| Author | Message | ||
     Phelan |
And if so, how much do you think one could gain by going from a 15lb wheel to a 10 or 11 lb wheel? I was just curious, because part of my rebuild project is converting to 10-spoke Ducati wheels (Marchesini/Brembo), which are significantly lighter than all 4 of the factory Buell variants (Marchesini cast, Castalloy, PM slotted, and PM not slotted), especially if I get a deal on some forged ones from the S/R models. | ||
| Sleez |
my educated guess, is no. though it may increase the response, therefore moving the curve around slightly, but i doubt it would change the dyno peaks very much, if at all. like i said, educated guess. i imagine the suspension response would be more beneficial than any horse power gains. and of course the HP/Weight ratio will effect the acceleration times. | ||
| Petethekiller |
I would guess yes, but not much...Less rotating mass to turn will burn less Hp... Its the same concept Drag racers use, They dont use ultra light rims cuz they look pretty. They use them because they reduce unsprung weight and rotating mass which in turn gives better response times and more usable HP over a heavier steel wheel | ||
| Ratbuell |
Inertia - an object at rest tends to want to stay at rest. There is a reason VRSC drag riders have a kit out to use an XB front wheel assembly on their bikes... Think heavy flywheel, but take it one step further. Er...further towards the back of the bike, that is  | ||
| Sleez |
you all make valid points, it only effects the time to spin up, not the ultimate HP number though. at least that is how it seems, i have no actual proof. | ||
| Texastechx1 |
my guess is that you wouldn't be able to really tell on the dyno... but less rotating mass does make it EASIER for the engine to put power to the ground. run you bike with the stock wheel and one of them carbon fiber ones and see... we might all get proven wrong! | ||
| Sleez |
just talked to fireman jim, he agrees with me. and he's seen a load of dyno runs. | ||
| Court |
It matters if you are buying dyno time by the second. | ||
| Sleez |
court, that would be an.... wait for it .... accurate statement! | ||
| 4dwuds |
It takes HP to move weight, the more weight , the more HP needed. A dyno dosen't measure HP at a steady throttle, it measures it in a pull. The heavier the wheel, the more weight the motor has to pull. So if a wheel weigh's 20# the motor has to work twice as hard as a 10# wheel, and less HP shows up at the wheel because the energy (HP) is used up trying to get and keep the heavier mass rotating. That's my story and I'm sticking to it. (Message edited by 4dwuds on March 15, 2009) | ||
| Texastechx1 |
I agree with the logic... but I just don't think that the few pounds you could save would actually show up. how much difference is the between the cast 3 spoke and the lightest wheels made for our bikes like the carbon fiber ones... 10lbs? I don't know but 10lbs in rotating mass with just ONE wheel isn't going to make a big enough difference to notice... not on a bike. Just my .02  | ||
| Phelan |
Think of it this way. Do you feel a difference in fatigue after riding all day wearing a 5 lb helmet compared to a 3 lb helmet? Or another example- will you see adifference in your 400 meter times if you wore combat boots compared to Nike shox? Can't be more than 3 or 4 lbs difference, right?... | ||
| Littlebuggles |
Regardless of measured power, wouldn't you see a difference in acceleration and improved handling because of unsprung weight? Plus if you drop 8-10 lbs off your bike, that ought to do something for you. I sure feel it when I drop a couple pounds extra weight. | ||
| Ducxl |
One of the best investments in performance that i've made.Unsprung weight loss is VERY satisfying.So is the "made in USA" stamp  Don't listen to Court.He's negotiating a Porsche Caymen and not a similar and cheaper Corvette | ||
| Court |
>>>It takes HP to move weight, the more weight , the more HP needed. The problem here is that a dyno does not take acceleration (the only component that weight affects) into account. It's the reason folks at Bonneville often add weight to their bike. Weight impacts acceleration, not power. Here. . . if you want to see the ultimate wheel, complete with $1,000 lug nuts, I took this yesterday of a friends car. . . . tires are $700 each as well.  | ||
| Ducxl |
 ...Ti lug nuts? BST is the ultimate MOTORCYCLE wheels.CF wheels seem to have been derived from F1 cars.Porsche now applies Ceramic disks as well? For uncompromising quality,we do not look to Buell or Chevy | ||
| Court |
>>>Porsche now applies Ceramic disks as well? They do. The PCCB option is $10,180. The word from most the guys is that they are neat for track days but of no value on the streets. Rotors last a long time but are over $10,000 at replacement time. The yellow calipers are the "tell" for the PCCB option.   Artie was begging someone to buy a car yesterday . . . "please guys,, just a deposit". Porsche is one of the few automakers currently holding a strong profit line. But there are some killer deals. One of the guys in our club brought his "2nd car" yesterday he's considering trading on a PDK. The PDK is the HOT number.  My poor Ford pickup (barely visible in the corner) looks so frickin' out of place.  | ||
| Ducxl |
Well,both my ceramic disks and CF wheels made MY machine feel much more nimble.Dropped some weight too. The test that initially sold me was by holding a stock rotor in my hand and QUICKLY snapping rotation.I couldn't feel ANY inertia on the lightweight ceramic one.The stock one hurt my fingers. Dropping unsprung weight is ALWAYS a good thing with regard to motorcycles'  | ||
| Langperf |
