I understand that this is a "true simulation" and is "hardcore". With no driving aids or trainers or safety webs for drivers. But I seem to notice something about the brakes on certain cars. I think it's most noticeable in the Formula BMW.

There seems to be an "Antilock Brake System" effect when I slam on the brakes at speeds 65+ mph. I do not hear or see any skidding when I slam on the brakes at higher speeds. It also slows down very dramatically and quickly. I thought that it was just that the FBM did this because of the immense amount of grip present in its front tyres. Though, it is ALSO very apperent in the XRG as well.

Anyone have any comments on this "problem" or "bug"?

Is brake help on in the options (Options -> Driver -> Brake Help)?

It's more difficult to lock wheels at high speed in cars which produce downforce because the downforce increases tyre grip. As for the xrg, perhaps you just have the brake force set too low?

No ABS as far as I know, maybe you have "Brake help" turned on?

Brake help... Interesting... I will fiddle with that tomarrow morning... I am kinda busy with some stuff right now...

Long time ago when I was just starting to learn about the physics, I thought that big brakes were nonsense - for if one could lock up the tires (tested at low speed only of course) I thought it was the same no matter what speed.

Then I learned that the brakes don't just have to work against the momentum of the road; at higher speeds they also have to fight against the rotational inertia of the wheels themselves. That's why tires lock up easier the slower you go, and why powerful brakes really are useful/necessary the higher the speed the car is capable of reaching.

Downforce matters (most noticable on the winged single seaters). It makes the tires more grippy and require even more violent braking force to 'dislodge' (lock up). In such cars more than others, one can brake extremely hard at first, then must quickly let up on the brake pedal or face skidding tires.

How much weight is on the tires also matter. On a formula style car it doesn't matter much - one can slam on the brakes. But on the road type cars one should come on the brake somewhat smoothly to allow the car to 'settle' or 'lean' it's weight on the front tires, which produces more grip, which allows more brake pressure and braking. Slamming on the brakes will cause locking up much easier than a smooth employment.

Quote from Mikkomattic :

Long time ago when I was just starting to learn about the physics, I thought that big brakes were nonsense - for if one could lock up the tires (tested at low speed only of course) I thought it was the same no matter what speed.

Then I learned that the brakes don't just have to work against the momentum of the road; at higher speeds they also have to fight against the rotational inertia of the wheels themselves. That's why tires lock up easier the slower you go, and why powerful brakes really are useful/necessary the higher the speed the car is capable of reaching.

Downforce matters (most noticable on the winged single seaters). It makes the tires more grippy and require even more violent braking force to 'dislodge' (lock up). In such cars more than others, one can brake extremely hard at first, then must quickly let up on the brake pedal or face skidding tires.

How much weight is on the tires also matter. On a formula style car it doesn't matter much - one can slam on the brakes. But on the road type cars one should come on the brake somewhat smoothly to allow the car to 'settle' or 'lean' it's weight on the front tires, which produces more grip, which allows more brake pressure and braking. Slamming on the brakes will cause locking up much easier than a smooth employment.

QFT. Good post.

beat you to it huh tristan hehe

Why are many people using aggressive engine braking to help slow the car down? If the brakes are powerful enough then it's the grip of the tires which decides how quickly you can slow the car down. And shifting down gears aggressively can't magically give you any extra grip can it?
Even the bible (Speed Secrets by Ross Bentley) says that the engine is designed to make the car go faster, not slower

Oh btw.. Hi all. I'm quite new to LFS. Well, actually I've had the license for years but I've never quite liked this sim...until now. Suddenly I've started to like this sim much more than other racing sims.

Quote from Mikkomattic :

Then I learned that the brakes don't just have to work against the momentum of the road; at higher speeds they also have to fight against the rotational inertia of the wheels themselves. That's why tires lock up easier the slower you go, and why powerful brakes really are useful/necessary the higher the speed the car is capable of reaching.

first things first... the road doesn't have momentum the car (including the wheels and the drivetrain) has kinetic energy which has to be converted to heat through friction between the brake pads and the brake disks... a small percentage of that energy is converted to heat on tyres and road (due to friction again).
the car's kinetic energy due to rotation of the wheels, when going from 100mph to 200mph, increases four times.
the car's kinetic energy due to forward motion of the entire car, increases four times as well.

indeed the brakes have to fight against wheels turning but doing this at a higher speed, it is proportionately the same as they have to fight against the car moving forward... the ratio of energy of rotating wheels to energy of entire car is the same.

and something tells me that the kinetic energy of all four wheels turning is not significant compared to the kinetic energy of the entire car.

but i have not calculated anything (yet) soooo

Quote from tepi :

And shifting down gears aggressively can't magically give you any extra grip can it?

maybe they do it so that the engine stays in high revs for when you are done braking and want to get back to accelerating

Quote from tepi :

Oh btw.. Hi all.

you should have come here earlier :slap:

welcome

Quote from amp88 :

Is brake help on in the options (Options -> Driver -> Brake Help)?

