Ride heights & corner weights

Originally the ride heights were set by simply winding in the spring platforms until the chassis sat a consistent height above ground level, in the case of my Mojo about 100mm front and rear.  However, this can lead to the possibility of the corner weights not being ideal.

The concept of corner weights- or wheel loads- is quite difficult to understand- it took me a while to get my head around it, so I will try and explain it here.  For a car with adjustable spring platforms like the Mojo, you have the possibility to shift the wheel loads independently of the ride height.  It is only possible to increase the load on two diagonally opposite wheels, while reducing the load on the other two wheels.  Here is an illustration:

Imagine a car with perfect 50:50 weight distribution, both front to rear, and left to right.  Now imagine it has no suspension and has a perfectly rigid chassis.  The corner weights will therefore be exactly the same at each wheel (assuming it is parked on a flat surface).

Now imagine that same car with some kind of suspension, where initially the spring platforms are all adjusted to still give exactly the same corner weight at each corner.  Now, if you were to wind the spring platforms in on the front left and rear right by one turn, and wind out the front right and rear left by one turn, the ride heights at each corner would remain the same.  However, the load on the front left and rear right wheel would increase, and decrease by a similar amount on the front right and rear left.

Confused?

Well, in that example the optimum setup would have been with 4 equal corner weights, as it was without suspension fitted.  In this case, that would also have meant the same number of turns on the spring platform adjustment, however, when you move to a non-perfect weight distribution, things aren't so easy!  But, the key thing is that you are aiming for the same wheel loads as you would get if you had no suspension fitted at all- the ideal corner weights can be calculated based on some simple maths with the knowledge of the centre of gravity location of the vehicle.  "How do I know where the CofG of my car is?" I can hear you ask!  Well, get the corner weights measured, and then use this excel spreadsheet to work it all out for you!  For those of you interested in the calculations, this is basically what happens:

1. Calculate total axle loads front and rear
2. Calculate the total wheel loads on the left and right
3. Calculate front : rear axle load ratio
4. Apply this ratio to the right and left totals to work out the target corner weights

Now, I am rather lucky in that I have access to corner weighting facilities at work.  The input values in the spreadsheet are those first measured on my Mojo- you can see that the corner weights on the front left and rear right were a bit low compared with ideal, for all three loading configurations I chose to measure (unladen with full fluids, driver only, driver & passenger).  Interestingly, the Mojo's front : rear distribution stays almost the same in all three configurations, which has to be a good thing!  I have now optimised the corner weights with a small tweak to all 4 spring platforms.