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HONDA... A picture says a thousand words

ohio

ohio

The Fresno Kid
Nov 26, 2001
6,649
24
SF, CA
Steve from JH said:
The vehicle does not have to be accelerating for there to be load shift. I used to think that too. I came to realize it wasn't true just a little while before I got this Cossalter book.

The load shift is dependent on a force couple between the thrusting force at the ground and an equal and opposite force acting at the CM. If we assume the air resistance acts at the CM, it doesn't matter whether the force is all reaction to acceleration (launching off from a standstill) or whether part of it is reaction to acceleration and part wind resistance, or whether it's all wind resistance (steady velocity on level ground).
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I noted this force, but pointed out it doesn't apply to bikes. The frontal area, and speeds involved are so small that it has no significance. However, as I also pointed out, you can have a similar situation while pedalling uphill.

And another also: With a rider of any skill, motocycles hit their drag limited top speed long before they flip over.

Steve from JH said:
Another corollary of this is that it's easier to wheelie from acceleration on a motorcycle the faster you're going when you start the acceleration. It's hardest (takes the most acceleration) when you wheelie from a standstill.
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Sorry fella but this is demonstrating a basic misunderstanding of engine power and gearing. The faster your moving, the more difficult it is for your engine (or your legs) to produce the force necessary to wheelie. Air resistance might help you wheelie, but not nearly as much as gobs of torque.

Again, not sure what this has to do with bicycling. I just like pointing out when you're wrong. ;)
 
S

Steve from JH

Chimp
Jul 5, 2002
52
0
ohio said:
I noted this force, but pointed out it doesn't apply to bikes. The frontal area, and speeds involved are so small that it has no significance. However, as I also pointed out, you can have a similar situation while pedalling uphill.

And another also: With a rider of any skill, motocycles hit their drag limited top speed long before they flip over.



Sorry fella but this is demonstrating a basic misunderstanding of engine power and gearing. The faster your moving, the more difficult it is for your engine (or your legs) to produce the force necessary to wheelie. Air resistance might help you wheelie, but not nearly as much as gobs of torque.

Again, not sure what this has to do with bicycling. I just like pointing out when you're wrong. ;)
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Motorcycles hit a drag limited top speed before they reach the theoretical maximum velocity because their engines are deliberately limited to avoid the situation. It would be incredibly dangerous. They easily could put powerful enough engines on the bikes to reach that point.

If the bike could in fact approach the theoretical maximum, it would require only the tiniest increase in force to cause a (probably fatal) wheelie. That's what I meant by saying it was easier to wheelie the higher the velocity. I had a motorcycle back in the late sixties that would wheelie more readily in third gear than in first. Now I know why. Above third gear it was running out of extra torque. But theoretically a bigger engine could have taken care of that.

An approximate formula for the acceleration needed to wheelie is g*b/h - F/m, where g = the acceleration of gravity, b = the horizontal distance from rear contact point to center of mass, h = height of center of mass, F = aerodynamic drag force, and m = total mass.
 
ohio

ohio

The Fresno Kid
Nov 26, 2001
6,649
24
SF, CA
Steve from JH said:
Motorcycles hit a drag limited top speed before they reach the theoretical maximum velocity because their engines are deliberately limited to avoid the situation. It would be incredibly dangerous. They easily could put powerful enough engines on the bikes to reach that point.
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Now you're just talking crazy. "Motorcycles are deliberately limited to avoid that situation"? No. They are functionally limited, because no one really wants to ride a motocycle with that much weight in the middle of it, and a road going moto with the power to go faster than ~160MPH is impractical and dangerous for a whole lot more reasons than it will flip backwards when you hit 180.

Steve from JH said:
If the bike could in fact approach the theoretical maximum, it would require only the tiniest increase in force to cause a (probably fatal) wheelie. That's what I meant by saying it was easier to wheelie the higher the velocity. I had a motorcycle back in the late sixties that would wheelie more readily in third gear than in first. Now I know why. Above third gear it was running out of extra torque. But theoretically a bigger engine could have taken care of that.
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We agree that wind resistance could cause you to wheelie. I'm still not sure what that has to do with bicycles. And I'm not sure where you're headed with this theoretical limit... it increases with a reduction in C, or a lowering of CoG, or an increase of downforce. What exactly are you trying to illustrate with it by heading this far into theory rather than practice?

