The one time I can thing of locked brakes being good is when you're in a high speed spin and you know it isn't going to be good... hit the brakes HARD with the other foot on the clutch until you hit something or (hopefully) come to a stop without damage.... in LFS nobody gives a shit about damage though .
ajp71: In a car with lotsa downforce you absolutely slam on the brakes really hard early on because there is so much grip being generated by the downforce that you can slam on the brakes without locking them.. so it's not necessarily how the brakes/tires are designed but because of the downforce available... then you have to ease off because you lose downforce and of course because you start steering.
I don't get the "locking the brakes to catch a slide." Care to explain how it works? The way I see it is to catch a slide you need more weight on the rear.. definitely not locking up the brakes so that the weight is transferred to the front, which results in even less grip in the rear. If you're understeering through a corner you get off the gas and maybe a bit of brake if you're in real trouble... I don't see how doing the same thing could help you get rid of a slide.... except that when you completely lock the fronts you overload them and they lose grip, but with locked fronts you also lose all steering.
"Locking brakes on gravel = shorter braking distance": I don't see how this could be true for anything except really deep and soft gravel.. with any kind of a hard base and loose gravel on top proper braking with proper tyres will stop you much faster than locking up, I could be very wrong though.
Eeeeh? You sure about that? Because I have seen a litle comparison, live on a test track in driving school. Same car and the driver, one run with and without ABS and when ABS was enabled the distance was dramatically degreased, and on a slippery surface the difference was offcourse much more bigger. And there is a point in that locking up is the best way to stop, in real life if you have to do a emergency stop you really don't have the time ease up from the brake and if you do you there is a risk that may go even further and take the hit. Offcourse this is a different situation on a slippery surface, now Im talking slippery surface which in scandinavian standards is ice where you lock up you are totally a passenger, the car just keeps going, going, going and going...and going and then you hit something and stop.
But in LFS, and in racing I think the locking up the wheels isn't a good thing, maybe on a slow speed they can lock a bit just before you stop behind the spinned car in SO. I personally like to have some extra braking force, so you can stop more quicker and don't use the 100% of the brake travel on normal brakings on corners. It's not fun when you are doing your normal speed and notice that there is someone stopped front of you and you can't dodge, you press the brake pedal down much as you can but the car does't slow down much as it could because its a fresh WR set from inferno with tiny tiny allmost zero braking force. As said here, on high speed you can have more force to your brakes, and start slowing down much faster, and that can actually help you to dodge the car in front.
No this is true for small single seaters both winged and unwinged of course different racing tires/brakes will behave seperatley. Whether LFS simulates this is a different question as brake temperature is not simulated and neither is cold brakes 'biting' which can easilly spin a car out of control when one wheel locks.
No no - that's a myth. Look at this graph carefuly (it mirrors in the line y=-x for braking). Slip ratio is (wheel speed - car speed)/(car speed). With locked wheels you loose about 30% of the braking force achievable at optimum slip ratio.
only reason I'm aware of for intentionally locking your wheels is when things have gone past the point of no return, and you want to limit damage / exert vague control over direction. in a spin without locked wheels you can have them gain traction and cause consiberable problems (rollovers, veering into walls, etc)
Never heard of regaining traction causing problems. It's more common to have a choice in locking up into a wall or spinning the car and risk rolling it in the gravel. I know someone who chose the second option and rolled it at Le Mans Classic (no belts = punctured lung + broken bones :doh.
Two things that affect the most to braking: tire surface and road surface. If your tires are made of steel you get less grip and different equations/graphs than if you use rubber. Same thing with different road surfaces. Asphalt is not = gravel in terms of slip ratios & stuff. When you apply force to soft surface (=gravel, rubber, big girls) they act differently than with harder surfaces (steel, asphalt, XRR...)
Next thing you say is that asphalt = plastic or asphalt = shampoo
There is very sunny weather outside. Why don't you go to beach, take a tire with you and experiment with them
I was talking about once already in a spin. locked wheels will bring the car to a stop as quickly as possible and avoid spearing off crazily when any wheels find grip. Of course, no extra braking force is required to be able to do that - I can see no reason for having more braking force available than the max possible for any corner.
Yeah. The greatest advantage is control under braking. With ABS you can just smash the brake pedal and swerve. The car will swerve, tyres squirming etc, but you have a lot of control. Without abs, you crash.
I do not know what you saw at the test track, but are you sure that the instructor gave his 100% ability when braking without abs? i do not want to sound patronising, really, but i think that sometimes when we try to teach people something we exagerate to get the point across. For example, the instructor, trying to convince you that ABS is double-plus-good (it is, but i do not want to rely too much on automagic to control a vehicle...), would not try hard when braking without the ABS.
