Why is the LGT spring softer up front?

Some forum members have calculated the 2005+ LGT spring rates to be approx. 200 lb/in. front and 300 lb./in. rear. Tein's H and S Techs are softer up front compared to the rear springs as well. Why would Subaru make the front softer? In front engine cars, aren't the front rates usually HIGHER/STIFFER than the rear rates first to support the mass of the engine and second to promote understeer? Does it have something to do with AWD and the differentials? Have I embarassed myself again and gotten this all wrong in public?

it has to do with suspension design and geometry. depending on mounting point and leverage, a spring that's 50% stiffer in the rear may effect less force at the wheel than the front.

yeah suspension geometry and leverage play an important role in that. i think the front is like 20/80% and the rear looks like 40/60% leverage

By leverage, do you mean the length of the arm the wheel is mounted to? The longer the arm, the greater the leverage, so the stronger the spring has to be relative to a shorter arm?

stronger spring goes with longer arm.

The spring rate doesn't really matter. It's rate at the wheel that matters. In the case of the LGT, the front suspension is a strut, where the wheel rate is pretty much equal to the static spring rate. In the rear, we have a multilink setup, where because of the leverage of the suspension arms the effective wheel rate is much lower than the spring rate.

Ahh, Boostjunkie, you are wise in the ways suspension.

The spring rate doesn't really matter. It's rate at the wheel that matters. In the case of the LGT, the front suspension is a strut, where the wheel rate is pretty much equal to the static spring rate. In the rear, we have a multilink setup, where because of the leverage of the suspension arms the effective wheel rate is much lower than the spring rate.

 

+1

What is wheel rate?

It is the effective spring rate at the wheels.

 

In other words, if the control arm is 2 feet long, and the spring sits at the 1 ft point, the effective wheel rate will be half the spring rate. The leverage difference is what creates this. Where the spring is mounted and the suspension geometry are combined to create the wheel rate vs. the spring rate...

 

Ted

So, what's the equation to find the wheel rate on our rides?

In addition spring diameter has play with that too.. however, Mr. Junky is on the money

Motion ratios of MAC struts are usually in the 95% range.

 

A rough estimate of our multilink motion ratio is somewhere between 70-75%.

 

Meaning if you were to put say 100 lbs springs front and rear the Front wheel would see about 95 pounds per inch and the rears would see about 70 pounds per inch.

 

This is why the springrates are biased.

Just wanted to pop in years down the road and revive this dead thread to give thanks to the contributors. I'm glad I read this before I ordered new springs for my coilovers. *thumbs up*