Do these brake discs need replacing
Discussion
38911 said:
Nope, still wouldn’t affect the friction or braking power under normal use. The amount of heat generated even from a high speed emergency stop, is nowhere near enough to overwhelm the heat absorption abilities of a worn brake disc.
You might - after repeated deliberate high speed emergency stops - overheat the disc, but I’ve driven a car on a track so hard that I had the brake discs glowing red - literally - and have the photos to prove it. The brakes were still every bit as effective as when they were cold.
I tempered my front discs on the Cavalier SRI 130 - on the public road.... fully Lauren car 5 up full boot of luggage and the “spirit of youth”. Down a long hill dead straight 2 lands up one down 2am foot pedal went rock hard at a certain point and it simply wouldn’t slow the car - luckily for me the road was long and totally empty else I’d simply never have stopped. Brakes stank and were glowing red - when they cooled and got home my old man just happened to glance at the discs and knew from he rainbow colour in thecentre of the disc that I’d be hugely stupid. You might - after repeated deliberate high speed emergency stops - overheat the disc, but I’ve driven a car on a track so hard that I had the brake discs glowing red - literally - and have the photos to prove it. The brakes were still every bit as effective as when they were cold.
Never ever done that since - track sure public road nope. And yes my old man back then gave me a b
king of a lifetime rightly so. Welshbeef said:
It’s efficiency is less - handbrake brake test only has to achieve 15% of a brand new part....
Its efficiency is NOT less. At worst, the amount of heat it can absorb before its efficiency drops is very, very slightly reduced. If indeed the effect of a mm of wear is even perceptible. But unless that point is below the level seen in use, its irrelevant.
CrutyRammers said:
Nope. As long as disks and pads are within operational limits, stopping distance should be the same as new ones.
Those discs we saw at the start of the thread are moderately scored, and more importantly the outer quarter of the pads don't seem to be bearing on the discs at all. Both of those factors will reduce the available braking effort for a given pedal pressure. Unless all the other wheels happen to have identical problems, this will reduce the car's maximum braking ability. You could debate how urgently they need replacing, but they definitely need replacing.
GreenV8S said:
Those discs we saw at the start of the thread are moderately scored, and more importantly the outer quarter of the pads don't seem to be bearing on the discs at all. Both of those factors will reduce the available braking effort for a given pedal pressure. Unless all the other wheels happen to have identical problems, this will reduce the car's maximum braking ability. You could debate how urgently they need replacing, but they definitely need replacing.
Again - you’re confusing the symptoms with the cause. Replacing the discs and pads will not fix whatever has caused them to go rusty in the first place.The problem is very likely to be either a sticking calliper, or the car is stood for long periods of time and/or not covering much mileage.
Fix the cause and you no longer need to change the disc as the rust will go away through that wonderful thing that brakes generate : FRICTION!
Anyway, I’m rather bored now and all the twoddle being spouted on here is becoming nauseating. I’ve done my bit - but this isn’t ‘care in the community’ so I’m not going to keep correcting the mis-informed.
Good luck OP.
Welshbeef said:
They “pass” the test.
Remember for the handbrake to pass an MOT they only needs to meet 15% of the original specification....
Fact is his stopping distance WILL be longer /nearly the longest possible from a discs and pad perspective currently v brand new plus of course going into the winter season it’s the last thing you need.
Do you run your tyres down to 1.6mm too? It’s legal but under 3mm they have used up 90% of the wear and in wet conditions are vastly longer stopping distances.
To me stopping distance and lighting is the most important part of vehicle safety period - and for a few quid your be pretty daft not to change it
Remember for the handbrake to pass an MOT they only needs to meet 15% of the original specification....
Fact is his stopping distance WILL be longer /nearly the longest possible from a discs and pad perspective currently v brand new plus of course going into the winter season it’s the last thing you need.
Do you run your tyres down to 1.6mm too? It’s legal but under 3mm they have used up 90% of the wear and in wet conditions are vastly longer stopping distances.
To me stopping distance and lighting is the most important part of vehicle safety period - and for a few quid your be pretty daft not to change it
38911 said:
Again - you’re confusing the symptoms with the cause. Replacing the discs and pads will not fix whatever has caused them to go rusty in the first place.
The problem is very likely to be either a sticking calliper, or the car is stood for long periods of time and/or not covering much mileage.
Fix the cause and you no longer need to change the disc as the rust will go away through that wonderful thing that brakes generate : FRICTION!
You assume there's some other fault causing the corrosion, but I'm not convinced. In any case, those discs aren't going to fix themselves. The surface is no longer flat, and any pads you fit are going to get chewed up trying to bed in to it. This will cause more local overheating and hardening of the disc which will make the problem more likely to get worse than better. They're knackered. They need replacing. The problem is very likely to be either a sticking calliper, or the car is stood for long periods of time and/or not covering much mileage.
