Setting Corner Weight

[tonywy]

Has anybody else out there done this on a street car ? I'm looking for numbers to compare to.

[davekp]

With me in the car, 302 efi, 3/4 tank of gas.
LF:574 RF:510
LR:694 RR:667

[CraigS]

Mine are similar. W/ just a driver the car is left side and rear heavy.

[tonywy]

This is what I ended up at:
LF 648
RF 623
LR 680
RR 649
LEFT 51% 1328
REAR 51% 1329
CROSS 50% 1303
TOTAL 2600 WITH ME IN THE CAR

[CraigS]

That is very good.

[Erik W. Treves]

If you have sway bars did you disconnect them? just asking.

[GTBradley]

Where are people getting the scales? Can they be rented?

[GFX2043mtu]

Borrow or buy scales. Just make sure they are good ones. I have a set of Longacre Computer scales and they work great. Very accurate and repeatable. Just make sure you also get run off pads with stops.

[Jeff Kleiner]

With me in the car, 302 efi, 3/4 tank of gas.
LF:574 RF:510
LR:694 RR:667

What was it without you Dave? I think I remember you saying that I had it set pretty close.

Jeff

[davekp]

Without me (with 3/4 tank of gas):
LF:526 RF:515
LR:620 RR:625

Yeah, pretty close!

[Avalanche325]

Honestly, unless you have done something VERY unusual in your build, there really is no need to corner weight a street car. I don't think I'd buy $1000 scales for a single use.

Race tuning shops should have them. Not sure how much a tuning session would cost. Maybe they would rent them to you.

[NAZ]

Agree with Avalanche. Adjust ride height even on side to side and drive it (I won't get into proper ride height adjustment and how that affects suspension geometry -- do your own research). Static weight distribution should be set to meet performance needs when designing and building the car. You are not going to be adjusting wedge on a street car.

I have scales as I race my car and adjusting wedge for weight transfer can make a difference in performance but it is track and set-up specific. For a street car you are operating on an infinite variety of road and weather conditions. And there is no one size fits all or "best" corner weights.

[i.e.427]

Race tuning shops should have them. Not sure how much a tuning session would cost. Maybe they would rent them to you.

We charge between $200 to $250 depending whether the car is solid axle or IRS. I don't think many shop would be willing to rent them, I know I wouldn't. Every F5R car that leaves our shop is corner-weighted. These car were all derived from racecar technology with very stiff chassis and near zero flex, a standard daily driver is not the same. Having near the same downward force on all 4 corners will give greater braking performance.

[mike223]

I don't think I'd buy $1000 scales for a single use.

I agree.

But if you notice one front brake locking (regularly) before the other - you can practically guarantee it's caused by corner weights.

And it's easy to fix.


1- Know your ride heights - know which corners could stand to be a little higher - know which corners could drop a little (they're never all going to be "perfect").

2- If one front locks early - add one half turn to the coilover on that corner or the diagonal opposite (one corner only) - OR - take half a turn off one of the other two corners (one corner only).

3- Repeat until you're convinced the fronts lock at essentially the same time.

4- When you get around to checking your corner weights later they will be "very good" (no further adjustment needed).

[tonywy]

Started the alignment process today...took most of the afternoon.
Caster: 4 degree Right side. 3 3/4 degree Left side
Camber -3/4 degree Right side. -1/2 degree Left side
Didn't get to the toe yet.

[Bob Cowan]

Honestly, unless you have done something VERY unusual in your build, there really is no need to corner weight a street car.

I would disagree. After install your chassis set up could be way off, especially if your ride heights are exactly the same left to right. If you're not racing, there's no need to get the balance exactly 50/50. But getting it pretty close will make a huge improvement in transient response and braking - the two most important facters in an emergency maneuver.

Many (most?) builders will spend a great deal of time tuning the engine for every last bit of power and drivability. But then fail to pay as much attention to the suspension. Power is nothing without control.

[davekp]

Do you have power steering?
If so, you probably want way more caster.

[Avalanche325]

I would disagree. After install your chassis set up could be way off, especially if your ride heights are exactly the same left to right.

Has anyone built one, set the ride heights per the manual, and had dangerously ill handling car? I haven't heard of one. You would have to do something radical, or have made a major mistake to be that far off.

There is nothing wrong with suspension tuning, especially for competition. So I am not saying that. Remember that he is talking about a street car. As soon as you add a passenger or change fuel loading, there go your perfect corner weights. "Strap in honey and we'll go to dinner." "OK, now let me put the sand bags in the drivers seat and roll her up on the scales." (Just trying to be funny)

[Jeff Kleiner]

Has anyone built one, set the ride heights per the manual, and had dangerously ill handling car? I haven't heard of one. You would have to do something radical, or have made a major mistake to be that far off.

Oh yeah! Not my build but one that came in for paint. The owner asked me to take a look at the brakes while I had it because he had a major lockup problem on one front wheel. While taking the wheels off to remove the body I noticed how radically different the spring collars were adjusted. He had it "cross jacked" with one set of diagonals tight and the other diagonal loose...for example RF and LR were actually taking most of the weight making the LF and RR light even though the ride height measured right. Guys don't realize that spring adjustments act in diagonal pairs; crank up the RF that puts weight on the LR and so on. The way I always explain it is to think of a 4 legged bar stool with one short leg---you will be teetering between the two legs on the opposite diagonal. This is what the car does if the weights are significantly off. I reset the springs and like magic the front corner didn't lock up anymore!

