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Mechanical and Technical Mechanical and technical topics, help, and discussions

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Sep 25th 2018, 06:40 PM   #1
 Sentinel's Avatar
 
  Jun 2016
  Poor Tortured

  2015 Kawasaki Concours 14 - The Origame Sea-Dragon
Is there an equation for brake?

I was thinking it is possible to put too much braking on a bike. A light weight bike with heavyweight brakes might be prone to unintentional stoppies or locking up the front wheel: both bad.

so it occurs to me that braking capacity (max design deceleration rate) would be a programmed value: it can be whatever they want it to be.

and so, when we gripe about entry-level bikes having "crappy" brakes, we probably mean two things:

1) cheap to produce
2) beginner-level deceleration rate

1) is intuitive and i think not even argued by the OEM's.

2) just never comes up in these terms, IIRC.

So, does anyone know the real story of whether and how they design deceleration rates (braking "power")?

Is there an equation other than the Newtonian F=ma kinda stuff?

note: I've read this: https://en.wikipedia.org/wiki/Braking_distance

curious about bikes (and if-applicable, to cars).

peace!

What we think is gonna happen:


What usually happens:

Edited by Sentinel on Sep 25th 2018 at 06:42 PM
Sep 25th 2018, 10:17 PM   #2
 
  Apr 2016
  Spokane Valley

I don't have an answer to your question but I do agree with your theory about a "programmed deceleration rate". However I don't think there's much math behind it as opposed to just trial and error testing. Put a test rider on it and have them hammer the brakes, observe and maybe check a sensor, then adjust from there.

I also think when people complain about braking power on entry level bikes, it's never an objectionable view. They are used to much better brakes so something with less feels "crappy". Look who usually complains, journalists who are riding everything you can imagine from the hyosung to the bmw hp4, veteran riders who just picked up said entry level bike to commute with and the other motorcycles they own are of a much higher build quality. You don't hear that complaint from new riders because you only know what you've tried so far, right?

As far as stock components go I got to test out mine today on my ride home when some inconsiderate puke pulled across the street in front of me. I had to grab a handful and those stock 14 year old rubber lines coupled with ebc hhs and fresh fluid changed before my last track day did my very best to imitate picture one. It skyed the rear, bottomed out my forks as evidenced by my zip tie flush with the bottom of the triple tree but I didn't end up like pic 2 thankfully.

Mostly stock components seem to be okay to me, lol
Sep 25th 2018, 10:22 PM   #3
 Motorbiker's Avatar
 
  Jan 2016
  Silverdale, WA

  1987 FZR 1000
Ask the guys who program ABS. They probably have a clue. I'm thinking tires, road surface, and temperature play a large part.
Sep 25th 2018, 11:16 PM   #4
 liberpolly's Avatar
 
  Jan 2016
  Seattle

  Ducati Diavel, Aprilia Scarabeo
I guess it is possible to put too much braking on a cheap bike, but it's fairly expensive so nobody is doing it?
Sep 26th 2018, 12:21 AM   #5
 Pavement Tested's Avatar
 
  Jan 2016
  Bremerton

  '08 GSX1300R, '06 GSX-R 750, '17 KTM 690 Duke
Are you asking: Is there engineering that goes into putting brakes on cheap bike or if they just throw something on it?


I am no expert and will never claim to be but, there is undoubtedly a large amount of mathing that goes into every braking system no matter how cheap the bike is. There is certainly a braking threshold dictated by some oversight and regulating body that dictates stopping distance safety and places a requirement for system performance on manufacturers. Basic, entry level, cheap, the bike doesn't matter. The system has to be engineered to stop the bike within a maximum distance based off it's characteristics (i.e. weight, speed capability, etc). Rotor size, caliper piston size & quantity, master cylinder size and efficacity all go into it. You don't need a 6 piston monoblock Brembo on a CBR250R when a 4 piston Nissin will do.

Shit bikes have shit brakes because that's all they need per the regulatory body so why put a superbike system on a Ninja 250 when it doesn't need it? Save for high end manufacturers, swapping to braided brake lines and HH pads is a well know remedy for solving rider opinionated poor braking performance.

Brake pads are also directly related to stopping power. The vast majority of riders want a long lasting, low dust pad and seldom know the difference in pad compounds. Those who go fast and need to decelerate more quickly than the average bear place a higher value on stopping than avoiding maintenance. It's the vast majority the manufacturers cater to since it more economical for them.

