Corner Weighing

[Doubleup]

Corner weighing my car for 90% track use... It seems the rear wants to be heavier. Am I really trying to hit 50% front/rear?

Also besides all the talk of how much to lower a car 3/4" - 1" downd from stock; any recommendations frame to ground (center of axle) front/rear? I have no clue what my car was stock. Motons here so fully adjustable...

THANKS!

 

[Viperless]

Corner weighing my car for 90% track use... It seems the rear wants to be heavier. Am I really trying to hit 50% front/rear?

Also besides all the talk of how much to lower a car 3/4" - 1" downd from stock; any recommendations frame to ground (center of axle) front/rear? I have no clue what my car was stock. Motons here so fully adjustable...

THANKS!

In order to get 50/50 static weight distribution front & rear and side to side, you'd have to move weight around in the car. Not an easy task. You can't do it by jacking the corners. However, you can change the cross weight.

Here's a decent explanation:

Corner Weighting

 

[mjorgensen Woodhouse]

Corner cross weights being equal is the important thing, being heavy in the rear may also work to your advantage with all the power, don't sweat it.

 

[Viper X]

Check the ACR manual for frame to ground info. If I remember correctly, it's about 4 inches front, 5.3 inches rear for the smooth track setting with OE size tires.

I've managed 50 / 50 front rear and corner to corner with my 01 GTS ACR and my 09 ACR myself in the car. Took lots of trial and error and not really worth the trouble I learned later. Close is good enough when doing static setups like this and cross weights are more important as Mark says.

Don't forget to disconnect the sway bar end links front and rear.

Dan

 

[MTGTS]

I'm @ 49/51 with me in the car.

 

[Doubleup]

Thanks guys! Should save me some time, could spend a weekend under here looking for perfection.

I wish I could just decide on ride height, right now I have about 4.25"F and 5.0"R measuring from frame at axle center point. Not worried about scraping here just the best handling.

 

[Viper X]

Double up,

What are your spring rates and lengths front and rear?

You won't want to go too low with soft springs.

Also, what tire sizes are you running front / rear?

What rims? Watch the offset on non-OE rim offsets.

Dan

Dan

 

[David Pintaric]

I'm @ 49/51 with me in the car.

In a Viper that's better than 50/50...

 

[AZTVR]

I wonder if corner weighting is worth paying to have done at my low-intermediate level of driving. I just don't have a feel for the car yet, such that I can say whether it needs more "this" or "that" when my Viper tech asks me those kind of questions. So, he is not recommending to do it as of now. The engineer and hobbyist in me would like to play with it at home before taking it in for an alignment; but, no "inexpensive" way to do it for a one time deal that I have found (other than finding someone to borrow scales from.)

 

[Doubleup]

Viper X - I am currently running 8" Hypercoils on moton club sports 700f/1000r with 18" SSR's 11" Front and 13" Rear... Not sure the spring rates are the best setup however love the tight feel...

 

[GTS Dean]

1000# in the back is pretty stiff. Do you have aero? I like springs that let the suspension work thru the sweet spot of the camber/toe curves, and shocks that keep everything under control.

 

[Doubleup]

No Aero... However I am beginning to wonder if my original problem was wrong springs... I had 600/900 7" Eibach's and the rear always felt spongy and would actually feel the suspension bottom out in rear and tires would hit inner fenders in hard downhill corning/apex's. The front tended to push a lot and overall just did not feel right. With those springs I was at about 4.5f-5.25r and did play with it quite a bit however was never happy with it.

Long story short think it was the 7" springs that were not right and not so much the rates??

 

[mjorgensen Woodhouse]

Rates are rates 7" or 8" unless you are getting into spring bind. I had tried the 600/900 route also with no luck, and went lighter in the front to 550 and was much happier. I also use 750# in the rear which made the rear plant better IMO. This also gives me an equal wheel rate front and rear. Not ideal for everyone either, but gives me a great tuning base to make small adjustments from. I also have only 1/4" rake front to rear so the higher the rates in the rear the higher the ride height should be back there in my experience.

Also having the wheel rates similar let's you tune from the same settings on shocks front to rear for even smaller tuning adjustments. This is mostly for autocrossing set ups, but I do track events also and have had great success even though the rates are a bit soft for road course only cars.

No Aero... However I am beginning to wonder if my original problem was wrong springs... I had 600/900 7" Eibach's and the rear always felt spongy and would actually feel the suspension bottom out in rear and tires would hit inner fenders in hard downhill corning/apex's. The front tended to push a lot and overall just did not feel right. With those springs I was at about 4.5f-5.25r and did play with it quite a bit however was never happy with it.

Long story short think it was the 7" springs that were not right and not so much the rates??

 

[Viper X]

Doubleup,

Opinions on springs vary, kinda like opinions on blondes vs brunettes. Shock settings, gas pressure, tires (sidewall stiffness), sway bar bushings all come into play here.

I'm no expert, but I've tried a bunch of spring rates at various tracks on Aero and non-aero Vipers.

The spring rates you mention are in the ball park. As a general rule of thumb, shorter springs don't compress as much as longer ones under the same load, so you can go a bit lower with shorter springs. Go to the Eibach website for more info. On my 09 ACR (with big Aero), I went to 6-inch, 1300 lb/ in springs out back and 7-inch 900 lb front springs on Moton Motorsport shocks at the OE mounting location. With Hoosier R6's, 315 x 30 x 18 front / 345 x 35 x 18 rear on SSRs and a bunch of negative camber front / rear and toe out front / toe in rear, the car seems to defy physics.

On my non-aero 06 coupe, which I set up for my wife, I've been very happy with 8-inch, 600 in/lb Eibach springs up front. I run 160 psi in the Moton canisters and set the shocks at 3 compression, 4 rebound with Hoosier R6 tires, 315 x 30 x 18 (or Kumho Ecsta V700s in 305) on SSR wheels. Ride height is about 4.25 to the frame. Camber is -1.5, toe is set to zero. No fender rubbing or bottoming.

Out back, I run 800 in/lb 8-inch Eibach springs, 160 cannister pressure, set the shocks at 3 compression, 4 rebound with Hoosier R6 tires, 335 x 30 x 18 (or Kumho Ecsta V700 335 x 30 x 18)on SSR wheels. Ride height is about 4.75 inches, maybe a bit less. Camber is -1.0, toe is set "in" at about 1/16 per side.

I run the shorter rear tires on this car for two reasons, first to lower the center of gravity and increase rear traction and second to lower the gear ratio.

I've also installed polyurethane sway bar bushings, which helps stiffen the car up, i.e. adds to the roll resistance.

This car sticks very well and handles extremely well for a street car and a mostly street alignment.

If you are running stock size rear tires, you'll have to be careful with the rear ride height or you will rub the fender liners. Minimum would be about 5.3 inches IMHO, especially if you are running over "candy striped" berms on the track at speed.

Good luck,

Dan

 

[Doubleup]

Thanks Mark And Dan. I have another AutoX this weekend and just received my own set of scales so will play with these spring rates for one more event and then if not happy will soften up as Mark suggested...