suspension opinions, semi trailing arms..

[CrzyMR2T]

id like to know your opinions on how well semi trailing arms work vs multilink, and strut type suspensions. the mazda fc3s rx-7 uses the semi trailing type suspension in the rear, and so do a lot of cars today.

[quaddriver]

Originally Posted by CrzyMR2T

id like to know your opinions on how well semi trailing arms work vs multilink, and strut type suspensions. the mazda fc3s rx-7 uses the semi trailing type suspension in the rear, and so do a lot of cars today.

to tell the truth, each has its pros and cons, assuming you are driving on the road or nothing more strenuous than lime rock, even rear live axles will do well, springing, stabilization and tire choice are more important - for example

you dont want it sprung so hard that while yes, steady state grip is improved, even a small bump in the road upsets the who car

you dont want it so over stabilized in the front that it understeers immediately on any off camber surface

you dont want it so over stabilized in the rear (esp on fwd) that it oversteers early

you dont want a tire compound so soft that they are like pencil erasers as a daily driver, yet you dont want one so hard that it rolls the sidewall under (less tread on sidewalls yanno ;-)

[CrzyMR2T]

yea i know the basics of what you want in a good suspension design, but i just wanted to know peoples opinions on how well the semi trailing arm system works compared to other types of suspensions, or if you know how well it works based on tests, actual racing experiences from car companies, and how it does technically speaking, then that would be great.

[Moppie]

From my own experiance; under most conditions you will ever encouter on the road it is just as good as any other independant set up. Its actual ablity being more dependant on how well it was set up, than the actual nature of the design.

The only time Iv ever had a problem with it was on a race track in a large 4dr car that would lift the inside rear wheel midcorner. But it was more a problem with set up, the car had no sway bars front or rear, and was known for its extreme body roll.

[MagicRat]

Originally Posted by CrzyMR2T

yea i know the basics of what you want in a good suspension design, but i just wanted to know peoples opinions on how well the semi trailing arm system works compared to other types of suspensions, or if you know how well it works based on tests, actual racing experiences from car companies, and how it does technically speaking, then that would be great.

Semi trailing arms are not all that great, in theory.
They are very space efficient, so they do not use up much room under the car, and they are light, so unsprung weight is low.

Of course, how the suspemsion is set up and its application is vital, but unequal length control arms is better.
However, semi trailing arms have a tendency to change aspects of their alignment (their camber and toe) as they move through their travel.

This is fine, in a straight line, but if you are conering reasonably hard, and you hit some bumps, the rear end of the car wants to steer itself, so the back end moves around in an unexpected fashion. If you are used to it and know what to expect, it is no real problem, but it is disconcerting.

BMW loves semi trailing arms in the rear, and has taken steps to reduce this problem over the years. My BMW's always had this problem, though.