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stopping distances car vs bicycle


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#1 mariner

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Posted 24 August 2017 - 18:40

There has just been a high profile criminal case in the UK where a cyclist collided with a pedestrian who unfortunately died of head injuries from falling down. It is unusual to charge a cyclist with Manslaughter and he was aquitted of that charge but found guilty on a lesser one.

 

The key issue was the cyclist was on a bike which was illegal for  road use as it had no front brake.

 

A cycling supporter wrote the following  "Front brakes are important on bicycles. In an emergency, a skilled cyclist will get all their stopping force from the front brake because of the effect of the bicycle and rider decelerating. Unlike a car the limit of effective braking on dry level ground is reached at the point where the rear wheel lifts off the ground potentially pitching the rider over the handlebars. Studies in David Wilson’s seminal work Bicycling Science demonstrate that a deceleration of 0.5g is the maximum that a seated rider can risk before he goes over the handlebars. Unlike a car driver, a cyclist cannot safely achieve the limit of adhesion of the tyre to the road, which in the dry is typically about 0.8g. Braking with the rear wheel alone can achieve only 0.256g before the rear wheel locks up and skids".

 

The cyclist was estimated to be doing 18mph which was quite legal even if quick in traffic. Putting  aside all the emotion I have two questions

 

1) Is 0.5 g really the maximum G on pedal bicycle? Some Brembo data from Austin gives a max. Moto GP braking as 1.8g and average as 0.8G. On that basis the 0.5G for pedal  bike sounds reasonable.

 

2) I don't agree that 0.8G is a road car maximum braking G. I would have thought that 1 to 1.1 g was achievable today in panic dry braking . That implies that car stops twice as quick as pedal bike in city traffic - is that probably true?



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#2 gruntguru

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Posted 24 August 2017 - 22:38

1) 0.5 sounds about right. 0.25 for the rear sounds pretty good. Rear-only braking feels worse than that on my bike. I brake front-only in most cases. I can almost achieve front-wheel lockup (which would be close to 1g) by "lying down" with my chest on the saddle. This both lowers the CG and moves it rearward. (Maximum g in vehicles where braking is limited by toppling is obviously a function of CGH and horizontal distance from CG to front tyre patch.) The problem with this technique is the weight shifting must be performed before braking so I have never been able to use it in a panic stop.

 

2) Depends mostly on tyre quality these days, especially with ABS proportioning the braking effort.



#3 Wuzak

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Posted 25 August 2017 - 01:55

 

2) I don't agree that 0.8G is a road car maximum braking G. I would have thought that 1 to 1.1 g was achievable today in panic dry braking . That implies that car stops twice as quick as pedal bike in city traffic - is that probably true?

 

 

I understood the statement to mean that the theoretical braking of a bicycle was 0.8G based on tyre grip, but practically not achievable because of the going over the handlebars thing.



#4 Greg Locock

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Posted 25 August 2017 - 06:04

Yup,cgz/wheelbase is the thing that controls the braking limit on a pushbike. Traffic tends to routinely brake at up to 0.4g, thats about the limit for a haulage truck. Lightly laden pickups will struggle to exceed 0.7g, cars should be 0.8 or more.

#5 Cirrus

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Posted 25 August 2017 - 09:40

I think I'm right in saying that the cyclist mentioned in the first post had no rear brake either. He was relying on the fact that there was no freewheel on the bike and therefore he could slow down by simply resisting the turning of the pedals. I wonder what the maximum "braking" g would be in that situation?



#6 Charlieman

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Posted 25 August 2017 - 10:58

Yup,cgz/wheelbase is the thing that controls the braking limit on a pushbike. Traffic tends to routinely brake at up to 0.4g, thats about the limit for a haulage truck. Lightly laden pickups will struggle to exceed 0.7g, cars should be 0.8 or more.

I thought mu (co-efficient of friction) maxed at ~0.8 for road tyres. If centre of gravity is a little above axle height for a road car, then max braking tends towards 0.7g. For road with a damaged surface, oil spills, marbles, litter etc, potential braking capacity falls very quickly to 0.4g...



#7 mmmcurry

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Posted 25 August 2017 - 13:21

I think I'm right in saying that the cyclist mentioned in the first post had no rear brake either. He was relying on the fact that there was no freewheel on the bike and therefore he could slow down by simply resisting the turning of the pedals. I wonder what the maximum "braking" g would be in that situation?


Yeah, it was a fixie, do the braking power would be what his legs could manage against the momentum of the rear wheel, plus what control he had.

I tend to use my rear brake to bleed off speed more than actual braking. The front brake has most of the power. Then there's the whole rim brake Vs disc and cable Vs hydraulic.

