Quote from Bob Smith :

But it isn't a passive clutch pack, it's Sailsbury type (IIRC). Isn't the locking of those diffs torque sensitive? In which case it can't be a constant TBR.

The locking torque is indeed variable and controlled by the combination of wheel torques coming into the unit. The torque bias ratio itself is constant, however. Both are correct

Quote from JeffR :

Hmm, one of my posts never made it into this thread, my fault, should have checked.

I wanted to know what type of limited slip differential was being modeled by LFS, and if anyone here that races in IRL think the differential model is correct yet, but as posted it's still in development, so it's probably not there yet.

The point about kinetic friction reducing with speed would probably have some effect on a single pair of clutch plates type differential, but it would be minor. I went a bit off track here, sorry about that.

Similar to your thread at RSC, I wanted to ask if differentials with multiple clutch plates, and selectable ramp rates could be implemented.

Jeff, Scawen appears to have done the new LSD model properly. Your comments about decreasing friction coefficient with velocity at the clutch mechanism in the differential is probably correct to some extent, but is most likely a very minor thing. Any graphs I've seen on torque bias ratio on such differentials indicate it to be a constant anyway. I'd be very surprised if the variation was large enough with velocity to notice a difference. The variation in what the tires are doing when the slip ratios are vastly different would probably overpower this to the point where you'd not notice the difference between modelling or not modelling that.

My guess, and it's just a guess, is that the torque bias ratio in LFS's LSD model is a constant.

I think police pursuit would be quite a lot of fun

I mostly drive the FZR. What fixed this for me was actually increasing the power side diff. Don't remember what I'm using but I think it's fully up at 80%. If the back is stepping out too much when you release the throttle, then increase the coast side diff too. If you tinker with those a bit you can get it to drive quite nicely at part throttle and off throttle.

Usually what I do going into turn one is let off the throttle just a bit early and very lightly touch the brakes before going to full braking. This way the guy behind me has a better chance of reacting in time when he sees my brake lights and thinks I'm stomping the pedal. Turn one is actually a bit tricky for me too because I just can't seem to figure out a braking point at many of the tracks. Coming from a dead stop the speed isn't usually as high.

I too will just move out of the way and let people pass. Nine times out of ten there's a huge pile up and you're really only a couple of seconds behind the leader anyway, so if you're faster you'll catch up. If not, then it's better for them to be out front anyway.

No problem. Glad to help.

Wow, simultaneous posts

Quote from Handler :

During a race any time I go to the Pits and make changes or normal stop, the fastest speed that I can get up to is around 47 m.p.h. Can anyone tell me if I'm doing something wrong or is it something wrong with the software. I sure would like some help on this one.

thanks,
Handler

Turn off your speed limiter. I think it's L on the keyboard, but am not sure. It can be mapped in the options to whatever you want.

Hi Bob

Indeed, you could argue either way and still be right

Quote from Bob Smith :

I've read (although I've no hard data) that the tyre in LFS are not particularly load sensitive which has both plus and minus points. Considering the very small differences in cornering speeds between the road cars (although some weigh twice as much as others) this seems to be accurate.
I think making them more load sensitive would help with acceleration in the RWD cars, since you'd lose grip from the front and gain at the rear the harder you pressed the throttle, which must be of some benefit.

Actually, making them more load sensitive would reduce the RWD grip under acceleration. You'd get more tendency toward power-on oversteer and power-off understeer.

On tire pressures and under/oversteer: This is a confusing area until you see some graphs and try to code the effects into a sim

Basically, when you increase tire pressure you're doing two things:

1. Increasing the stiffness of the tire, i.e., cornering stiffness. This means that if the force peaked at 12 degrees slip originally, the force might peak at only 10 degrees once you cranked up the air pressure. Imagine your rear tires peak at 12 degrees. Assuming the maximum grip is the same at both ends of the car and doesn't bother to change with tire pressure, cranking up the front pressures can induce oversteer. If you're in a turn and the front tires are maxed at 10 degrees and the rears are maxed at 12, you have an oversteer situation by definition, even if all the tires have exactly the same amount of grip they had before the pressure change. This car will wallow all over the place and want to turn in really quick and not stop rotating. Spin city... I've read that slalom and autocross racers will frequently crank up their front pressures to the max to take advantage of this, even if they lower the total amount of available force at that end, it now oversteers.

Decreasing front pressures to get the fronts to peak at 13 degrees will make the car nice and stable. Your max cornering speed is the same, but now the car is understeering ever so slightly and it's more stable on the straights as well. It took me awhile to figure this out. My own sim car would wander all over and was a trick to drive when I first got it going. Eventually it dawned on me that increasing the rear stiffnesses above the fronts would stabilize it and get rid of the oversteer. Perhaps this is one reason many racing cars use wider and probably stiffer tires at the rear.

2. Increasing tire pressure can either raise or lower the over all grip. LFS at the moment seems to produce peak grip at rather low pressures (which is realistic). But because of #1, if you decrease the rear pressures to increase their grip, you can still wind up with an oversteering car if the rear cornering stiffness is lower than the front. I.e., you might be at 15 degree peaks at the rear and 12 up front. The car oversteers like crazy, but in all actuality it has more grip at the rear than it had before

So, as others have said, it's probably best to play very gently with tire pressures in little increments rather than trying to make huge jumps because of the two combating effects. It's very likely that you may start out lowering the rear pressures a bit and find you're getting more understeer because of the increased grip, but the moment those rear tires peak at a slip angle greater than the fronts, the situation will reverse itself. At that point, lowering air pressure further will cause oversteer, even though the rear grip is higher. Wierd, huh?

Last edited by jtw62074, Thu, 8 Sep 2005 18:30.