I'll believe the guys with the championship titles. For open wheelers I'm sure it's true- don't use the engine. Got touring cars, you'd better engine brake.
I think it has significance to the car balance while braking. No doubt that engine breaking exists as the drive-train is not a lossless system. Engine breaking doesn't contribute an overly large portion of the total braking system available to the driver but it isn't completely insignificant either. Also wondering if it maybe a subject of reliability throughout the race. Given that (correct me if wrong) most of these cars (e.g. btcc) finish their races with nearly no brake disc material remaining so it would be wise to use every available source of braking you have at your disposal, even if that means teething off a little brake pad usage time with early on engine braking. (ofc though the engine braking is going to be there all the time you have your foot off the accelerator).
I think you may have read it out of context. You are correct in saying that locking all your tyres is not the quickest way of slowing down the car. However, when compared to only a front or rear side lock up, then having all 4 tyres lock-up will decelerate quicker but at the cost of sever tyre wear (e.g. heavy flat-spotting). Here is my understanding/reasoning of perhaps why... Imagine a scenario where your car is set-up with too much forward brake bias for a given load distribution whilst under braking, resulting in your front wheels locking first as you go past the point of threshold braking. Then imagine that whilst decelerating under braking, you purposefully modulated the brake pressure just right so that you maintained only front wheel lock up. So you would be using only 70% of the maximum braking traction available of the front tyres from the moment you locked your wheels to a full stop. This 30% reduction in front tyre braking is also a reduction to the cars overall braking capacity. As a result, less braking force = less weight shift forwards and thus increasing the rear tyre load distribution = increased rear tyre's maximum braking traction available. In this very instance, you now need more rear end braking in order to reach the rear tyre's full braking capacity. I assume that Carroll is saying that a car with front wheel locked up + rear wheel well below lock up takes decelerates slower than all four wheels locking up for the above said reasons. So again, i don't think he is saying that it is preferable to lock up all four tyres even if there were no adverse tyre wear affects but is simply making a comparison to only some tyres locking up.
This is a must see. Very nice to listen to and very informative at the same time. Funny thing is, even when I didn't look very much into the technical side of braking alone, I always used degressive braking in med/high downforce cars (formula cars) instinctively. It's so logical: driving at 300kph, the wings produces a HUGE load on the tyres, make them grip extremely well, so you can slam the brake (obviously not over the limit of traction) much harder then when a 150kph slower, because the load decreases. So logically, you need to step on the brakes hard, and immediatly decrease braking force as the car decreases speed, thus tyreload. I like all this I think the discussion about the quote about locking up all four tyres is the fastest way to slow a car down, is a bit out of context. I'm with DrR1pper on this one..
I disagree, if you have locked your front wheels then there is no reason not to increase your braking pressure until your rear wheels are at maximum braking force. If you then locked your rears then the cars total friction will substantially reduce again so you will never experience higher grip when locking It is basic physics that static friction is higher than kinetic friction. This means any object that is static requires a larger force to get it moving than it requires to continue moving. Place an object on a ruler and then increase the incline of the ruler steadily, you will find you get to a certain angle before the object starts to slide down the ruler. Now move the ruler to a smaller incline and give the object a bit of a push to break the static friction, at this point the object will slide down the ruler even through the ruler is much less steep than before. You can take this further by realising that to stop the object sliding you need to reduce the angle of the ruler even further - just as you need to reduce braking pressure much below what you normally would use to break in order to unlock your wheel. With tyres rotating it gets a little confusing because they are moving and the road is moving, but the surfaces are almost in a static state in relation to each other. It is when the wheel locks that kinetic friction comes into play (the tyre is sliding over the surface just like the object on the ruler) and hence braking force is substantially reduced. http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/ben_townsend/staticandkineticfriction.htm
Well I was saying it all the time, sometimes accused of being "elitist", "overly smart".. braking is a difficult skill, just as difficult as cornering. And more than half of simracers are doing it wrong..!
