Safe Speed Forums

I don't understand! I thought all vehicles did that!?



Huh? There won't be any significant downforce on a roadgoing Ferrari at the speeds we were talking about (60). In any case, my money would be on it being a LOT heavier than a Panda!



This is something that's been kicked about in this thread a few times. Do you have any figures by any chance? I stand to be corrected on this but I still get the feeling that (comparing like with like, i.e. superbike vs. supercar), the car would stop a bit better.

I think you are drifting around here a little mole, if you really want to analize stuff why not bring in the age of the brake fluid, the temp at the time,the eficiency of each individual brake caliper piston,.. you can end up going so deep into subjects that the simple answer is overlooked. I gave a comment which was clear, I followed it with a statement later. In equal conditions a modern bike in competent hands can stop quicker than most cars including SOME sports models. Do I have to give you disc measurements along with performance of brake calipers. The simple way to look at it I have already indicated....average bike 200kilos average car 1.5 to 2 tons Bike tyres by design create more frictional grip than car tyres which is why they wear out much quicker. The effect of weight transfer from rear to front during braking is the same mathmatics for both car and bike and if you did the math you shouldnt be asking these loaded questions to support what seems to be your own agenda.Your theory so far it seems would suggest a 40 ton artic can also stop just as quick as car or bike after all they have bigger brakes and more of them with even greater aplication of pressure on those brakes, yet if it were unladen without load sensors it would skid in all circumstances unable to use its max brake capability so technology intervenes preventing its over use whereas on most bikes there is no abs for example interfering and max effort can be applied with skilled hands. There is a place for science but its actually other people who test the theories. As for figures mole, you seem to have too many to play with and I cannot be bothered to play science lab tutor when there are simple proven answers out there, like actual comparative tests in real world ,not on a piece of paper following some theory that only works on poorly designed models that dont take on board all factors even when they think they have in a classroom, science is no different to statistics, the conclusion is only as good as the info and detail put in which is why Newton and Einstein ahve been found wrong or inaccurate by following scientific theory. Had enough with this one now, didnt know this site was 'open university' I thought it was to do with safety forums. silly me.

The type and size of the brakes are irrelavent - I can easily lock the back wheel of my 500 and that's only got a drum brake on the back. I SUSPECT I could easily lock the front (single side twin-pot) too, but I'm not stupid enough to try.

Likewise I can easily get the ABS running on the car.

A modern artic with ABS on the trailer will out-brake any car empty and braking when laden is limited by load security as much as anything else.

The major difference being that cars can brake hard whilst cornering.

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Science won over religion when they started installing lightning rods on churches.

In my quest to find something concrete on this subject I found something else interesting.

Not sure if this shouldn't be a separate thread, (soz), but I wonder if others think the same as me?

I know I woffle. When I was born and the midwife smacked my bum I said "Hey! Do you mind? In years to come that'll be child abuse and anyway what gives you the right to......"

http://www.stoppingdistances.org.uk/sim ... ances.html


Edit. I think it should mods. I have got sooo much to say on this...

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

If you put a wooden block operated by a stick onto brake discs then the size and type of brake would certainly matter, perhaps you should tell Mercedes who have developed some of the biggest discs and most powerful calipers in motoring history that size and type doesnt matter, but you are talking about rear brakes locking, if you are locking them then that is down to you,put pillion and luggage on the back and the use of rear brake for effective stopping becomes more relevent in conjunction with the front brake. .
You have answered my point about technology intervention with your second point, but overlooked reality, the artic still weighs about 12 to 14 ton and as Ive driven them up until the last 4 yrs for about 29 yrs I think you are being optimistic, comparable maybe,but out brake ANY CAR very optimistic
Cars can brake hard cornering?......Well in the first instance they shouldnt be braking in a corner anyway, its a sign of poor driving, secondly if called upon I can brake hard in a corner in artic or on a bike and have done so enough times in the past but I run the risk as does any car driver of upsetting the veh in question and interfering with the frictional charactoristics of the brake effect through the tyres depending on the surface and angle of the road, its where skill comes into brake use rather than technology(after all,uncle tom cobly and all have ABS and just look at crash figures many of which resulted from over acceleration or braking on corners).If you think cars are the only veh that can brake hard when cornering you would be wrong.

Shall I put this into simple terms for you Herbie?

At the point the wheel locks you have reached the limit of the retarding force that can be applied through that wheel. All a bigger and more powerful brake does is allows you to achieve this peak force more easily at higher speed and for longer without cooking the friction material / brake fluid. Once you have a brake powerful to lock the wheel, the imrovements in braking technology simply serve to improve life and reliability.

A bike has less rubber in contact with the road. Full stop. Even if you increase the coefficient of friction between the road and the wheel by having stickier tyres, if you have a smaller contact area then you will be able to put less force down. The mass of the vehicle is largely unimportant, as the friction, momentum and kinetic energy are all directly proportional to it and therefore cancel each other out.