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#8 MatsNorway

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Posted 26 August 2017 - 13:10

I personally will never own a bike with no brakes! fixed crank or not. And i love a good feeling front brake. leaning back on the rear wheel means you can stop seriously quick once you have loaded up the front wheel. One of my favorite things with cycling. And for some reason i get the best feel from a regular V-brake. You can feel the front slip a little while the rear is dancing up and down from the ground depending on loading. And you can control it all. Well could.. been a while.  Disc brakes have yet presented the correct feel for me. Often they have too much bite and too much flex. Perhaps some hydraulic system with small master cylinder would do the trick. but does one get to chance the hydraulic brake cylinder?

 

But what i dislike the most is that accidents cant just happen anymore. Its all guilty this or that.

 

"you had no reflex on your bike.. your a murderer"

"you must leave humanity behind and become... a machine" 

 

Kids get reported to the police for climbing in scaffolding these days. (nearly, janitor was a sane man and said, just let the parents know) 


Edited by MatsNorway, 26 August 2017 - 13:10.


#9 mmmcurry

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Posted 26 August 2017 - 22:45

I personally will never own a bike with no brakes! fixed crank or not. And i love a good feeling front brake.

Disc brakes have yet presented the correct feel for me. Often they have too much bite and too much flex.

But what i dislike the most is that accidents cant just happen anymore. Its all guilty this or that.


Agree, a good front brake is a must.

My Hope discs had the best feel of any brakes I've had (cantis, V's, hydraulic rims, cable or hydraulic discs). Shimano are good, but not Hope good, shame I can't afford the Hopes anymore.

What annoys me is that the cyclist was demonised for initially slating the poor woman for walking out when looking at her phone. Yes his bike was illegal and he sounds like he wasn't in control, but she shouldn't have walked in front of him, unfortunately she paid the ultimate price.

Steve.

#10 Tsarwash

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Posted 27 August 2017 - 08:55

As somebody mentioned, you can shift your weight a lot. I do tend to do this, but it takes time to change position and not likely in an emergency. You can also lose a lot of speed by 90 degree skids, but by that point you have essentially lost control. Sometimes having the weight forward can be a boon. I was once, stupidly going very fast through a little corridor of stationary cars either side of me, when suddenly a car pulling in from a side road blocked my path. I had almost no warning, I braked but didn't have time to lose much speed, however because of the emergency braking, my weight/momentum was shifted forwards and thus when I hit the car I flew straight over it and landed in the road on the other side, which must have given the driver a he'll of a shock. I was more or less fine despite actually leaving knuckle shaped dent marks in the side of his car. 



#11 saudoso

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Posted 28 August 2017 - 00:51

How much behind the contact patch your CG is divided by how high it is will give you your max stopping force.

When you hug the frame you're decreasing height faster than you decrease distance, hence the increased braking force

#12 Lee Nicolle

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Posted 30 August 2017 - 00:14

Being of the firm belief that bicycles are far to dangerous for our streets,, even without other traffic that I very seldom ever ride one. My 10 speed has been hanging on the shed wall for well over a decade. I had a mountain bike that I aquired and have now sold. That actually had better brakes but still about a 1/4 as efficient as the average motorcar. When I was young and stupid I rode bikes a lot and luckily was never hit or hit another vehicle, though did go off the road a few times in avoidance.

 

This riders attitude evidently was it was the womans fault, and in part it was. BUT the typical bicycle wankers attitude is that the world should get out of my way as I wobble along blindly! The roads are only there for their hobby.

 

I feel brakes are not essential here in Oz? Though obviously required. Not so long ago most bikes were fitted with a back pedal brake on the rear wheel only was all that you got. A board track [fixed wheel] bike should never be on the road and as far as I am concerned not even on a track. And yes I have ridden them.

 

Blind freddy can see that a very narrow hard pumped tyre has very little grip and coupled with about a square inch of friction material has very little effectivness.  Especially if the rider does  not move their weight around. And having a pedestrian  jump out in front of you gives you no time to do so.

 

Bicycles should really be banned from the roads, bloody dangerous things that often  block up the roads at 15mph or less. And should never be allowed on the footpaths as has happened in too many places. And causing injuries regularly to the pedestrians!

 

Look at the news and you see hordes of them crash every bike event. They ride far too fast for the lack of braking and take each other down. This on closed roads. And they do it on public roads as well and kill themselves. And that is always the motorists fault!! One recent fatality here was a rider blindly racing down hill hit a car that was actually stopped. Giving way to traffic. And with no insurance the car owner is well out of pocket. And got the usual media crap!

 A year or three ago I saw a pack of the wankers in a pack take each other down in front of Sunday traffic. This alongside a million dollar bikeway that it is not trendy to use.

 

These days ofcourse IF you are trendy you have the lightest available equipment that goes as fast as possible for the least effort. Then they hit potholes and the frames  and wheels break, regularly. And then they blame everyone else ofcourse!

