Re: Extensive article on Rivendell and Grant Petersen

On 9/25/2024 5:39 AM, Catrike Ryder wrote:

 
A few weeks ago, after posting about braking, I tested the Catrike's
brakes at 15 MPH. I stopped at about 6 feet, keeping the chain rings
off the ground.

>
No you didn't, unless your "about 6 feet" has a tolerance of something
like 50%.
>
For the engineers in the crowd: It's a simple constant (negative)
acceleration problem. Acceleration (or deceleration) is given by V^2/2X
where V is initial speed, X is stopping distance. 15 mph = 22 ft/s
>
(22 ft/s)^2/(2*6ft)= 40.33 ft/s^2 deceleration. That's 1.25 times the
acceleration of gravity. For that, you'd need tires with a coefficient
of friction of at least 1.25, which would be very, very unusual. (0.9 is
a typical upper limit.) But more important, you'd need to _immediately_
apply the brakes to the very limit of traction with no skidding; and
you'd need no weight on the unbraked rear wheel, so all the decelerating
mass was contributing to braking traction. You'd also need exactly the
same amount of braking on each front wheel so as to prevent a spin,
given that the rear wheel would have to be raised.
>
Oh, and whether or not the rear wheel would raise to put all the weight
into front wheel traction depends on the geometry of the bike+rider. The
elevation angle of the total center of mass would have to be precisely
right, not too high nor too low.
>
All this is based on the physics of the real world. Those living in
other universes should post their math, or their videos.