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Science won over religion when they started installing lightning rods on churches.

Sixy, if I have understood you correctly, I'd have to disagree. A good brake can do a lot more than lock the wheel. If that's all they had to do, we'd still be on drums now! They need to turn the vehicle's kinetic energy into heat and then get rid of the heat as quickly as possible. A locked brake stops doing that (and starts trying to make the tyre's contact patch do it instead). The best brakes (in terms of stopping power) are the ones that can keep the tyre almost on the point of locking up whilst lobbing heat out to the atmosphere as quickly as possible.


Herbie. I'll trouble you no further on this one. There's no "hidden agenda" - I'm simply disagreeing with some of what you say and giving my reasons. I wasn't after calculations (although I'd welcome them) - the real life examples you cite would have been just fine. I'm always keen to improve my knowledge, but it looks like there's no immediate danger of that happening through your posts thus far!

When the wheel locks the braking gets worse, as in the bike/car takes longer to slow down.
The tread deformation during heavier braking means that there is more rubber in contact with the road than in light[er] braking.
Fortunately, my bikes abs takes care of the more mundane problems in stopping fast, like wheel locking and front/rear balance. The servo means I don't have to ruin my right hands muscles either.

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The world runs on oil, period. No other substance can compete when it comes to energy density, flexibility, ease of handling, ease of transportation. If oil didn’t exist we would have to invent it.”

56 years after it was decided it was needed, the Bedford Bypass is nearing completion. The last single carriageway length of it.We have the most photogenic mayor though, always being photographed doing nothing

I agree with whoever said something like never mind the maths, where's the tests? After all, if you shunt someone you can't say "Well that shouldn't have happened in theory". So, assuming we are not in a race suffering from brake fade etc.

For cars @ 30mph ~ 14m

It depends on loading but for bikes @ 30mph ~ 11m to 15 m

References..

http://www.msf-usa.org/imsc/proceedings ... stance.pdf

http://www.britain.tv/motoring_carstopdistance.shtml

http://www.initium.demon.co.uk/converts/metimp.htm


I expect it depends on which car and motorbike but it would appear there are more variables with the motorbike. There are probably cars which will be less than 9 meters and I, for one, wouldn't like to try and out-brake any car in the wet on my motorbike.

_________________
The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

Mole. You have misunderstood me I think. The point I was trying to make is that the size and power of the brake doesn't matter so long as it is CAPABLE of locking the wheel (and maintaining the 'almost locked' state for long enough to stop the vehicle), and the limit to the amount of retardation you can apply has more to do with traction than the size of the brake.

Putting a mahoosive great brake on a wheel made of polished steel isn't going to stop you as fast as a piddly little brake attached to a wheel (of the same weight and diameter ) made of sticky rubber.

Of course braking gets worse when the wheel is locked because the amount of kinetic energy disipated is much lower.

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Science won over religion when they started installing lightning rods on churches.

Locking the wheel is failure to brake efficiently. when you lock the wheel the veh concerned actually speeds up momentarily as the recoil force is released when the friction of tyres is interrupted. Im talking about vehicle brakes being used by a competent driver/rider ( should I type that down YET AGAIN?) People who delve into science when they really dont fully understand the science anyway are the kind of people who wont listen and will rely on science and technology to stop them rather than a skill in conjunction with an understanding of what the brakes and veh are doing when braking. ive never read so much B***ox on a subject than this. The friction itself can increase during braking process yet I havent seen the fragmented science users on here mentioning how that works, Nor the fact that the greater controlled braking effort increases the front tyre surface area as more weight is transfered to the front compressing the tyre, being softer tyres on bikes gives greater proportion increase. I made a simple comment earlier that modern sports bike can stop quicker than most cars including some sports cars, I gave simple reasoning but unfortunately Ive stumbled into a site full of experts !

Herbie, You said:






The trouble is your "simple reasoning" is wrong. As long as the brakes are big enough the weight of the vehicle and size of the discs are irrelevant. Many of the posters who have replied to you are engineers and are fully aware of the many factors that can affect stopping distances. We also know that there will always be differences between different vehicles for many reasons (even two supposedly identical vehicles will be different). The simple fact is that in real conditions on a real road with varying surface quality, water, oil, white lines etc. the stopping distances of bike and cars are not significantly different. What happens under test conditions gets swamped by other factors on public roads. Modern bikes and cars can decelerate from 60 to 0 in around three seconds on a dry road(around 2.5 seconds under perfect conditions) so with a safe gap of two seconds between vehicles there should be plenty of space for both to stop without colliding, no matter which vehicle is in front. Bigger brakes just allow you to do it more often before they fade.

