Handling is a difficult subject for many people to wrap their heads around. Many cars, especially lower end sport compacts have a reputation for awful handling that can’t be fixed or for some makes their owners insist that their car handle but none get any noteworthy results on the track even if their internet forum collective always gives themselves high fives for effort. If you want a good place to start to learn about suspension and handling, may I suggest you read our handling guide articles as a starting point.
Some cars that are popular to modify like the Nissan Sentra, particularly the B14 variant and the EP3 Honda Civic have a reputation for bad handling. Well, the bad news is yes these cars handle poorly in stock form and even with basic bolt on mods. The good news is you can fix this stuff, it might take a little effort, some fab work and some knowledge but its all doable and not as hard as you might think.
A lot of the trouble with the handling of economic sport compacts is that they usually have McPherson strut suspension. Not all cars with McPherson struts handles poorly though. Some strut equipped cars handle exceptionally well, cars like the E36 and E46 BMW, Nissan S Chassis and Porsche cars all are examples of strut cars that handle well. However, most compact FWD econoboxes do not have as good of a front end geometry as these cars do. We feel that the cheaper sports compacts often suffer from parts bin engineering where the geometry is compromised due to the cost savings of using a mash-up of pre-existing components. Also, cheaper cars are probably engineered for worse drivers and a lot of understeer is built into the geometry.
The main problem with McPherson struts is as the car gets lowered, the lower control arm gets set to where it is actually pointing upwards towards the spindle. This causes two problems, one the roll center gets really low, this makes the distance between the roll center and the center of gravity longer. This distance is called the roll couple and it is the lever arm that centrifugal force uses to cause body roll. Longer roll couple more roll. The other problem is once the lower control arm angle to steering axis line gets to be greater than 90 degrees, the suspension will start to gain positive camber. This is not great as the car rolls, the tire will start tipping toward the outside putting the load on the outside edge of the tire.
The other problem with McPherson strut suspensions is bump steer. Bumpsteer is when the tie rod and lower control arm are out of plane with each other. When the suspension compresses, the tie rod and lower control arm travel in different arcs. the difference between the arcs is bumps steer as the spindle will steer with no input from the driver. Sometimes this is done on purpose to cause toe in under roll to increase understeer. Many other times the bump steer is just the byproduct of sloppy engineering and cost-cutting, most likely so existing parts can be used to reduce costs on a new model.
When a car with poor strut geometry is lowered, things get worse, sure the propensity to roll is less due to the lower height of the center of gravity but the roll couple gets longer and the tires will start to lose negative camber with roll until they are rolling up on their outer edges on the cars heavily loaded outer side. As you can see in the above picture, the bump steer will get worse as the ride height gets lower as well.
On good handling strut cars like BMW’s, Porsches, and Nissan S Chassis the location of everything is designed to be in the right place so negative camber loss, bump steer and roll center migration are not as serious issues. This is not true on most econoboxes, their geometry is not so great to begin with and gets even worse when lowered.
The Nissan B14 Sentra and 200SX compacts have been popular cars to modify, especially the versions powered by the SR20DE engine. However, these cars have some most the most diabolical front-end geometries. When lowered these cars have half the amount of bump steer as wheel travel. This means when the suspension compresses an inch, the toe changes a half inch! They also gain positive camber as the vehicle rolls. This adds up to a vicious understeer that in the old days was tuned out by raising the rear spring rates to astronomical levels. They also have twichy steering due to the bump steer.