Don´t know if this is a bug or simply poorly simulated...

The XF GT is a 4 cilinder inline 2000 cc and it weights about 900 kgs, in the aston circuit by the descent i noticed that the brake effect from engine compression resultant of downshifting or lifting gas on high revs(well all revs) is almost non existent!!!! this as a tremendous impact on car behavior...i´ll try more cars and see if this is general or only xfgt...

In real life a prepared car with similar specs should almost lock wheels while releasing gas on max revs in first gear, and should have a tremendous brake power if done in 2 gear....

Engines are not simulated very well yet as they are extremely complex, and even harder to implement. However, I don't know about real cars locking their wheels, why would that happen? Cars weigh a lot, I think it's more than enough to provide enough downward force on the tires to make them grip the road. I've pushed my car to the redline in 1st gear a couple of times, and while it's true that there was a lot of engine braking when I let go of the gas, the wheels never locked.

But, it's true that the engines in LFS need an overhaul.

The wheels will NEVER lock on engine braking on a small engined car like this. Get a g-meter in your real car, and measure the rate of decelleration with engine braking. It'll be around 0.1g, maybe 0.2g. Now do the SAME test in LFS with the SAME overall gearing (including tyre size) and look at the built in g-meter. You'll probably find that it's about the same (near enough), but you can't feel it because you're not in the car.

Quote from shiny_red_cobra :

Engines are not simulated very well yet as they are extremely complex, and even harder to implement. However, I don't know about real cars locking their wheels, why would that happen? Cars weigh a lot, I think it's more than enough to provide enough downward force on the tires to make them grip the road. I've pushed my car to the redline in 1st gear a couple of times, and while it's true that there was a lot of engine braking when I let go of the gas, the wheels never locked.

But, it's true that the engines in LFS need an overhaul.

Its not locking per se, but more like this:
your doing 200kph. the ground is going backwards 200kph, and your wheels are rotating at 200kph. youo downshift HARD, and let go of the clutch, and now, suddenly, your wheels are going @ 130kph, why YOU are going @ 190... the wheels arent locked, but neither are they gripping.

worse, if this happens when you are braking harshly, the sudden loss in grip in the wheels (in the moment they loose traction due to seddenly loosing 50kph) the brakes make them lock completely.

Gotta test in lfs if by major engine braking the wheels stop compltely, or just spin a lot slower than they should, given your forward velocity.

In that case, it's simulated fine. Using engine braking will either decrease braking distances (use it to your advantage!) or make your brakes lock when you get on them hard. There's nothing really wrong there at all!

My 1.3 Mk2 Escort used to do the same if I slammed it from 3rd into 2nd before it really wanted to. Sometimes it was useful, sometimes it was a bit of a surprise as it wasn't intentional.. and I actually had the same happen the other day in the BM when coming off the M25 as I was trying to get round a set of lights before they changed and changed down gears a little too hastily while pretty hard on the brakes.. but it got me round the corner nice and quickly

The XRG in particular I found would simulate this pretty well.. bit moreso than the XRT but both seem to work in this respect pretty much how any of the RWD cars I've driven IRL.



Regards,

Ian

I said they should almost lock...not full lock cause engine will not stall...

I drive a lot in real life and very fast sometimes, i do not race professionaly or in circuits but i have driven many many cars from the weakest to exotics. Now in rear wheel driven cars some of you may have already noticed that in hard downshifting even without braking you can make your rear wheels spin slower then the front ones, its not a full lock but they do spin and can get you out of control almost as an handbrake.

I can reproduce what i said in the first post in a citroen saxo 1,6 16v (1076 Kg) in first gear at almost 8000 rpm it goes at 55 Km/h and if suddently release gas the tarmac better be good and dry or wheels simply go to only a bit faster than ralenti speed in less than 1 second...but the point is i think engine compression should be stronger while braking and when releasing gas even without braking...i think most you drive real cars and noticed that when you downshift you loose much more speed than in LFS...unless your engine is missing a spark

Rubbish. Lift off at 8000rpm in a Saxo (do they even rev that high?) and you'll just slow down a bit. You won't lock wheels, lose control, or even slightly lock the wheels. It's just a slight decelleration, and it's pretty much right in LFS.

Try it.

I can shift lock fine (both in my 1.8L Miata and the XR GT and XRT).. all you need to do is enter a corner, shift down one (or two if you don't care about your transmission) step further than you normally would in racing conditions without blipping the throttle, and you'll get a wheel slip. It's fine as is in LFS

well, when i clutch in as i am entering a corner, the rear wheels lock up and i skid out of control...

You clutch in and the wheels lock? What on earth are you doing to the controls, headbutting them?

Quote from tristancliffe :

You clutch in and the wheels lock? What on earth are you doing to the controls, headbutting them?

no, nudging them with my fingers...

Quote from atlantian :

well, when i clutch in as i am entering a corner, the rear wheels lock up and i skid out of control...

Not exactly sure what are you talking about here. How is that even possible?

Quote from xtm :

Not exactly sure what are you talking about here. How is that even possible?

idk how this works, but when i am in the pit and cruising, i stop abruptly when i step on the clutch

Quote from atlantian :

idk how this works, but when i am in the pit and cruising, i stop abruptly when i step on the clutch

If the only thing you do is step on the clutch, you should just keep rolling. Do you slow down or just come to an instant stop?

