Quote from bbman :

Problem is that almost all bumps are going over the whole stretch of the track, so you'll hit them with both wheels at the same time... And I've never felt longitudinal force through a wheel, neither in RL nor otherwise... That you'll only feel with your body...

There are many many bumps in LFS you hit with one wheel first and the other later (or never), like sewer, tramway rails, curbs, grass, most bumps in south city. IRL you can feel through steering wheel longitudinal forces caused by track irregularities when they affect only one wheel or both wheels differently, and it happens very often.

For example IRL steering wheel is pulling one side when you have a wheel on a curb isn't it? Here roads are very bumpy and I can feel everything with the steering wheel. On smoother roads it requires to go faster but there is always a speed for which you can feel road surface.

In LFS no irregularity will pull your steering wheel, and this is really missing badly because it even suggests tracks are flat which is not the case, and hides amount of work done to improve track surface detail.

We should feel all bumps, even large ones because most of time we do not hit them exactly at the same with both wheels, and this bump feedback should be stronger when speed increases, as more energy is lost on bumps.

Quote from Juls :

There are many many bumps in LFS you hit with one wheel first and the other later (or never), like sewer, tramway rails, curbs, grass, most bumps in south city. IRL you can feel through steering wheel longitudinal forces caused by track irregularities when they affect only one wheel or both wheels differently, and it happens very often.

For example IRL steering wheel is pulling one side when you have a wheel on a curb isn't it? Here roads are very bumpy and I can feel everything with the steering wheel. On smoother roads it requires to go faster but there is always a speed for which you can feel road surface.

In LFS no irregularity will pull your steering wheel, and this is really missing badly because it even suggests tracks are flat which is not the case, and hides amount of work done to improve track surface detail.

I think what you really feel is a LATERAL torque due to one wheel loading/unloading, something that is modeled in Lfs, as you said yourself... Especially the tram tracks can be quite nasty, I get quite a jerk when driving over them sometimes...

Try driving a FWD car like the FXO with a sensible setup in South City and see how much it actually torque-steers...

Quote from Juls :

We should feel all bumps, even large ones because most of time we do not hit them exactly at the same with both wheels, and this bump feedback should be stronger when speed increases, as more energy is lost on bumps.

Rubbish... Apart from the racecars, you have quite an amount of lift at speed, so you should feel LESS, as the wheels are already less loaded...

Quote from bbman :

Rubbish... Apart from the racecars, you have quite an amount of lift at speed, so you should feel LESS, as the wheels are already less loaded...

Forces caused by the track and track irregularities increase with the square of speed. It compensates easily for this lift. If you were right we could take speed bumps at 100kph as we could feel less than a 10kph.


Something is missing with bumps in LFS. More narrow bumps first. But something else too.
I am not sure what else is missing, but I can't help thinking about it when I can drive one wheel on curb or on grass without the steering wheel pulling.

And I suppose this is what they focused on with iRacing...it looks like bumps in iRacing have a different effect on the tyres/car and pull the steering wheel noticeably, and this requires correcting all the time and makes the experience more immersive.

Anyway, this is only an attempt to explain differences between sims FFB. Only one thing is sure...we need to feel tracks are less smooth in LFS, whatever it requires to change/improve.

try a UFR on southcity it does pull around quite a lot, I think the effect is definitely there.

I just remembered something... Didn't Scawen said at one point that FF only gets updated when the steering position changes? I searched for half an hour now but I can't find it...

If that's (still) true, that could be the reason why bumps are not felt: if you hold the wheel perfectly still, there is no change in FFB force happening, thus a bump will go unnoticed except for the visual feedback...

Quote from JJ72 :

try a UFR on southcity it does pull around quite a lot, I think the effect is definitely there.

Yes, UFR gives a very good feeling for bumps, because it if FWD and it loses grip one side or the other because of different normal of the track under each wheel. It is called something like torque steering if I remember well.
I would like to feel bumps as well with RWD.

Anyway, looking with forces activated, curbs and grass do not have any braking effect on the wheels. It gives only vertical forces. Sand has an effect and pulls the steering wheel. Other surfaces not.
I can see that most bumps (surface normal changes) in LFS do not give longitudinal forces at all. Only very big ones like speed bumps on Kyoto.

And this time I am sure it is not my imagination

After watching carefuly what happens with my car (FWD, so geometry is supposed to have a scrub radius close from zero), I noticed:

- I do not feel most bumps through the steering wheel. I feel them through acceleration, and if I feel like the wheel is trying to shake my hands, it is in fact the contrary happening: my arms and hands try to shake the wheel because they are pushed by lateral and vertical acceleration on bumpy surfaces. Maybe in iRacing they put a part of lateral acceleration into FFB to simulate this effect.

- I can feel bumps smaller than tyre width through the steering wheel. They impact the tyre on one side only, and it is like scrub radius is not zero anymore. Smaller bumps give a lot more feeling even on cars with zero scrub radius. Maybe that is what is missing here.

- In my car, FFB strength seems to be directly proportional to steering angle. I mean if I turn the wheel 40 degrees it seems to resist two times stronger than when I turn it 20 degrees. I know this is not very logical when you think about caster effect...which is proportional to sin(angle).
There is this document, about steering wheel torque in a nascar car:
http://www.mscsoftware.com/sup ... manHaas_steering_feel.pdf
Look at figure 1. Steering torque is directly proportional to lateral acceleration (which is proportional to steering wheel angle before grip limit).
There is another document from a Renault driving simulator test. They try different laws for steering torque/steering angle dependance, and the default law they use is linear.
http://www.pervasive.jku.at/Te ... vingSimulator_Toffing.pdf
Look at figure 3.