Fix the cause and you no longer need to change the disc as the rust will go away through that wonderful thing that brakes generate : FRICTION!
Kawasicki said:
Ahbefive said:
Surely not serious.
Yeah, dead serious. I’ve based my decision on braking distance testing and abs calibration work I’ve carried out. I have a weird relationship with risk though, I drive to the conditions.Surely anyone can feel how much worse a tyre becomes as it nears the end of its life?
What do you gain from letting them get so low? Maybe save a pair of tyres after 6sets?
Ahbefive said:
Kawasicki said:
Ahbefive said:
Surely not serious.
Yeah, dead serious. I’ve based my decision on braking distance testing and abs calibration work I’ve carried out. I have a weird relationship with risk though, I drive to the conditions.Surely anyone can feel how much worse a tyre becomes as it nears the end of its life?
What do you gain from letting them get so low? Maybe save a pair of tyres after 6sets?
Not “some” testing. Years of testing, thousands of tests.
What do I gain from letting my tread wear to 1.6mm depth?
Dry braking generally improves with tread wear, steering and handling too. Most of my driving is in the dry, like most people. Wet braking can also improve, but it depends on water film depth. Slowing down is a good idea if Aquaplaning is possible.
Other advantages? I also enjoy better fuel economy due to lower rolling resistance and safer high speed running in hot weather. I often sit at top speed in my car for extended periods and knowing I have low tread depth is reassuring!
Finally I get less flat spots when I park over a weekend!
I think worn tyres are just great.
Why do you change yours at 3mm tread depth?
I change mine close to the legal limit, never had any problems but I drive to the conditions. I am aware I will be more prone to a puncture but over almost 750k miles I had one puncture so I think I am ok. Sometimes I change earlier if we happen to have excessive rain. Surely 3mm is arbitrary safety threshold. If you are happy that’s great why not change at 4mm? Certainly even safer?
CrgT16 said:
I change mine close to the legal limit, never had any problems but I drive to the conditions. I am aware I will be more prone to a puncture but over almost 750k miles I had one puncture so I think I am ok. Sometimes I change earlier if we happen to have excessive rain. Surely 3mm is arbitrary safety threshold. If you are happy that’s great why not change at 4mm? Certainly even safer?
Why 3mm and not 4mm. The tests have been done and also done on 5th gear which should you the performance from new tyre to 3mm is very consistent hardly any drop off- but below 3mm it dramatically tails off. A bit like wanting an old diesel to rev you hit peak power then it falls off a cliff
In my experience I don't find that tail off, it works for me.
I am not sayng there isn't a tail off, I am sure the tests show that but for me is not that noticiable could be that I adjust my driving to the conditions.
As for 4mm suggestion was tongue in cheek but certainly a 4mm thread left would certainly disperse water better than a 3mm one.
In the end... if 3mm is the holy grail, why does the government allows it to be used up to 1.6mm? Surely if the evidence was so strong the government in any modern nanny state would just make it illegal to have tires with less than 3mm thread and pocket a bit more tax on the extra sales?
And this is not only in the UK... My point is although no argument that a tire with more thread is better in the wet for most drivers, it does not mean that I cannot safely drive my car in the rain with less thread than that. I have done so and will continue to do. It is my personal choice based on my personal experience.
I am not sayng there isn't a tail off, I am sure the tests show that but for me is not that noticiable could be that I adjust my driving to the conditions.
As for 4mm suggestion was tongue in cheek but certainly a 4mm thread left would certainly disperse water better than a 3mm one.
In the end... if 3mm is the holy grail, why does the government allows it to be used up to 1.6mm? Surely if the evidence was so strong the government in any modern nanny state would just make it illegal to have tires with less than 3mm thread and pocket a bit more tax on the extra sales?
And this is not only in the UK... My point is although no argument that a tire with more thread is better in the wet for most drivers, it does not mean that I cannot safely drive my car in the rain with less thread than that. I have done so and will continue to do. It is my personal choice based on my personal experience.
CrgT16 said:
In my experience I don't find that tail off, it works for me.
I am not sayng there isn't a tail off, I am sure the tests show that but for me is not that noticiable could be that I adjust my driving to the conditions.
As for 4mm suggestion was tongue in cheek but certainly a 4mm thread left would certainly disperse water better than a 3mm one.
In the end... if 3mm is the holy grail, why does the government allows it to be used up to 1.6mm? Surely if the evidence was so strong the government in any modern nanny state would just make it illegal to have tires with less than 3mm thread and pocket a bit more tax on the extra sales?
And this is not only in the UK... My point is although no argument that a tire with more thread is better in the wet for most drivers, it does not mean that I cannot safely drive my car in the rain with less thread than that. I have done so and will continue to do. It is my personal choice based on my personal experience.
