |
Court
| | Posted on Thursday, March 19, 2009 - 10:30 am: |
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By the way . . . the wheels are actually less now and can be had for just shy of $4,000 so it may make more sense. Much better deal than the ones I posted the above photo of on the car . . .they are $9,000 per wheel plus $1,000 for the lug nuts.
We are performance junkies!
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Pammy
| | Posted on Thursday, March 19, 2009 - 11:22 am: |
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"So . . . a lighter wheel makes more horsepower?"
In a technical sense...no. It has less parasitic effect on the calculations.
Just like losing 10 lbs will give you 1 extra HP. Really you aren't gaining 1 HP you are just not dragging down the torque that is required to make 1 more HP.
But in the case of a chassis dyno...yes, a lighter wheel equals more HP...doesn't make more Hp just allows more HP to be calculated. |
Blake
| | Posted on Thursday, March 19, 2009 - 12:31 pm: |
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I agree. Anything that effects the acceleration of the dyno drum will affect the HP reported by an inertial dynomometer. A heavier rear wheel increases drivetrain inertia and thus reduces the power available to accelerate the drum of an inertial dynamometer.
INcreased drivetrain inertia acts like a bigger flywheel, or in electrical terms a bigger capacitor; as the engine is accelerated the drivetrain inertia, including the rear wheel, stores some of the energy being produced. This only happens if the engine and drivetrain are accelerating at a significant rate. If held at near steady speed, the drivetrain inertia has insignificant effect on HP as discerned by a dynamometer.
Imagine if you replaced the cast aluminum rear wheel with a solid lead disk. Your engine has the same power, but it won't be able to accelerate the same. A brake type dyno will measure the same HP as it holds the engine at a steady or near steady speed and measures torque. An inertial dyno however will see a much reduced level of power available at the rear wheel to accelerate its dyno drum.
In inertial mode (spinning up a drum to ascertain HP), a dynomometer actually only measures the time interval of each drum rotation. From that time interval data and its rate of change (acceleration) and given the known inertia of the drum it is a fairly simple step to calculate HP. Once the HP is calculated, engine speed data (RPM), if collected, can be used to figure the engine torque. No engine speed data, no torque, just HP.
Brake dynos however, do measure torque and then calculate HP. |
Reepicheep
| | Posted on Thursday, March 19, 2009 - 02:18 pm: |
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Beautiful! This is so seldom understood correctly everywhere else, and so often explained right here on BadWeb. Y'all are making me proud to be a Bueller.
Lighter wheels *will* make a bike accelerate faster (quite a bit, as accelerating rotational weight eats power much faster then just accelerating weight). Lighter wheels will *not* change the power a bike puts out. Nor will they change top speed.
So lighter wheels accelerate faster because they require less power to accelerate... not because there is more power to be had. And given sufficient time, any weight wheel will eventually reach the same terminal velocity, generally limited by the power required to overcome the drag associated with displacing air.
Inertial dynos (the most common kind) will be "fooled" into believing you have more power with lighter wheels, as they simply measure the time it takes a known mass (the inertial drum) to a known velocity. It imputes the horsepower as a result.
It does not (to my knowledge) try and account for the rotational mass of the drivetrain that is in contact with the drum. It likely makes a guess at a reasonably median weight, and tolerates errors that come from lighter or heavier variations.
They could though, which might be an interesting variation for future dynos. The would have to have an initial "zero" or "tare" procedure, where you accelerate the bike up to X mph (as measured by the drum), then put in the clutch, and let it naturally decelerate under light drag (maybe an air pump / fan on the drum).
The computer in the dyno ought to be able to measure the divergence of this deceleration from a baseline, and reach some reasonable guesses of the inertia of the drive train, which it could then use to "factor out" the rotational weight from the horsepower calculation.
They probably don't bother, as there are so many other ways the calcualation is full of noise (altitude, wear, traction, etc), that they don't even bother to fix it. The purpose of the dyno is to discover "before and after" differences for the same bike on the same dyno, hopefully under the same conditions. Inertial dynos do that *great* for a an affordable price. |
Froggy
| | Posted on Thursday, March 19, 2009 - 02:33 pm: |
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Now I might have to pickup a pair of those magnesium Buell rims from the race catalogue 
3.5Lbs less in the rear, 2.5 less in the front |
Court
| | Posted on Thursday, March 19, 2009 - 03:01 pm: |
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Blake . . . I think I'm on board but I'd want to change the word "parasitic" to "inertial".
The greater mass adds no "parasitic" (the type of thing that actually CONSUMES part of the energy of the process) it simply adds inertial and requires greater force to accelerate in a given (fixed) time period.
Sound right? |
Id073897
| | Posted on Thursday, March 19, 2009 - 03:34 pm: |
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They could though, which might be an interesting variation for future dynos. The would have to have an initial "zero" or "tare" procedure, where you accelerate the bike up to X mph (as measured by the drum), then put in the clutch, and let it naturally decelerate under light drag (maybe an air pump / fan on the drum).
The drum driving the wheel is always part of a dyno run that is worth it's money.
This allows errors, caused by different wheel mass, transmission friction and similar, to be corrected and you're required to do it for the calculation of clutch power anyway. |
Reepicheep
| | Posted on Thursday, March 19, 2009 - 03:55 pm: |
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Cool! As usual, my great ideas are already common knowledge |
Blake
| | Posted on Thursday, March 19, 2009 - 05:05 pm: |
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I agree Court. Excellent call. Parisitic loss is never to be regained, other than via heat energy. Not so for the energy stored within a spinning drivetrain; it can be converted to vehicular thrust in short order, as anyone who's ever employed the clutch to send front wheel skywards can testify.
