Caster angle

[Corvus]

Is the caster angle referenced from vertical or horizontal?

Is the caster angle always the same as the rake angle?

[Blackal]

From vertical, as far as I am aware.

Al

(what's "castor" ? )

[Bikerhoss]

I've edited my original post because I found this link and pictures sometimes make these things a lot easier to explain:

http://books.google.co.uk/books?id=84hF ... 3F&f=false

So yes, measured from vertical and no, they are different

[Corvus]

In the context of motorcycle geometry and with respect to the tyres, what is the relevance of the radius of torus?

I wonder. In a quiet moment!

[Corvus]

I've edited my original post because I found this link and pictures sometimes make these things a lot easier to explain:

http://books.google.co.uk/books?id=84hF ... 3F&f=false

So yes, measured from vertical and no, they are different

Thanks for that very interesting snippet.

Yes, we look at a conventional motorcycle and assume that rake angle and caster angle are the same thing. They are on a conventional motorcycle, but not by definition, as I understand it.

It does seem though, that sometimes the caster angle and/or rake angle is referenced from the horizontal, although this seems not to be the "convention".

[Corvus]

In the context of motorcycle geometry and with respect to the tyres, what is the relevance of the radius of torus?

I wonder. In a quiet moment!

http://books.google.co.uk/books?id=rJTQ ... us&f=false

I get a better idea now. Doesn't the radius of torus depend on perfect circles? If it does, then how do we allow for the fact that tyres aren't perfect circles?

I wonder!

[Bikerhoss]

Jeez that's getting deep Corvus

Anyhoo, I reckon centrifugal forces and the tendancy for a tyre to flex make up for the changing torus measurement, plus no matter what angle of lean you have, will the tyre not be rotating on the same 'circle' of rubber until you change direction or lean angle that is, I suppose that's how the stunt folk manage hands free circling etc

Let's face it, a bike is (supposedly) at it's most stable when it's going in a straight line at a steady speed with the engine just pulling enough to overcome friction, Everything else is just luck and adhesion

[The Teutonic Tangerine]

Caster is a type of Sugar. Castor is measured from vertical. - I'll get me coat

[Corvus]

Jeez that's getting deep Corvus

Anyhoo, I reckon centrifugal forces and the tendancy for a tyre to flex make up for the changing torus measurement, plus no matter what angle of lean you have, will the tyre not be rotating on the same 'circle' of rubber until you change direction or lean angle that is, I suppose that's how the stunt folk manage hands free circling etc

Let's face it, a bike is (supposedly) at it's most stable when it's going in a straight line at a steady speed with the engine just pulling enough to overcome friction, Everything else is just luck and adhesion

Yes it is a bit deep. Sorry!

The only reason I asked about the radius of torus is that I noticed it on a cossalter diagram while I was looking for info on caster angle. That got me wondering why he put it on the diagram in the first place. The extract from his book is quite extensive and I'll definitely have to go over it a few times! But I think I understand a bit more about the theory. As you say though, theory and practice are two different things. Surely a tyre is nothing like a perfect arc in practice. Not when the bike is doing its thang.

I notice a lot of his diagrams show the tyre in section as a perfect circle. Maybe he modifies that "basic" concept a bit further in the book. Anyhow, thinking of it like that helps get your head around a few things at least.

[Corvus]

Caster is a type of Sugar. Castor is measured from vertical. - I'll get me coat

You'll be telling me next there's no such thing as aloominum.

The reason I asked in the first place was that I've understood it to be referenced from the vertical. But someone on another forum asked why his bike model had been altered from 26 degrees to 64 degrees caster angle and that the alteration seemed extreme. I'll say!

I suggested that, as the two figures added together equal 90 degrees, it suggests that they're both saying the same thing, but one from vertical and one from horizontal.

I scouted around on tinternet and found that castor can be caster and it can be referenced from the horizontal, depending on convention.

[SP250]

Me - I gave up trying to understand all the maths and Greek geometry when I realised I could make double the salary as a salesman after years qualifying as an engineer.
So now I just ride the buggers and enjoy them once they have been set up properly.