Speed limits - people who ignore them

gilbert_and_sullivan

Strider590 wrote: »

Because the discs are cross-drilled/vented, they don't fade, it has big twin pot callipers, the pads are a special sprint/track compound and the tyre's are so soft that driving on a freshly "dressed" road means you'll be spending half an hour pulling stones out of the tyre thread with a pair of long nose pliers.

It will lock a wheel if you go over a bump or minor pothole in the road whilst braking, because for a fraction of a second that corner of the car has less contact with the ground and when you consider the weight, that doesn't leave much down force on that wheel. Oh and no it's not easier, it's actually harder because the brakes have no vacuum assist unit on the master cylinder.

Don't know how to multiquote, so McPitman i'll include you in this reply if i may.

You're both comparing apples and oranges.

It doesn't matter how many holes are drilled or groves in the discs to keep them cool, if they're large enough to dissipate the heat from a full speed stop they'll do the trick.

Formula cars bear no resemblance whatsoever to road going cars, special tyres that wouldn't be road legal anyway.

I'm asking how a road legal car of similar weight on the point of locking up or even locked up can be stopping any quicker than another car on the same tyres and similar contact area/weight ratios.

We're on the point of lock up, how do you stop the car any faster than by keeping it at that point, how do you beat the physics of tyre grip, you could possibly double your present braking performance if you had enough money for ceramics but you still have only a certain amount of grip.

Yes your kit car probably weighs half or slightly less my old Merc coupe, E320 W124 by the way, so given ideal road conditions billiard smooth and bone dry and clean (find that if you can), in that perfect world you would halt the weight faster, but the world isn't perfect, the roads are abysmal they are seldom clean and dry and importantly unworn.

Yes i know in the right hands a non ABS car can stop faster, if the driver has the feel for perfect cadence braking to maximise the weight/grip transfers, but drivers with that skill level are few and far between now and most likely already have some race experience anyway.

Interesting stuff this, i hope to learn something.

bazster

Cornucopia wrote: »

Not really. Examiners like to see people "make progress" in their tests because it demonstrates confidence and a good awareness of limits and hazards. But it shouldn't be taken as official sanction to hare around for the rest of one's driving career at the limit or above it. Once you are paying for your own car, fuel and brake pads you may wish to determine a driving style that is more suitable.

I never mentioned "haring around", but I did say driving significantly below the speed limit in good conditions. You see the qualifications which you have chosen to ignore?

Cornucopia wrote: »

Possibly, but single-carriageway roads (even those with NSL) are very variable. There are some that are dead straight for miles, and others that are like roller-coasters. It is necessary to adjust your driving style to the situation (and not over-generalise about X mph being bad, slow or inconsiderate).

Which is why, as I said, my remarks were qualified. If the qualification was not clear enough for you allow me to elaborate: driving at 45 mph in a 60 mph limit, where the low speed is not dictated by weather, road or traffic conditions, is plain bad driving, and the ignorance and stupidity of the driver is usually highlighted by them continuing at 45 mph when they come to a 30 mph zone.

welfayre

gilbert_and_sullivan wrote: »

Other more advanced systems will be able to stop faster i have no doubt due to better/faster electronics on the brakes and suspension..

Please explain how a car without ABS and firm suspension can stop faster, lighter pedal effort yes maybe we've all driven overservoed cars and boy are they horrid things, often so called warm hatches.

The main purpose of ABS isn't to stop you quicker it's to allow you to maintain control of your vehicle while under heavy breaking. Stopping distances will depend on road, weather and vehicle conditions.

Say you have two Clios, they're identical except for one has ABS and one doesn't. If they were on a wet road the ABS one would stop quicker than the other. If you were on gravel the non ABS car would stop quicker. If you were on a dry road they'd probably stop around the same.

"If your vehicle is fitted with anti-lock brakes, you should follow the advice given in the vehicle handbook. However, in the case of an emergency, apply the footbrake firmly; do not release the pressure until the vehicle has slowed to the desired speed. The ABS should ensure that steering control will be retained, but do not assume that a vehicle with ABS will stop in a shorter distance."

https://www.gov.uk/general-rules-all-drivers-riders-103-to-158/control-of-the-vehicle-117-to-126

https://www.safedrivingforlife.info/drivers-and-riders/drivers/driver-knowledge-centre/controlling-your-vehicle

https://www.aaafoundation.org/faqs-anti-lock-braking-system-abs#stop

Info in those links about it.

Strider590

gilbert_and_sullivan wrote: »

It doesn't matter how many holes are drilled or groves in the discs to keep them cool, if they're large enough to dissipate the heat from a full speed stop they'll do the trick.

Cross-drilling and grooves are not so much about heat, as they're about gas and removing said gas from the friction surface, they also ensure that water/debris is removed quickly and actually with the pads I use, the braking efficiency is much higher at high temperatures, hence why the discs are not vented types.

I've explained a few times now, i'm not sure how much more I can simplify it.......... If your braking hard and one wheel momentarily loses it's downward force (slight dip or pothole), that wheel will lock up, on an ABS car it'll recover quickly, but without ABS that wheel will remain locked until you come off the brakes.

DaveF327

angela110660 wrote: »

He was on a dual carriageway doing 57mph but was pointed to the info you gave and was told because he drives a Berlingo for his business he was speeding.

