So I'm building a 1985 RX-7 track rat and I'm trying to figure out what is a good performance ride height for it.

I have a Ground Control Coilover setup in front and eibach springs in the back I can cut (several dead coils). I don't have a trilink or panhard set up.

The car has not been lowered so it's pretty much at a stock height now.

the question is: what is a good ride height that lowers the car while still maintaining good suspension movement? AND where do I measure ride height from?

any help from PRO7, ITA7 or track gurus appreciated.

ps. car will be used in fairly fast tracks (Infenion raceway, Laguna Seca, Thunderhill)

thx.

General motorsports practice is as low as you can go without bottoming out. This reduces the amount of air flow under the car as well as gets the roof further out of the air stream. To low and you scrub speed when bottoming.

That being said, you must take other aspects into account for the SA and FB. On the front of the first gen you are limited by shock travel. when you lower the car utilizing the stock mounting for the strut tops you will in effect be shortening your shock travel. Your shocks will be sitting further into the housing at static ride height. This means you have less bump travel available before you bottom out the shocks. Some people combat this by using super heavy spring rates that limit the compression. Super heavy springs are not the best for mechanical grip in normally circumstances, thus they are giving up grip for a smaller return in aerodynamics. Better alternative is to use shorter shock inserts and cut the strut housings shorter to hold them. This allows you to lower the car to a desired height but still have plenty of bump travel before bottoming the shock.

The rear of the first gen introduces special circumstances due to the geometry. The upper arms, lower arms and watts arms all fight against each other in bump travel. This geometry gets worse the lower you go with the ride height. This can only be fixed by changing the geometry. There are a number of ways you can do this, some being custom and others being off the shelf. A custom 4 link setup with a pan hard is a great option. This involves the custom fabrication of new upper arm pick up points in order to lengthen the upper arms and locate them differently on the rear end. Another good option is a single upper arm located in the middle of the chassis centerline that eliminates the need for stock upper arms. This setup can be purchased from G-Force Engineering.

Now to answer your question directly most rules will have you measure the ride height on the rockers, not including the welded seam. When we ran ITA this was 3" by the rules. We ran 13" wheels with a 45 series tire. With stock rear suspension arms you will not desire to run the car to low. Your tire diameter will have a huge impact when comparing others ride heights to your own.

As an exercise to establish a good rear height starting point measure your rocker height with the rear lower arms fully horizontal to the ground. Then raise the body a bit to angle the arms down 1/2 a degree as they go to the back of the car.

Let us know what you come up with and your tire diameter.

-billy

Glad to see you found the forum okay. And, what did I tell you about getting facts, eh? lol.

cool. thanks. i'll measure this weekend.