He's right. Horsepower is a measure of work over time. Lighter parts will reduce the amount of work required and the amount of time to move them. Therefore the horsepower increases.


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He's right. Horsepower is a measure of work over time. Lighter parts will reduce the amount of work required and the amount of time to move them. Therefore the horsepower increases.

:+1:
ChaChing!!

Lighter wheels have a lower moment of inertia, meaning it takes less energy (torque) to rotate.

 

No you will not make more horsepower...

It will improve the power to weight ratio. Acceleration could improve but you will not have a higher top speed.

You would not see an increase in HP on a dyno by lowering the weight of your wheels.

 

:headshake not true. You will see a noticeable Hp increase on the dyno from lighter components. A 520 chain conversion is good for about a 2Hp increase alone. Anything lighter weight will affect horsepower.

But don't confuse that with torque. Torque will remain the same, but horsepower will increase. Power-to-weight also is changed, but the rotational mass is more important because of its effects on the power.

 

indeed, HP produced by the motor won't increase, but lighter driven components will require less HP for the given demands, thus transferring more HP to the ground.

 

This. Its the difference between crank hp and wheel hp. You will have a higher wheel hp with lighter wheels because there is less parasitic loss from the drivetrain. The motor wont produce more power, you will just use more of the motors power to actually move the bike.

 

Well I have at least learned one thing. That I was justified in asking the question. I questioned the clerk because he said he saw a 2-3 hp bump on the dyno when he swapped his wheels. I guess I should have clarified my question. Would you see the increase on the dyno, everything else being equal?

 

I think that the main reason I questioned his statement is because when you are evaluating an engine's horsepower, it is irrelevant what chassis it is attached to. My 2008 corvette had a 430 hp engine. When Chevy dropped that engine into the truck (I forget the model name), it was still the same 430 hp engine. Just because the truck weighed 1000 more pounds, it was still a 430 hp engine.

 

Why there are engine dyno's & chassis dyno's (or real world measurement of power, as in what is transferred to the ground.)


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That made me laugh dude,

sorry, not at you, but the fact that a Guy who used to Tune Bikes is now working behind the counter selling helmets tells me me that he wasn't a vey good engine tuner anyway.

 

I thought the same thing, Lol.


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So then, would the change in wheels (less rotating mass) increase the numbers on either dyno?

 

^^^^ you should see a small but noticeable HP increase but not torque....as skydork stated earlier. lighter wheels,520 conversion, etc......anything to save weight will help. it's not giving or actually adding horsepower to the bike/engine but simply making it much more easy and efficient for said HP to be given quicker to the rear wheel. same reason you can have 2 identical bikes at the strip and one rider weighing alot less than the other will "make the bike quicker" so to say, this is if all other variables in the equation are the same..ie-skill level,bike setup and mods,tires,etc....the way it was explained to me a long time ago was like this. if you can run flat out in the 40 yard dash at say 5 seconds flat (for arguments sake) then it you either gained or lost 10-15 pounds, you should/would be able to cover the same distance slightly quicker or slower. i heard somewhere that for every 5-7 lbs you can drop from a bike that in real world terms it comes out to a couple ponies at the rear wheel.....or something like that.your bike won't go any faster in the long run BUT it will get there alot quicker.

 

KINDA off the subject but sprocket selection affects tire dyno HP and the curve too. SLIGHTLY. If you have a 15-45 or 17-51 (same ratio 3.0), its less strain on the motor and will move the power curve around. Very SLIGHTLY. SHHHHH don't tell anyone. Cocktails got me telling secrets :thumbsup:

 

:lol:....drink another and spill the beans buddy!!!:beer:...:heyyou:

 

Thanks for all the input, guys. I think I understand the concept as far as what is happening when you lighten the wheels, but one final question. Then, all else being equal, would you see the difference in hp on the dyno? (assuming, of course, that it is a dyno reading taken at the wheel)

 

I'll say no

 

u wiil see about i hp increase per l lb. decrease in rear tire weight on a dyno. tire weight being farther out on the circumference of the driven rotating weight has more affect than wheel weight. been measured and proven.

 

yes,for the cost you can make that decision, also the bike will turn quicker and have different characteristics.

 

A dyno is a rear wheel measurement. So yeah youll se it on a dyno. This is where "rwhp" comes from. Its the usable hp you get. If that cashier knew what he was talking about he shouldve explained this like any good tech should, but like lee said probibly why hes nota tech anymore.


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Thank you all for your input. I appreciate you taking the time to help a guy out!