If his goods vehicle is under 7.5 tonnes then the national speed limit is 60 on a dual carriageway and 70 on a motorway, unless a lower limit is shown by signs. 57 is not exceeding the national speed limit (unless it was really a single carriageway?), so your OH should have gone to court to be acquitted if he can show evidence of the road type, vehicle type, laden weight, and posted speed limit.

Talc1234

agrinnall wrote: »

Your title seems at odds with the content of the first half of your post, people driving at 45 in a 60 limit are NOT ignoring the limit, they have simply chosen not to drive AT the limit. While it may be annoying (I find it so myself) there's nothing wrong with it unless it's on one of the few roads that has a minimum speed posted.

Failing to make sufficient progress - i.e. driving too slow, is cause to fail a driving test

gilbert_and_sullivan

Strider590 wrote: »

Cross-drilling and grooves are not so much about heat, as they're about gas and removing said gas from the friction surface, they also ensure that water/debris is removed quickly and actually with the pads I use, the braking efficiency is much higher at high temperatures, hence why the discs are not vented types.

I've explained a few times now, i'm not sure how much more I can simplify it.......... If your braking hard and one wheel momentarily loses it's downward force (slight dip or pothole), that wheel will lock up, on an ABS car it'll recover quickly, but without ABS that wheel will remain locked until you come off the brakes.

Sorry Strider, but no one yet has answered my question.

I asked it because you asserted, and another agreed, that your brakes were so much better than other, shall we say more mainstream cars and that cars like yours could outbrake them.

Basically all i asked was why can a car on the point of lock up, given similar tyre/grip/weight/contact area stop any quicker than another.

It's obvious one car can have braking capability way above it's weight ans way above normal, but unless you have found a way to stop tyres skidding (ABS, EBS etc understood, but you don't have those) i'm still not getting how you can put the extra braking to any meaningful use.

I'm not getting the answer, but thanks anyway.

mcpitman

gilbert_and_sullivan wrote: »

Sorry Strider, but no one yet has answered my question.

I asked it because you asserted, and another agreed, that your brakes were so much better than other, shall we say more mainstream cars and that cars like yours could outbrake them.

Basically all i asked was why can a car on the point of lock up, given similar tyre/grip/weight/contact area stop any quicker than another.

It's obvious one car can have braking capability way above it's weight ans way above normal, but unless you have found a way to stop tyres skidding (ABS, EBS etc understood, but you don't have those) i'm still not getting how you can put the extra braking to any meaningful use.

I'm not getting the answer, but thanks anyway.

Morning! :j

We are back to friction co-effecients, although wikipedia is not the best source, this page gives a good overview https://en.wikipedia.org/wiki/Friction

Back to your point....
If you have 2x identical cars, with identical tyres, identical axle weight, identical discs, pads, brake fluid & servos then there is no difference apart from driver ability (or lack thereof) or the friction surface (grass/tarmac/gravel). In theory they will stop at the same place and within the same amount of time.

However, change any of the variables above and you will see a difference (and in some instances a dramatic difference) in braking ability.

Discs/pads/tyre quality can vary by age of part, correct fitment, quality of part and materials used to produce the part.

As can brake fluid, in addition to brake fluid degrading over time and potentially becoming hydroscopic, lowering the boiling point redcucing braking effort.

I hope this helps, but it is the variables not the constants that will change the affect of braking and it's effeciency/use.

gilbert_and_sullivan

mcpitman wrote: »

Morning! :j

We are back to friction co-effecients, although wikipedia is not the best source, this page gives a good overview https://en.wikipedia.org/wiki/Friction

Back to your point....
If you have 2x identical cars, with identical tyres, identical axle weight, identical discs, pads, brake fluid & servos then there is no difference apart from driver ability (or lack thereof) or the friction surface (grass/tarmac/gravel). In theory they will stop at the same place and within the same amount of time.

However, change any of the variables above and you will see a difference (and in some instances a dramatic difference) in braking ability.

Discs/pads/tyre quality can vary by age of part, correct fitment, quality of part and materials used to produce the part.

As can brake fluid, in addition to brake fluid degrading over time and potentially becoming hydroscopic, lowering the boiling point redcucing braking effort.

I hope this helps, but it is the variables not the constants that will change the affect of braking and it's effeciency/use.

Thats more like it, can't disagree with any of that.

I really wanted to know what trick i was missing, i maintain my brakes to the Nth degree and always have, used to fit Ferodo pads when they were available common place because they gave a much softer pedal with better feel and werent so abrasive to discs as standard OE Textars and such of the time.
Still replace discs way before others would (never needed drilled/grooved except maybe on one fast 90's Rover the brake friction area of which simply wasn't enough for the speed/weight) and remove pads for thorough examination and the usual clean/lube of the calipers at the same time, regular fluid replacements.

Having worked on many other's cars in my time it's astonishing the neglect that brakes see, and the poor standard of some mainstream dealer maintenance where people can be bothered to get the car serviced at all.

I couldn't see how another car given the equal status could necessarily outbrake a well maintained well designed in the first place car on the point of lock up of all 4 wheels.

Yes the variables have it, thankyou.

Car_54

mcpitman wrote: »

As can brake fluid, in addition to brake fluid degrading over time and potentially becoming hydroscopic, lowering the boiling point redcucing braking effort.

/QUOTE]

Pedandry alert!

It's hygroscopic, not hydroscopic.

And brake fluid doesn't degrade and become hygroscopic, it's hygroscopic to start with, which means it absorbs water and thus degrades.