Corner weight/height questions

[nhromyak]

OK,

So I did the corner weight / jacking thing.

I found I get

..........Front
Left..............Right
580..............600


780..............780

..........rear

These weights are with sway bar disconnected and no driver weight. GREAT right?

Except the drivers side (front 25" and rear 24 1/4") is about 1/4" lower than the right side (front 25 1/4" and rear 24 1/2").

My question : If I raise the drivers side front and rear, will this put 1) MORE weight on the drivers side or 2) LESS weight on the drivers side?

I am initialling thinking the springs will put 1) more weight on the drivers side, however, I am also thinking like a teeter/totter if the weight is ANGLED over to the passenger side, maybe all will be well?

Finally, how does adding driver weight to the drivers seat affect weight distrubtion? Does the weight strictly go to the drivers side? Or will it go in a criss-cross pattern?


The car has stock torsion and (non-adjustable) sway bars.

TIA

[masraum]

Jacking one end/side/corner of a car up should add more weight to the opposite side, so your question, raising the driver's side should decrease the weight on that side and increase it on the passenger's side.

Personally I would add your weight or at least as close as possible to the car when you corner balance since the purpose is to make each wheel carry it's correct share of the load when driving to ensure correct handling at the limit. Also if you weren't aware there is a formula or also a spreadsheet available to ensure that you get the proper weight distribution since it's not equal side to side or obviously front to back.

[Greg S]

Nick, I would just back slowly away from the car. 1/4" is within the spec that I read and the weight is darned close. Any more fiddling on our cars & something has to go wrong!

I haven't weighed mine yet, but just getting the front heights close was more of a job than I expected.
Greg

[nhromyak]

My concern is the car is lower than US or Euro spec.

This isn't REALLY a problem unti I drive on a bad freeway area.

I also have to be a little more careful on my steep driveway, but...

As it sits, the drivers side is lower. When I get IN the drivers side, it goes lowers still. Kind of disappointing...

I would be MUCH happier if I can rais both front and left atleast 1/4"

I am worried that by doing this I jack more weight on the drivers side when there already is no driver. Is this the case?

As I recall if I raise the front drivers side, the rear passenger side will get more weight "jacked" in. So now if I raise the drivers rear, this will put more weigth jacked in the passenger front. SOOOO

This means my heights will look good, but WILL I have more weight on the passenger side with no driver?

I might shoot for getting 20 lbs more weight on the passenger side rear and front (40 total) with no driver... please "steer" me in the right direction - pun intended

[Colby]

What kind of scales are you guys using to do this? The one in my bathroom doesn't go that high (and the gf wouldn't let me take it out to the garage anyways)...

Colby

[911pcars]

Nick,
By my calcs, you weight distribution is:
Vehicle Total: 43% front, 57%
Left side: 42.6% front (25"), 57% rear (24.25")
Right side: 43% front (25.25"), 56% rear (24.5")

The objective is get both right and left sides close to the overall front-to-rear weight proportion irrespective of the side to side weight (unless you have a formula-type car).

You're pretty close. You're also correct in that raising the driver's side which is now low by 1/4" will add more weight to the driver's side. Simultaneously, it will remove a like amount from the opposite corners while also lowering the opposite corners. You may have to fine tune the heights, then live with a little height difference at each corner to arrive at a close chassis balance.

BTW, you should add an equivalent driver's weight to the front seat to simulate dynamic vehicle weight. In addition, consider switching over to adjustable drop links. Your corner balancing efforts are compromised by the fixed-length drop link connections to the suspension. If the drop link bolts don't just slide in at rest, then there is a slight preload to the suspension which favors one corner over the opposite side.

Here's a corner-balance worksheet you can use.

Sherwood Lee
http://members.rennlist.org/911pcars/cornerbalance.htm

[nhromyak]

Colby - I am using a hydraulic weight scale made by Deco, purchased from http://www.speedwaymotors.com/

Sherwood - I used your worksheet, although, I am not sure how that helps me...

Basically, I am going after aesthetics now, without screwing up performance and alignment too much.

I understood I should go after right and left balance with sway bars disconnected...right? So basically, this is done.

Porsche specifies the weight differences can be off my 40 Kg. This does not say, if it is per wheel 40Kg, or if it is per side by 40Kg. I guess, that is my question.

The second question I am facing, should I lower (less weight) the drivers side due to driver weight...correct?

I want to RAISE the drivers side due to aesthetics. : rolleyes :

On the plus SIDE It drives like a dream!! (provided the road is not trashed!)

Before it pulled to the right when braking, and when hitting some ruts on the fwy or roads.