 

IF bicycles continue on public roads the riders must wear a proper helmet, not the dumb things they wear currently. Have reflecto hivis attire and proper lighting and warning device. not tinkle tinkle which you never hear in a car. Let alone a truck. And machines made to a proper standard suitable for the road. Which does not mean lightweight alloy or carbon fibre! And ofcourse at least third party property insurance and registration and number plates. To protect other road users and pedestrians. Currently if able they do a runner and leave others to pay for the damage.

 

A bloke I know who used to build bike frames says that only steel is reliable, though  I guess moly comes under that.

And yes I expect flack for my comments. But they are all true!


Edited by Lee Nicolle, 30 August 2017 - 00:19.


#13 kikiturbo2

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Posted 30 August 2017 - 08:36


And yes I expect flack for my comments. But they are all true!

 

well, the steel frame comment is pure BS for start.. as is the helmet comment (and I am a living proof that bicycle helmets do work)

Also if you compare fatalities, you will see that motorcyles are signifficantly more dangerous..

In fact, most accidents are linked to driver/rider error and bad road conditions as well as car drivers behaving like di$%heads when they see a bicycle on the road.. so nothing really different from other road accidents apart from the fact that on a bike you do not have a 3000 lb steel cage around you.



#14 Lee Nicolle

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Posted 31 August 2017 - 23:42

Motorcycles go a LOT faster and there is a lot more of them as well. 

Bike helmets are a piece of  holey styrene with some plastic. Little face protection and little temple and back of head protection. A lady friend of mine had the front wheel go from under her on sand on the road, wearing a helmet and got minor concussion, severe road rash to her face and broke her arm. This at probably 5kmh.

I concussed myself after slipping on moss, and took some skin off as well. This being 1980!  That and bloody buses  [running me into kerbs and parked cars] stopped me riding as I stopped and looked at myself and realised I was silly.

Oh, and steel frames? I have seen several occurences of bike races with the alloy frames breaking on the news. Maybe if they made them far thicker,, maybe but then moly would be lighter anyway.

And carbon fibre is for board racing but fools ride them on the roads and complain about the potholes! Drrrrrr!!


Edited by Lee Nicolle, 31 August 2017 - 23:45.


#15 404KF2

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Posted 01 September 2017 - 01:20

I had a good crash a couple of months ago while test riding a motor assisted bike and the Giro helmet prevented a possible brain stem injury and at the very least a nicely detached scalp flap.  Would never ride without one now.  I do 4000-5000 km a year typically (this has been a bad year for distance, only 2200 so far) and I have two steel bikes and one carbon fibre Cervélo.  The thing about carbon is you are basically renting the frame, so the saying goes.  So far mine has lasted 6 years (first frame cracked around the BB and was replaced at no cost under warranty!).  Steel is forever unless you sweat too much on it (I do on hills) or crash it too hard.  Even sweat will take decades to do its worst.  I rustproof the inside of the seat tube.

 

About braking, getting low and rearward makes good decelerations (I would guess about a half g) possible but the type of tire used will also affect distance/deceleration.  Super sticky race tires will probably do better than the endurance spec Michelins I use.



#16 MatsNorway

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Posted 01 September 2017 - 12:13

A smaller bike stops earlier because you get your ass behind the wheel. In a way a BMX really is the most agile thing you can ride

 

Watch this Lee


Edited by MatsNorway, 01 September 2017 - 12:18.


#17 Kneifzange

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Posted 02 September 2017 - 09:16

A smaller bike stops earlier because you get your ass behind the wheel. In a way a BMX really is the most agile thing you can ride

 

Watch this Lee

 

What is the meaning of his insurance company to this??    :stoned:



#18 kikiturbo2

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Posted 05 September 2017 - 08:34

  The thing about carbon is you are basically renting the frame, so the saying goes.  So far mine has lasted 6 years (first frame cracked around the BB and was replaced at no cost under warranty!).  Steel is forever unless you sweat too much on it (I do on hills) or crash it too hard.  Even sweat will take decades to do its worst.  I rustproof the inside of the seat tube.

 

About braking, getting low and rearward makes good decelerations (I would guess about a half g) possible but the type of tire used will also affect distance/deceleration.  Super sticky race tires will probably do better than the endurance spec Michelins I use.

 

Steel is forever because most steel frames weigh a ton... Make a 2 Kg Carbon frame and it will be bulletproof (Try a 1000 g steel frame and let me know how long it lasts)... The think about carbon is that it will never break from use, if it is engineered properly, but will crack in a crash... Also, if done properly they are realy comfy, unlike most steel frames..

Alu is the worst offender as it will age and crack...

Titanium is just forever and really comfortable.. No wonder ultimate touring bikes are made out of the stuff..



#19 Fat Boy

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Posted 06 September 2017 - 16:36


A bloke I know who used to build bike frames says that only steel is reliable, though  I guess moly comes under that.

And yes I expect flack for my comments. But they are all true!

 

Lee,

 

Sometimes I wonder if you aren't just having fun with us by the use of self-satire. Other times, I'm sure of it.

