Body roll and weight transfer

[Petrus]

Always a bit difficult to explain in cars and yet quite a thing leading to much confusion about lowering, stiffer springs, wider track, anti rollbars per example.

When cornering all of the above will greatly affect body roll and although weight transfer is impossible to escape, body roll can add to it. It is important though to distinguish the two.

I am currently faffing with the geometry of my Nimbus sidecar and it struck me that this makes a very good and illustrative example:

Image the motorcycle with the sidecar wheel, a bit ahead of the rear wheel. No suspension. All wheels rigidly fixed to the chassis.

Now take a corner away fromf the sidecar.
It is obvious that the weight of the motorcycle with its center of weight rather high will want to tilt towards the sidecar, push the sidecar down. In extremis lift the rear wheel, topple over the sidecar wheel even.
This is weight transfer.

Now add suspension.
It is obvious that the sidecar wheel suspension will be compressed, relatively raising the centre of mass of the motorcycle.
Ditto that the suspension of the bike will extend, especially the rear, raising the mass even more.
The load on the sidecar wheel is higher, the rear tyre does next to nothing; the set offering less total traction, and speed at which the thing will lift the rear wheel, topple over is lower.
Thát is body roll added to weight transfer.

On cars it is much the same, just less vividly imaginable.
Now we can easily grasp that:
- lowering the body
- stiffer springs
- stiffer arb
lessens body roll and weight transfer.

Ah and reducing weigh affects both too :-)

[Dev]

That all works well but as you go stiffer and lower you then suffer from other more serious problems and that is a loss of damping control which is the result of less stroke and less shock oil.

 Many ways to solve this and that is to reduce unsprung weight and more oil using external reservoirs apart from an entirely different vehicle design. 
 This is why there needs to be compromises on real roads and the more aggressive you make the car it becomes edgy and a bit unforgiving when you mess up. Some cars are better left alone unless you know what you are trying to achieve than adding parts in the belief that more is better without understanding there is a downside.


 

[Petrus]

without understanding there is a downside.


 

Conformation with the surface being but one ´detail´ ;-)

[Dev]

without understanding there is a downside.


 

Conformation with the surface being but one ´detail´ ;-)

 I had an interesting discovery over the last month. I had to take several back roads in my heavy luxury car which is the polar opposite our little roadster.
 Fortunately I bought the rare version that has standard dampers not the air suspension that has so much unsprung weight. 
 
 The suspension is not tight, its made to be luxurious but at the same time it dampens extraordinarily very well to stabilize the car. The back roads surfaces are smooth but they will give the car a work out because the payment is uneven as far as small hills, dips and uneven road surfaces that it makes driving fun.
 I was able to plow though it at the same speeds I would the roadster but the sensation of speed was lessened.  Even though the car has quality all season tires there was plenty of grip because of the weight over the tires. 

 The big differences I found is one car is more agile and fun where as the other car felt secure that you when you looked at the speedometer it was much higher then you thought it would be as everything seems slower.
 

 

[Petrus]

There is a reason why in the days of the DS and CX Citroën was such an awsome and succesful choice in the toughest of raids 
Long wheel travel combined with effective anti-roll.
Lowering, stiffer/shorter wheel travel is the poor man´s alternative on smooth surfaces.  ....ánd for sidecars