Because we still have the max stopping distances of a ford Angola as the requirement. I am not sayng there isn't a tail off, I am sure the tests show that but for me is not that noticiable could be that I adjust my driving to the conditions.
As for 4mm suggestion was tongue in cheek but certainly a 4mm thread left would certainly disperse water better than a 3mm one.
In the end... if 3mm is the holy grail, why does the government allows it to be used up to 1.6mm? Surely if the evidence was so strong the government in any modern nanny state would just make it illegal to have tires with less than 3mm thread and pocket a bit more tax on the extra sales?
And this is not only in the UK... My point is although no argument that a tire with more thread is better in the wet for most drivers, it does not mean that I cannot safely drive my car in the rain with less thread than that. I have done so and will continue to do. It is my personal choice based on my personal experience.
There was a crazy idea to move MOTs to every 2 years allowing some idiot owners to run around with illegal tyres as either they are too stupid to realise or chancres who don’t give a toss.
I think that does not really portrait the kind of owner I am. I don't change it at 2-1.6mm because it's the legal limit, I find that at that wear it is time to change. I don't tend to save on any items I find are important. I don't use winter tires because where I live I don't really need them. I use currently MPS4S on my car all year around and quite happy with them rain or dry. They are changed when need for the same or equally premium product.
I agree too many idiots out there, I have known stories where MOT's where failed due to bald tires to then be passed a few hours later on the same car with different set of wheels but with legal tires. What can the tester do? He borrows his mates set of wheels to pass MOT but keeps driving with bald tyres...
Anyway we are just discussing a detail, in the end, regardless of tests, etc, it depends how you drive and as I said, in my hands I have not found the need to change them at 3mm. In my wifes car I will just because she is less aware of the available traction and albeit a good driver she lacks some road awareness.
Modern cars cocoon the drivers too much with traction controls, etc, etc and no doubt they save lives but they also de-skill the drivers. Most of them just smash the throttle like a switch, no finesse in feathering the throttle. I think track time helps a lot, even simple karts where you can develop skills such as trail braking or learn to "feel" the traction limits. Sometimes that extra awareness can make a different on the road in adverse conditions.
I agree too many idiots out there, I have known stories where MOT's where failed due to bald tires to then be passed a few hours later on the same car with different set of wheels but with legal tires. What can the tester do? He borrows his mates set of wheels to pass MOT but keeps driving with bald tyres...
Anyway we are just discussing a detail, in the end, regardless of tests, etc, it depends how you drive and as I said, in my hands I have not found the need to change them at 3mm. In my wifes car I will just because she is less aware of the available traction and albeit a good driver she lacks some road awareness.
Modern cars cocoon the drivers too much with traction controls, etc, etc and no doubt they save lives but they also de-skill the drivers. Most of them just smash the throttle like a switch, no finesse in feathering the throttle. I think track time helps a lot, even simple karts where you can develop skills such as trail braking or learn to "feel" the traction limits. Sometimes that extra awareness can make a different on the road in adverse conditions.
Welshbeef said:
CrgT16 said:
In my experience I don't find that tail off, it works for me.
I am not sayng there isn't a tail off, I am sure the tests show that but for me is not that noticiable could be that I adjust my driving to the conditions.
As for 4mm suggestion was tongue in cheek but certainly a 4mm thread left would certainly disperse water better than a 3mm one.
In the end... if 3mm is the holy grail, why does the government allows it to be used up to 1.6mm? Surely if the evidence was so strong the government in any modern nanny state would just make it illegal to have tires with less than 3mm thread and pocket a bit more tax on the extra sales?
And this is not only in the UK... My point is although no argument that a tire with more thread is better in the wet for most drivers, it does not mean that I cannot safely drive my car in the rain with less thread than that. I have done so and will continue to do. It is my personal choice based on my personal experience.
Because we still have the max stopping distances of a ford Angola as the requirement. I am not sayng there isn't a tail off, I am sure the tests show that but for me is not that noticiable could be that I adjust my driving to the conditions.
As for 4mm suggestion was tongue in cheek but certainly a 4mm thread left would certainly disperse water better than a 3mm one.
In the end... if 3mm is the holy grail, why does the government allows it to be used up to 1.6mm? Surely if the evidence was so strong the government in any modern nanny state would just make it illegal to have tires with less than 3mm thread and pocket a bit more tax on the extra sales?
And this is not only in the UK... My point is although no argument that a tire with more thread is better in the wet for most drivers, it does not mean that I cannot safely drive my car in the rain with less thread than that. I have done so and will continue to do. It is my personal choice based on my personal experience.
There was a crazy idea to move MOTs to every 2 years allowing some idiot owners to run around with illegal tyres as either they are too stupid to realise or chancres who don’t give a toss.
From the tech leaders in the tyre industry...none of this is even considered controversial...
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