 

Honestly, you have just about enough knowledge of bikes to be dangerous and most of that is out-dated.

 

Modern carbon frames can be made for any environment. If you want a 600 gram frame that's good for, maybe, 5-10,000 km, they exist. If you want a 1.5 kg frame that you can ride forever, they exist, too. Carbon frames can be made very stiff or quite compliant, it all depends on the application.

 

Modern AL frames come in a little over their carbon counterparts (1.5-2.0 kg), but are equally strong. With hydroformed tubing and really intense engineering, they've been able to make AL frames ride every bit as nice as carbon, it's just a bit heavier (and much cheaper).

 

Modern Steel frames get to about the same weight as AL bikes. Some of the tubesets are really high-end in terms of their metallurgy. They're essentially the finest steel alloys in existence and they have complex tube shapes. If these were introduce in the 1980's, AL would have never happened. Again, the bikes can be made stiff and responsive or more compliant with a better ride. It depends on the application. Steel frames are largely from boutique builders.

 

Brakes on a road bike suck. Shimano probably does the best job, but it's no easy task. They're trying to haul down a bike with a caliper that is at an absolute minimum weight. If you've ever ran well set up disc brakes on a bike, you know they work an order of magnitude better than a rim brake. Caliper, Canti, V, whatever....they all suck compared to a good hydraulic setup. A good cable disc setup still beats a rim, it's just not quite as nice as a Hydro. The biggest differences are grip effort and modulation. On a disc you can use 1 or 2 fingers and slow at your max. With a rim  brake, you may be using your whole hand. You can still lock the tires, but your ability to control the bars and modulate lock-up goes to ****.

 

Riding on public roads is dangerous, but largely because motorists have their attention pulled in 10 different ways and they kill innocents. Yes, bikes will inconvenience a car at times, like when you have to get across lanes for a left turn (or right for you in Oz). Most of the time when a cyclist gets hit it's because the car has drifted into the bike lane. There is simply no excuse for this and it should be treated as manslaughter. The other problem is bikes riding on the wrong side of the street and getting hit for doing so. You can't blame the cars for that.

 

I learned about longitudinal load transfer on a bike. Initially (i.e. as a FSAE kid), I was under the impression that spring rates had something to do with the magnitude of weight transfer. I was mistaking cause/effect. Anyway, I had blown up my car engine and was riding a friends bike to and from school. The rear brake could be applied maximum without locking the rear. However, as I started applying the front, the rear tire would lock. Hmmmm, I thought. Then I started moving my weight back to get the rear rolling again. There were no real springs in play, so light bulbs started dimly glowing.

 

Bikes are a lot of fun, but I've shifted my riding away from the road and towards mountains. In the dirt, you might get dinged up a bit, but you're not likely to get any real damage if you ride within yourself. On the road we get a lot of people in my area killed for simply trying to exercise. I don't need to be a statistic.



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#20 Lee Nicolle

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Posted 08 September 2017 - 00:34

Lee,

 

Sometimes I wonder if you aren't just having fun with us by the use of self-satire. Other times, I'm sure of it.

 

Honestly, you have just about enough knowledge of bikes to be dangerous and most of that is out-dated.

 

Modern carbon frames can be made for any environment. If you want a 600 gram frame that's good for, maybe, 5-10,000 km, they exist. If you want a 1.5 kg frame that you can ride forever, they exist, too. Carbon frames can be made very stiff or quite compliant, it all depends on the application.

 

Modern AL frames come in a little over their carbon counterparts (1.5-2.0 kg), but are equally strong. With hydroformed tubing and really intense engineering, they've been able to make AL frames ride every bit as nice as carbon, it's just a bit heavier (and much cheaper).

 

Modern Steel frames get to about the same weight as AL bikes. Some of the tubesets are really high-end in terms of their metallurgy. They're essentially the finest steel alloys in existence and they have complex tube shapes. If these were introduce in the 1980's, AL would have never happened. Again, the bikes can be made stiff and responsive or more compliant with a better ride. It depends on the application. Steel frames are largely from boutique builders.

 

Brakes on a road bike suck. Shimano probably does the best job, but it's no easy task. They're trying to haul down a bike with a caliper that is at an absolute minimum weight. If you've ever ran well set up disc brakes on a bike, you know they work an order of magnitude better than a rim brake. Caliper, Canti, V, whatever....they all suck compared to a good hydraulic setup. A good cable disc setup still beats a rim, it's just not quite as nice as a Hydro. The biggest differences are grip effort and modulation. On a disc you can use 1 or 2 fingers and slow at your max. With a rim  brake, you may be using your whole hand. You can still lock the tires, but your ability to control the bars and modulate lock-up goes to ****.

 

Riding on public roads is dangerous, but largely because motorists have their attention pulled in 10 different ways and they kill innocents. Yes, bikes will inconvenience a car at times, like when you have to get across lanes for a left turn (or right for you in Oz). Most of the time when a cyclist gets hit it's because the car has drifted into the bike lane. There is simply no excuse for this and it should be treated as manslaughter. The other problem is bikes riding on the wrong side of the street and getting hit for doing so. You can't blame the cars for that.

