Jump to content

Recommended Posts

  • Member Contributer

I have been wondering what the CoD numbers might be for a 6th Gen?  I wonder if honda ever published this data?

 

Of course rider and rider position must have a large effect.

 

I would love to get some rudimentary numbers so I can play around with HP calcs.

Link to post
Share on other sites
  • Member Contributer
13 hours ago, lplplplp said:

I have been wondering what the CoD numbers might be for a 6th Gen?  I wonder if honda ever published this data?

 

Of course rider and rider position must have a large effect.

 

I would love to get some rudimentary numbers so I can play around with HP calcs.

You can also work backwards using known variables.

 

1. top-speed of bike+rider

2. bhp @ RPM of top-speed

3. cross-sectional area of bike+rider. Can be obtained from photo

4. air-density @ time of top-speed run

Link to post
Share on other sites
  • Member Contributer

It's pretty much the same as a bag of wet garbage. 😄

  • Like 1
Link to post
Share on other sites
  • Member Contributer
12 hours ago, DannoXYZ said:

You can also work backwards using known variables.

 

1. top-speed of bike+rider

2. bhp @ RPM of top-speed

3. cross-sectional area of bike+rider. Can be obtained from photo

4. air-density @ time of top-speed run

True. But that would take effort! LOL

 

the ecu I am looking at has a virtual dyno built in. But at the end of the day it matters little since its only for tuning.

 

 

Link to post
Share on other sites
  • Member Contributer

"The average passenger car on the road today has a drag coefficient (the measure of air resistance) of about 0.3 (a lower number being better). Even a large, blocky car like a full size SUV or my ’87 Westfalia camper rate around 0.4. A racing motorcycle with a smooth, full fairing and professional rider in a full tuck? 0.6. In other words, those 5’9” jockeys crunched up behind the windscreen of a tiny Moto3 grand prix bike create more drag in the air than a Chevrolet Suburban"

 

So it might seem to be closer to 1....I think the table above might be for unfaired MC with an upright rider.

 

Although this line  "tiny Moto3 grand prix bike create more drag in the air than a Chevrolet Suburban" suggests the author doesn't understand Cd.

Link to post
Share on other sites
  • Member Contributer

As long as I am faster than the other guy (or woman) the CoD is sufficiently low. 

  • Like 1
Link to post
Share on other sites
  • Member Contributer
5 hours ago, lplplplp said:

Although this line  "tiny Moto3 grand prix bike create more drag in the air than a Chevrolet Suburban" suggests the author doesn't understand Cd.

 Not far off though in total drag. Ave bike w/rider requires about 12hp @ 65mph. Cars typically require about 16hp @ 65mph. Even without numbers, it's obvious bike+rider is nowhere nearly as slippery. 

Link to post
Share on other sites
  • Member Contributer
1 hour ago, DannoXYZ said:

 Not far off though in total drag. Ave bike w/rider requires about 12hp @ 65mph. Cars typically require about 16hp @ 65mph. Even without numbers, it's obvious bike+rider is nowhere nearly as slippery. 

Yes, this is a good point. With the ride on we are not as aerodynamic as we think.

Link to post
Share on other sites
  • Member Contributer

IIRC Honda released Cd figures for the 5th gen, because it was much better than the 4th gen. 

 

6th gen was a step backwards in Cd I believe. 
 

From what I remember from aerodynamics study, the frontal area (compression drag) of an object is the low side of the drag equation. Thus regardless of shape frontal area drag is the same. Except for where air hits multiple times.
 

So cars have low frontal resistance. They also have relatively stable sides & a clean ish flow front to rear. Plus being longer helps flow control. 
 

Low pressure drag is the larger part of drag, basically the low pressure area behind a moving object in a fluid. Effectively sucking it backwards. Bikes suffer from multiple frontal area strikes & disruptive flow, due to their broken sides. Being short they pack a big drag pocket behind them with no clean flow. All of which gets worse the faster you move. 
 

  • Like 1
Link to post
Share on other sites
  • Member Contributer

Love those dimensionless numbers!

 

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

 

Generally a small front area and greater length (in the direction of flow) is lower drag.  But a motorcycle with a person is a bumpy object no matter what.  Don't forget drag is proportional to the square of velocity in immersed flow...

Link to post
Share on other sites
  • Member Contributer
11 hours ago, lplplplp said:

True. But that would take effort! LOL

 

the ecu I am looking at has a virtual dyno built in. But at the end of the day it matters little since its only for tuning.

 

 

I'll just throw in my that it's probably worthless and for sure not close enough to calculate a meaningful Cd.  It's going to tell you a calculated power from what it thinks is happening and what it can see, not any kind of direct measurement like a stress and strain gauge type of sensor on a shaft somewhere (which is rarely reliable anyways).  Even if you have a dyno run to map to RPM, it's going to be different than actual power at that moment.

 

The problem you will have in the middle is you will have two variables, drag force and power output, so you can't balance one side of the equation or the other in a meaningful way.   

 

Link to post
Share on other sites
  • Member Contributer
15 hours ago, ShipFixer said:

I'll just throw in my that it's probably worthless and for sure not close enough to calculate a meaningful Cd.  It's going to tell you a calculated power from what it thinks is happening and what it can see, not any kind of direct measurement like a stress and strain gauge type of sensor on a shaft somewhere (which is rarely reliable anyways).  Even if you have a dyno run to map to RPM, it's going to be different than actual power at that moment.

 

The problem you will have in the middle is you will have two variables, drag force and power output, so you can't balance one side of the equation or the other in a meaningful way.   

 

I certainly don't expect this to be in anyway equivalent to a real dyno. the ECU software asks for a Cd so I started thinking down the path of what the VFR might be, that's all. I realize it won't give me a real number but I do think it will be a useful tuning tool, esp with extensive data logging capabilities along side. 

 

It occurs to me that without some sort of sensitive IMU I dare say the graph will not resolve fine details.  hmm I think that might even be an option. 

anyway i'll report back if I get some meaningful results. ...whenever I get a chance to do it.

Link to post
Share on other sites
  • Member Contributer
17 hours ago, Mohawk said:

IIRC Honda released Cd figures for the 5th gen, because it was much better than the 4th gen. 

 

6th gen was a step backwards in Cd I believe. 
 

From what I remember from aerodynamics study, the frontal area (compression drag) of an object is the low side of the drag equation. Thus regardless of shape frontal area drag is the same. Except for where air hits multiple times.
 

So cars have low frontal resistance. They also have relatively stable sides & a clean ish flow front to rear. Plus being longer helps flow control. 
 

Low pressure drag is the larger part of drag, basically the low pressure area behind a moving object in a fluid. Effectively sucking it backwards. Bikes suffer from multiple frontal area strikes & disruptive flow, due to their broken sides. Being short they pack a big drag pocket behind them with no clean flow. All of which gets worse the faster you move. 
 

Theoretically the under-tail exhaust "should" have positive effect by giving the bike a tail!  so maybe that makes up for its inferior aerodynamics.

I remember this being talked about on the mc-chassis list (in the 90's!) I think Tony Foale (chassis guy ) was active then (but my memory sux so maybe we were just talking about him 🙂

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy.