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Old 04-23-2009, 02:43 PM   #1
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weight vs. hp

i've read in a few places that every 7-10 lbs. of sprung weight eats up about 1hp.....and every pound of unsprung weight equals to about 10lbs. of sprung weight

weight does NOT make MORE hp, but frees up the HP needed to haul the heavier weight.

so say 2 different people weighing in at 200lbs. and 100lbs. rides the same bike....the lighter rider has the advantage of 10-15 HP over the heavier rider.

makes you say WHOA, i'm a doesn't it? i just got back on a diet and workout schedule last week since i've been lazy over the winter, gonna try and shave off 30lbs from my belly. so far 6lbs down, 24 to go.
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Old 04-23-2009, 02:47 PM   #2
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Curt (MaxGs) worked this out to an equation over the winter.

Cost of losing 30lbs < Cost of full exhaust system thus adding 10hp.

Do BOTH and take probably 50lbs off the bike = 17+ added HP.
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Old 04-23-2009, 02:47 PM   #3
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30LBS = 4HP
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Old 04-23-2009, 02:51 PM   #4
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Im 155 on the R1.. Ballllin
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Old 04-23-2009, 03:00 PM   #5
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i got your power:weight ratio!
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Old 04-23-2009, 03:28 PM   #6
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30LBS = 4HP
Nope.

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Old 04-23-2009, 03:32 PM   #7
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Nope.

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Enlighten...

3.75HP? I'm going off 8lbs per HP
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Old 04-23-2009, 03:33 PM   #8
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So....basically I should be Super Fast
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Old 04-23-2009, 03:35 PM   #9
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The specifics to a T aren't the point, lose the gut and free up some HP!! GL Tony.
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Old 04-23-2009, 03:37 PM   #10
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Unsprung weight only counts for more than sprung weight when it has to be spun up to speed, aka rotated. A swingarm is only as hard to accelerate as the weight of the swingarm. A tire (at the outward end of the spinning mass) must be accelerated forward and rotationally at the same time, so the force required to accelerate it is much more than if it were just strapped to the seat of the bike. A brake rotor (at the inward end of the spinning mass) is easy to accelerate since the weight is near the center. By that logic, larger wheels, same weight, are harder to accelerate. So are rim mounted disk brakes. Weight in the middle of the wheel hardly affects acceleration. Here is where it gets difficult: If you have two wheels, one outweighs the other, which accelerates faster? To figure out which wheel spins up easiest you'd have to know how far out the center of mass is from the axle center and how much it weighs to compare, and not just assume a lighter wheel accelerates quicker.

As for tires, they are the most critical in terms of spinning weight up to speed. Race tires are light weight not because the bike needs to be light to be fast, rather because the wheelset needs to be light so it can be rotationally accelerated and stopped the quickest.

This logic also explains why going -1 on the countershaft sprocket is a better solution than going +2 to +3 on the rear sprocket, when you consider the rotation of the chain and sprockets as slowing down your acceleration. But this is offset by the friction of bending the chain around the tight corner on a -1 versus regular countershaft sprocket. Better solution is to reduce the weight of the chain and sprockets by going ti or aluminum and reducing the overall chain size (i.e. 520 instead of 530).

Last night did roll ons from 10 - 40 on my XR80 versus my CRF150. Me, 185 lbs, my son, 105 lbs. Roll on, me on the 150, him on the 80, dead even until 40 mph when I slowly pulled one bike length. Me on the 80, him on the 150, he left me for dead with a 20 bike lead by 40. Weight plays a huge roll. If he could ride like me on the track he'd win every thing he entered. That's why these little 110 pound women can get so fast so quick.

Another factor we can't ingore is how weight plays a role in "accelerating" when you take a turn. To turn, you are actually accelerating the bike in three axis:
1. You accelerate it left or right to actually make the turn, and the less the rider weighs the easier it is to turn the whole package. So on the track you put significantly less stress on tires, chassis, and ultimatley the earth to take a turn on the race track.

2. You also "accelerate" and then "decelerate" to make the bike point the right direction (think of it as a slow motion Hollywood sidestand parking lot turn).

3.And finally you "accelerate" and "decelerate" it twice to initiate the lean angle, stabilize the lean angle, initiate return to upright, and stopping the motion to upright it.

