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Motorsport Wheel Alignment Fundamentals

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You were not talking about the influence of an LSD by a front car in the different phase of cornering. How do you handel it?

Ok so I have little to no experience with FWD differentials, but I think I can infer why it hasn't been covered in alignment. Ultimately, no matter what differential you have, it's only doing something of note once engaged, which is only a fraction of your driving. As for a static alignment, or any of your static settings really, you're trying to set things up to best suit you overall, not within the narrow window that your differential is active. While you can absolutely change things to try and mitigate problems resulting from your differential, adjustable ackerman, and maybe toe curves, you're doing it at the cost of having them correct under other conditions.

Is there a problem you're trying to solve or just understand what's going on?

It was just a question because I do have some experience. The differential of a front-wheel drive definitely has an influence on the cornering behaviour. I have made the experience that a too strong locking differential tends to understeer the car towards the middle of the curve. Accordingly, you can go later back to full throttle to accelerate out of the corner as quickly as possible.

That's why I asked this question, because not only the spring rate, shock absorbers and alignement including tyres has influence of behavior of car cornering and must also be taken into account. Unfortunately this does not make the whole thing any less complex. It is always a complex compromise to find ways to make the car faster. But it is extremely interesting and you are learning every day more if your reflecting your doing.

Watch one of the fastest frond driven aspirated car in Europe. [url=https://www.youtube.com/watch?v=7l545MWUvFk&t=328s]https://www.youtube.com/watch?v=7l545MWUvFk&t=328s

Its probably easiest to view a LSD, front or rear, separate from most of the other settings, or even as a driver influenced condition. Depending on the type of differential, and where it locks, and to what degree, it may become an influence purely based off the difference in between inside and outside wheels while cornering. Following that, it would also be a function of the corner you're negotiating, as a long sweeper requires less steering angle, and less difference in speed between the 2 wheels.

So ultimately, for any given corner, the differential will, or potentially wont engage at a certain point. You can tune the diff to lock below certain thresholds of a corner, and as the driver, force it to on corner exit by accelerating until you overload the inside front. Having both tires locked by itself, not including any acceleration will result in understeer, which for steady state cornering, is likely undesirable.

However, understeer really isn't a bad thing, atleast in the correct situations. When you exit a corner, the entire goal is to accelerate as quickly as possible, and reduce your cornering as you transition onto the throttle. Understeer here really isn't too big of a concern. Unwinding the steering rack a little slower to account for your line altering is a simple fix, if the differential is allowing for a quicker exit.

So, while under and oversteer can get very complex the further you dig, an LSD can simply be viewed as a function of the ackermann steering angle, or limited to transient conditions. When you narrow down the points where it's active you can look to adjust the accompanying parameters. Dampers are massive considerations in transient conditions controlling the rate of load transfer(lateral or longitudinal), or adjusting the diff to suit the necessary corners where it locks. Once the engineering half of it's taken care of you can start focusing on where the diff locking is driver influenced due to the amount of acceleration.

That Civic looks insane, hill climbs like that may have too many hairpins(too many high steering angle corners) to optimize the diff to prevent lock during steady state. You may have better chances focusing on dampers to control rate of load transfer on some of the shorter duration corners where the diff is causing understeer.

Not something I have direct experience of, but have discussed with FWD folks before, so commentary rather than advisory.

Going to depend a lot on the type of LSD used, and how it's set up, how the car is set up, and how the vehicle is to be used. Generally, one wants to limit the LSD affect under no-load conditions and use just enough to avoid inner tyre loss of traction on exit. For most people, a Quife, or similar, may be best as it's progressive BUT has a bias limit of around 6:1 - it needs some torque load to work and so, if the inner is very lightly loaded, or lifts, it won't work. A plate type can be set up with different pre-loads and ramp angles - over-run and power - and will still work quite well if the inner is unloaded or lifted. Some have used spools, or fully locked, 'differentials' but these will be very heavy on the steering, will have a LOT of understeer unless 'chucked' into the corner and so unload the inner, but are immune to lifting the inner, which may be a good thing as they are generally still prone to understeer under power unless the inner is unloaded or the tyres are already sliding.

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