If you want to see what ABS is all about, go about 100kph, stomp on the brakes before entering a rather tight bend and steer normaly.
It wasn't about convinsing or brainwashing that the ABS is a must, it was just a demonstration of the differences. There is a difference and the car did stop litle quicker than with full locked wheels. ABS is a great, great invention specially on very slippery surfases and when you have to dodge something, but the funny thing is that when it came back then whenever it was, the cars which had it had more accidents than the same car without it because the drivers thougth they were invinsible and left their brakings too late and drove faster. As you said, you should never trust too much to technical aids, if you notice them working you are a sucker driver
decent abs systems will run more than one channel - so brake pressure can be applied more individually between the wheels, shortening stopping distances.
the single brake pedal is a compromise. given a perfectly talented alien, with a brake pedal for each wheel, I'm sure they'd do a better job than any abs system.
I was taught to do my own ABS years brefore it was popular, at the time it was called 'pulse braking or safety braking'.
Any time you locked the wheels on gravel or wet road ( for training puposes), it was drummed into our heads that a locked wheel has no grip therefore to turn, swerve at moderate speeds.
Release brake when wheel is locked, turn steering wheel,allowing tyre to grip and car to swerve, pump brake, to reduce speed, and repeat, releasing on brake turn wheel off brake car steers around object etc etc , saved me on wet roads at traffic lights from running up the backside of dumb car that wanted to stop dead on a yellow light etc at up to 60 klms
My 2 cents worth
Still, it drops and that's enough to make my point. It really depends on the tyres. And how far does Todd's graph go for slip ratio? Does it reach the 100%? Link?
It's not a myth, tested that some times ago in practice for my school project (different speeds between 40-120 km/h, dry clean tarmac, car was Renault Safrane) The car stopped in shorter distance when all wheels were locked than with ABS turned on. We ruined quite few tyres that day btw. Of course the car is unsteerable (is that a word ) then but it's the most efficient way to stop on dry tarmac. That's why it's called emergency braking.
When a tyre locks up it looses grip. No grip, no braking. Same as it does laterally when going around a corner though with braking rather than inducing lateral G through cornering, which can be helped by thicker tyres; greater contact patch, with braking you have a longitudinal force. Treat braking like you would be going around a corner. The tyre will loose grip, start skidding, at some stage of the braking process. Once it does it looses maximum decelleration. Similar to the way a car drifts when it's looses lateral grip in a corner. Maximum braking ability is found right at the boundary between grip and skid. This is where the wheel is actually mechanically slowing the car down by applying controlled friction to the axle, once entering a skid the cars momentum easily overcomes any braking friction that the rubber has with the road surface. This is not a good scenario as it is un controllabel exept in a few circumstances.
Rally drivers obviously use loss of grip to increase rotation through the bendy stuff. Rally cars can develop more forward traction than they can by braking so by getting all four (Or two) driven wheels facing the direction of intended travel as fast as possible the better. You couldn't do this without letting the arse have a good 'ol slide around.
Someone mentioned the Nascars locking up the fronts in an effort to regain control. The only way I can see that working is that the brake bias must be such that the rear virtually gets no braking other than a token amount. Resulting in what can be lickened to a trailing anchor on a ship riding storm. The anchor (Rear brakes) trails behind in the current keeping the ship facing into the storm. With the front wheels locked the rear has more braking potential thus slowing the rear down faster than the front. This means that with a bit of careful steerage you can regain control of the front end because it naturally wants to point in the direction of travel.
But other than a few specialised techniques there is no advantage to locking up your tyres under braking.
Who said ABS is good? illepall ABS doesn't allow the wheels to slip enough for tramac, so that they don't slip more than they need to on a slipery surface. That doesn't change the fact that braking with locked wheels is not optimal. A good driver will beat ABS on most surfaces by a substantial margin. Most moms who drive their cars like shopping troleys won't though.
EDIT: Put it this way. Look at my picture. With ABS you have enough grip left over so that you don't lock the wheels on a wet surface and also you can maneuver on tramac. This is probably safer for your average driver. However, electronics will never beat a good driver.
@Funnybear - you are not entirely correct. With locked tyres you get 70% of your maximum achievable traction force and practically no lateral force.
Eh? Have you done a driving lesson? You will fail your test if you lock the wheels during the emergency stop (unless you immediately release the brake somewhat and reapply).
Tukko - Just re-read what Axus/Funnybear said, they couldn't be more correct.
You never know how good a driver they used for best effort tests. Seriously, I promise you - if you pull a driver out of F1 or any major racing series they will out-do ABS by a substantial margin.
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) then but it's the most efficient way to stop on dry tarmac. That's why it's called emergency braking.