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


http://www.superstreetbike.com/how-to/bigger-rear-sprocket-makes-more-horsepower-mythbusters

[His Dudeness]

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

[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.

[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....




 

[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]

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 :P



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 

[lew600fazer]

  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 :P



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-difference-between-torque-and-hp-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 


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

[Oldgit]

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

[His Dudeness]

I learned this sort of stuff in a general way rather than specifically about cars and bikes and engines so this is how I’d look at it some people might find it interesting most probably won't 

I learned Metric rather than Imperial so I use standard SI units and formulas. Here’s a link on SI units if you want to know a bit about them and why they’re used http://en.wikipedia.org/wiki/International_System_of_Units The good thing about using SI units is that there’s only seven base units and you get all the other units for everything that's measurable in the world by either multiplying or dividing those seven base units. In general when you’re doing calculations you always convert the numbers back to those base units before you get started because one of the handy things about SI units is that if you know the unit your answer is in you can work backwards and figure out what the formula used to get the answer was.

Take Torque as an example. With bikes we all know about torque wrenches. So you set your torque wrench to 50Nm and give it a turn until it clicks job done. Well the formula for Torque from an engineering and maths point of view is Torque = Force x distance. So that makes sense you put a force on the end of the wrench, the wrench is a set distance from the bolt so you get a torque on the bolt.  If you want a higher torque you put more force into the wrench. If you look at it from a maths point of view the SI unit for Torque is Nm which stands for NewtonMetre. Newton is the unit of Force and metre is the unit of distance. Putting them beside each other is a quick way of saying they’re multiplied together. So if you know Nm is the unit of Torque you can work out that the formula for Torque must be Force multiplied by distance which it is. Force(N) x distance(m) = Torque (NM)

Like I said you can do that for anything that’s measurable so another one that everyone knows is velocity (or in other words speed). The engineering definition of velocity is it’s the rate of change of distance with respect to time which is basically how much distance you covered in a certain amount of time. The higher you’re velocity the more distance you’re covering in that amount of time which makes sense. The SI unit for velocity is m/s which is metres divided by seconds so from that you can see that the formula for Velocity must be Velocity = distance(m) / time (s) because the units are m/s . So you can use that idea to work out anything and for doing calculations on the performance of bikes and cars and engines and that sort of stuff you’re mostly interested in speed and acceleration which is called linear motion. Then you’ve got power and torque which is angular motion. They don’t all directly relate to each other but with a bit of manipulating of the formulas and bring in some other stuff you can get them to link together. If anyone is interested I could get into it a bit when I've got some time to write it up or if this stuff is putting ye to sleep I won’t bother

[Frosties]

Any chance you could talk to my mrs about this?
 
I'd call it payback for all those years of asking "so how was your day love"

[Val]

Here is  my understanding how the secondary transmission ratio and acceleration works.

Based on my strictly scientific research because of looming chain and sprockets change 

If I increase my secondary transmission ratio say from stock 15/48 I go for 13/53 sprockets, the bike will have more acceleration (foots per second) and pulling force (lb per foot).

Obviously you can't change the torque or the engine power. Engine delivers different power during different RPMs. The engine power/torque to RPM graph is constant. The graph below shows 2 lines one is for torque (nm) and the other is for power (hp) during different engine RPMs. BUT the graph is the same for ANY ratio!!! That means engine produces some amount of power when doing some RPM and you cannot change that. You can change only how you transfer that finite amount of power to the wheel using the gears (and the final drive ratio):



You ONLY can change the way how you transmit the power/torque to the wheel. The variables are only acceleration (foots per second) and pulling force (lb per foot).

Say with the stock 15/48 in second gear doing the same RPM say 4600 I will have 10 fts2(foot per second squared) acceleration going with 31 mph and the pulling force will be 210 lbf.

With the custom 13/53 in second gear doing the same RPM say 4600 I will have 14 fts2(foot per second squared) acceleration going with 25 mph and the pulling force will be 270 lbf.

Here is the way you change the power delivery for the above example for second gear:




[url=http://motorcycleperformanceanalyzer.com/yamaha/fzs-600-fazer-1998/]http://motorcycleperformanceanalyzer.com/yamaha/fzs-600-fazer-1998/[/URL]

You see clearly what you loose transforming your constant power into higher acceleration and more pulling forces - you loose the top end speed. The peak for high ratio 13/53 is around 48mph compared to 64mph for standard fazer 15/48.

If you look at moto gymkhana you will see they use ginormous sizes for rear sprockets - they need big acceleration and not much speed obviously no motorway commuting during the gymkhana LOL. Simples.


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[celticdog]

WoW! Awesome Val! You are definitely awarded a BSc ( bronze swimming certificate) 

The rule of thumb for me is torque equals force times radius

[His Dudeness]

Any chance you could talk to my mrs about this?
 
I'd call it payback for all those years of asking "so how was your day love"

I could be persuaded with some pics of the wife