Saab White paper on FWD vs RWD
December 29, 2012 in Saabology
Saab’s first chief engineer, Gunnar Ljungström, in 1960 authored a white paper covering many aspects of basic chassis design.
Mr Ljungström came from a family of engineers. Both his uncle and father were accomplished engineers who among other things designed turbines, an automatic transmission and apparently a bike with a freewheel hub. It was Mr Ljungström’s team who engineered the first Saabs and they must have done something right…
I accidentally stumbled across Ljungström’s whitepaper last summer. Anders Isaksson, a former Saab employee, kindly made available a copy of the whitepaper on his blog.
Unfortunately the document is written in Swedish. As a Norwegian I can understand most things written in Swedish, but half-way thru I abandoned my translation project due to the complexity involved. (sorry)
But even so, I wanted to draw some attention to this little gem. Who knows, maybe a good English translation exists out there somewhere?
In any case, the document can be summed up in one sentence: “FWD good, RWD bad, mmm’okay?”.
Some of the key elements discussed:
- Stability. A car should have a low center of gravity and a good suspension system. FWD helps by eliminating the long drive shaft.
- Comfortable. The lack of a drive shaft through the middle of the car usually means more room for the passengers.
- Weight distribution. Putting the engine up front means 60% of the weight rests on the front wheels. FWD means the drive wheels have more grip. Useful when pulling the car through snow on a slippery surface.
- Center of gravity. The lack of a long driveshaft makes it easier to put heavy parts of the car closer to the ground, as well as have the driver and passagers seated in a lower position. This helps reduce side movements and the ride feels more comfortable.
- Under-steering is easy to correct. Just let go of the big pedal.
“When loosing grip due to applying too much throttle, or even due to engine braking, a RWD car can easily reach a state where it becomes impossible to correct its course.” (I actually managed this with my 9000 once. My rear fenders were packed full of ice, snow and slush. The braking effect of all the gunk caused my rear wheels to loose traction now and then, and the end result was me pulling a 180 degree turn on the main road. This made me realize the importance of putting the best tyres on the rear wheels, not because I think they’ll magically keep my fenders clear, but because I want to avoid loosing grip!)
Mr Ljungström acknowledges that a RWD car might be able to get up a steep hill covered in snow. As the angle increases, more weight will rest on the rear set of wheels. A driver of a RWD car can ask someone to sit in the back, or put a bag of sand in the trunk, “but where to find a spare passenger late in the evening? It is easier to simply ask your potential passengers to step out in case you encounter a particularly troublesome hill”.
Of course, a lot has happened over the last 50 years, but I find it difficult to not notice the many German cars stuck in the right lane after a little snow has been added to the mix. It isn’t easy to beat fundamental physics.