It's more difficult to lock wheels at high speed in cars which produce downforce because the downforce increases tyre grip. As for the xrg, perhaps you just have the brake force set too low?

So... if I put a large lip spoiler on my car, it can potentially help me with braking?

Quote from danowat :

No ABS as far as I know, maybe you have "Brake help" turned on?

I have "Brake Help" turned off. Apparently, I am just good at braking...

I got "pro" for all my training sessions...

I actually think that "Brake Help" means the driving line thing that appears when you press "4".

Hey i use brake help! (sometimes)

Quote from ssm :

So... if I put a large lip spoiler on my car, it can potentially help me with braking?

Yes. Increasing the wing angle will increase downforce at speed. When you have more downforce you have more weight acting downwards on the tyres. This gives you more grip. So, the faster you go, the more grip you have. That's why it's easy to lock wheels at 40mph but much more difficult to do so at 150mph. A side effect of the above is that as your speed decreases the downforce bleeds away. This means you get decreasing amounts of grip as your speed decreases, so you have to ease off the braking pressure to avoid locking the brakes. To get an idea of the difference in downforce, go to the pit and select the downforce tab. Look at the values for the lift and drag on the wings and undertray on the right hand side. Move the speed slider (and take a look at the lift/drag values changing).

Just a thought, but could it just be that the setup that you are using has been designed to have a max break pressure so that you can't lock the wheels. Most of the sets I use are set this way yet if you increase the max break pressure in the setup options you will easily look wheels.

george_tsiros - the important thing to remember here is slip ratios. Say you need -10% slip to brake fully. At 20mph, you only need to slow the circumference of the wheel to 18mph before you are braking fully. At 200mph, you've got to get them down to 180mph before you are braking full. That's substantially more momentum to shave off the wheels, tyres and brakes before you're at full braking force, so you want that to happen fast. The brakes have to slow the wheel and tyre, which creates the restant force. So as I see it, a tyre takes as much braking force to lock at high speed as it does at low speed (all other things being equal), but it will take longer to lock.

Quote from ssm :

So... if I put a large lip spoiler on my car, it can potentially help me with braking?

Not in the strictest sense, as the brake bias will be set to reach the limit of the front tyres first, so more rear grip isn't useful. The extra aero drag will help slow you at higher speeds though.

Nice post Mikkomattic.

Also, I heard Heidfeld say (I believe it was him) that an F1 car can brake extremely hard from 300+ to 50, but it's no good below 50 KPH.

And I still need to test if an F1 really brakes harder (on high speeds) with just 0% throttle and brake, then a road car can brake. I'll try that now! :P

Quote from tepi :

Why are many people using aggressive engine braking to help slow the car down? If the brakes are powerful enough then it's the grip of the tires which decides how quickly you can slow the car down. And shifting down gears aggressively can't magically give you any extra grip can it?
Even the bible (Speed Secrets by Ross Bentley) says that the engine is designed to make the car go faster, not slower

This is probably because of the tire's properties in LFS. (I've heard that) the tires in LFS have too much grip on higher slip angles.

The result: some sliding during the braking due to quick downshifting doesn't hurt the deceleration too much and it's reasonably easy to handle. Quick downshifting can also be used to prevent the car from understeering when entering a corner. With these progressive tires a good driver can kind of move the brake balance by downshifting, set the car into a corner smoothly with big slip angles and thus hit the apex even with a locked diff. Quick downshifting doesn't even hurt your car at all so it's too useful, at least for hotlapping purposes.

So this is all down to LFS' physics issues, mostly tires I guess. I wish this makes sense... There's a lot of talk about it on this forum, done by people that seem to be more familiar with this stuff.