 

I learned about longitudinal load transfer on a bike. Initially (i.e. as a FSAE kid), I was under the impression that spring rates had something to do with the magnitude of weight transfer. I was mistaking cause/effect. Anyway, I had blown up my car engine and was riding a friends bike to and from school. The rear brake could be applied maximum without locking the rear. However, as I started applying the front, the rear tire would lock. Hmmmm, I thought. Then I started moving my weight back to get the rear rolling again. There were no real springs in play, so light bulbs started dimly glowing.

 

Bikes are a lot of fun, but I've shifted my riding away from the road and towards mountains. In the dirt, you might get dinged up a bit, but you're not likely to get any real damage if you ride within yourself. On the road we get a lot of people in my area killed for simply trying to exercise. I don't need to be a statistic.

I have seen broken c/f bikes on a few occasions, one an aquaintance crying over his $10000 bike that broke hitting a pothole. Only a few months old!  Another a track bike that broke,, on the road. And another in the media, again a track bike.

Chrome moly is steel, expensive but strong, though if made too thin bends and breaks wonderfully, as another aquaintance found out after hitting a car! Which cost him quite a lot in repairs to the car. He could not do a runner like most do!

Though my first bike a huge heavy [and secondhand then]  28" is still going about 70 years after it was made. My nephew says he gets more exercise riding it! Not on the road though.



#21 gruntguru

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Posted 08 September 2017 - 02:37

I have seen broken c/f bikes on a few occasions, one an aquaintance crying over his $10000 bike that broke hitting a pothole. Only a few months old!  Another a track bike that broke,, on the road. And another in the media, again a track bike.

Chrome moly is steel, expensive but strong, though if made too thin bends and breaks wonderfully . . .

Carbon fibre breaks. Chrome moly steel breaks. Shucks everything breaks.

 

The real point is - for the same frame weights, carbon fibre will be the strongest, aluminium next, then steel. If you have seen a lot of broken CF frames, that is because they were ultra light.


Edited by gruntguru, 08 September 2017 - 02:37.


#22 mmmcurry

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Posted 08 September 2017 - 12:52

If you have seen a lot of broken CF frames, that is because they were ultra light.


Or badly made.

Steve.

#23 MatsNorway

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Posted 08 September 2017 - 22:32

Carbon fibre breaks. Chrome moly steel breaks. Shucks everything breaks.

 

The real point is - for the same frame weights, carbon fibre will be the strongest, aluminium next, then steel. If you have seen a lot of broken CF frames, that is because they were ultra light.

But how many high load cycles can they take tho? Alu is known to have had some issues in some cases. 



#24 JacnGille

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Posted 09 September 2017 - 16:57

The brand of bikes at our shop are placed on a shaker rig. We've been told that the manufacturer stopped the rig after more than a million more cycles than it took to damage their aluminum frames without damage to their carbon frames.



#25 MatsNorway

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Posted 09 September 2017 - 17:48

Did they compare to steel?



#26 JacnGille

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Posted 10 September 2017 - 01:12

Sorry, don't remember.



#27 404KF2

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Posted 10 September 2017 - 07:01

I had a hard crash in 1993 on my ancient 1978 Raleigh Super Course - Reynolds 531.  The crank arm was bent and the frame distorted at the bottom bracket. I had some nice road rash and a rearward dislocated left shoulder too.  

 

Put it on a frame rig and straightened it out and I have continued to ride this bike for decades after the crash.  That crash would have killed a carbon bike.  There is also the matter of how the material yields when it exceeds its strength.  Carbon shatters, steel deforms then in extreme deformations cracks.  A friend of mine hit a good big bump on his Cervélo R5 and his fork shattered and he had a bad crash as a result (he may well have fallen even without the broken fork, it's hard to say).



#28 404KF2

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Posted 10 September 2017 - 07:10

36948258626_70763dee0a_b.jpg

 

This is the photo he took when the bike was back at his home.



#29 Tenmantaylor

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Posted 10 September 2017 - 20:50

I think I'm right in saying that the cyclist mentioned in the first post had no rear brake either. He was relying on the fact that there was no freewheel on the bike and therefore he could slow down by simply resisting the turning of the pedals. I wonder what the maximum "braking" g would be in that situation?

 

As demonstrated by police, next to F-all. I would never ride a 'fixey' on the roads. A skilled fixey rider (usually couriers like the perp) claim they can stop extremely quick doing skid stops. I've witnessed it, and given enough time and space they could probably stop quicker than the average cyclist when only using a rear brake. Anyone with a front brake will stop much quicker and safer.

 

From what I've heard another issue here was that he didn't attempt to stop, she walked out in front of him, he swerved then she stepped back into his path like when trying to avoid someone walking towards you and you both make the same move simultaneously.