Think about things this way Guy, to properly downshift without causing damage to drivetrain or loss of traction, you have to match rpm to wheel speed. In order to do this, you are not using engine braking during this period. Heel toe braking allows you to come close to maintaining the brake pressure at threshold while shifting down, but is not as accurate as only using the brakes, thus you lose a little bit of threshold as well as the engine is only braking for short periods on each downshift due to the speed of deceleration. A properly modulated brake will be more efficient in stopping the car without wheel lock than using the engine brake technique as long as the bias has been tuned correctly for the car. This is all just math and you can't argue with the math.
Great stuff there. Thanks for sharing/posting. I needed this to read to help me in the GT class - Endurance Series mod for rFactor.
I had forgotten about the brake balance in the rain. I've been messing with it lately and I was wrong earlier. As for locking up all 4 tires- in another book Smith says that a blocked wheel will lose 30% of its grip. So it will slow the car down of course, but 30% worse than braking right on the edge of traction.
Yes, thats why racers dont like ABS. Its continous locking. Life saving for ordinary drivers (me, I depend on it), but slower for racers.
But they then don't know that it is not always so, depends from tires and conditions. My source for this is this: It is only 153 pages, but shows nicely difference between radials and bias tires. They do still offer you bias slicks, popular in hill climbing and lower class racing because of some of characteristics it has.
@jtbo Yes if your talking about dirt,rally,motocross ,speedway,drags ect but on tar unless your on a drift mod your dreaming. Locking or spinning the tyres will allways cost you,either in wear or flatspots and loss off traction.
Yes, flatpots will occur, tires will wear but stopping can be faster, however not very sensible. With bias-ply tires peak slip is achieved at lockup when braking however, on tarmac. It is in that study which I mentioned, also there is different surfaces and for example on loose gravel locking is fastest way to stop. Now when we in future get gravel physics in rF2 it will of course create more interesting driving, with real road changing where stuff is more loose and where it is tightly packed + gravel marbles, it will be really dynamic experience and true challenge for driver to know which technic to apply. On tarmac, it is of course insanity to lock wheels, no matter if you would stop better, unless when avoiding accident it can be beneficial to know all the data which allows to make best choices.
Now I'm not sure I understand you nikos or maybe you mistyped? The point of ABS is the exact opposite, to *prevent* any wheel locking. It's called Anti-lock braking system after all, lol. With such advanced systems today I'm pretty sure ABS on F1 cars wouldn't make them slower, in fact they'd probably be a tenth or two faster, that's why it's banned because drivers wouldn't have to care about gradual releasing of brake pedal at all.
ABS lockes up, eases off, locks up, eases off etc on and off to keep you at the limit of traction all the time but a driver can do it a lot better than an ABS system can. It'll make a slower driver faster but a fast driver slower. I've read that ABS gains you huge time in the rain, but you lose time in the dry.
I don't think so; not when we're talking about F1 where if ABS was allowed, they would spend millions dollars just on this one aid and make it react REALLY fast. Of course 40 year old ABS from a Cadillac is not going to make shorter braking distance than Vettel's left foot, but with today's tech? In rain, definitely.. in dry probably too
The way I understand it and feel it, slipping occures momentarily all the time during braking with ABS. From wiki: ABS...is an automated system that uses the principles of threshold braking. Threshold braking or limit braking is a driving technique most commonly used in motor racing, but also practiced in road vehicles to slow a vehicle at the optimum rate using the brakes. The technique involves the driver controlling the brake pedal (or lever) pressure to maximize the braking force developed by the tires. The optimal amount of braking force is developed at the point when the wheel just begins to slip. I remember racing drivers hated ABS, I also remember Mclaren F1 road car wasnt fitted with ABS for that reason, racing drivers wanted to judge for themselves the traction limit. Maybe these systems did get better, I dont know.
