[200q20v] Re: Strut tower maximum lateral force

HAUPT,DAVID (A-Sonoma,ex1) david_haupt at agilent.com
Fri Mar 9 12:27:38 EST 2001

> From: Bernie Benz <b.m.benz at prodigy.net>
Math check request:

If the tire-to-road coefficient of friction is 0.3, then you're probably
driving on snow.  Seriously, for a car to pull a 0.8G turn, the coefficient
of friction needs to be 0.8.  Unless I've hopelessly forgotten my freshman
courses in dynamics.  

So I think the maximum lateral force on the tire at the road is more like
2000 lbs.

Assuming the remainder of the suspesion geometry evaluation is correct, this
translates to around 1500 per strut, or 750 for the brace.  Methinks we'll
get some compresson of the EMT at this force, but it's still orders of
magnitude stiffer than the rubber bits.

That value can rise if you happen to hit a curve while making that 0.8g
turn, but if you do that, the strut brace is the least expensive item you'll
have to replace.

On the other hand, I am prepared to get a lesson in dynamics, as I haven't
actually solved such a problem in 20 years.


> Come on guys, Lets get realistic!
> There is just no need for anything heaver in a strut brace, as there is
> much latteral force at that point.  I went thru this with another lister
> months ago, but neglected to keep a copy.  He finely saw the light and, in
> interest of keeping the economy strong, decided to just chrome plate the
> thing!  But, it went something like this:
> Front axle gross vehicle weight (fully loaded) being Audi defined as 2469
> Now estimate the max. weight on the front outside wheel in a max.G turn,
> ultimate being with the inside wheels off the ground, i.e. the full 2469
> on the outside front wheel.
> If the tire to road coefficient of friction is 0.3, the maximum latteral
> cornering force transmitted to the suspension at the axle would be 740
> The suspension geometery divides this force between the lower link and the
> upper strut anchor point by the ratio of these two distances from the
> On the type 44 chassis, Axle C/L to ball joint C/L = 4", axle C/L to strut
> piston rod anchor w/ a compressed suspension = 20".  Therefore 4/20 x 740
> 150 lbs force.  This is  the theoretical, far out, maximum latteral force
> the strut tower will ever see!  (My strut brace further equalizes this
> between the two strut towers to 75 lbs max.)
> Bernie

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