Also, shit brakes on entry bike is probably a way to prevent newbies from killing themselves when they panic brake in a parking lot. Of curse, in this day and age of electronics doing everything for the rider, it doesn't much matter anymore. Soon they'll have those fancy gyros on all bike so a foot on the ground won't be needed at a stop light.

Edited by Pavement Tested on Sep 26th 2018 at 12:26 AM
Sep 26th 2018, 11:49 AM   #6
 Brassneck's Avatar
 
  Apr 2016
  Seattle, WA

  '79 XS650; '01 FZ1
There is a science to braking. This is not arbitrary nor a trial and error process. Furthermore, there are various components that impact a quality braking system...and every bike at some point in it's creation was held to a specific standard to meet regulations of that time period. Those standards do change, of course, but the principle is the same. Nevertheless, there are bikes that have great braking systems, and some that are not as great...yet both meet the standard.

I would argue, many entry level or base models have a braking system that is of a more universal fit, rather than a custom, purpose built application. Thereby meeting the "standard" but not necessarily being all that great for that particular bike. I don't believe there is any reason other than it's cheaper to put a universal part (that meets the standard) across various low-end production bikes vs. custom building each brake to the bike's needs.

Case in point, I have an older yamaha that came with a stock braking system that was essentially used on many models across their line of bikes. Some of those bikes had dual caliper brakes and some single, yet they used the same master cylinder. Those with dual caliper brakes worked fantastic with this set up, the singles however weren't so great. Simply swapping the master cylinder to a smaller bored piston made the brakes come to life on a single calipered bike. Adding SS braided lines, etc. help as well.

Thus my opinion is that it comes down to cost and what's already available/in production that currently meets the standard...that is what gets put on low-end/entry level bikes.
Sep 26th 2018, 08:48 PM   #7
 DocB's Avatar
 
  Feb 2016
  Poulsbo, WA

  Aprilia RSV Mille, CB77 (AMA Nat'l landspeed record holder), CB750K, CB750F
I guess everyone's Google is broken.

https://deepblue.lib.umich.edu/bitst...pdf;sequence=2
Sep 27th 2018, 06:27 PM   #8
 Sentinel's Avatar
 
  Jun 2016
  Poor Tortured

  2015 Kawasaki Concours 14 - The Origame Sea-Dragon
Quote:
Originally Posted by DocB
I guess everyone's Google is broken.

https://deepblue.lib.umich.edu/bitst...pdf;sequence=2
Um, no. We're doing it old-style, and having a conversation based on people's education and experience and willingness to share. And we get to be witty and bitchy at the same time, with no meaningful feedback because internet.

so, win win.
Sep 27th 2018, 07:59 PM   #9
 DocB's Avatar
 
  Feb 2016
  Poulsbo, WA

  Aprilia RSV Mille, CB77 (AMA Nat'l landspeed record holder), CB750K, CB750F
Very good, thanks for the clarification. I'll keep that messy science stuff to myself.
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Sep 27th 2018, 08:53 PM   #10
 Bald Guy's Avatar
 
  Jan 2016
  Kennewick

  KTM SAR Husqvarna Strada, Ural Patrol and a shit load of BN125
I looked and looked at the FMVSS for motorcycle braking. Holy Shit, what a bureaucratic cluster fuck of craptastic gobbledygook! I looked at the RCW for motorcycle braking standards the state requires and found that the same standard that applies to cars, applies to motorcycles. The legal requirement is that at 30 MPH or below a motorcycle must decelerate at a rate of 17fps. Above 30 they must stop at 14 fps. You could damn near use your feet to Fred Flintstone that bitch to a stop.

Manufacturers put materials on a bike the fit their profile of potential customers and still make a profit at a certain price point.

Most bikes can come close to the Holy Grail of a 1 g stop. Most riders cannot. Even the cheapest braking systems can out perform an average rider.

The difference is repeatability. A Star 250 can pull a stop in excess of 1 g. Once. The brake fade kicks in and stops get worse and worse. Most riders can stop at a .7 to .8 g. The cheap brakes on a Star 250 are better than the average rider, hence are completely adequate for their purpose.

The difference between expensive and cheap brakes it that expensive brakes can repeat their best stops again and again with consistency.

So, manufactures can put cheaper components on certain bikes with the knowledge that the less expensive materials will perform well enough to meet the expectations of a majority of riders who purchase those machines.

That is my 3 beer opinion.

Dusty
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