Buzzin

iTrader: (1)

Silkworm are you racing in SFR SCCA?

Cheers!

We are talking about 2nd gen rx7 here right? there is no camber gain for macpherson suspension. Camber gain is NEGETIVE for this type of suspension. Are you saying the tire wall has an equivalance of 1600 lb/in spring rate? or are you saying you can run 1600 lb/in springs with street tires?

jgrewe

iTrader: (1)

The 1600 lb number would be the side wall rate. That was a number I heard an engineer use as a rule of thumb in computer modeling of suspension. And the negative camber gain depends on the angle that your lower control arm starts out at. If you've lowered the car so much that it is pointing way down toward the middle of the car then you are correct. The other problem is the car probably leans more degrees than the suspension can gain with the right geometry and struts. As for what spring rate, what ride rate can you handle? If you are driving on the street most of the time don't go to high it will wear you out. I stand by my "a little compliance can be good" statement though. Ever race at Nelsons Ledges? It's a washboard surface in a lot of places and a softer car is faster.

I'm still dusting off the racing brain cells, I may have to go soke them in Rum again! LOL
John

gnx7

iTrader: (10)

I ran -2* up front an -1* out back. Daily driver that was road raced on the weekends at a real track by switching to RA-1's. Worked well for me.

I ran K2RD.com coilovers (400#/275#) with KYB AGX shocks/struts, camber plates, Energy Suspension poly bushings, rear toe elims, T2 front sway bar, stock rear bar. Worked great for me.

Gene

iTrader: (1)

Everyone who hasn't should read the following, all by Carroll Smith:

Prepare To Win
Tune To Win
Engineer To Win

Carl Byck

YUP

jgrewe

iTrader: (1)

Ok guys, I thought about why I sounded stoned or something. When I wrote "camber gain" I was refering to the increase in the amount of neg. camber. With that in mind does my post sound any better? If a guy tells you to put some MORE camber in the front wheels do you straighten them up or lean them in? If I'm still out to lunch let me know and I'll splash more rum on the brain cells.
John

DamonB

When racecar guys talk of adding camber they always mean negative camber; tilting the wheels inward more.

Camber gain on the other hand is the fact that an unequal double wishbone suspension has camber which becomes more and more negative as the suspension is compressed. Strut suspension geometry is completely different and has no camber gain. What the camber is set at is what it is regardless of ride height. Because of this fact strut suspensions usually require more static negative camber, assuming you can even get it.

jgrewe

iTrader: (1)

You actually get some camber change as the control arm swings up and down because of the arm forshortening. Picture your car with no engine and trans and the wheel has a huge amount of positive camber. The same thing would happen if you could compress the strut far enough. Thats why its better to have your lower arms slanting down to the outside if you can so you can get a little tiny bit of more neg camber as it swings up. It also puts your roll center in a better location.

It's all coming back to me now
Keep me honest,
John

DamonB

Not with a true strut unless the car has suspension travel measured in feet. the strut itself is the upper "arm" of the suspension since it locates the top of the upright. Since the strut itself travels in a straight line so does the top of the upright and thus there is no camber change. The strut body moves in only a tiny arc as the suspension goes from full droop to full bump. Because of this you cannot change the camber throughout motion of the suspension.

Now if you could get the outer balljoints of the lower arm to be pointed sharply downward when the car is at static ride height then you could generate a very small amount of negative camber change since the lower joint would effectively move away from the chassis as the suspension responds in bump. The downsides are that when the suspension goes into droop you would have terrible camber settings, using the lower arms at this angle would impose a terribly high roll center (and be nearly impossible to mount on a stock type car anyway) and the tires would have large amounts of scrub during movement of the suspension. All these reasons is why you don't try and do that with a strut, the negatives outweight the positives.