This was a topic from the old forum and there were some interesting comments from 06blue and others. I'd like to refresh my memory about this again.

I know hp is not affected by weight. A 575 lb bike that will do 187 mph will do it with either a 120 lb rider or a 280 lb rider, assuming their skills are equal. The featherweight will just get to top speed in a shorter distance.

Does anyone know how 1 lb of weight can be expressed in terms of reducing acceleration? Something like, "1 lb = x seconds of time from 0 - 187mph." It would depend on the kind of bike being used too but maybe there is a general rule someone is aware of.

Yes, the mass effects acceleration. For objects with different masses (not objects with changing mass because F=ma does not apply to these situations, such as a rocket) an equivalent force will accelerate objects with greater mass at a lower rate. The lower the mass the greater the acceleration for a given force..

This is the best confirmation I could find that weight does effect horizontal acceleration but the formula this guy gave wouldn't mean squat to anyone looking for a real world answer.

I can not give any proof, I've just heard it all my life. But for cars, 100 lbs. equals .10-sec.

If you had a 5 gallon bucket of water could you tell if someone removed 2 ounces from the bucket? You could always ride around with a 1/2 gallon of gas in the tank that would drop an easy 30lbs of the bike but that would require a lot of stops and some pushing from time to time LOL. Ditch the stock exhaust and get some lighter wheels if you want to do something meaningful in terms of weight lost. You could always go on a meth diet and drop 100lbs in a few weeks BAM the bike would be a lot faster. LOL

If it's 1/10th second for every 100 lbs on a car, I would think it would be the same for a bike or for any lighter vehicle with approximately equal aerodynamics and friction with the ground. The bike or smaller car is just a lot lighter to begin with so it's acceleration is quicker than the bigger car that makes the same hp.

I would guess about the max we could loose from bike weight on a 14 through substituting lightweight parts and removing uneccary parts would be ~80 lbs. A lot of us could loose 20 lbs off ourself and still be healthy. That might be really worth it for a drag racer. Even though they don't hit top speed in a 1/4 mile I would think they could shave .05 seconds off their time.

For most of us, the difference in handling has to be the most significant change in weight reduction, it would seem.

.....and if I go on a meth diet, I think I'd be dead in a day. I'm already on a mod diet. The less you spend on food, the more you have for mods!

ok rook ..i'm gonna bite ..from what i'm told 7lbs = 1 hp and 20lbs =1tenth .. and no your teachings is wrong . if weight don't matter then why is there a weight limit on planes to hp .. same applies to bike if a 250lb rider vs a 145lb rider did a topend run on a 175hp bike .. the fat guy would never reach the speeds of the skinny rider .. and i don't care how long a road you got..

now back to the rocket ..if you tried two rockets with same size motor but differant weights .. the lighter rocket will go higher and faster .. wal-mart sells a rocket kit

* Last updated by: Badzx14r on 7/24/2009 @ 8:48 AM *

Say my son weighs 80 pounds less than I do. If we both had the same (equal) skills at accelerating from a dead stop, I would think he could get to 150mph (or some high speed) maybe .8 second faster than I could. So that would make it .1 second for 10 pounds. Maybe the difference is greater. Maybe he could get there 1.6 seconds faster. That would make it .2 seconds for 10 pounds. That may be in the right ballpark, anyway... -bg

Rook, I don't have real numbers for you, but I can do some equations this weekend for fun if I have time to see the correlation between variables. But as a former physics major I can tell you Badzx is right, mass does make a real difference in acceleration. HP is a measure of engine's strength and not related to weight, but a 300 HP convertible car will go a hell lot faster than a 300 HP SUV b/c of mass difference. It's like asking a ripped guy to push a baby cart and a truck - same strong guy, but very different results! 100lbs difference is huge on a bike (especially if most of that weight comes off the rear), b/c it makes the bike + rider about 13-15% lighter overall. This isn't the case for a car b/c that's only 3-5% of it's weight.

The formula should be different for cars and bikes b/c of different drag coefficients (i'm no expert on drag coefficients, but I'd expect them to be different due diff. in surface area).

