if you wanted maximum braking, where would you sit?

[Zilfondel]

if you could position your center of gravity anywhere, to ensure maximum braking power, where would it be?

obviously over the front wheel is no good, you would flip.

there is a point, leaning either ahead of the front wheel, or behind the back wheel, that the opposite wheel is off the ground.

clearly those are 2 limits, the answer must lie between them.

if there were very little friction, it would hardly matter.

assume a level road, brakes that can cause a skid no matter what.

ok, so where do you sit?

state assumptions, like coefficient of friction between tire and road, weight of bike and rider.

show your work.

now for extra credit, make it a function of road slope.

[iluvphish]

No disagreements here. Sheesh, one guy accidentally gives more information than was required, and everybody jumps to conclusions about it's implications...

[iluvphish]

Nevermind; I just looked at the picture, and it was the ONLY steering.

Okay...Wow! Cool...integrated steering.

Okay, on a second look, I think I see spindles and control arms. Do you steer with the brakes, with the front wheels, or with the rear wheel? What control do you operate to steer? Do you steer with the handlebars, which then aim the front wheels through control arms?

[iluvphish]

That is so cool, it makes me want to go and build one right now.
Unfortunately, there are any number of limiting factors, such as my lack of equipment, supplies, knowledge, ability, money, and time.
I've got the enthusiasm, although with my short attention span I don't know if it would last long enough to finish the project.
http://www.ihpva.org/com/PracticalInnovations/weld.html under the section titled "Trike steering geometry", sub-title
"Ackerman steering compensation", steering is treated as if there was a live axle with no differential for the front wheels. I think such trikes are nearly all rear wheel drive, leaving no need for a live axle; why would there be front wheel scrubbing?

Does your trike use Ackerman steering compensation?

[Vexed]

Not much, it is relevant to the braking issues that this thread is about.

“All other things being equal: a skilled driver can stop a car faster without ABS than with its "assistance". No!

No driver can make the 50+ pedal corrections per second (and that was using the actuator technology in use 14 years ago when I wrote abs software as an engineer at General Motors). In 1993, Roger Penske made a public rebuttal against competitor accusations his Indy cars were using abs to pick up an unfair advantage.

Plus the abs system has the ability to correct each wheel slip independently through varying coefficients of friction and even split coefficient of friction surfaces (tires on differing surfaces) found in contact with the tires.

Only on surfaces in which a locked wheel forward packs the surface (snow, sand, loose gravel) in front of the tire can a non abs vehicle be brought to a stop as quickly or quicker as an abs equipped vehicle. On water or ice the abs stopping advantage gets overwhelming. In all cases, the steering control issue favors abs.

The major motors sports organization have long recognized the technological superiority of abs even with the most skilled of drivers, and most have barred this competitive tool either on expense grounds or due to taking a driver skill element out of competition.

”Also at issue in the 'vette vs. Fiero braking match: I don't know the numbers, but I'd bet the poor little Pontiac is quite a bit lighter than the 'vette.”

The Fierro was about half the weight, but also much narrower tires.

”A final random tid-bit: 50/50 front-to-rear weight balance can be achieved in a front engine car by putting the gearbox/transaxle in the rear. Examples: C5 and C6 Corvette and Porsche 924, 944, 928, and 968. “

Surprises me that those cars have a 50/50 balance since the engine is still much bigger than the gearbox & transaxle, but I’ll accept your report. That makes a nice handling collection of vehicles with sophisticated suspension and low cg become a nicer handling vehicles.
The rearward weight movement helps under braking with further braking optimization at the expense of handling achieveable if more rearward weight bias were also achieved!

[~radioactive sheep~]

I think the issue here is tyres with poor traction, not brake design at all. With proper road tyres you will have greater braking available.

[lileddie]

One reason that MTB's are more likely to lock the front wheel during a sudden stop is the fact that most MTB's have front suspension. If you jam on the front brake before the forward weight shift has made it's way through the springs and into the contact patch, available traction will be reduced.
Bikes with strong damping will be less effected by this.

