Ninjette: Horsepower and Speed

SmithSwede · August 29th, 2012, 03:11 PM

Was fooling around with an online horsepower/drag calculator, which I found very helpful in explaining the real world experience of riding the 250. I'm sure this is well known to the engineer types.

Based on my assumed variables, I get the following horsepower requirements for these speeds:

60 mph only requires 10 horsepower (30% of max)
65 takes 12.5 HP (41%)

70 needs 15.4 HP (51%)
75 takes 18.7 HP (62%)

80 takes 21 HP (70%)
85 takes 26.8 HP (89%)

90 takes 30 HP. (100%)

This is presumably why I find the "sweet spot" for cruising to be 60-65 mph--still lots of HP in reserve, great fuel economy. 70-75 is ok too, but the engine is definitely reaching its limit. But if you are running 70 mph and hit a sudden gust of 15 mph headwind, you will suddenly need to go from 50% of max power output to 90%! That's probably why cruising more than 75 seems like a strain to me, because it is often pretty windy where I ride.

Also of interest. Assuming my inputs are correct, if it takes a full 30 HP to run 90 mph, it would take an additional 7 horsepower just to increase speed to 95 mph. So even if your performance mods get you a few extra HP, it gains you very little in terms of top speed.

(I assumed a CD of .5 and 12 square feet of frontal area. If anyone has more accurate data, I'm interested in seeing it)

Panda · August 29th, 2012, 03:40 PM

Out of curiosity how did you come up with the CD?

Jiggles · August 29th, 2012, 03:52 PM

Cool stuff though your numbers are quite a bit off. A stock ninjette on a good day will do 26hp and I believe stock will make it to 100mph indicated (~95mph)

Also 100% hp occurs at only 1 specific point, the rest of the time your power is already limited. In case you want to play around with some more accurate numbers heres a 2fiddy dyno

SmithSwede · August 29th, 2012, 04:39 PM

For the CD I just used the low end of the suggested cd range for motorcycles. Seems like I read somewhere that the ninjette was pretty aerodynamic. Would be interested in knowing the actual figure.

alex.s · August 29th, 2012, 04:48 PM

.5 seems awfully good for a drag coefficient... i guess its pretty small

choneofakind · August 29th, 2012, 05:38 PM

Maybe in a full tuck? Idk I think I have to take a fluids course next year. I'll get back to you more on that then.

Motofool · August 29th, 2012, 05:49 PM

Quote:

Originally Posted by SmithSwede

.........(I assumed a CD of .5 and 12 square feet of frontal area. If anyone has more accurate data, I'm interested in seeing it)

The correct way of doing it is using a power-torque curve as the one posted by Sean above and the proper gear-chain reduction for a specific speed.

The exponential relation is only natural.
A Hayabusa needs 280 HP's to reach 220 mph

http://www.schultzengineering.us/aero.htm

A pretty accurate Cd can be calculated this way:

http://en.wikipedia.org/wiki/Drag_coefficient

For force, use power/speed.

SmithSwede · August 29th, 2012, 06:09 PM

I'm thinking my CD is probably too low, and the HP is too high at 30 for a stock bike. Guess you need to base the calculation on rear wheel HP, not at the crank.

Jiggles · August 29th, 2012, 06:10 PM

Yup

The applied force is generally the one that matters

Panda · August 29th, 2012, 08:21 PM

Quote:

Originally Posted by SmithSwede

I'm thinking my CD is probably too low, and the HP is too high at 30 for a stock bike. Guess you need to base the calculation on rear wheel HP, not at the crank.