Oh I just love the 'Look at me' crowd, engineers wouldnt listen to experience and understanding when they built the Humber bridge which is why it took yrs longer than expected. But I will indulge you, if they are engineers why then are they using fragmented science and contradicting each other in the process?The BRAKING CAPABILITY IN QUESTION RELATES TO EQUAL CONDITIONS AND THE HANDS OF SOMEONE CAPABLE TO USE BRAKES EFFICIENTLY and in that respect the rest is irrelevant to the clear point I was making, It doesnt take much for 'The Boffins' to see their own agenda in a piece that has nothing to do with a point being made. Listen I will give you all a gold medal and brownie points for having a certificate above the mantlepiece but having read what has been stated by your engineers I am very disappointed as there is liitle or no clarity nor very much scientific accuracy, in fact what has been written so far could be accomplished by a school kid in their final year, I unlike many of you I suspect have actually carried out practical tests on this subject and because they are limited to buget and availability I wouldnt presume to use them in a detailed fashion. I was ONLY taking about the Modern sports bike against the Majority of cars ( there are a lot you know) and including SOME sports cars. I admit losing grip on the subject having been dragged off at a tangent by the science class. Do you want me to simplify on the Bike stops quicker than car argument, I will....Take the same test surface, take a modern sports bike, take average car, take them down the road at say 80mph and stop as quickly as you can under control. Up to 2 ton of Car brakes generating huge ammount of friction heat which heats disc/pads/wheel/brake fluid in pipes and tyres reducing rapidly the efficiency of the brakes.Bike does same,brakes open to air cool quicker, because of large disc and brake pads can sustain max friction for longer, friction is less due to less weight to stop. Now would you like the geometry/physics and scientific data to go with that or would you settle for a bag of chips. I am certain this will get a reply but I wont be reading it.I have noticed the gramer graduates in here along with the pompus arrogance of some who like to think themselves superior and it doesnt impress. Ive been personally aquainted with engineers in my life and associated with one for many years and my experience is they spend a lot of time dealing in trial and error and stumbling on solutions often being directed to it by others or by accident, they also spend a lot of time going back to projects to correct their own errors or moving the goal posts to fit a criteria, do I have faith in engineers.....give them lots of time and resources then yes, give them problems to solve here and now then NO.Two things about all the engineers Ive met, 'arrogance' and no matter what topic...'over egging the pudding when its completely unnecessary'. This is supposed to be a safety theme site yet all I seem to read is clat! Most people who are prepared to visit a site like this are more likely to be interested in how best to stop a car or bike in any given circumstance than they are likely to want to know about the frictional charactoristics of the brake linings or tyres or if a fag paper will stop a free running steel wheel from rotating.I speak plainly, get out there and show me the average car can stop quicker than the average sports bike as this seems to be the contention, then all this b***ox in here can be shelved.I have taught all kinds of boffins including engineers and they all have something in common and that is their ability to come up with indepth questions/quotes and science but its all from books/papers or their work yet they have no better ability to apply their wealth of data knowledge to a practical application.If their knowledge ( which comes across as 'I know my stuff cos Im an engineer or scientist') is so good why then do they need me to help them pick the bike up when they clearly havent listened? if they can tell me exactly what all the forces are involved in riding a bike down to a detailed thesus or data paper why then are they usually the most difficult people to teach and to see results from? The next time you feel like trying to put someone down collectively or individually at least be clear and accurate yourselves and demostrate your ability to read what is there and not what your agenda radar sends you off on!

Those that can, do. Those that can't teach...

If you watched the Grand Prix on Sunday you will have seen some of the best drivers in the world, in the best cars with the best brakes, the best tyres and loads of downforce sliding off the road when they tried to stop in the wet. That's what happens in the real world - powerful brakes are still limited by road/tyre friction.

But its the racers themselves who are more instrumental in the brake improvements as with all the developments in racing, but here we go again off at a tangent, this has absolutely NO relevance to the point I am making, none at all. So a racer brakes too hard or goes over a tiny pebble when braking unsettling the friction or whatever....so what? And as far as yet another cloaked comment of ridicule goes you should also be aware that 'Those that CAN 'can also teach as well as those that CANT, 'CANT'

I nearly fell asleep comming on here , I have just read through this thread and I must say, the last postee has a point even if he is a bit off topic himself.Hope I dont offend anyone.

Oh joy yet another thread reduced to a p**sing contest

As for the original question I think on the whole car drivers stay clear of bikes because they see us as a bunch of Satan worshiping, baby eating, virgin despoilers and that just the girls




Okay maybe they just see us as a little threatening

Barkstar

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The difference between intelligence and stupidity is that intelligence has limits.

Safety cameras save lives.

And the relevance of your repeating this slogan to the foregoing thread is .......?

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Richard Ceen
We live in a time where emotions and feelings count far more than the truth, and there is a vast ignorance of science (James Lovelock 2005)

sorry what was the question again ?

of all the people on this site i have alot of respect for mr mole, not because i know him particularly well but because his posts are often backed up by sound principles and alot more experience than i can muster.


[on a side note i'm quite amused at the concept of a vehicle accelerating when a wheel becomes locked, perhaps some of the more advanced tyre models would predict this but i'd be impressed to see a vehicle with accurate enough instrumentation to back this up!]