Steve from JH said:
An approximate formula for the acceleration needed to wheelie is g*b/h - F/m, where g = the acceleration of gravity, b = the horizontal distance from rear contact point to center of mass, h = height of center of mass, F = aerodynamic drag force, and m = total mass.
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Sure, and as we all realize, aerodynamic drag force increases exponentially with speed, which is why it is almost completely negligible as a compressive moment on a bicycle especially as speed where you would be pedalling roughly and hindered by bobbing (climbing).
 
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skinny mike

Turbo Monkey
Jan 24, 2005
6,415
0
this thread should have been limited to 1000 words. :rolleyes: i still want to know how much its gonna cost! i would die of happiness if i could ep that thing.
 
T

thaflyinfatman

Turbo Monkey
Jul 20, 2002
1,577
0
Victoria
Steve from JH said:
Yes, you've got the cancellation thing down now. But the two ways of looking at it are still not the same as far as the actual physics is concerned. Two fairly large moments cancelling out is not the same as no moments. They can't both be right.
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Yes they can, and are. As I showed before with the example of the beam and pulley, you can take moments about or including anything as long as you're consistent (which is what I failed to realise before). So for that exact reason, they ARE the same thing, of that I'm quite sure. Moment equations are linear functions (if they are from point forces rather than distributed loads, which here they are) and so multiplying and dividing by a set ratio of radii (the wheel and the cog) does actually give you the same results. You could take moments about the top of the wheel if you were so inclined and the results would still line up. It does also make sense that you can make these calculations independently of pivot position (for a given instant, obviously) if you know the axle tangent, which brings me back to my very first point: axle tangent is still the dominating factor of suspension geometry (for a given gearing, chainline, chain tension etc).

And why oh why did air resistance get brought into this? Yes I can see what you mean now, but I've never ever seen air resistance get brought into bicycle suspension equilibrium equations - they just don't go fast enough for it to be a problem (and who complains about bobbing when they're heading down the odd part of a course that IS ~70km/h?).

Anyway I'm happy we got all this sorted. Cheers for a healthy discussion.
 
DHS

DHS

Friendly Neighborhood Pool Boy
Apr 23, 2002
5,094
0
Sand, CA
so who would win in a fight, Ohio, Steve, or thaflyingfatman?

sweet info, my head hurts, but sweet info.

any news on the honda pricing yet? (obeying the topic thread now sorry)
 
DHS

DHS

Friendly Neighborhood Pool Boy
Apr 23, 2002
5,094
0
Sand, CA
S.K.C. said:
...pricing will be somewhat more than ridiculous, but just shy of obscene...

...and that's in Euros.

:D
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but see i doubt that, i'm pretty sure honda knows and has looked into this market. so they should know whats up..
 
E.C.

E.C.

Monkey
Mar 14, 2004
271
0
South Central Pa.
I have nothing to ad other than to say, if they incorperate a VPP suspention into that design, I am not above kicking, scratching and hitting below the belt to get to the front of the line to buy one. :thumb:
 
T

tacobelldhr

Monkey
Jun 1, 2005
231
0
lake forest
E.C. said:
I have nothing to ad other than to say, if they incorperate a VPP suspention into that design, I am not above kicking, scratching and hitting below the belt to get to the front of the line to buy one. :thumb:
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.



ummmm...vpp crap os overated and still to this day does not work as good as most single pivots.... :stosh:
 
E.C.

E.C.

Monkey
Mar 14, 2004
271
0
South Central Pa.
Dude I'm not going to get into a debate with you about VPP vs single pivot. I own both I prefer VPP for racing . If you take the time to set it up right it does everything very well. Ride what YOU like.
 
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