In numbers 2 and 3, the closer (more tightly packed together) the mass is to the center of mass, the quicker you can do 2 and 3.

For 2: A short wheelbase, lightweight forks, central location of the motor, swingarm, wheels, tires let you turn the bike quicker. This is why manufacturers spend so much time on stacked transmissions, longer swingarms / shorter motors, leightweight tailsections, wheels.... As with all motions of the bike, the tires are asked to rotate the bike and so have less available traction for actually turning you where you need to go.

For 3: A lower rider position, leightweight bodywork, and narrow crankshaft and motor let you bank it easier. Wider bars make it easier to muscle around, but ultimately your tires are asked to do the banking. That takes away from available traction to turning.
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Old 04-23-2009, 06:33 PM   #11
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Quote:
Originally Posted by yellowjacket View Post
Im 155 on the R1.. Ballllin
From my fat winter ...

Cruiser weight for me is 140lbs. (165lb. w/ gear) on the 440lb RC. For me, less is more! Should be less with the Spartan leathers and Sidi boots.

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Old 04-23-2009, 06:59 PM   #12
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Quote:
Originally Posted by -=DReaux=- View Post
From my fat winter ...

Cruiser weight for me is 140lbs. (165lb. w/ gear) on the 440lb RC. For me, less is more! Should be less with the Spartan leathers and Sidi boots.

DReaux
lucky you! i'm 215 lbs. without gear

need to get my fat back to 180....then i won't have to work out anymore since i'll be losin calories by fightin the ladies off all day.
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Old 04-23-2009, 07:01 PM   #13
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Quote:
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....then i won't have to work out anymore since i'll be losin calories by fightin the ladies off all day.
LMAO!!!

I'm about 240lbs now. I was 250 before the season started, and I switched my workouts from weight-intensive to cardio-intensive. I'd spend 20mins on the treadmill and 20mins on the exercise bike (with resistance). Then of course you gotta watch what you eat.
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Old 04-23-2009, 07:05 PM   #14
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Quote:
Originally Posted by bigzona View Post
LMAO!!!

I'm about 240lbs now. I was 250 before the season started, and I switched my workouts from weight-intensive to cardio-intensive. I'd spend 20mins on the treadmill and 20mins on the exercise bike (with resistance). Then of course you gotta watch what you eat.


couple more pounds off and we'll have to watch each other's backs.....some of these ladies will have boyfriends and husbands.....so needless to say, it's gonna be an intense workout.

Co-ed workout session following the fight club.
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Old 04-23-2009, 07:47 PM   #15
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Quote:
Originally Posted by -=DReaux=- View Post
Cruiser weight for me is 140lbs. (165lb. w/ gear) on the 440lb RC.
That would explain your title as Amature Pig Wrestler. At 220 lbs, my RC used to routinely win at our on track wrestling matches. Those bikes are a blast to ride though, for at least half of the trackday!

Another nice thing about being smaller is that the stock suspension on most bikes will be better suited for you. That is my latest issue now (I have already given up on being the fastest rider out there) is how to dial in stock suspension on a 600cc machine.
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Old 04-23-2009, 08:02 PM   #16
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Quote:
Originally Posted by Shadman View Post
Unsprung weight only counts for more than sprung weight when it has to be spun up to speed, aka rotated. A swingarm is only as hard to accelerate as the weight of the swingarm. A tire (at the outward end of the spinning mass) must be accelerated forward and rotationally at the same time, so the force required to accelerate it is much more than if it were just strapped to the seat of the bike. A brake rotor (at the inward end of the spinning mass) is easy to accelerate since the weight is near the center. By that logic, larger wheels, same weight, are harder to accelerate. So are rim mounted disk brakes. Weight in the middle of the wheel hardly affects acceleration. Here is where it gets difficult: If you have two wheels, one outweighs the other, which accelerates faster? To figure out which wheel spins up easiest you'd have to know how far out the center of mass is from the axle center and how much it weighs to compare, and not just assume a lighter wheel accelerates quicker.

As for tires, they are the most critical in terms of spinning weight up to speed. Race tires are light weight not because the bike needs to be light to be fast, rather because the wheelset needs to be light so it can be rotationally accelerated and stopped the quickest.

