Does weight play a role in acceleration? Who wins??

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Jun 21, 2012 | 01:30 PM

#41

blarg

Road Captain

Joined: May 2011

Posts: 505

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From: Houston

Does weight play a role in acceleration?
yes.

Who wins??
your dealer/mechanic

Jun 21, 2012 | 01:33 PM

#42

cruzmisl

Thread Starter

Road Master

Joined: Jun 2010

Posts: 757

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Bahaha....sooner or later we all pay

Jun 21, 2012 | 01:33 PM

#43

Ovaltine Jenkins

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Joined: Mar 2010

Posts: 430

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From: Dirty City

Quote:

Originally Posted by mkguitar

a 'rule of thumb" is that the reduction of 7 pounds weight is "equal" to a gain of 1 HP

Quote:

Originally Posted by fella

Who's thumb? Not disagreeing, because I don't know, but I always heard 10lbs=1hp.

How many pounds "equals" how many HP depends on how much of each you start with. Because it's not a flat equivalence, but a ratio.

In reality a 50% decrease in weight roughly equals a 100% increase in HP. A 25% decrease in weight roughly equals a 33% increase in HP.

Or, to put it another way, the inverse of your final weight over your starting weight is the ratio of final HP equivalence to starting HP.

Example:

Dropping from 500 lbs. to 400 lbs. puts you at 400/500ths of your starting weight, which is the equivalent of having 500/400ths of your starting HP. So if your starting HP was 60, you're now equivalent to 500/400ths of that, or 5/4ths, or +25%, or 75 HP equivalent.

So if you want to look at bang for the buck, decide which is better: dropping from 500 to 400 lbs., or increasing from 60 to 75 HP.

In this specific case every HP is equal to 6.7 lbs when taken in total. But if you do the same with a 1,000 lb. bike and bring it down to 900 lbs., that's the equivalent of increasing its 60 HP motor to only 6.7 HP, to 66.7, or having each HP be equal to 15 lbs. when taken in total.

All of this, of course, neglects the rider weight, which must also be factored in, as well as how much of the loss of mass comes from sprung versus unsprung locations.

Jun 21, 2012 | 01:36 PM

#44

Dew Me

Elite HDF Member

Joined: Jul 2008

Posts: 3,524

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From: Maryland

Does a fat kid like cake?

Jun 21, 2012 | 01:44 PM

#45

icepick

Cruiser

Joined: Jul 2008

Posts: 233

Likes: 0

From: Mississippi

thanks Gearhead for adding that in. In cars, it is generally considered unsprung weight, that is, all the weight not supported by the suspension, that has to be moved first. the engine turns the tranny which turns whatever to the wheels that have to turn first to get the whole thing going, then the sprung weight gets moving forward, including driver/rider. The lighter the rotating mass or unsprung weight, the "faster" you can get the engine into the sweet spot of highest torque, which increases the rate of acceleration. so yes, lighter wheels and tires get you going faster but the net effect is simply getting the engine rpms up faster which increases rate of acceleration. bottom line is, the lighter, the quicker if torque and HP is the same.