[ChrisBennet]

"The wheel-load difference from left to right on the front and rear axle may not exceed 20kg (911 turbo max. 10kg)."

That's from page 44-2b in the Carrera workshop manual.

[nhromyak]

Thanks Chris! 20Kg... I stand corrected. ~ 35 lbs then.

[Clark Griswald]

Don't worry about the left to right weight distribution.

When corner balancing your goal is to get the F/R ratio the same left and right. That is LF/LR = RF/RR.

1/4 inch isn't much, but when you get in the car it will drop another 1/4 inch or so (depending on girth). That is more than I would accept.

Smart move is to corner balance and set ride height with your weight simulated in the driver seat.

Also, I would balance and height adjust with the sway bars connected. Your goal is to have the height and balance correct when driving, and you're going to have the sway bars connected then. Adjust everything for real world conditions.

[911pcars]

"Also, I would balance and height adjust with the sway bars connected. Your goal is to have the height and balance correct when driving, and you're going to have the sway bars connected then. Adjust everything for real world conditions."

If you leave the sway bar drop links connected, then you introduce a spring rate from the sway (anti-roll) bar into one end of the chassis (both corners) as you adjust the height. This is called preload, and it's not desireable unless you're going after a certain chassis effect (e.g. going around a circle track in one direction). After balancing the chassis, each corner height may be slightly different. Adjustable drop links maintain the corner balance by placing the sway bar in a neutral position.

Sherwood Lee
http://members.rennlist.org/911pcars

[jluetjen]

TIA;
For starters, good job getting to where you are. It does not look like your car is too far off. There might be a couple of places to improvement.

A) Are you concerned with you're car's corner weights with just the driver in the car or a driver and a passenger? If it is the latter (Driver and passenger), I'd recommend that you quit where you are. It looks like your car is pretty "square" which is a good thing!

B) If you are concerned about the corner weights with just a driver in the car, then there is some room to further optimise the set-up.

1) As others have already pointed out, you need to ballest the drivers seat with something approximating your weight. Unfortunately, by adding weight to the drivers side, the corner weights will change (I believe) in proportion to the change in location of the Center of Gravity for the car.

2) Jacking up the drivers side will not necessarily just shift the weight to the other side. It all depends on where the center of gravity of the car is. Go back to the analogy of the 4 legged stool. By corner weighting the car you are trying to ensure that it is not tettering on two (opposite corner) legs. If it is sitting evenly on on four legs, cutting two adjacent legs shorter will not shift the weight to the opposite side -- it will tip the stool towards the short legs and you will most likely wind up with those legs carrying more of the weight (if the stool doesn't fall over!). Now with a 911 it is even more complex since about 60% of the weight is in the back.

So if you raise the drivers side (for the sake of example ignoring the recommendation to ballest the drivers seat), I suspect that you'll be rolling weight ON-to the passenger side in roughly 40/60 ratio front to back. I suspect that this will then throw your corner weights off since the RR will pick up more weight then the RF. And the LF will lose less weight the LR. So I think that you'll find the corner weights shift significantly. No matter what my prediction is, you will mess up the corner weights. Frustrating huh? This is why lots of people don't bother and end up suffering so-so handling. But it does make a difference in the handling!

Here's an example. I used to race a front wheel drive car at Lime Rock which has all right hand corners (except for one left). The longest corner (Big Bend ~180 degrees) is entered while trail-braking from the longest straight. As a result the LF tire always had the highest temp's. I found that if I took a little weight off of the LF (by removing some shims over the spring) that the LF tire temperature went down and the car was happier trail braking into big-bend. BUT... going around the next turn (a throw-away left turn) the car would feel like it was on tip-toes. Ultimately my times came down so I continued to shift the corner-weights whenever I went there.

[Clark Griswald]

911pcars

I agree that the best scenario is to have adjustable drop links and dial it in with no preload, then put on the drop links as you recommend.

However, if he is going to use fixed drop links he should set the balance/height for the real world condition (eg. drop links attached).

[911pcars]

"I agree that the best scenario is to have adjustable drop links and dial it in with no preload, then put on the drop links as you recommend.

However, if he is going to use fixed drop links he should set the balance/height for the real world condition (eg. drop links attached)."

Chuck,
I need to clarify. I was referring to setting the car height, corner balance AND installing adjustable drop links so the final vehicle has a neutral sway bar setting. You cannot have different corner heights with fixed-length sway bar drop links without introducing preload in the suspension. Using fixed length drop links pulls the side-to-side height even, but doing so adds sway bar tension on the suspension and negates the initial effort of accurate corner balancing.

Sherwood Lee
http://members.rennlist.org/911pcars