lower kit?

[yarrr]

Originally Posted by markitect

First thing you need to verify is the diameter of his springs, The Yaris is 2.5in front and 3.5 in rear (ID).

or backwards of that

Originally Posted by markitect

If those springs match up, the next thing is to determine what they will do to your car. First see if you can find the spring rate for the springs your friend has, and have him measure the height.

First you need to know the corner weights on the spring. I don't know if anyone has published numbers for that, so you would have to figure them out.
The rear is easiest, so while the car is on the ground measure the height of the rear spring, then unbolt the shock and jack the car up and take the spring out, and measure again. The difference between these is the displacement so your corner weight will be about so D(in inches) * spring weight is the corner weight on top of the spring. The rears are 120lb/in.

Now both sides should be about the same so you just need to find the front. That would be a huge pain, so simply take the rear weight*2 and subtract that from the curb weight, then divide the result by 2 to get the front weight.

If someone already has these numbers hopefully they'll be nice and post them.

Now for both the front and back, take the weight you just calculated, and divide by the rate of your friends spring. This is how much they will compress. Now simply subtract that from his uncompressed spring's height, and you will know about how tall the spring should be if you put it on your vehicle.

Now simply compare those numbers to the height of your springs on your yaris, sitting on the ground, and you will find out how much drop/raise you will end up with.

Finally post the results if you do this.

The rest is pretty inaccurate as well. Springs don't compress with a linear rate(i.e. if one inch = 120 lbs then 5 inches != 600 lbs) All that work and measuring and you'd probably be better off with an educated guess.