Using the Front Brake - Do the math!!

This thread appeared on the SabMag list. Merlins explanation
of why you should use the rear brake is definately worth


 From: Honda Sabre and Magna Motorcycle Owners
 [mailto:SABMAG@MITVMA.MIT.EDU]On Behalf Of Phil Ross
 Sent: Tuesday, July 18, 2000 4:45 PM
 Subject: Re: Maggot sightings at WIMC; Mid-O races (long) (fwd)

 OK, question time. My feeling is that a stoppie really isn't maximum
 deceleration--or is it? Wouldn't a front brake at 3/4 lockup
 (vs impending
 lockup, which is going to put the tail in the air) together
 with the rear
 at impending lockup (thus larger contact patch) give you a quicker stop
 than a stoppie? But yet, if you can loft the tail of a VFR with linked
 brakes ... would ABS work any better? Hmmm.

 Phil Ross  pwr(a)  Columbus, OH
 AMA#637232   COP#0016  IBA SS1K, BBG, 50CC
 1985 VF1100S V65 Sabre, "The Couch Rocket"



 From: Honda Sabre and Magna Motorcycle Owners
 [mailto:SABMAG@MITVMA.MIT.EDU] On Behalf Of Marc W. Mauss
 Sent: Tuesday, July 18, 2000 4:49 PM
 Subject: Re: Maggot sightings at WIMC; Mid-O races (long) (fwd)

 The answer is: You're right.  I sent the following off-list the other day.
 It explains how and why you're right.  BTW, size and number of
 contact areas  have NOTHING to do with it.

 Let's assume that the total weight of bike and rider is 700 lbs.

 Let's assume an initial front/rear weight distribution of 50/50.

 Let's assume a coeficient of friction of 1.00 (just to make the numbers
 simple) and that both tires have the same coeficient of friction.

 In this situation, before applying brakes, each wheel has 350 lbs of
 downward pressure (50% of 700), and therefore (with c of f = 1) will
 maintain traction with up to 350 lbs of braking force.  Each  wheel will
 slip  on the road surface (lock up) if MORE THAN 350 lbs of brakeing
 force is applied.

 When you start braking, weight is transferred to the front wheel.
 You soon  reach the point of 60/40 weight distribution - 420 lbs on the
 front and 280 lbs on the rear.  At this point, (again with a C of F = 1)
 the front wheel  can sustain 420 lbs of braking force before locking up,
 while the rear can only handle 280 lbs of braking force.

 You then reach a point of 80/20 weight distribution, with the front whell
 bearing 560 lbs and the rear bearing only 140 lbs.  At this point, the rear
 wheel can only take 140 lbs of braking force before locking,  while the front
 wheel can take 580 lbs of braking force.

 By the time you reach a weight transfer of 100/0 (all the weight on the
 front wheel, as in a stopie), the rear wheel will lock with any braking at
 all, while the front can take 700 lbs of braking force before locking.

 At all times, the sum of rear wheel breaking and front wheel
 braking is 700  lbs (using the 700 lb weight and a C of F = 1),  but as
 more weight  transfers to the front, the front wheel gets more traction,
 while the rear  wheel gets less.

 If you're trying to stop in the shortest possible distance, you want that
 700 lbs of braking force applied until you stop.  When you start braking,
 the front can only provide 350 lbs, increasing to 700 by the time the rear
 wheel lifts.  But up until that point, you're "wasting" available braking
 traction by not using the rear brake.

 (formerly Marc W. Mauss)
 Honorary CSA Consul to Cyberspace
 MSF Instructor
 Coram (Long Island), NY

 '83 Sabre V45  "Just for Fun"
 '85 Shadow VT1100C - "Barney" (it's PURPLE) (hers)
 '86 Shadow VT1100C - (hers)
 '86 Shadow VT1100C  - "Little Wing"
 '84 Voyager 1300 - not yet running

 Cordura IS a fashion statement.