There's a story about Mr. Haughton and his cherished S2 at the drag strip that demonstrates the principle quite well. Maybe we can get him to tell it again.
Or maybe the incident that spawned the infamous T-Shirt? ![: ]](http://www.badweatherbikers.com/buell/clipart/proud.gif)
There's always my ride home yesterday. |
Pammy
| | Posted on Thursday, March 19, 2009 - 06:36 pm: |
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I respectfully disagree. Parasitic loss can be prevented to a certain degree. Anything that reduces(bleeds off) the energy/power of the engine is considered parasitic loss. That also means the peripheral parts including, but not limited to the dyno, itself. |
Pammy
| | Posted on Thursday, March 19, 2009 - 06:44 pm: |
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Wind drag, weight, clutch slipping, friction, bad bearings, low tire pressure...all examples of parasitic loss of energy. Even the wheelie you mention, It propels the bike upward as well as forward, leeching from the forward propulsion. |
Court
| | Posted on Thursday, March 19, 2009 - 07:01 pm: |
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Inertia can be changed by changing the mass . . the very subject of this discussion.
Parasitic losses can not be changed by any element in the equation, simply overcome more quickly with more power. If a chain, as an example has a 90% efficiency, it'll be 90% if the motor is 10HP or 1000HP.
It's just that the torque, required to create the greater HP will overcome it easier.
I loved these problems in school.
Blake . . . we agree. . . during the course of the wheelies however, that the sum of the vectors remains constant. . . some element of forward and a complimentary upward component.
(I cheated . . . I am sitting here looking at Abe's equation and the diagram he drew. ) |
Pammy
| | Posted on Friday, March 20, 2009 - 09:14 am: |
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Parasitic loss
Article ID: 2658674
-------------------------------------------------- ------------------------------
Table of Contents
1 Parasitic loss in internal combustion engines
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In short, Parasitic Loss is a loss that a parasite consumes from its host which may or may not be beneficial to the host.
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Parasitic loss in internal combustion engines
In the internal combustion engine almost everything including the driveline causes parasitic loss. Bearings, oil pumps, piston rings, valve springs, flywheels, transmissions, driveshafts, differentials, etc., all are responsible for parasitic loss. One would not consider running an engine without lubrication such as an oil pump so in this instance the oil pump is a necessary parasite that consumes at least some power from the engine (its host). The Parasitic Loss term is often applied to devices that consume energy from the engine to create more energy for the engine. For instance, a supercharger derives its power from the engine to create more power from the engine. The power that the supercharger consumes is parasitic loss and is usually expressed in horsepower (hp). While the hp that the supercharger consumes in comparison to what it generates is small, the hp is still measurable or calculable.
One of the desirable features of a turbochargerover a supercharger is the turbocharger's lower parasitic loss.
Another common use of the term is where a new or different design reduces parasitic loss. For instance, a dry sump improvement over a wet sump results in lower parasitic loss. The reason may be less friction or many other variables that cause the design to be more efficient.
Wikipedia
It is the terminology we, in the motor biz, use and we relate it to what is being discussed here.
But of course we are not rocket scientists or nobel prize winners. We just know that it works in this genre' to convey a meaning. |
Blake
| | Posted on Friday, March 20, 2009 - 09:37 am: |
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Agreed, but to clarify, the above is only addressing driveline frictional (parasitic_ lost, not storage of energy within driveline rotating inertia. Most of the energy stored via a flywheel's (rear wheel) rotating inertia is not lost, just stored. Parasitic losses are lost, gone, never to be reclaimed, at least not for propulsion, just heat. |
Pammy
| | Posted on Friday, March 20, 2009 - 12:24 pm: |
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noted. |
Phelan
| | Posted on Friday, March 20, 2009 - 12:54 pm: |
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Wow, this is getting a lot deeper than I expected it to. Nothing wrong with that, just surprising. So short answer to my initial question is YES, on an inertial Dyno, a lighter wheel will give me a higher RWHP figure. I can live with the fact that it's not actual power increase, but I take heart in also acknowledging that the lighter wheel will make the bike accelerate like it DOES have the extra power, which is a huge plus for my purposes. Instead of buying the Buell race wheels, though, I will go the route I mentioned above. Even the cast aluminum Marchesini/Brembo rear wheel from a 999 is almost 3 lbs lighter than stock, while the forged one is 5 lbs lighter than stock. There is a reason all the S and R model Ducatis have forged wheels but almost no engine power difference... |
Jeffreyh
| | Posted on Tuesday, March 24, 2009 - 10:49 am: |
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"When he got to the shoot out in Daytona, they ran his bike on a dual drum dyno(2 rear wheel drums vs 1) and as a result he made just over 189. Between the ambient temperature difference(we made no jetting changs on site) and the extra weight of the drums, there was a considerable loss of HP."
This is wrong. The Dyno Software knows whether it's a single or dual drum dyno and does it's calculations accordingly. It's something you tell it when you install the software. The Dyno also measures the temperature and factors it into the results unless you specifically turn off correction.
"Any dynomometer only measures torque. It calculates HP."
Wrong again. A brake dyno works that way. An inertia dyno however measures horsepower and calculates torque. That's why it won't show you torque unless you use the tach pickup so it can also know rpm. It knows the horsepower, it just also needs rpm for calculating the torque.
"Anything that reduces(bleeds off) the energy/power of the engine is considered parasitic loss."
Wrong again. Nothing is lost when you store it. Like Blake said it's only lost when friction makes it go away as heat.
Think about this. before you said a heavier flywheel increases torque. More torque means more power at a given rpm right? Now you say a heavier flywheel causes a loss. Both can't be right. Actually both are wrong. |
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