 

Doesn't excuse his illegal bike or attitude, had he had a front brake he could have made the tiniest last minute decel. that could have saved her life.


Edited by Tenmantaylor, 10 September 2017 - 20:51.


#30 kikiturbo2

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Posted 11 September 2017 - 02:09

Did they compare to steel?

Hard to compare to steel as there are no real steel options in the sub 1000 gram frame weight  class...  and you wouldnt want to ride a 1000 gram steel frame either



#31 chunder27

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Posted 11 September 2017 - 10:07

I cannot believe anyone would ever get on a treader that did not have brakes.

 

It is as simple as that.

 

Regardless of how dangerous bikes are in the first place on some roads.

 

I would say most cyclists I encounter out in the open are fine, but this cycling gear offers no protection from gravel rash, the most likely thing you will suffer from in a self inflicted crash.

 

it's a bit like wearing trackie bottoms riding a moped or scooter.

 

Helmets seem to be an accessory rather than a real aid, gloves should be mandatory as should perhaps ankle protecting boots be.

 

The main thing I see that is bad is lights. So many people riding bikes without lights



#32 Charlieman

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Posted 11 September 2017 - 11:07

Helmets seem to be an accessory rather than a real aid, gloves should be mandatory as should perhaps ankle protecting boots be.

 

The main thing I see that is bad is lights. So many people riding bikes without lights

Helmets generate a false sense of safety. For children, they make great sense. Kids fall off bikes and may crack the top of their heads. Adults don't fall off bikes often -- maybe on slippery or icy roads. They tend to get hit by four wheeled vehicles. Whilst a helmet may protect the skull, few offer protection to the back of the head, chin, nose etc. They offer zero protection from organ injury.

 

No lights -- very stupid. Flashing lights -- just as bad because they are "off" half of the time. On a soggy UK November night, it is hard to keep track of a flashing light manoeuvring around parked cars.



#33 Charlieman

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Posted 11 September 2017 - 11:24

And for some reason i get the best feel from a regular V-brake. You can feel the front slip a little while the rear is dancing up and down from the ground depending on loading. And you can control it all. Well could.. been a while.  Disc brakes have yet presented the correct feel for me. Often they have too much bite and too much flex.

Rim brakes work well owing to the high relative velocity of the rim/braking material -- three or four times higher than for a disc brake. It is pretty straightforward to make a rigid system of lever, cabling and callipers. In theory a disc system will be better at all but very low bicycle speeds but it is much harder to design a rigid mount for the callipers.  



#34 MatsNorway

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Posted 11 September 2017 - 19:02

Flex in the fork could be a part of it too. on disc brakes you get the loads further down than on a regular fork. There is also higher loads through the spokes etc. So the fork and wheel has to be stiffer/heavier. If one where to make the lightest bike possible a Rim brake would be a given.



#35 Fat Boy

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Posted 11 September 2017 - 20:46

I have seen broken c/f bikes on a few occasions, one an aquaintance crying over his $10000 bike that broke hitting a pothole. Only a few months old!  Another a track bike that broke,, on the road. And another in the media, again a track bike.

Chrome moly is steel, expensive but strong, though if made too thin bends and breaks wonderfully, as another aquaintance found out after hitting a car! Which cost him quite a lot in repairs to the car. He could not do a runner like most do!

Though my first bike a huge heavy [and secondhand then]  28" is still going about 70 years after it was made. My nephew says he gets more exercise riding it! Not on the road though.

 

No question, carbon fiber bikes can break. If you're talking about a bike that is worth about $10k, then you're talking about a genuine racing bike. It's the same as a racecar. It's disposable. Don't hit potholes, they will not put up with it. On the bright side, if you break your frame in this manner, the manufacturer will generally replace it.

 

Track bikes for the street are a poor choice. They're meant for a billiard table smooth surface.

 

Your old, heavy bike is still running. It's really no surpise. They were built in a time when racing was pretty much unheard of and roads were very rough. They also tend to have bigger tires and more sidewall, which softens the ride significantly.



#36 Fat Boy

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Posted 11 September 2017 - 20:48

Rim brakes work well owing to the high relative velocity of the rim/braking material -- three or four times higher than for a disc brake. It is pretty straightforward to make a rigid system of lever, cabling and callipers. In theory a disc system will be better at all but very low bicycle speeds but it is much harder to design a rigid mount for the callipers.  

 

FFS, this is stupid. Just stop.



#37 Kelpiecross

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Posted 12 September 2017 - 03:56

FFS, this is stupid. Just stop.


Why do you say this? I thought Charlie's analysis of the situation was quite reasonable.

#38 chunder27

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Posted 12 September 2017 - 07:15

I think you can blame the media obsession with treader road racing and certain peoples need for a nice toy for the proliferation of racing bikes on UK roads and ***** in lucre everywhere.