I have the feeling FFB in LFS is not proportional to steering angle, and that is why it is very soft close from center and a lot harder further. Should it be proportional? Is it proportional most of time IRL?

Edit: Finally it makes sense for me...FFB should be directly proportional to steering wheel angle (tyres not sliding).
It comes from rack an pinion mechanism. To explain quick and dirty (I know it is very very simplified):

- Rack displacement is proportional to steering wheel angle.
Disp=c1.SteeringwheelAngle
- wheels angle are in asin(Disp/steeringArmLength)
WheelsAngle=asin(Disp/steeringArmLength)
=asin(c1.SteeringWheelAngle/steeringArmLength)
- trail, hence FFB is in sin(WheelsAngle)
FFB=c2.sin(WheelsAngle)
=c2.sin(asin(c1.SteeringWheelAngle/steeringArmLength))
=c2.c1.SteeringWheelAngle/steeringArmLength
this is directly proportional to SteeringWheelAngle.

Is it the case in LFS? For me it does not feel proportional, but it may come from the FFB wheel mechanism. IMO it feels like in LFS wheels angle is steering wheel angle divided by steering ratio. In that case...FFB is no more proportional to steering wheel angle.

Quote from Juls :

I have the feeling FFB in LFS is not proportional to steering angle, and that is why it is very soft close from center and a lot harder further.

logitech wheel? if so try changing the force setting to something in the 101-105% range... logitech muddles the forces round the center a bit with the standard setting

Quote from Juls :

- Rack displacement is proportional to steering wheel angle.
Disp=c1.SteeringwheelAngle

Some cars use changeable gear ratio (dependent on the angle) here.

Quote from Juls :

- trail, hence FFB is in sin(WheelsAngle)
FFB=c2.sin(WheelsAngle)

I don't understand this part. That would mean you can't feel any force when the wheels angle is 0, which is not true. Using cosine in that formula would make more sense to me, that is if I have even the most remote understanding of what it's all about.

Quote from w126 :

I don't understand this part. That would mean you can't feel any force when the wheels angle is 0, which is not true. Using cosine in that formula would make more sense to me, that is if I have even the most remote understanding of what it's all about.

I talk here about cornering forces....forces applied by the road on the wheels through the trail (mostly mechanical trail caused by caster*sin(wheelsangle)). Obviously these forces are zero when wheel is centered (in LFS and any other sims), and increase with wheel angle. Mechanical trail is almost zero when wheels are in line.

Quote from Shotglass :

logitech wheel? if so try changing the force setting to something in the 101-105% range... logitech muddles the forces round the center a bit with the standard setting

Yes, tried that, but I think this does not come from the wheel. When I turn in LFS FFB does not increase linearly with steering wheel angle. It increases more like a parabol or a sine function...do you see what I mean?

When I have time I will check it...there is a tool somewhere to see precisely which force is sent to directX. I will use a constant speed, then turn the wheel a given angle, wait for steady state and check the force strength. Then I will see if it's a line or a sin curve.

OK I checked right now...FFB in LFS increase linearly with steering wheel angle. Don't know why I was feeling it different, but it is exactly as it should be...a line first and then a bit slower increase, because it is in fact something like sin(atan(wheel angle)). Once again I was wrong

No way...the only thing missing are bumps...tiny bumps acting differently on left and right wheel...local areas of the track with slope changes like the end of T1 in SO6 if you put the left wheel on this area where the track is a bit larger. There the slope is different and you HAVE to take it into account when close from the limit. This is great!

Quote from Juls :

I talk here about cornering forces....forces applied by the road on the wheels through the trail (mostly mechanical trail caused by caster*sin(wheelsangle)). Obviously these forces are zero when wheel is centered (in LFS and any other sims), and increase with wheel angle. Mechanical trail is almost zero when wheels are in line.

Is it the same mechanical trail that is defined below?

Quote :

Mechanical trail is the longitudinal distance measured in side view between the center of the tire contact patch and the intersection of the steering axis with the ground. Mechanical trail and caster determine the moment arm about the steering axis for lateral (cornering) forces acting at the tire contact patch.

(http://www.tamusae.org/index.p ... w&id=29&Itemid=48)

Imagine a car sliding laterally with no polar body rotation (to make it simple) and the wheel centered. Wouldn't you have some force on the steering wheel?

Quote from w126 :

Is it the same mechanical trail that is defined below?(http://www.tamusae.org/index.p ... w&id=29&Itemid=48)

Imagine a car sliding laterally with no polar body rotation (to make it simple) and the wheel centered. Wouldn't you have some force on the steering wheel?

Sorry my mistake. Mechanical trail is constant. I should have written: torque caused by mechanical trail is zero when wheels are centered.
Remember I talk all the time about a car rolling in usual conditions on a flat and horizontal road, not sliding. On flat road, wheels rolling not sliding, you feel no torque on the steering wheel when wheels are aligned, and when you turn the steering wheel, you feel a torque directly proportional to steering wheel angle.

Anyway, I checked with Yoda from x-sim and this is exactly how it works in LFS. FFB is proportional to steering wheel angle.

Quote from Juls :

When I have time I will check it...there is a tool somewhere to see precisely which force is sent to directX. I will use a constant speed, then turn the wheel a given angle, wait for steady state and check the force strength. Then I will see if it's a line or a sin curve.

Now I understand, you meant the situation of varying wheels angle at a constant speed. Then FFB is directly proportional to sin(WheelsAngle), because it's inversely proportional to the turning radius (if a car is running well below grip limit) and the turning radius is inversely proportional to sin(WheelsAngle).