Quote from Bob Smith :

george_tsiros - the important thing to remember here is slip ratios. Say you need -10% slip to brake fully. At 20mph, you only need to slow the circumference of the wheel to 18mph before you are braking fully. At 200mph, you've got to get them down to 180mph before you are braking full. That's substantially more momentum to shave off the wheels, tyres and brakes before you're at full braking force, so you want that to happen fast. The brakes have to slow the wheel and tyre, which creates the restant force. So as I see it, a tyre takes as much braking force to lock at high speed as it does at low speed (all other things being equal), but it will take longer to lock.

hmmm the circumference of the wheel in your example is moving 0mph (stationary) at the bottom (contact patch) relative to the road surface and 40mph forward (on the top), relative to the road surface anyway... ok you may be talking about linear velocity of the wheel relative to the car... anyway, the slowing down of the wheel doesn't happen instantaneously. to get from 200 to 180 you are braking during that 20mph transition. the problem with high speed braking is that the power dissipation we are asking of the brakes is relative to the speed of the car. when braking with 1g at 200mph you are asking of the brakes to dissipate TWICE as much power than at 100mph, even though the rate of decelleration is the same. 1g.

i will think about it again though. been browsing 4chan a bit too much.

Quote from george_tsiros :

first things first... the road doesn't have momentum

Except it is travelling 900mph as the Earth rotates and in another direction at 67,000 mph as it orbits the Sun. Then of course the whole solar system is moving relative t....

Quote from Darkone55 :

...
And I still need to test if an F1 really brakes harder (on high speeds) with just 0% throttle and brake, then a road car can brake. I'll try that now! :P

Cool! With the XFG I got 1.12 G while fully braking (with Bob's road going setup). In the end of the braking zone this was 1.06 G. With the BF1 on full speed (322 KPH) I got 1.27 G very briefly. On 285 KPH it was just 1 G.

So, yes, the BF1 brakes faster without using the brake then an average roadcar can do, probably, but it's for a very short moment.

:P

Quote from Storm_Cloud :

Except it is travelling 900mph as the Earth rotates and in another direction at 67,000 mph as it orbits the Sun. Then of course the whole solar system is moving relative t....

see? that kind of thinking doesn't get you anywhere for the purposes of this discussion, the road doesn't have momentum it has infinite inertia though...

I think you'll find that the inertia of the wheels, tyres and air within them is quite considerable, and imparts heavily on the braking ability (and the ability to lock up) of a fast moving vehicle.

Just take your bicycle, and accelerate on it. Then fit solid rubber tyres, and try again. Even at low speeds you can feel the change for the worse, and the brakes will feel awful. I know this, because I used solid "puncture proof" tyres when I was about 14 after suffering a spate of punctures as I cycled around East Anglia.

I would have changed back, but I couldn't afford to waste a set of rubber, and had to wear them out... which took forever almost!

Darkone: I've heard drag only decellerations of over 2g suggested for real F1 cars (but I have no proof, just what I've heard over the years). That suggests that LFS doesn't simulate quite enough drag at high speed. Just a though...

Quote from Bob Smith :

Not in the strictest sense, as the brake bias will be set to reach the limit of the front tyres first, so more rear grip isn't useful. The extra aero drag will help slow you at higher speeds though.

I meant something like this:

Quote from tristancliffe :

I think you'll find that the inertia of the wheels, tyres and air within them is quite considerable, and imparts heavily on the braking ability (and the ability to lock up) of a fast moving vehicle.

tristan. dude. i took into consideration the inertia of the wheels, the moment of inertia of the wheels, together with the tyres and the air within them. the ratio: (energy of a part) / (total energy) does not change with speed.

energy of wheels ~ moment of inertia * angular_v^2, angular_v ~ linear_v
energy of car ~ mass * v^2

so if you go twice the speed, then the energy is four times as much
but any part contributes four times the energy it did at lower speed

it's not like at higher speeds the wheels start contributing disproportionately more due to rotation... everything contributes more due to increased speed.

and when braking, everything loses energy at a rate that is proportional to its initial contribution ratio. otherwise you'd be left with wheels that turn at 100mph and a car that goes at 120mph. not fun. :P

Quote from tristancliffe :

Just take your bicycle, and accelerate on it. Then fit solid rubber tyres, and try again. Even at low speeds you can feel the change for the worse, and the brakes will feel awful.

of course, because at the same speed you have more energy due to more mass and moment of inertia, but irrelevant

Quote from tristancliffe :

Darkone: I've heard drag only decellerations of over 2g suggested for real F1 cars (but I have no proof, just what I've heard over the years). That suggests that LFS doesn't simulate quite enough drag at high speed. Just a though...

lfs: ~1.2g at 280kph with 0% engine brake reduction and full downforce setup

I know that the behaviour I described in my big post was essentially correct, but the physical explanation might be lacking or wrong. I want to know the exact truth more specifically, so here's the question. Try to answer as briefly and layman-ish as possible (so that I might pass it along to non physics majors)

What causes the wheels to be harder to lock up the faster you are going?