Jeff

[rich grsc]

Jeff, you're correct, a car that has been improperly adjusted needs correcting. On the other hand if you set the shocks by measuring the spring length, and not how the body looks compared to the wheels or ground, it will be so close as not needing to be adjusted for a street car. My car was setup by measuring the compressed spring length. I matched the front pair, then the back pair, side to side, not front to back. Our club has a set of scales, it was at one of our members as he had a new build and wanted it checked before he drove it. After his was scaled and adjusted I pulled mine on, I had over 2000 miles but never weighed it. Pulled on shut off the engine, looked over at the guy manning the readout, he looked up, said,"you're done, back it off", it was so close we couldn't have gotten it any better. So measure the shock spring, not the wheel opening.

[Avalanche325]

Are you saying that the ride heights were good with the corner weights that bad? Did you scale the car, or unload and redo the shock collars resetting ride height?

I have seen threads where people used gap from the tire to body, how many turns on the shock, and other strange things. I could also imagine if the whole car was low, and you really cranked one shock up to start with, you could get things in a strange setup. I just can't imagine that if everything is within manufacturing tolerances and installed correctly it will be grossly off.

I certainly consider both Bob and you as guys that have deep levels of knowledge.

I am certainly ready to hit the "I stand corrected" button if needed.....and head for the scales.

[GoDadGo]

I had no knowledge of how to do this, but with my trusty floor jack, some wood blocks and my jack spreader bar I got it darn close.

1. I disconnected the front sway bar before I started.
2. I set the front at 4.5" and counted the threads on the collars.
....The jack was on the differential in the center and I lifted it just enough for the rear wheels to be off the ground.
....I rolled the car back and forth as I adjusted the front collars until the car was level.
3. I did the same for the rear by jacking the front up in the center of the frame.
....I had to remove the front tires since the suspension was drooping.
....I rolled the car back and forth as I made adjustments to the rear collars until the car was level at the rear frame section.
4. I put the wheels back on and drove the car and came back to check my right heights.
....I adjusted only one side of the car to relevel it and found that my left to right colar thread counts were within roughly one thread count.
....When we eventually scaled the chassis, it was pretty close to 50/50 left to right and 50/50 front to rear.
....I don't have the typical rear weight bias because my drive-line is about 6" further forward than most and all iron, except for the intake.
....Also, my transmission clutch and flywheel are nearly 200 lbs so I've basically got fixed ballast sitting mid-ship.
5. I plan to re-scale the car when the body comes off for paint.

This is probably exactly what you don't want to do, but I got it pretty close by simply measuring the ride height and counting the threads on each collar.

https://youtu.be/CaRlqMmKIzk

[i.e.427]

Just an FYI for any of you, regardless of what way you setup your suspension. Step # 1 is always to set air pressure in your tires.

[Jeff Kleiner]

Are you saying that the ride heights were good with the corner weights that bad? Did you scale the car, or unload and redo the shock collars resetting ride height?

I have seen threads where people used gap from the tire to body, how many turns on the shock, and other strange things. I could also imagine if the whole car was low, and you really cranked one shock up to start with, you could get things in a strange setup. I just can't imagine that if everything is within manufacturing tolerances and installed correctly it will be grossly off.

I certainly consider both Bob and you as guys that have deep levels of knowledge.

I am certainly ready to hit the "I stand corrected" button if needed.....and head for the scales.

It would go something like this:

"Oh look, my LF is low, I'll just crank the spring up a little"..."well, now my RR is low so I'll adjust the spring tighter to raise it"..."well darn, now the LF is down again, I'll give it another turn"...

Next thing you know the springs are all jacked up with a bunch of weight on the LF & RR and the RF & LR kind of floating along. Remember what I said earlier about spring changes reacting on the diagonal---tightening the LF not only pushed that corner up but sent the RR down, then raising that corner sent the LF down again. In the end the tight springs on the LF and RR will weigh higher than the other two corners. Again, back to the stool...the short leg and it's diagonal companion will never bear the weight that the other pair of diagonals do.

Clear as mud yet? Man, this is getting to be like trying to explain how to determine pinion angle

Cheers,
Jeff

[NAZ]

I’m not sure everyone out there understands what you’re really accomplishing by putting a car on scales and adjusting spring preload. I’ve seen some posts refer to 50% weight bias but spring preload adjustment is not how you move weight around in a car. As Jeff said, you can adjust spring preload on one corner it will also influence the diagonal corner. A NASCAR racer will call this wedge but the more sophisticated sports car racers call this cross-weight. Add preload to the right front and the right front tire carries more of the car’s total weight but so does the left rear.