Quote from xtm :

If the only thing you do is step on the clutch, you should just keep rolling. Do you slow down or just come to an instant stop?

i slow down very quickly

Quote from atlantian :

i slow down very quickly

Are you sure you're not mapped clutch and handbrake wrong, and as a result you are talking about the handbrake ?

Quote from ATHome :

Are you sure you're not mapped clutch and handbrake wrong, and as a result you are talking about the handbrake ?

[sarcasm]oh, yeah, i pull the handbrake to shift[/sarcasm]

Quote from tristancliffe :

You clutch in and the wheels lock? What on earth are you doing to the controls, headbutting them?

'Attention whore' is the phrase that springs to mind. Pitiful really.

I need to install greasemonkey at work here so I can filter its posts without needing to be logged in.


On the topic in hand, I've never ever ever had a car lock up from pure deceleration, least of all a FWD (HTF would that work, logically!?).. can you imagine the accidents that would cause



Regards,

Ian

Can't disagree with Iah H. on the "attention prostitution" verdict.

On the topic though:

If you were going say in 4th, and then shift into 1st and just drop the clutch, the wheels would probably skid (not lock up, for that to happen the engine must stall) for some time, until the revs match their rotational speed. This would probably also ruin yor gearbox and clutch In a FWD its not too much problem, while you still have control in the steering, in the RWD the slip in the rear wheels might be enough to cause a spin.

However I doubt anything drastic can happen when dropping down 1 gear, the wheels might just get a bit of slip for a second, but noting extreme like mentioned above

Quote from TONI_PT :

In real life a prepared car with similar specs should almost lock wheels while releasing gas on max revs in first gear, and should have a tremendous brake power if done in 2 gear....

The only way I'd imagine that happening is if there was way too much dive (i.e. really soft and impractical front suspension). I seriously doubt it would happen on a flat road and if done in 2nd gear the effect would be even less pronounced.

If you want to have such an effect more pronounced in LFS, though I could never understand what for, just up the coasting lock on the differential.

The topic says Engine Compression, so I doubt OP would talk about race tuned engines gives more 'lift off deceleration' than road purpouse engines?

In F1 car without engine brake reduction at lift off you have ~1G of deceleration, which is more then full braking force in road going car.

In first post is example of XFR with race prepared high reving engine and it should produce more braking force at lift-off than road cars, right Toni?

A race engine will have LESS engine braking because engine braking is a LOSS, and you don't like LOSSES in racing.

The huge decellerations when lifting off in F1 are due to AERODYNAMIC DRAG.

They use 'Engine Brake Reduction' so that they can put a lot of energy into the front brakes without worrying that premature downshifts might snatch a rear wheel.

Really? In let say 4 banger with higher compression ratio in exact moment two cyl had open valves and only losses are friction and inertia, but they are the same as in normal comp. ratio engine so don't bother about them.

The third cylinder is doing compression, here the losses are higher than in normal engine.

Fourth cyl. should do work, but at lift-off he is generating the push-force gathered only from compressed air (which will be slightly higher due to higher comp ratio) and from heating this air, so it will increase pressure.

In this case the loses will be higher than in normal car, but when you're in full throttle the positive aspect from 'bang' in more compressed cyl. should decrease the meaning of losses in cyl. doing compression, so the end result will be more power at full throttle and more engine braking and lift-off.


F1 aerodynamics are terrible, but at lower speeds engine does great lift-off braking too. I've read about it somewhere and in LFS it works perfectly, try it.

Oh, I heard that Engine Brake Reduction will be banned in '08 seaseon too.

Quote from pasibrzuch :

Really? In let say 4 banger with higher compression ratio in exact moment two cyl had open valves and only losses are friction and inertia, but they are the same as in normal comp. ratio engine so don't bother about them.

Except that a race engine has less ring:wall pressure and therefore has lower friction.

Quote from pasibrzuch :

The third cylinder is doing compression, here the losses are higher than in normal engine.

Not really. It takes a fraction more energy to overcome the higher compression ratio, but not that much more. It certainly doesn't increase engine braking, because if if did NA Diesels would lock the driven wheels each time you lift off (>22:1 CR)

Quote from pasibrzuch :

Fourth cyl. should do work, but at lift-off he is generating the push-force gathered only from compressed air (which will be slightly higher due to higher comp ratio) and from heating this air, so it will increase pressure.

Which offsets the losses in Cylinder 3 anyway, so consider 3 and 4 to do no net work on the wheel torques.

Quote from pasibrzuch :

In this case the loses will be higher than in normal car, but when you're in full throttle the positive aspect from 'bang' in more compressed cyl. should decrease the meaning of losses in cyl. doing compression, so the end result will be more power at full throttle and more engine braking and lift-off.

The losses will be lower in a race car, not a road car. But the engine differences are some numerous that it's not a fair comparison anyway. But sadly the amount of output doesn't match the amount of engine braking that occurs. Some engines have no engine braking but produce LOTS of power.

Quote from pasibrzuch :

F1 aerodynamics are terrible, but at lower speeds engine does great lift-off braking too. I've read about it somewhere and in LFS it works perfectly, try it.

What sort of figures were they quoting for low speed engine braking decellerations (and in what gear/rpm?)? Because the 1g thing is TOTAL drag braking from about 160mph when on a trailing throttle.

Quote from pasibrzuch :

Oh, I heard that Engine Brake Reduction will be banned in '08 seaseon too.

It is, and it's far more important than traction control from a spectator point of view, because you will see more cars losing it in braking zones than on corner exit.