Hi all,

just wondering if there is any general advice people can give in regards to setting up preload correctly. Cheers

Herbz

I'm shamelessly quoting myself here, but it seems like that explanation is generally correct and easy to understand, so there you go...

Quote from AndroidXP :

The more preload you add, the more the car will behave like with a locked diff during the change from being "on power" to "engine braking" (or the other way round). A clutch pack LSD without preload completely opens up (read: it's like a open diff) if there is no torque acting on it, which can have a very bad effect if you were relying on the stabilizing effect of the LSD.

So, it mainly affects you during the short time after braking for a corner, where you're almost not on the throttle yet (neutral load on the diff). If the car is oversteering in that situation, add preload. If it is too hard to turn and understeers off all the time, remove preload.

Thanks

At the risk of sounding completely nubbish (yes, I poked through LFS Manual...), how do I figure out the Locking/Coast percentages? By default, I think they're set for 80% on both braking and coast, and I understand what braking and coast are (duh), but what I can't seem to figure out is what the percentages mean.

If someone could simply explain that, I think I could get it all figured out with the help of Android's 'english version of how preload works'. Thanks!

Hi there,

quite a few posts about this, here are a couple.

http://www.lfsforum.net/showth ... amp;highlight=clutch+pack
http://www.lfsforum.net/showth ... amp;highlight=clutch+pack

Also Bob's setup guide is great:
http://lfs.thefloatingwidget.net/guide.html

At 80% locking, one driven wheel can receive up to 80% more torque than another driven wheel (e.g. the inside wheel would get 10% while the outside would get 90%). Under power, increasing locking increases oversteer, while under coast, increasing locking increases understeer.

Thanks, Bob, exactly what I needed

Quote from Bob Smith :

At 80% locking, one driven wheel can receive up to 80% more torque than another driven wheel (e.g. the inside wheel would get 10% while the outside would get 90%). Under power, increasing locking increases oversteer, while under coast, increasing locking increases understeer.

Thank goodness. Someone who can explain it without resorting to maths! Thanks Bob.

Here's a snippet on preload from a GTR-Motec guide.

Guide removed as it was deemed to be a load o' Bollocks...

Last question (for now)

The preload setting in the garage goes up to 800Nm, what is a "normal" starting point from which to make the tweaks suggested in other posts?

(I'm open to some mathematical answers if need be)

Personally I start with 100Nm. Depending on car power, size and weight I might start out a bit lower or higher, but it's generally around that value. Everything else then comes from driving and testing.

Regarding this GTR Motec guide, I think that explanation is actually not quite accurate.

The real clutch LSD is just like an open differential, but with clutches placed inside, that, depending on how hard pressed together, limit how freely the individual wheel can rotate related to the other. How hard the clutches are pressed together (and thus how much torque difference they sustain) is controlled by the torque coming from the engine. The more torque the engine puts on the differential, the more the clutches lock together. I'm not going to pull out maths now (because I suck at it), but the percentage of locking basically means how much of the engine torque is used for pressing the clutches together. However, this setup also means that at NO engine torque (when neither positive/power nor negative/coast torque acts on the diff) we're basically driving with an open diff.

This is where preload comes into play. It is actually a few springs pressing the clutch plates together, so that the situation of a open differential never occurs, because there is always a minimum pressure exerted on the clutch plates. By adjusting preload you set the strength of these springs, but instead of adjusting the springs directly, in LFS we're actually setting the resulting torque resistance of the clutches - which does make a lot more sense in my opinion.

Atm I'm using about 60Nm in the road cars and 100Nm in the race cars, for very rough guides. I'm having to remove understeer from the springs as well to compensate (or rather, I had to add additional understeer before to compensate for the lack of pre-load).

I will admit to having very little time to really play with things yet.

Remember with both pre-load and coast locking, they are adding understeer, so (potentially) making the car slower at the gain of stability, so you should be trying to use as little as possiblo of both, IMO. If you're having to use high values to keep the car drivable, then you're probably just making up for a problem elsewhere in the set (just like locked diff sets are often very oversteery when used with a proper LSD).

Thanks again gents
AndroidXP thanks for your explanations, they are very clear and helpful.

Quote from Herbz :

Here's a snippet on preload from a GTR-Motec guide written by WR304.

this gtr stuff is a complete load of rubbish but you come to expect these things from people who think a tyre curve should look something like this
http://upload.wikimedia.org/wi ... rmatt_landscapeformat.jpg


anyway is there a telemetry analyzer that shows the torque difference between the driven wheels ? would be interesting which maximum difference you can get with a locked wheel on all cars to have a theroshold above which theres not much point using a clutch pack in the first place

Quote from Shotglass :

this gtr stuff is a complete load of rubbish but you come to expect these things from people who think a tyre curve should look something like this
http://upload.wikimedia.org/wi ... rmatt_landscapeformat.jpg

For a guide:

Bob's road car preloads are actually quite close to RL examples I encounter. In practice, anything over 100Nm is considered quite a lot for road cars.

For reference, the optimum preload for a Pajero 2-way clutch LSD is actually 100-110Nm for 31 inch tires (OEM). This is very much on the high end of OEM recommended preload settings. Coupled with its 4 pinion high dynamic locking factor design, no wonder it is one of if not the best performing OEM supplied clutch LSDs of all time. All without loss of LSD center durability and excessive rear tire drag whilst making slow and VERY tight turns.

In LFS, 150Nm of preload is enough to bring RWD behavior much closer to RL RWD behavior. It's also sufficient for putting power to the ground. Personally I don't need anything more than 200Nm on the road cars in LFS. With the race cars and their stickier tires and stiff suspensions allow more preload without as much penalty in understeer.