This logic also explains why going -1 on the countershaft sprocket is a better solution than going +2 to +3 on the rear sprocket, when you consider the rotation of the chain and sprockets as slowing down your acceleration. But this is offset by the friction of bending the chain around the tight corner on a -1 versus regular countershaft sprocket. Better solution is to reduce the weight of the chain and sprockets by going ti or aluminum and reducing the overall chain size (i.e. 520 instead of 530).

Last night did roll ons from 10 - 40 on my XR80 versus my CRF150. Me, 185 lbs, my son, 105 lbs. Roll on, me on the 150, him on the 80, dead even until 40 mph when I slowly pulled one bike length. Me on the 80, him on the 150, he left me for dead with a 20 bike lead by 40. Weight plays a huge roll. If he could ride like me on the track he'd win every thing he entered. That's why these little 110 pound women can get so fast so quick.

Another factor we can't ingore is how weight plays a role in "accelerating" when you take a turn. To turn, you are actually accelerating the bike in three axis:
1. You accelerate it left or right to actually make the turn, and the less the rider weighs the easier it is to turn the whole package. So on the track you put significantly less stress on tires, chassis, and ultimatley the earth to take a turn on the race track.

2. You also "accelerate" and then "decelerate" to make the bike point the right direction (think of it as a slow motion Hollywood sidestand parking lot turn).

3.And finally you "accelerate" and "decelerate" it twice to initiate the lean angle, stabilize the lean angle, initiate return to upright, and stopping the motion to upright it.

In numbers 2 and 3, the closer (more tightly packed together) the mass is to the center of mass, the quicker you can do 2 and 3.

For 2: A short wheelbase, lightweight forks, central location of the motor, swingarm, wheels, tires let you turn the bike quicker. This is why manufacturers spend so much time on stacked transmissions, longer swingarms / shorter motors, leightweight tailsections, wheels.... As with all motions of the bike, the tires are asked to rotate the bike and so have less available traction for actually turning you where you need to go.

For 3: A lower rider position, leightweight bodywork, and narrow crankshaft and motor let you bank it easier. Wider bars make it easier to muscle around, but ultimately your tires are asked to do the banking. That takes away from available traction to turning.
And just remember....a quick wrist can come along and trump it all. John Haner anyone?
-Gabe
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Old 04-23-2009, 10:17 PM   #17
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Ok this is likely dumb but for what its worth.

One day long ago in another life bored in a physics 101 class and thinking about drag racing an old car I had I came up with the following:

HP = ((Weight) x 200)/ T^3

Or if you prefer

T = (HP / ((Weight x 200)))^ 0.333

HP = Horse Power
T = 1/4 mile drag time in seconds
Weight = Weight Lb

<>

Example:

Consdier a 575 pound bike (BUSA)with a 210 pound rider that runs 10.0 second 1/4
How much HP does it have?

HP = ((575+210) *200) / 10^3

HP = 157000 / 1000 = 157 HP at the rear wheel

And there seems to be about 20Hp lost between crank and Rear Wheel
so crank is 177 HP

Yes it is crude but simple and often seems to be good for ballpark estimate.
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Old 04-23-2009, 10:23 PM   #18
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that dieting.
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Old 04-23-2009, 10:43 PM   #19
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Quote:
Originally Posted by Sassy Chassis View Post
So....basically I should be Super Fast
Me, too. What's going on here?

Math >> real life.
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Old 04-23-2009, 11:24 PM   #20
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Question 600cc Or RC

Quote:
Originally Posted by mcd View Post
That would explain your title as Amature Pig Wrestler. At 220 lbs, my RC used to routinely win at our on track wrestling matches. Those bikes are a blast to ride though, for at least half of the trackday!

Another nice thing about being smaller is that the stock suspension on most bikes will be better suited for you. That is my latest issue now (I have already given up on being the fastest rider out there) is how to dial in stock suspension on a 600cc machine.
Yeah, my wife sold a suh-weet R6 Raven 2005 (hers), which I should have tracked, but "Thee RC" is one -of-a Machine" ... with the proper pilot...

She will, ultimately, Kick the livin' out of you during the later afternoon sessions.

Bring the pain I say...
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