If I had to guess the Cd is probably north of .6

August 29th, 2012, 03:11 PM	#1
SmithSwede ninjette.org member Name: Prescott Location: Terrell, Texas Join Date: Nov 2011 Motorcycle(s): 2007 BMW F800S; 2012 Ninja 250; 2013 Moto Guzzi V7 Stone, 2016 Triumph Street Triple Rx; 1996 Ducati 900 SS CR Posts: 77	Ninjette: Horsepower and Speed Was fooling around with an online horsepower/drag calculator, which I found very helpful in explaining the real world experience of riding the 250. I'm sure this is well known to the engineer types. Based on my assumed variables, I get the following horsepower requirements for these speeds: 60 mph only requires 10 horsepower (30% of max) 65 takes 12.5 HP (41%) 70 needs 15.4 HP (51%) 75 takes 18.7 HP (62%) 80 takes 21 HP (70%) 85 takes 26.8 HP (89%) 90 takes 30 HP. (100%) This is presumably why I find the "sweet spot" for cruising to be 60-65 mph--still lots of HP in reserve, great fuel economy. 70-75 is ok too, but the engine is definitely reaching its limit. But if you are running 70 mph and hit a sudden gust of 15 mph headwind, you will suddenly need to go from 50% of max power output to 90%! That's probably why cruising more than 75 seems like a strain to me, because it is often pretty windy where I ride. Also of interest. Assuming my inputs are correct, if it takes a full 30 HP to run 90 mph, it would take an additional 7 horsepower just to increase speed to 95 mph. So even if your performance mods get you a few extra HP, it gains you very little in terms of top speed. (I assumed a CD of .5 and 12 square feet of frontal area. If anyone has more accurate data, I'm interested in seeing it)

August 29th, 2012, 03:52 PM	#3
Jiggles Jigglin' your Jiglets Name: Sean Location: San Jose, Ca Join Date: Jun 2011 Motorcycle(s): 2009 K1300S, 2013 Ninja 300, 2011 Ninja 250R, Faster than Unregistered's ninjette Posts: Too much. Blog Entries: 1 MOTM - Apr '13	Cool stuff though your numbers are quite a bit off. A stock ninjette on a good day will do 26hp and I believe stock will make it to 100mph indicated (~95mph) Also 100% hp occurs at only 1 specific point, the rest of the time your power is already limited. In case you want to play around with some more accurate numbers heres a 2fiddy dyno __________________________________________________ If the Ninja 250 doesn't have enough power for you, then you don't know how to ride it. AFM #676 Supersports are for n00bs

August 29th, 2012, 04:48 PM	#5
alex.s wat Name: wat Location: tustin/long beach Join Date: Sep 2009 Motorcycle(s): wat Posts: Too much. Blog Entries: 5 MOTM - Oct '12, Feb '14	.5 seems awfully good for a drag coefficient... i guess its pretty small __________________________________________________

August 29th, 2012, 06:10 PM	#9
Jiggles Jigglin' your Jiglets Name: Sean Location: San Jose, Ca Join Date: Jun 2011 Motorcycle(s): 2009 K1300S, 2013 Ninja 300, 2011 Ninja 250R, Faster than Unregistered's ninjette Posts: Too much. Blog Entries: 1 MOTM - Apr '13	Yup The applied force is generally the one that matters __________________________________________________ If the Ninja 250 doesn't have enough power for you, then you don't know how to ride it. AFM #676 Supersports are for n00bs

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August 29th, 2012, 03:40 PM	#2
Panda not an actual panda Name: dan Location: philadelphia Join Date: Aug 2012 Motorcycle(s): 2008 Ninja 250, 2009 CBR600RR (Sold) Posts: A lot.	Out of curiosity how did you come up with the CD?

August 29th, 2012, 04:39 PM	#4
SmithSwede ninjette.org member Name: Prescott Location: Terrell, Texas Join Date: Nov 2011 Motorcycle(s): 2007 BMW F800S; 2012 Ninja 250; 2013 Moto Guzzi V7 Stone, 2016 Triumph Street Triple Rx; 1996 Ducati 900 SS CR Posts: 77	For the CD I just used the low end of the suggested cd range for motorcycles. Seems like I read somewhere that the ninjette was pretty aerodynamic. Would be interested in knowing the actual figure.

August 29th, 2012, 05:38 PM	#6
choneofakind ninjette.org certified postwhore Name: . Location: . Join Date: Feb 2011 Motorcycle(s): . Posts: Too much. MOTM - Feb '13, Feb '14	Maybe in a full tuck? Idk I think I have to take a fluids course next year. I'll get back to you more on that then.

August 29th, 2012, 06:09 PM	#8
SmithSwede ninjette.org member Name: Prescott Location: Terrell, Texas Join Date: Nov 2011 Motorcycle(s): 2007 BMW F800S; 2012 Ninja 250; 2013 Moto Guzzi V7 Stone, 2016 Triumph Street Triple Rx; 1996 Ducati 900 SS CR Posts: 77	I'm thinking my CD is probably too low, and the HP is too high at 30 for a stock bike. Guess you need to base the calculation on rear wheel HP, not at the crank.