Understanding Corner Weights

Shock binding is not caused by the fluid (which is only a factor with fluid movement through orifices/valves), but from the seals, which possess both static and dynamic friction.

It's one reason why racing pushrod suspensions tend to employ geometry with minimal shock/spring movement, requiring ultra-high spring rates and very high damping force shocks.

Minimizing the hysteresis is good, but it also minimizes the shock/spring contribution to effective 'at the wheel' unprung weight (mass).

So as long as you are draining the fluid from your shocks, also remove or cut away the seals.

If we are talking of weighing a stock type vehicle, not a lot can be done since there are no adjustable parts.

 coil overs are a whole different thing.

Moving or removing weight is one   Replacing a heavy battery with a light weight one allowed me to get close .

Be sure to have the weight of the driver in the seat.

I found that the tire will absorb side loads quite well and was repeatable. Rock or bounce the car helps.

If you shocks are working normally they are not worth worrying about.

Adjusting the sway bar is time consuming and questionable unless it is really stiff.

On my ZX2SR my cross weight was consistently in the 49% range.   I didn't  hunt for that missing 1 %.

Here's a poor mans way to reduce the effects of tire scrub/binding when the car is lowered onto the scale pads:

Get a large heavy plastic shopping bag.

Spray Pam into open bag to coat and lube the inside, rub the bags between your hands to distribute.

Lay the bag flat onto the scale pad, partially open to vent, lower the car into the bag.

Can do to just left sides or right sides, or to all 4.

A jumbo ziploc bag prevents lube from escaping when not in use.

Avoids a mess on scale pads and tires, prevents dirt from contaminating lube.

Take care that the car does not accidently slide off the scale pads.

(I suppose cooking oil, motor oil, KY, or Astro-Glide would also work)

flatlander937 said:

Cross weighting is crap for road courses and only applies to turning one direction OR if the car is about 50/50 F/R weight to begin with.

Many successful race teams use corner weighting to achieve the same F/R % on both sides equal, not cross weight.  Andy Hollis does this.

 

So LF/LR = RF/RR is what you shoot for. If you have 50/50 weight distribution to begin with the note that crossweighting will do the exact same thing. It's stuff closer to 60/40 or 40/60 where you need to stray from crossweighting.

 

Then there is what I do for FWD stuff... That is forget the rear weights entirely, and just balance the fronts to be equal. My left rear is something like 150lbs heavier than the right rear, with both fronts even at ~740lbs each on a 2425lb FWD car.

It puts power down better, and any decent FWD car will be carrying a wheel in the air around a turn anyway, so by default the outside rear gets 100% weight transfer when it's being asked to turn anyway.

 

There are many ways to corner balance a car. Don't just blindly cross weight it thinking it's the "right" way. Then if it's for a particular road course, you will find several seconds optimizing for select turns and throwing any of the above methods out the window... A friend's Chump Car found 2 sec at VIR making it turn right better than left.

 

Go out and experiment with it.

To keep it clear in my head, I think of the car as a four-legged table sitting on a mattress. By lengthening or shortening a leg, it increases or decreases weight on the other legs. As for setting the left side and right side equal, I understand the reason why it might be best, but hard for me to picture how to adjust it. Guess I have to try it.

Corner weighting is huge. We had a good Miata set up for ST. It was a good car. Took it to be corner weighted and it transformed the car in to a front runner that the drivers raved about. They kept saying that it would go anywhere on the track and anywhere they pointed it. 

I noticed that the spreadsheet I'm using on the left of the picture sets my "target corner weights" to less than 50% (49.6%), why is that?

I'm off by 0.1% (see numbers on left side of the spreadsheet).

This is for a race prepped 1984 Audi 4000 quattro (2375lbs. dry)!

In reply to Typ85 :

Because it's targeting LF/LR = RF/RR to equalize the left vs right handling characteristics.

I borrowed some scales to weigh my Tercel tomorrow.

Now here is a question...tire pressures... I vary mine alot depending on conditions, so should I say...set them where I would at the beginning of an average day for autoX?  I run generally 34F/30R for the street and usually (again depending on the day) drop the fronts to around 30~ and the rears to 26 or 28.  The last event in the rain i actually had the rears up to around 38.

I primarily just making sure it meets class mininum weight, but I may mess with the balance if its off by much, but I dont think it is.

Set them to hot pressures is the norm as I understand it. At least for road racing. Unsure about autox 

malibuguy said:

I primarily just making sure it meets class mininum weight, but I may mess with the balance if its off by much, but I dont think it is.

For that level of caring, I wouldn't think too much about it. Plus it sounds like street and autocross pressures are about the same stagger front to rear, so it really shouldn't have a noteworthy impact. Just make sure none of them are flat or wildly overinflated. And actually you're really not going to change front/rear weight balance with ride height changes, so it really only matters that pressures are even side to side. 

dps214 said:

malibuguy said:

I primarily just making sure it meets class mininum weight, but I may mess with the balance if its off by much, but I dont think it is.

For that level of caring, I wouldn't think too much about it. Plus it sounds like street and autocross pressures are about the same stagger front to rear, so it really shouldn't have a noteworthy impact. Just make sure none of them are flat or wildly overinflated. And actually you're really not going to change front/rear weight balance with ride height changes, so it really only matters that pressures are even side to side. 

Ok sounds good.  Yeah generally its the same stagger 9/10 times. I just run higher pressure for the street

I feel mine is pretty close as is.  And I cannot really move any weight around.  I guess I should work on losing weight personally (i am 220~)

In reply to Cloud9...68 :

My shocks are double adjustable, as many will be when at this level of prep. I just back all of the damping off totally. Then the car will move more easily from one setting to another. It also helps when shaking the car to take the bind out of the linkages. The overall effect is much like having no shock in the equation. 

clshore said:

Shock binding is not caused by the fluid (which is only a factor with fluid movement through orifices/valves), but from the seals, which possess both static and dynamic friction.

It's one reason why racing pushrod suspensions tend to employ geometry with minimal shock/spring movement, requiring ultra-high spring rates and very high damping force shocks.

Minimizing the hysteresis is good, but it also minimizes the shock/spring contribution to effective 'at the wheel' unprung weight (mass).

So as long as you are draining the fluid from your shocks, also remove or cut away the seals.

 

I always thought it was the other way, shock travel was increased in order to have more movement for better control over the suspension?

In reply to mr2peak :

Examine a modern push/pull rod suspension, particularly if it uses a crank link to transform the
rod movement from the wheel to the coilover movement.
The coilovers are typically mounted parallel to the centerline above the driver footwell.
You can see that the leverage ratio in the crank link reduces coilover (and thus shock) travel, and
that as a result the coil springs must be quite beefy and stout, 600 lb/in or more.
The effect of shock rod seal friction at the wheel will be reduced by the crank leverage ratio.
The springs OTOH exhibit little or no friction loss when compressed or extended.

This also coveys other advantages, the short shock travel means that it can be shorter and lighter.