Peter <
[email protected]> wrote in message news:<
[email protected]>...
> Nate Nagel wrote:
> > Frank Krygowski wrote:
> >
> >> Brent P wrote:
> >>
> >>> In article <[email protected]>, Frank Krygowski wrote:
> >>>
> >>>> Brent P wrote:
> >>>>
> >>>>
> >>>>> I would suggest Frank ride his bicycle through a decreasing radius
> >>>>> turn that wasn't visable until he was in it such that it forced him
> >>>>> to brake hard. This would probably be the best lesson as to why
> >>>>> this sort of design should be avoided. Braking while turning is as
> >>>>> ill-advised on a bicycle as it is driving. Probably more so.
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> Almost every time I make a turn on the bike, it's done with a
> >>>> decreasing radius, and with braking while in the turn! This is
> >>>> normal for a bicycle!
> >>>
> >>>
> >>>
> >>>
> >>>> Sheesh. Newbies!
> >>>
> >>>
> >>>
> >>>
> >>> Not braking by coasting frank. braking with the brakes. Coasting is
> >>> normal on the road, not squeezing the hand brakes.
> >>
> >>
> >>
> >> Yes, braking with the brakes, Brent. While in a curve. Every day.
> >> It's quite normal.
> >>
> >>
> >
> > google for "friction circle" to see why that's a bad idea (yes, on a
> > bike too.)
>
> It's only a bad idea if you enter the turn at a speed where *all* of
> the available traction is used for cornering, i.e. too fast. But since
> many turns are entered before the driver can completely see the
> turning radius throughout the turn he should always leave sufficient
> margin so there is still traction available for braking in addition to
> cornering. Fortunately the mathematics of perpendicular vector addition
> help us out here. The equation of a circle is x^2 + y^2 = r^2 where we
> can use 'x' for the traction available for braking and 'y' for the
> traction available for cornering, and 'r', the resultant is the total
> available traction. Let's assume the total traction is 1. Then
> entering the turn so fast that cornering alone requires a traction of
> 1.0 would leave nothing available for braking. But entering even a
> little slower, say where cornering only requires a traction of 0.9 now
> allows us to use some braking up to a traction of sqrt(1-.9^2) = 0.44
>
I'm not going to check your math, but it sounds about right,
neglecting the fact that a typical friction circle for a car is more
of a friction oval-esque kind of thing (and generally can't be found
under acceleration, unless you have ridiculous amounts of power.)
However, on principle, I try to do all my braking before a corner at
least on the street as, what happens if I enter a corner at what I
think is 6/10 and it turns out to be 10/10 and I suddenly find that I
can't brake? (the exact situation Frank's been chastising me about
and claiming I'm unskilled for finding myself in.) What would have
happened had I followed Frank's recommendation to "slow down" once I
discovered the curve was tighter than I thought? What would have
happened if I'd entered the initial part of the curve "hot," planning
on trail braking to the apex?
Alternately, if I'm planning on trail braking into a corner, that
might leave me closer to the circle than I want to be on the street,
even if it's not a 10/10 corner...
I guess my point is that you are correct there is a time and place for
trail braking but generally I don't really see much need for it on the
street. I generally try to corner under very light power so I'm
holding a constant speed and have as big a cushion between my actual
state and the limits of the friction circle as possible at any given
time and speed. (obviously depending on the corner that might be
difficult on a bike unless you have short cranks, but you get the
idea)
nate