 

i just bought a set of CZ wheels
and ill be dynoing at end of march ill tune back in and tell dyno results lol

 

Dont have the patients to read all the pages...
Useing liter wheels does not give a higher in total out put of hp..Seeing the engine does not have to work as hard to get up to the same speed it in a way gains hp...The hp you gain is hp that was already there...
Just for an example and usin simple # if an engine was designed to put out 100 hp on a dyno then put in a bike it will loose a % of its hp due to parasitic drag and even fluid dynamics...100 on the dyno in the bike its 85...Add lighter wheels/thinner oils/treated internals or even lighter internals you gain some of that % back...
You will not have a 100 hp and add some lighter parts and eventually get 120 hp......
Seeing you added new wheels lighter wheels,get some bearings to add to the lower resistance of the wheels...Look up a company called micro blue...Now that ya did the wheels your gonna be able to tweek suspension to for the unsprung weight..

 

Technically you are gaining wheel horse power.

But you are right, the engine output will be the same.

 

To a clear and concise answer. YES you gain Rear wheel hp. Less roating mass sucks up less HP and you dyno higher numbers. simple.

IE an stock Zx10 might have 190HP at the motor but you only dyno 160 at the wheel with lighter wheels you might now dyno 164. So yes you have picked up measurable hp at the wheel. Even though you are still making the same 190 at the crank. Crank HP is irrelevant anyway the only HP that matters is rear wheel HP.

 

And we are not talking about the same performance effect as drooping 5lbs for another part of the bike. IE if i drop 5lb from the body work it would have no where near the effect as 5lb lighter tires. There is around a 10 to one ratio from total weight to rotating mass. IE drop one pound off the tires would be the equivalent of drooping 10lbs from the chaise.

 

Horsepower is defined as the equivalent of 550 foot-pounds of work done per SECOND. Going back to elementary school math class, any time you change the TIME factor, horsepower will go up or down. It's measurable, it's proven, it's the way it is.

People and manufacturers have been doing this for years with lighter moving parts in engines, friction reducing components, lighter drive train components, etc. It's the simplest easiest way to get more power out of an engine that hasn't really changed its basic design in over 100 years. Air and fuel still have to get mixed and burned at the right ratio as it did back then. One of the ways to get more power out of an engine is to reduce the weight of the objects flying around inside it. Change nothing else except the weight of the crank/rods/pistons, and the engine will put down more power. Reduce the friction....more power.

Now, the same is true with drivetrain components. Light wheels equals more "effective" horsepower. Lighter chain, sprockets, ceramic wheel bearings, etc. all produce higher horsepower since its measured at the wheel and that's what's most important.

 

Scenario 1: Measure the power of the bike on an inertial dynamometer (the conventional Dynojet type). Then put on the lighter bits, then measure it again on the same dyno. The measured horsepower goes up. (It will.)

Scenario 2: Measure the power of the bike under given conditions on a brake dynamometer (a REAL dynamometer - one that is capable of holding the powertrain at steady speed while absorbing the torque/power produced). Then put on the lighter bits, then measure it again. The measured horsepower won't change! (And it won't!)

What's the difference?

The brake dynamometer is measuring the actual power output of the powertrain. Inertia has no effect under steady state (no acceleration) conditions. It could be as much or as little as you want. Under steady state conditions with no acceleration - it doesn't matter. "Force to change the speed of an object = mass x acceleration" ... if acceleration is zero then the force required to change the speed of the object is zero, regardless of the mass.

The inertial dynamometer is measuring the power output minus some amount that the powertrain is taking up internally in order to accelerate itself to a higher speed. If you change that mass (actually, moment of inertia, but let's keep the terminology simple for the non-physicists and engineers) then you change the amount of power that is taken off the top by the inertia.

Bottom line ... Lighter rotating parts (and lighter parts in general) don't change the amount of power that the engine is producing in the first place. But they most certainly will affect how much gets to the ground when accelerating. Once you get up to steady-state maximum speed, though, they will have no effect ... since the amount of power that the engine is producing in the first place doesn't change.

Strictly speaking, there may be some small secondary effects (lighter weight puts less weight on the tires which reduces the rolling resistance a little bit) but when nearing top speed where the inertia starts not mattering so much ... aerodynamic drag is BY FAR dominant over rolling friction, and it is only a secondary effect on the rolling friction at that. It's sufficiently accurate to say that within reason, lighter rotating parts will have an effect on acceleration but not on top speed.

 

Well said sir:+1:

 

Hey guys, thank you for all of the intelligent, coherent responses. I really appreciate how those on this forum who are well educated and passionate about all aspects of this sport, particularly the technical aspects, do not hesitate to take the time to share their knowledge, and do so in a non condescending manner. Thank you!

 

^^^^ it's what we're here for man and what makes this forum the best on the interweb IMHO!!!!!

 

he is correct if your engine has to work less to produce horsepower, its still going to be doing the same amount of work just more is going to happen because of the loss of weight.

just like if you had 2 horses pulling a carriage and you had one carriage way heavier than the other, the lighter one will be going faster. given you have the same horses..... get it?

 

this same debate is currently taking place on another board, found this dyno run there of before and after BST wheels installed dyno run.

I considered these wheels for my 2010 drag bike set up but am reluctantly afraid of riding on non-metallic wheels, but they appear to work as advertised

 

You can always get some magnesium wheels.