Does a bigger rear sprocket give more horsepower???

[unfazed]

Here is something I came across today, when bored from looking out at the wind and rain and it looking moe like the 1st Jan than the 1st June :rolleyes


http://www.superstreetbike.com/how-to/bi...ythbusters

[His Dudeness]

How could anyone think that just bolting a different size sprocket onto an engine would give the engine more horsepower :lol

[unfazed]

I have met a few, despite my best efforts telling them hp at the crank cannot change without engine tuning, I left them in their deluded world.
Acceleration and terminal velocity yes, but hp no. :lol

[the cueball]

I don't agree... I mean you see all those cars with an extra 200bhp with their M Poooooowwwer and Turbo stickers from Hellfrauds...


Must be true....




:rollin :rollin :rollin

[sadlonelygit]

just paint it blue.............worth at least 20hp.
on a serious note the race bikes all run 520 chain because
a) short use cycle and (allegedly) high maintainance schedule
b) less mechanical loss therefore more RWHP

[bigralphie]

You cant have something for nothing

[BBROWN1664]

You wont increase the power output of the engine by changing the sprockets but could reduce losses in the drive train therefore increasing the power at the wheel. The percentage lost in the chain etc is minimal though and certainly not 20HP.

[His Dudeness]

You wont increase the power output of the engine by changing the sprockets but could reduce losses in the drive train therefore increasing the power at the wheel. The percentage lost in the chain etc is minimal though and certainly not 20HP.

I presume you mean that replacing worn out sprockets with new ones will reduce losses? That'll certainly help but replacing a new sprocket with a different ratio new sprocket will do feck all with regard to drive train losses

[BBROWN1664]

:agree

The sprocket alone wont do anything. With a new good chain that ahs low friction links it will help but with the old chain, it will do fec all unless you can somehow reduce the friction between the chain and sprocket (thinner sprocket to reduce edge friction?) but even then it will be fec all of a change and you would not actually notice the difference when riding it.

[Dead Eye]

Well no, you wouldn't necessarily alter the drivetrain loss to an appreciable level, but it does makes sense that you gain or lose WHP (Wheel Horsepower) due to the difference in torque multiplication through the final drive ratio - at least that's what it appears to show I believe

Though thinking about it, I guess you are more just moving the power band around at the rear wheel? Bare with me whilst I run this through my head... and write it all down



Acceleration can be altered by adjusting the final drive ratio. This seems sensible enough to me.

As Acceleration is a function of power (force) there must be a difference in power to obtain a difference in acceleration.

Therefore changing the sprockets (which we know alters the acceleration) must alter the available power at the rear wheel

[bigralphie]

you sacrifice top end for acceleration or vice versa 


Lots of ZX12 owners used to put an extra tooth front sprocket on that give more low down acceleration but meant the bike would now top out at around 170 mph

[bigbluebear]

you sacrifice top end for acceleration or vice versa 


Lots of ZX12 owners used to put an extra tooth front sprocket on that give more low down acceleration but meant the bike would now top out at around 170 mph

Surely you mean a tooth less ya foccin twonk  :lol

[lew600fazer]

:agree You gear down at the front to increase acceleration.

[His Dudeness]

Well no, you wouldn't necessarily alter the drivetrain loss to an appreciable level, but it does makes sense that you gain or lose WHP (Wheel Horsepower) due to the difference in torque multiplication through the final drive ratio - at least that's what it appears to show I believe

Though thinking about it, I guess you are more just moving the power band around at the rear wheel? Bare with me whilst I run this through my head... and write it all down



Acceleration can be altered by adjusting the final drive ratio. This seems sensible enough to me.

As Acceleration is a function of power (force) there must be a difference in power to obtain a difference in acceleration.

Therefore changing the sprockets (which we know alters the acceleration) must alter the available power at the rear wheel

You're mixing up power, acceleration and torque. What you're calling Wheel Horse Power is the Torque on the rear wheel. Changing the sprocket ratio will increase or decrease the torque on the rear wheel not the power. It'll also change the acceleration and the top speed of the rear wheel.

If you change the ratio so the rear wheel spins faster by say reducing the number of teeth on the rear or increasing the number on the front you'll obviously gain more top speed but you loose acceleration and torque. If you go the other way and change it for more acceleration you also gain more torque but loose top speed.

[BBROWN1664]

Torque talks. This explains it all

http://www.carthrottle.com/post/the-diff...explained/

[Dead Eye]

Acceleration is a function of Power and Power is a function of Torque (Horsepower = Torque x RPM/5252)

Also, from the article above, "One horsepower is the power needed to move 550 pounds (249kg) one foot in one second."

If altering the gearing causes increased acceleration, that power has come from somewhere.

As I mentioned previously, you are moving the available power around by adjusting the Torque at the wheel (as Power is derived from Torque and RPM). So you may have increased / decreased peak available power but at the expense of other variables.

... I think... it's all interesting stuff - good mind exercise

[Fazerider]

Acceleration is the result of force on a mass.
Power is the product of force and the distance moved (per second).
So, altering the gearing for acceleration gains you rear wheel torque (force at the contact patch), but you lose a corresponding distance travelled. So the power is the same.
Except… altering the final drive gearing for better acceleration will cause the loss of some power as seen by a dyno.
Firstly, it takes more force to turn the chain through the near 180º angle at the front sprocket because the radius of that turn is smaller with a smaller sprocket. Also, at any given bike speed, with a larger rear sprocket the chain will be travelling faster than it was with standard gearing so more chain length per second has to go round that tighter turn. Obviously, the lighter the chain is, the less energy is lost that way (one of the reasons belt drive is good).
Secondly, the energy lost at the tyre contact patch will be greater… more force means more deformation and slippage (not meaning a burnout situation, there is a small amount of slip in normal acceleration).

[Dead Eye]

That makes sense

I'm assuming the increased torque (force at the contact patch) outweighs the loss of the distance travelled (up to a point of course) which is what alters the values shown when on a dyno?

[bigralphie]

I was thinking that as I wrote it 50/50 chance lol  :rolleyes


The mod was to use a zzr1100 front sprocket I think ,I never did it myself ...I like my top end  :evil

[Oldgit]

Just stick two bottles of Buckfast in the tank, and it will be a real Zoomer  :pc