 

I have driven in Holland a fair bit and you don't see many people doing it there, a few of course, but not as much as over here, where on weekends in certain parts of the UK they are a downright menace and cause an unnecessary amount of congestion in hilly areas and narrow roads.

 

Although I might add, mainly because people are **** scared to overtake and seem to think a treader is as wide as a car, so queueing is rarely the cyclists fault.



#39 Charlieman

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Posted 12 September 2017 - 13:55

FFS, this is stupid. Just stop.

Tell me more, please. I have a degree in Mechanical Engineering, am co-author of an ancient academic paper still cited and whilst never practicing as an engineer, I read a lot. I'd like to know what I misunderstood.



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#40 Fat Boy

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Posted 12 September 2017 - 22:08

For starters, the logical fallacy of 'appealing to authority' comes to mind.



#41 MatsNorway

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Posted 13 September 2017 - 14:18

let me translate, in Sir David Attenboroughs voice. "Charlieman signals that he is ready to take on the challenge, but Fat boy avoids the challenge and continues the insults in an attempt to win through intimidation rather than through a display of superior technical insight"


Edited by MatsNorway, 13 September 2017 - 14:19.


#42 Fat Boy

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Posted 13 September 2017 - 23:48

First, Mats, I was busy and didn’t have time for a real response. Charlie is the one throwing his credentials around with no prompting. I’m some random dude on the ‘net. Listen to me or don’t…I don’t care. I just find it strange to see someone who clearly doesn’t know what they’re talking about write as an authority.

 

Second, I don’t comment on a subject unless I’m able to do so in a pretty comprehensive manner. I would think after enough drubbings, you’d figure this out.

 

Third, GFYM. Your sole redeeming quality on this board is the ability to take punishment like a Cuban welterweight. Like a child, you should be seen and not heard.

 

On to the actual reply:

  1. Charlie has reduced brake performance to relative surface velocity while ignoring the entire rest of the braking system. How could one think that reducing a system to a single variable would produce a valid analysis of anything?
  2. Rim brakes
    1. They either act on an AL or carbon fiber layup rim/braking surface. The first thing about these rims is that they are kept at an absolute minimum of weight (~350 grams for carbon or ~450 grams for AL). The lighter, race quality components minimize and compromise the thermal capacity of the components.
    2. AL and carbon braking surfaces don’t react well to high mu brake pads. AL is more forgiving. Originally, pads were made of a rubber compound, but now the best pads are a polymer. For carbon rims, a good pad material is a cork/rubber mix which has reasonable stopping power with acceptable wear. There are polymer pads for carbon as well, but there is always the compromise of rim wear/performance at play.
    3. Carbon rim shapes are optimized for aerodynamics, not brake track performance.
    4. A basalt coating is often put on carbon brake tracks to improve performance. These protect the rim, but can make for trickier braking.
    5. Clincher rims necessarily leave the brake track in a cantilever position which is poor for brake stiffness.
    6. Rim brakes mean cable actuated calipers (on road bikes). Dual pivot calipers have the best gripping power, but are heavier. Single pivot brakes are often favored for weight, but they really don’t work very well.
    7. Cable actuation itself isn’t horrible, but it does limit forces and have inherent friction issues, specifically with aero frames and internal routing.
    8. Prolonged or repeated brake applications (mountain descent) heat the rim, which directly influences tire pressure. This can contribute to a blow out of a clincher tube or melting the glue which holds a tubular in place.
    9. In rain or wet situations, you need about a minimum of one full wheel rotation before the rim is clean and the brake force starts to build. On a carbon wheel, this can be several seconds before the brakes start to grab.
    10. Off-road (most commonly in cyclocross), rim brakes are either of the cantilever or V-brake design. With a Canti, you either get braking power or mud clearance. Choose one. With the V-brake, you’ve made your choice, which is braking power. Excessive mud will fowl the lever arms and/or the cable across the top of the lever arms.
    11. Brake pad alignment is something you have to stay on top of. The pads have to maintain a certain amount of toe-in to reduce brake squeal and allow for smooth engagement. Pad spacing is also a concern because pad wear effects lever travel/engagement. Keeping the rim central between the pads allows for even engagement.
    12. Keeping the rim true is very important. As a rim goes out of true, you have to run the caliper wider (to accommodate total brake track width). This can reduce braking effectiveness by having to run the caliper ‘open’.
  3. Disc brakes
    1. Cable and hydraulic actuation are both used. Hydraulic is the best in overall terms, but even a low budget cable is preferable in most situations. I personally purchased a cable actuated disc brake cyclocross bike and the gain in performance over a canti/V-brake was substantial.
    2. Rim shape and construction is not compromised by brake duties.
    3. The discs themselves are ferrous. ‘Normal’ types of organic or semi-metallic pad materials are usable. Organic pads are quiet; semi-metallic pads are higher mu & more fade resistant.
    4. Discs are a bit heavier (100-200 grams) and have higher aerodynamic drag. They aren’t used in time trials or some road racing applications because of this.
    5. Downhill mountain bikes use hydraulic brakes universally. Rim brakes just do not have the power to slow a heavy bike from high speed repeatedly. They use relatively large diameter discs that can take a lot of abuse.
    6. Brake discs heat up easily. This has no effect on tire pressure, but it means getting the temp (& mu) in its working range is a not difficult to maintain.
    7. Unlimited mud clearance, but in heavy mud, the grime can hurt pad wear.
    8. Once caliper is centered on disc, it never changes.
    9. Hydraulic systems compensate lever travel for pad wear.
    10. The entire system is much, much stiffer than a rim-based system, which allows for better feel and modulation.
    11. Disc brakes are unaffected by water.
  4. Brake effectiveness is much more than just “it can lock tires”. On a bike, this is a trivial matter. Being able to modulate brakes with a single finger while keeping complete control of the handlebars is difficult. Doing this on a mountain bike while you’re hanging your ass off the back of the bike and rolling over boulders only makes it more so.
  5. Having a consistent lever feel and braking power in a race can seriously reduce fatigue. When every downhill section means using maximum grip strength and hoping for the best, it can be incredibly taxing.