[Vexed]

All numbers lbs or inches or G’s

26"cruiser wheelbase 46 rider wt 180 bike wt 30 bike cg ht 15 bike cg trl 28 decel 0.6 seat ht 42 rider cg over seat rider cg over seat 8 cg after seat 0 optimal seat positon behind lead patch: 53.66667 wheelbase
46 rider wt 180 bike wt 30 bike cg ht 15 bike cg trl 28 decel 0.6 seat ht 40 rider cg over seat rider cg over seat 8 cg after seat 0 optimal seat positon behind lead patch: 52.46667

CARBON prone wheelbase 38 rider wt 180 bike wt 20 bike cg ht 16 bike cg trl 25 decel 0.6 seat ht 30 rider cg over seat rider cg over seat 3 cg after seat -8 optimal seat positon behind lead patch: 47.2

roadbike wheelbase 48 rider wt 180 bike wt 20 bike cg ht 16 bike cg trl
30 decel 0.6 seat ht 42 rider cg over seat rider cg over seat 5 cg after seat -5 optimal seat positon behind lead patch: 57.6

recumbent mwb/clwb wheelbase 54 rider wt 230 bike wt 35 bike cg ht 24 bike cg trl 40 decel 0.6 seat ht 24 rider cg over seat rider cg over seat 6 cg after seat 3 optimal seat positon behind lead patch: 42.21304 wheelbase 54 rider wt 180 bike wt 35 bike cg ht 24 bike cg trl 40 decel
0.6 seat ht 24 rider cg over seat rider cg over seat 6 cg after seat 3 optimal seat positon behind lead patch: 42.27222

skycycle wheelbase 38 rider wt 180 bike wt 50 bike cg ht 25 bike cg trl
21 decel 0.4 seat ht 80 rider cg over seat rider cg over seat 8 cg after seat 0 optimal seat positon behind lead patch: 56.42222 wheelbase 38 rider wt 180 bike wt 50 bike cg ht 25 bike cg trl 21 decel 0.6 seat ht
80 rider cg over seat rider cg over seat 8 cg after seat 0 optimal seat positon behind lead patch: 75.41111

lowracer wheelbase 48 rider wt 180 bike wt 25 bike cg ht 18 bike cg trl
32 decel 0.6 seat ht 12 rider cg over seat rider cg over seat 5 cg after seat 4 optimal seat positon behind lead patch: 30.58889 wheelbase 48 rider wt 180 bike wt 25 bike cg ht 18 bike cg trl 32 decel 0.7 seat ht 9 rider cg over seat rider cg over seat 5 cg after seat 4 optimal seat positon behind lead patch: 30.43889

Unicycle wheelbase 0 rider wt 180 bike wt 30 bike cg ht 20 bike cg trl 0 decel 0.5 seat ht 34 rider cg over seat rider cg over seat 8 cg after seat 0 optimal seat positon behind lead patch: 22.66667 wheelbase 0 rider wt 180 bike wt 30 bike cg ht 20 bike cg trl 0 decel 0.4 seat ht 34 rider cg over seat rider cg over seat 8 cg after seat 0 optimal seat positon behind lead patch: 18.13333

LWB recumbent wheelbase 63 rider wt 180 bike wt 40 bike cg ht 19 bike cg trl 47 decel 0.6 seat ht 18 rider cg over seat rider cg over seat 6 cg after seat 3 optimal seat positon behind lead patch: 41.98889

You might be able to put drag motorcycle anti-wheelie bars behind the skycycle to go with the obvious rider weight well back of the wheelbase on this .6 G decell skycycle to keep it from going over before decel!

This is a repost of a 1/10/04 post I made to this thread that appears to have been lost on some servers, possibly a result of a variable name triggering a spam filter. I have substituted another name for that variable so if that was the issue, we are now unfilterred.

Rick O., this is the immediate preceding derivation I referred to responding to one of your posts that may have been invisible to you in which I reitterated an earlier tire load balancing desire.

[thersupermikey]

I can't imagine sitting when braking as hard as I can. I'd be afraid of endo-ing.

It's more like crouching with my butt somewhere between the back of the saddle and the rear axle.

[~radioactive sheep~]

Evidently maximum braking power is a function of the angle described between the ground and a line drawn through the contact patch and the CoG.
Hence for a given angle the CoG may move freely along that line without influencing the braking power. Therefore to maximise braking power I would position the CoG at the bottom bracket, assuming we are constrained to having it within the bike-rider structure; otherwise, at ground level below the BB or thereabouts (to have an even load on each wheel when not braking or accellerating).

It is extremely unlikely that front brake will cause a skid no matter what. If tyre traction is that poor then that is evidently the limiting factor on braking, and the CoG may roam freely.