Lighter rotating mass will effect the horsepower number. Most rear wheel dyno's are "inertia" dynos. They extrapolate a horsepower number from timing how fast your bike accelerates a given weight(the dyno drum usually around 2000lbs)to speed. So anything north of where the rear wheel touches the drum that rotates, has less friction or less mass will effect the RWHP(rear wheel hp)number.And in real life will make you accelerate faster also. Now an "eddy current" rear wheel dyno uses a computer to apply a magnetically variable resistive force to the drive drum and can hold the speed at a given torque if necessary, the rotating mass of your drivetrain wont effect the numbers on these dynos in a static pull condition | ||
| 4dwuds |
"The problem here is that a dyno does not take acceleration (the only component that weight affects) into account." "It's the reason folks at Bonneville often add weight to their bike. Weight impacts acceleration, not power." Ahhh, but wait Grasshopper, A Rear wheel HP number will be different than Crank HP. Why ?, because of drag at the rear wheel caused by chains, belts, gears, tranny oil, rear wheel,tire friction and all the other stuff in the driveline, The more these things weigh, the more HP the engine must dedicate to making them turn. On a chassis dyno it dosen't matter if Skinny Minny or Hungry Hippo is on the seat, Static weight has no effect because that is not what you are trying to move. Total vehicle weight and unsprung weight comes into play at the track or on the road. And that's the rest of the story, yup I is stickin to dat one also. (Message edited by 4dwuds on March 15, 2009) | ||
| Micromachine |
I think the word you guys a looking for is "parasitic loss" correct me if im wrong. | ||
| Tdman77 |
Lighter wheels will make you go faster! Last season I replaced the stock wheels on my STI and my 1/4 times went from 12.68 to 12.46. (Both passes made on the same day within 2hrs of each other.) No other changes were done to the car except changing the wheels/tires. Less rotational mass means more power put to the ground. | ||
| Phelan |
How much lighter were the wheels compared to the stock ones? I'm expecting a HUGE difference, but I do expect a significant one, since I'll be shaving 30% of the sprung mass of the wheel, which brings me to another pondering... Which is lighter, chain drive or belt? If I had to guess, I would think the XB belt and pulleys to be lighter than the tuber/sportser setups, but I don't know where the chain compares here. | ||
| Firemanjim |
Dynojet drums weighing what they do, I don't really think your 3 lbs will be noticeable. If you are charting HP vs RPM you will not see a difference. Now if you were charting HP vs time it takes to accelerate you would see a diff. Crankshaft HP is not what we are working with in the real world so does not factor in. But this is kinda like a "contact Patch" thread. | ||
| Phelan |
My question is, how does a dyno not take acceleration/time to accelerate into account? Do you not have to hit full throttle on the dyno run? If not, you are simply measuring the gear ratio, no? I mean, in a vacuum (assuming the motor was electric since our motors won't run in a vacuum), HP doesn't matter except for acceleration. Speed is all about gearing, so in a vacuum state you could simply change the hearing and go as fast as you want, right? It seems to me that if you are not full throttle on the dyno you would simply recreate a vacuum speed test. I don't know if I made my thoughts clear there or not... | ||
| Fast1075 |
Tdman77.....those are usual and to be expected gains when changing wheels from heavy to light....the gains are measurable and confirmable....its primarily the reduction in rotating mass...and secondarily the reduction in weight. | ||
| Id073897 |
You do not get more HP, this is forbidden by Newton's law: tau = I * alpha (here written for rotational motion). Tau is an engine constant, I is the inertial mass and alpha is the rotational acceleration. So it's easy to see, that reducing mass leads to a larger alpha, as tau is constant. Power in opposition is torque multiplied by rotational speed (P = tau * omega) - it does not play a role how fast this rotational speed is achieved as taken into account is only speed. Therefore, as tau is an engine constant, reducing wheel mass does not increase power. | ||
| Court |
>>> Therefore, as tau is an engine constant, reducing wheel mass does not increase power. Acceleration is an entirely different animal, as you point out, that what is being discussed here. Think of it this was . . . (and I grant this a an over-simplification to show that the wheel weight has NOThING to do with it ) but if your wheeled weighed ZERO acceleration would be instant. Cool . . . 0-60 in . . . . . wait . . .I'm already there. | ||
| Phelan |
That is an accurate statement  . I guess really I want explain that I KNOW it will affect acceleration, and I KNOW it will NOT affect HP at the CRANK. My question was if it would affect REAR WHEEL horsepower, which is less than crank horsepower because of the weight of the driveline resisting the power. So in theory, I know it will increase HP. I was just curious if anyone knew how much power is available by losing 5 lbs off the wheel. Then again, even the difference in weight between a new tire and a sticky tire with no tread depth left is noticeable on the BUTT Dyno... | ||
| Id073897 |
(and I grant this a an over-simplification to show that the wheel weight has NOThING to do with it ) but if your wheeled weighed ZERO acceleration would be instant. ??? Sorry, but I don't understand. If you apply force to a "null" mass (which is impossible due to the missing mass), then of course you get infinite acceleration. This is Newtons law. (Message edited by id073897 on March 17, 2009) |