But you can adjust both front springs up or down and it is not going to move more weight to the rear of the car. Well, unless you make some significant height adjustments in feet not inches. But for all practical purposes the only way to move weight front to back or side to side is by physically adding, subtracting, or moving mass – not by adjusting springs. But also, as Jeff has shown us, some of us builders are so talented they can mess up a simple ride height adjustment – so it’s good to understand what affect turning those simple springs can have and what they will not do.


Since you guys that like to turn left and right live by this magazine, I found a clip on cross-weight you might be interested in: https://grassrootsmotorsports.com/ar...orner-weights/

[Bob Cowan]

This is how I started with my FFR:

- Set tire pressure to 35 psi
- disconnected sway bars
- about 1/2 tank of fuel
- Whatever you normally have in the trunk. Including that 40 pound tool bag.
- Raise the front, and adjusted the collars until they just contact the spring
- Do the same in the rear.
- Settle the suspension, and measure ride height.
- Change left and right collars the exact same amount. Exactly.
- keep doing this until you get to the ride height you want. I liked 4.5" and 5.5"

Now put the car on the scales. Mine was so close to perfect, I didn't touch it after that.

BUT.. I put it on the scales to find out. I didn't guess. I didn't assume. I measured it to find out. This was a car that I had spent hundreds of hours in R&D. I had some custom made parts, and some of the best off the shelf parts I could find. I could make that car sing and dance. I miss that car. I'm still working on the new car to get it where I want it to be.

This is science. Engineering. Either do the basics right, or you're going to struggle to get where you want to be. IMO, the only people who believe corner weights are not important, are the ones who have not done it.

[rich grsc]

This is how I started with my FFR:

- Set tire pressure to 35 psi
- disconnected sway bars
- about 1/2 tank of fuel
- Whatever you normally have in the trunk. Including that 40 pound tool bag.
- Raise the front, and adjusted the collars until they just contact the spring
- Do the same in the rear.
- Settle the suspension, and measure ride height.
- Change left and right collars the exact same amount. Exactly.
- keep doing this until you get to the ride height you want. I liked 4.5" and 5.5"

Now put the car on the scales. Mine was so close to perfect, I didn't touch it after that.

BUT.. I put it on the scales to find out. I didn't guess. I didn't assume. I measured it to find out. This was a car that I had spent hundreds of hours in R&D. I had some custom made parts, and some of the best off the shelf parts I could find. I could make that car sing and dance. I miss that car. I'm still working on the new car to get it where I want it to be.

This is science. Engineering. Either do the basics right, or you're going to struggle to get where you want to be. IMO, the only people who believe corner weights are not important, are the ones who have not done it.

This is the best, and simplest answer right there.

[GoDadGo]

This is the best, and simplest answer right there.

Amen!

[NAZ]

That’s what I like about this forum, a lot of varied opinions derived from a broad base of education and experience and people willing to share them. I’m still not convinced a street car needs to be scaled and cross weight adjusted but I’ve also been tuning on race car chassis since the mid-60’s and know I’m not going to crank a bunch of wedge into a car when I set the ride height.

It won’t hurt if you feel compelled to put your car on scales and tweak corner weights so you are at 50% cross weight or whatever the conventional wisdom dictates. Or have we decided yet what’s the ideal cross weight for a street car? My race car’s at 49.96%. Most drag racers don’t worry about cross weight but I like to stop straight at the big end.

Hey, while you have the scales out why not determine the CG height as well? Maybe we can get a conversation going about ideal CG location and segue into a discussion on roll center and roll axis – two other important concepts in race car handling. It’s too cold to work in the shop so some of us have extra time on our hands and need something to do until spring.

[Avalanche325]

OK. I'm not hitting the stand corrected button!
I will happily make an amendment....

Not really needed for a street car........

[GoDadGo]

OK. I'm not hitting the stand corrected button!
I will happily make an amendment....

Not really needed for a street car........ unless the builder is prone to excessive bouts of nitwittery.

Call Me Mr. Nit For Short!

[Tom Veale]

The county has out door scales for weighing trucks full of salt for the roads.
They read within ~10Lbs and its FREE. This is fine for a street car.
I drive on one wheel at a time and record the weight.
I then adjust the coil-overs to get the cross weights with me in the car to as close as the scales will get me.

Here's my '33 street rod's figures:
With Driver
CW_WD_05_2012.gif

Without Driver
CW_WO_05_2012.gif

Sorry, I can't seem to find weights on my Spec Racer any more.

Tom

[Bob Cowan]

So.... you're saying that people who finely tune their machines are nit wits? To each his own, I guess. What about people who finely tune their carbs? Exactly set their timing? Dyno tune their EFI's?

I'm going to guess that you've never actually put your own car on the scales.

[Avalanche325]

So.... you're saying that people who finely tune their machines are nit wits? To each his own, I guess. What about people who finely tune their carbs? Exactly set their timing? Dyno tune their EFI's?

I'm going to guess that you've never actually put your own car on the scales.

You missed what we were talking about.....

We we talking about someone that does something completely ridiculous while setting their ride height resulting in horrific corner weights.

Equivalent to:
Making a carb adjustment by changing 12 jet sizes only on one side.
Adjusting timing by adding 35 degrees.
EFI fuel curve a 14.7 everywhere.