I was looking into the unsprung mass distribution of cars to try find an error on a program that MonkOnHotTinRoof is programming for us (tristancliffe, BobSmith and myself do the work from the physics point of view). The problem was that at some points in time we were getting a negative tyre normal load against the surface (long calculation - won't bore you with it now) and I assumed that the error may be from the unsprung mass being unevenly distributed. Here is a calculation I did based on some data that ColCob gave me.

mTotal - Total Mass

mUnsprung - Unsprung Mass

mSprung - Sprung Mass

distrTotalF - Total Mass distribution on front wheels

distrSprungF - Sprung Mass distribution on front wheels

distrUnsprungF - Unsprung Mass % of front wheels of total mass

mTotal = mSprung + mUnsprung

W = mg (Weight = mass * gravity)

Therefore when the car is not accelerating perpendicular to the road surface:

F = mTotal * g

F = (mSprung + mUnsprung) * g

F is the total force against the road exerted by all the tyres

When the car is stationary the force exerted against the road by both front wheels is:

FTotalFront = distrTotalF * (mSprung + mUnsprung) * g

distrTotalF * mTotal = distrSprungF * mSprung + distrUnsprungF * mUnsprung

distrTotalF * mTotal - distrSprungF * mSprung = distrUnsprungF * mUnsprung

Therefore the force exerted by the unsprung mass on the front wheels is:

FUnsprungFront = (distrTotalF * mTotal - distrSprungF * mSprung) * g

The total force exerted by the unsprung mass is:

FUnsprungTotal = mUnsprung * g

Therefore the percentage distribution of that mass on the front wheels is:

distrUnsprungF = [(distrTotalF * mTotal - distrSprungF * mSprung) * g] / (mUnsprung * g)

distrUnsprungF = (distrTotalF * mTotal - distrSprungF * mSprung) / (mUnsprung * g)

If you consider the fact that all those values come from a long calcuation with some slightly rounded-off values, they are probably considered 50:50 in LFS. This is inaccurate. A rear wheel should be much heavier than a front one on the FZ50 for instance and this could make quite a big difference as to the way cars handle. Seing as Scawen is busy on physics updates now, perhaps this can be added in the patch? It shouldn't take that long but it is something that would change the cars under certain conditions (high vertical acceleration) handle quite differently. Or do I have something wrong in my calculation...

Variable NamesVariable Names

mTotal - Total Mass

mUnsprung - Unsprung Mass

mSprung - Sprung Mass

distrTotalF - Total Mass distribution on front wheels

distrSprungF - Sprung Mass distribution on front wheels

distrUnsprungF - Unsprung Mass % of front wheels of total mass

CalculationCalculation

mTotal = mSprung + mUnsprung

W = mg (Weight = mass * gravity)

Therefore when the car is not accelerating perpendicular to the road surface:

F = mTotal * g

F = (mSprung + mUnsprung) * g

F is the total force against the road exerted by all the tyres

When the car is stationary the force exerted against the road by both front wheels is:

FTotalFront = distrTotalF * (mSprung + mUnsprung) * g

distrTotalF * mTotal = distrSprungF * mSprung + distrUnsprungF * mUnsprung

distrTotalF * mTotal - distrSprungF * mSprung = distrUnsprungF * mUnsprung

Therefore the force exerted by the unsprung mass on the front wheels is:

FUnsprungFront = (distrTotalF * mTotal - distrSprungF * mSprung) * g

The total force exerted by the unsprung mass is:

FUnsprungTotal = mUnsprung * g

Therefore the percentage distribution of that mass on the front wheels is:

distrUnsprungF = [(distrTotalF * mTotal - distrSprungF * mSprung) * g] / (mUnsprung * g)

distrUnsprungF = (distrTotalF * mTotal - distrSprungF * mSprung) / (mUnsprung * g)

ResultsResults

` `

Car Name Unsprung Mass Distribution

XF GTI 50.00088%

XR GT 49.95396%

XR GT TURBO 49.95229%

RB4 GT 50.09896%

FXO TURBO 50.02603%

LX4 49.97068%

LX6 50.02130%

MRT5 49.99528%

UF 1000 49.99533%

RA 50.01218%

FZ50 50.04772%

FORMULA XR 50.06078%

XF GTR 50.10655%

UF GTR 50.11179%

FORMULA V8 50.01272%

FXO GTR 50.09502%

XR GTR 50.00491%

FZ50 GTR 50.08479%

If you consider the fact that all those values come from a long calcuation with some slightly rounded-off values, they are probably considered 50:50 in LFS. This is inaccurate. A rear wheel should be much heavier than a front one on the FZ50 for instance and this could make quite a big difference as to the way cars handle. Seing as Scawen is busy on physics updates now, perhaps this can be added in the patch? It shouldn't take that long but it is something that would change the cars under certain conditions (high vertical acceleration) handle quite differently. Or do I have something wrong in my calculation...