Member 
Discussion Topic 

nb89
Starting Member
4 Posts
London, London
United Kingdom
(None)

Posted  05/17/2011 : 8:50 AM
Like

A very nice model. I was just wondering why when calculating Coef Hor./Vert (rear) the resultant of lateral and longitudinal force is used, yet for Coef Hor./Vert (front) only the lateral force is used. Is this to do with front/rear wheel drive? Thanks.
(Sorry if I'm posting this in the wrong section!)


James R. Davis
Administrator
17332 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500

Posted  05/17/2011 : 9:05 AM

Only the rear tire consumes traction as a result of driving force while both tires experience traction demands as a result of centrifugal force.
Of course both tires experience braking forces in addition to centrifugal force. 


nb89
Starting Member
4 Posts
London, London
United Kingdom
(None)

Posted  05/17/2011 : 9:16 AM

Ok that makes sense. One other thing I noticed was that the lateral force on the rear wheel remains constant at different longitudinal accelerations. Would it not change however as the vertical load on the wheel changes? 


James R. Davis
Administrator
17332 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500

Posted  05/17/2011 : 9:29 AM

Vertical load on the rear tire is called 'weight'. It is caused by gravitational acceleration.
Lateral acceleration causes 'sideways weight' felt as centrifugal force.
Lateral acceleration is an inertial function involving mass, speed, and radius ... not weight. 


Baltoe
Starting Member
6 Posts
Calgary, Alberta
Canada
HarleyDavidson
FLHXSE2

Posted  06/11/2011 : 11:01 PM

Gentlemen,
I have used the lean angle calculator  thank you very much for whoever put it together. What I would like to know is whether the lean angle is in addition to the super elevation of the curve being negotiated? The lean angle calculator tells me the lean angle is 14 to 15 degrees, and since there is no mention of any SE, I am assuming the curve is a flat road. When the SE is considered, the critical speed for the curve is higher, but is the lean angle calculated with respect to normal forces downward (gravity). I suspect the lean angle with respect to the road surface is less than 14 to 15 degrees, probably by the grade of the SE, which is 4 degrees. Weigh in if you can add to this query.
Thx 


rkfire
Advanced Member
1714 Posts
Stratford, CT
USA
Suzuki
Bandit
Peer Review:
Blocked

Posted  06/12/2011 : 9:30 AM

The lean angle calculator has a default 6 degree road corner banking. You can adjust that number though. 


Baltoe
Starting Member
6 Posts
Calgary, Alberta
Canada
HarleyDavidson
FLHXSE2

Posted  06/18/2011 : 9:39 PM

If tan (lean angle) is approximately V squared over radius times acceleration of gravity, then, at 27.77 m/s, then lean angle should be 14.68 degrees. That is what the lean angle calculator yields, so how is there a 6 degree road bank built in? Adn if so, how is it removed, and if so, why is it there at all? Thx,
Baltoe 


James R. Davis
Administrator
17332 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500

Posted  06/19/2011 : 5:41 AM

Yikes!
The model allows you to input the bank angle of the roadway  which IS the super elevation. Calculation of a bike's lean angle does NOT assume a 6 degree bank angle. The example settings provided with the model happen to have a 6 degree bank angle but, like all inputs, that can be set to whatever you want.
The bank angle setting does not affect the bike's lean angle  it helps determine what the bike's maximum speed through the turn can be.
Let me guess ... you are a student or recently began studying dynamics. That's great and I applaud that about you. But as such, you really need to get your terminology in hand. Your first question contained the following: quote: I suspect the lean angle with respect to the road surface is less than 14 to 15 degrees, probably by the grade of the SE, which is 4 degrees.
(Underline added)
'Grade' has nothing to do with super elevation. It is the amount of incline or decline that the roadway has. Grade plays no part in determining a bike's lean angle.
'Super elevation' is the bank angle, if any, of the roadway. It also plays no part in determining the bike's lean angle while in a turn.(At least that's what I believed when I wrote the model. < grin >)
'Lean angle' is ALWAYS relative to vertical. 