Another thing to consider is rotational weight. I'm not yet sure if this only makes difference in handling or also in acceleration... but as far as handling goes, shedding pounds off anything that rotates is much more important than shedding static weight off the bike. I believe shedding just 2 pounds off your rotors, for example, is about the same as shedding 6 pounds anywhere else AND makes noticeable difference in handling, especially tilting. The further away from the center of the rim you go, the more important weight becomes. This is why lighter wheels, although they won't save you a whole lot in terms of absolute weight, may actually be your best bet and make the most difference. But this may not the case at all for straight acceleration, I really don't know, look it up.

^^I think the length of road would be the entire key to equal speed for different mass. All other things being equal, the heavier rider will attain the same speed as the lighter one if given enough distance.

Now the lighter rocket would go higher and accelerate faster because both rockets would run out of fuel in a few seconds. That perfectly illustrates the point that a limitted distance to travel (such as a 1/4 mile drag strip) would be covered in less time by a lighter vehicle than a heavier vehiclemaking the same hp. Given adequate distance to run and fuel, I think the same two vehicles would do the same top speed as long as the drag from ground and air was the same.

I think that the motor of the vehicle has to have the power to pull the load in the first place. In effect, the motor has overcome the force of gravity for the purpose of horizontal movement. If that requirement is met, the motor will achieve it's top speed regardless of weight, as long as it has enough flat ground to cover.

It's all just my thinking. I have no proof. Lighter has to be faster for real world situations. It's just a matter of how real world a few fractions of a second is to you. If you drag race and 1/100 -1/10 of a second as important, then I would think a lot of other factors would need to be considered equally important. The height, shape, flexion of the vehicle, rotating mass, the drag created by the tires and all of the parts that move against one another.......on and on.

rook i'll shot holes in your thinking all day long ... look at it this way ..bulldozers both D9's .pushing dirt ..1 pushing half a blade the other pushing a full blade ..which is going to push the fastest and farthers and reach its top speed before it stalls out .. same as a tractor pull as that weight comes forward the tractor stalls before it gets to the finish line ..

same with 2 same airplanes both have a 175hp motor . plane 1 has twin 600lb fat womens and a 400lb pilot total 1600lbs .. then plane 2 has a 130lb pilot and 2 110lb supermodels 350lbs total ... i'll be willing to bet plane 1 never gets off the ground even if it has a 30 mile runway..and if it did it will run out of fuel in a short time ..

* Last updated by: Badzx14r on 7/24/2009 @ 10:02 AM *

1lb? WTF might aswell cover your lid in vaseline for the extra umph.

Garantee you won't notice anything losing a pound.

1lb? WTF might aswell cover your lid in vaseline for the extra umph

Thats the next mod its being marketed by Muzzy.

I remember a while back there was a politition who wanted to pass legislation to change the value of pi to 3.0 in order to simplify things.
I don't see a simple answer to the question like 1/10 sec per 100 lbs. The drag coefficient would have a significant effect on that ratio. Drag coeffecient is not static it changes with speed. Like the air feels thicker the faster you are traveling. So that's changing while your mass is not. You also have aerodynamics to factor in. Some body designs, and I would presume fairings, will greatly change the friction or required enertia by pulling the vehicle closer to the road. Which to the bearings and drive gear would appear to be increase in weight. (My porche would feel much tighter in handling at 100mph than at 35mph.) Of course it could have the opposite effect too depending on the body design.Because of this compairing a car to a motorcycle could only be done in a vacuum.
The ratio you're looking for can be generalized since we're only dealing with limited speeds and has nothing to do with top speed. But essentially it is a moving target.
I'd say that the faster you are traveling the smaller the ratio will be.

* Last updated by: Sharkey on 7/24/2009 @ 5:45 PM *

Great info guys. Explains allot.

Alex wrote:

But as a former physics major I can tell you Badzx is right, mass does make a real difference in acceleration. HP is a measure of engine's strength and not related to weight, but a 300 HP convertible car will go a hell lot faster than a 300 HP SUV b/c of mass difference. It's like asking a ripped guy to push a baby cart and a truck - same strong guy, but very different results! 100lbs

I would agree that mass does effect acceleration but top speed? - I don't know. It's interesting to think about airplanes and such but now you're talking about overcoming gravity and eliminating friction with the ground and it all becomes more complicated than land vehicles. As for human power, that is fuel by glycogen and oxygen which is depleted very quickly from muscles so it's an interesting but not very fair comparison to a machine.

It would be more simple to consider the exact same vehicle - a ZX-14 - loaded with a heavy rider and then a light rider. I can see no additional forward resistance added to the big guy. If the additional force is downward (gravity), it is not pushing against the direction of the vehicle's motion so if the engine has the power to pull the weight, it seems like it should be able to pull it to top speed regardless of what the amount of weight is.

The only reason I can imagine a ZX-14 with a heavier rider would go slower at top speed is because the big guy has more surface area, he's not able to tuck down as tight, his greater weight causes more friction in the wheel bearings and against the road. <<That is real world and I suppose when you add all of it up, it would make a real difference in top speed.

Rook quit thinking your making my head hurt .. bottomline go bowling get a heavy ball and a lite ball ..what would take more energy to throw .. and could you get the heavy ball to roll as fast as the lite ball ..

Not the first time Rook has over analyzed a question, LOL!!

It's been some time since I've read it but Brock did a few runs at Maxton for top speed runs. With Brock, at around 200 lbs or so, best speed was like 196 or so. Then he put a 125 lbs jockey on the same bike with the same tune. The jockey hit 200.94. His Dad was a member of the old site but I do not remember his name.

Here is the article Rook if you want to read it.

http://www.dragbike.com/dbnews/anmviewer.asp?a=2596&z=2

Thanks Phil. That would seem conclusive for real world application. I think the jock was 140 lbs and he did just under 201 mph. Brock close to 197. Considering the 60lb dif in weight, 4mph at close to 200 is not that big of a deal if you're not competing. At least I don't see that as any reason to go on a starvation diet for the ordinary street rider/occasional thrill seeker. If 1bad is right about his 7 lbs = 1 hp, it was like Brock was riding with ~5.75 hp less. Shoot, loose 60 lbs to gain 6 hp!?? I'd say go have a cheese burger and think about what NOS you want to install (or rather, eat some potatoes and save your money so you can go buy a NOS).

Bad with all these #s plugged in, if you are 100lbs heavier than slow ninja. Then we just -14hp from your bike. This will still put out front(power wise)by a large margin, correct ?

yes correct -14hp and i got HP to spare.. but the 20lbs = 1 tenth is the killer .. thats 0.50 advantage slowninja and thats a mile

* Last updated by: Badzx14r on 7/25/2009 @ 6:38 AM *

SlowMO Lites = __________________ Peak HP in a shortime.

FatSO BuckGeaRooSkis = _____________________________________________________________ Peak HP EQualed EQuation in a longer time frame. Both bikes have same HP. Then look at a dyno. It takes time to run up the ramp unit peak is sustained. If you load the brake, will the HP rpm run right back up to Peak?

Takes more HP or Time to get there is the same HP? Did not fatso and lites both hit red line to shift to the next gear? That make more sense is a brain bustearacing luster?

K-Mart sell rocket science lites? I needay beerskisayaboutime. Is it morning? Popiss me a cold one then.

This thread started with discussion about acceleration and somewhere changed to ultimate top speed.
It wasn't too long ago that Hub posted a U-tube clip of a young sweetie trying for top speed on her 14. She was practicing tucking and thinking light and had a pretty good run. Then her friend, an old guy with about 150 lbs on her, got on her bike and blew her numbers away. I'm sure we're all aware that there is another factor working here besides weight vs. horsepower.
I still say that weight alone will not influence top speed. The bearings and running gear is so effecient that once rolling the additional weight has minimal "friction" to overcome and becomes additional inertial moment. Aerodynamic resistance is a significant factor but that U-tube clip shows that it can be minimal. Only acceleration is affected by weight.

sharkey's on the same drugs rook is on ..ones form Cali and the other from Wisconsin .. interesting that it traveled that far so quick ..

* Last updated by: Badzx14r on 7/25/2009 @ 3:24 PM *

Rot... You are too Classic! So Funny [to me]!

Sharkey has a point. Maybe the girl pulled the cable like.......Like Rotty, say. Her guy made sure it wasn't the bike, so he takes a cable full and full of shitearighther battery wangear was low. He'zzzzz been yanking on it most of his life so a cable yank is going to be faster/faster/faster she says; and the time she pulls her Depends off, and he hass a hard on for the young cock sucker is all she wrote.

Times UP!