 

Anyway, that's my initial thoughts.



#43 Fat Boy

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Posted 14 September 2017 - 16:57

C'mon, Mats, you were talking $hi+.

 

Surely it wasn't all just posturing? Surely it wasn't just you running your mouth yet again with nothing to back it up? Surely it wasn't you chiming in on yet another thread with nothing meaningful to add?



#44 MatsNorway

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Posted 14 September 2017 - 17:56

I was not going into specifics about brakes, i know little about it. 

 

You get fired up really easy, must have been your biggest post here in ages. You took it. Hook, line and sinker. :up:



#45 Fat Boy

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Posted 14 September 2017 - 18:10

I was not going into specifics about brakes, i know little about it. 

 

You get fired up really easy, must have been your biggest post here in ages. You took it. Hook, line and sinker. :up:

 

Ya, your mom took it that way, too.



#46 mmmcurry

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Posted 20 September 2017 - 09:56

Fat Boy pretty much covered the disc vs rim brake. I have had a hydraulic rim brake (Magura HS33s) on the back of my Klein Pulse as there was no disc mount. Very powerful, but it did end up wrecking the rear rim after a year or two.

 

After over 10 years of mountain bikes with disc brakes I got a road bike for commuting and winter rides, the rim brakes were ok in good conditions, but as soon as they were wet the braking distance was significantly longer. My new road bike has cable discs, far better than cable rims, not as good as hydraulic discs.

 

Steve.



#47 chunder27

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Posted 20 September 2017 - 11:42

As an aside, I see that kid who ws riding that bike with no brakes in the UK was convicted.

 

Not sure how a bike like that can ever be sold!!

 

Was also refreshing on the commute home recently to see two lads, no doubt Eastern European, treading their way back from work with rucksacks and no helmets!!  Bless em, cheap transport is great when you need it!



#48 mmmcurry

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Posted 20 September 2017 - 17:17

Not sure how a bike like that can ever be sold!!


It's a track bike, think go kart or any number of open wheel racers. Not road legal, but fine on the track.

Steve.

#49 Lee Nicolle

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Posted 28 September 2017 - 09:13

I cannot believe anyone would ever get on a treader that did not have brakes.

 

It is as simple as that.

 

Regardless of how dangerous bikes are in the first place on some roads.

 

I would say most cyclists I encounter out in the open are fine, but this cycling gear offers no protection from gravel rash, the most likely thing you will suffer from in a self inflicted crash.

 

it's a bit like wearing trackie bottoms riding a moped or scooter.

 

Helmets seem to be an accessory rather than a real aid, gloves should be mandatory as should perhaps ankle protecting boots be.

 

The main thing I see that is bad is lights. So many people riding bikes without lights

And wearing trendy black lycra!



#50 Lee Nicolle

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Posted 28 September 2017 - 09:19

Helmets generate a false sense of safety. For children, they make great sense. Kids fall off bikes and may crack the top of their heads. Adults don't fall off bikes often -- maybe on slippery or icy roads. They tend to get hit by four wheeled vehicles. Whilst a helmet may protect the skull, few offer protection to the back of the head, chin, nose etc. They offer zero protection from organ injury.

 

No lights -- very stupid. Flashing lights -- just as bad because they are "off" half of the time. On a soggy UK November night, it is hard to keep track of a flashing light manoeuvring around parked cars.

As a  teenager and young adult I rode and fell off bicycles and was bloody lucky I am still here. 

I delivered local papers over a too large area so added overloaded to the equation. 

And yes the time I brained myself was the end, after also being run off the road and into a parked car by buses.

as for strobing lights,, so hard to estimate where they are. A very dumb invention.