Baltoe
Starting Member
6 Posts
Calgary, Alberta
Canada
HarleyDavidson
FLHXSE2

Posted  06/19/2011 : 2:04 PM

Maybe we are looking at a different model, because I don't see any input data labeled SE.
I did not assume the 6 degree lean angle, someone else posted that, and I was just checking to see what he was talking about.
Grade is a term used to denote a slope, and the SE of a road slopes from the high side to the low side.
So, that aside, the object of my query is to determine how close the handlebars of a particular bike might get to the ground while in a steady state going around a 300 meter radius corner with a 4 degree SE.
So, while some things have nothing to do with other things, all the things that I mentioned have to do with my problem.
To wit, I have leaned the bike over in three dimensional autocad and measured the distance from the gorund to the handlebar at each degree up to 22.5, even though the lean angle would have been 14.68 degrees, as per calculations.
And, with respect to your speculation as to how I might be labeled, 'student' is correct. Just to ensure that the 'model' we are talking about is the same one, could you post a link to it if you reply to this post.
Baltoe 


James R. Davis
Administrator
17332 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500

Posted  06/19/2011 : 2:20 PM

Please note line 15 of the spreadsheet which I highlighted for you in the picture below. That is 'super elevation' in motorcyclist speak.
'Grade' is the incline or decline of a roadway.
'Slope' is the inclination of that roadway laterally  usually called 'bank angle' (or 'super elevation' for academics).
As I said earlier, the lean angle is ALWAYS relative to vertical. Thus, you need to add the super elevation angle to it in order calculate the distance of the handlebar from the ground. 


Baltoe
Starting Member
6 Posts
Calgary, Alberta
Canada
HarleyDavidson
FLHXSE2

Posted  06/20/2011 : 10:15 AM

Don't know how to post a screen shot of the spreadsheet for the lean calculator, but it does not have any bank angle at line 15. I will email it to you. 


Baltoe
Starting Member
6 Posts
Calgary, Alberta
Canada
HarleyDavidson
FLHXSE2


James R. Davis
Administrator
17332 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500


Baltoe
Starting Member
6 Posts
Calgary, Alberta
Canada
HarleyDavidson
FLHXSE2

Posted  06/22/2011 : 9:29 AM

James  thanks for that link. Are you aware of any model that would allow one to calculate what the out tracking of a motorcycle might be in the 'wrong' direction when swerving to avoid a collision?
If you swerve to avoid a 6.0 foot obstacle at 62 mi/hr, and you were able to just avoid the thing within a distance of 140 feet, you would have to be describing an arc of approximately 3130 feet, from 140 feet out.
But the 140 feet already includes the initial countersteer to achieve the desired lean angle to avoid. Is there a way to fit this into a quadratic? Thx
Baltoe 


James R. Davis
Administrator
17332 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500

Posted  06/22/2011 : 10:16 AM

That question is far beyond my abilities except in theory. Further, it is not the subject of this thread. In other words, if you want to continue with this line of questioning, start a new thread.
After you have determined the necessary turning radius, everything else in your scenario is of no importance. That is, you have determined the arc of 3130 and from that can determine the radius of the curve it describes, thereafter you can ignore the object and its measurements.
So you have a speed and a radius, and what you are attempting to solve is the slip angle and lateral forces involved in that scenario. (I'm assuming a constant speed and slip angle and assuming that is what you mean by 'outtracking' because changing speed changes the slip angle.)
You start with an understanding of the geometry of the bike. Then you need to learn a great deal about the tires. You need to know whether they are radial or bias ply. You need to know tire pressure and diameter of the tire and the length of the tire patch and the camber angle of its profile  and its rubber composition (well, you need to know what the Coefficient of Friction is between that tire and the roadway.)
From there it's grunt work to determine the slip angle and lateral and longitudinal forces involved.
A model? Not that I'm aware of. You can start by reading an NHTSA paper (DOT HS807271) that discusses how to calculate tire forces.
Also, you will need to determine the slip angle of each tire so that you can determine the amount of over or understeer involved as that is what determines the actual path of travel. 


mstram
New Member
11 Posts
Toronto, Ontario
Canada
(None)

Posted  06/25/2015 : 12:16 PM

The "wheelbase" cell in the spreadsheet appears to only be used in the graph.
From internet searches so far, wheelbase seems to be a minor factor when calculating lean angle.
How much of a factor is wheelbase when calculating lean angle and lateral acceleration ?
Where would wheelbase be "plugged in" to the spreadsheet ?
Mike 


James R. Davis
Administrator
17332 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500

Posted  06/25/2015 : 12:41 PM

Wheelbase plays no part in determining the lean angle. 



Discussion Topic 
