Corner weights - what are the optimal settings

[wareaglescott]

What is a good distribution on the corner weighting front to back and left to right?

[CraigS]

If you put a simulated driver weight in your driver seat the car will always be left heavy. It is also always rear heavy w/ or w/o driver weight. For braking performance it would be best for the fronts to weigh the same but this isn't possible, at least on my MkII. I have a fairly crude measuring tool so it's maybe + or - 25# accuracy. I try to get the front to rear difference about the same on both sides so the cornering balance is the same going left and right. I may fudge that a bit to even our the fronts a little but cornering balance is more important to me. Since my gauge shows about 80# w/ no weight on it these numbers may not represent actual weights but my last session about a month ago I ended up w/ this;
LF 780 RF 740
LR 920 RR 900
So the left is 140 difference and the right is 160 difference, rear being heavier. And the fronts are only 40# different.

[wareaglescott]

thanks Craig

[Gromit]

I recall reading in one of Carol Smith books (I think it was Engineer to Win) short of moving things around in the car. The front to back and the right to left weight is what it is, ignoring fuel load. To that end you really want the cross weights to be the balanced . I like to imagine the car as a giant see-saw. As an over exaggeration imagine if you raised the ride high on the rt front and left rear (opposite corners). That would cause the car to "rock" back and forth across that axis. It would put more load on those 2 corners that are pushed down. It would cause those over loaded tires to loose traction first.

Now on a street car you need to turn left and right getting that balanced is the key

Lots of vehicle dynamics here braking into a corner pushes loads onto the front and outside front wheel while accelerating out of the corner shifts that load back and onto the outside rear.

If you were only turning left you can see how adjusting the cross weights (Indy cars, or wedge if your into nascar) can make a car loose into a corner or loose out. Even road course cars might not be perfectly balanced to gain an advantage on some corners and give up some on others

But for the streets I'd try to get it balanced

Chris AKA Gromit

[2bking]

What Craig said is right but for a little more detail its the cross weights that you are trying to equalize unless you are tuning the car to turn better one way or the other. Physics determines what the total axle weights will be as well as total left and right. Craigs show his the cross weights to be 780 + 900 = 1680 and 740 + 920 = 1660. There is something wrong with these weights unless his car actually weighs 3340 lbs but the cross weights are nearly equal. I spent a day weighing mine on a very flat floor and found when the frame height was equal left to right at the rear (4.5 inches on mine) and left to right at the front (4 inches on mine), the cross weights were nearly equal.

[Jim1855]

Craig,
I added the numbers and came up with 3,340. Can this be right?
I'm figuring my Challenge car be about 2,450 without me in it. Just approximations at this point so we'll see.
Jim

[NAZ]

As others have said, you can adjust cross weight (and thereby corner weight within limits) by using the coil-overs as weight jacks but you can't move front to rear or side to side weight by adjusting the suspension -- that requires physically moving weight, adding weight, or subtracting weight. I agree that for a street car you want the cross weight to be as close to even as possible, i.e. LF-RR the same as RF-LR. But this balancing act changes significantly as you add the driver and changes again as you add a passenger. Don't get wrapped around the Axle on corner weights for a street car. You're not going to put the car on scales before each time you drive it.

[wareaglescott]

Here is why I am asking and maybe ya'll can give me some recommendations on how to proceed.

When Whitby installed the body I had them take it to a local alignment shop and they set it up. The ride height was about perfect to me but that was with brand new springs and I was afraid as they broke in I would get some compression and end up to low. Car drives and handles very nicely and feels very stable during all the conditions I operate it in. Tracks straight and seems perfectly aligned.

Fast forward to about 1400 miles and I notice the right rear has sagged a bit and the other 3 corners have not. In an effort to correct that I raised the right rear up a bit and didn't mess with anything else. Visually it looked good and even but now I notice when I make a hard launch the car tends to bias left a bit. I am assuming the right rear is hooking up better than the left rear and that is causing the slight left motion. Prior to making this adjustment hard launches were straight ahead.

I am going to borrow some scales from a friend of a friend to see where I stood and wanted to have a good idea of how to proceed as far as adjusting all four corners.
I am just street driving. My cornering is well within the limits of the car so I am not cornering at a velocity that it is super critical for perfect balance. I do enjoy a hard acceleration off the line at times and would like to be confident in the rears hooking up pretty much equally. Plus I have not attempted a maximum braking maneuver since this started but I imagine whatever out of whack situation I have on acceleration would also affect my directional control during a hard braking maneuver.

Any thoughts/tips/comments are appreciated.
Thanks

[2bking]

The frame is very stiff but still a little flexible. So when you say the right rear seem to be sagging the left front should have seemed a bit high if was a spring change issue. The body may have shifted to cause the sag look and you corrected it with a spring change. Since you are going to weigh it, the measurements will tell what you have now so you can figure out what it was before your change. It is difficult to get correct weights one wheel at a time because of the added scale height vs the other wheel heights. I did mine one wheel at a time but blocked the three to the same height as the scales. It was time consuming and exhausting with all the jacking and reblocking.

[wareaglescott]

The frame is very stiff but still a little flexible. So when you say the right rear seem to be sagging the left front should have seemed a bit high if was a spring change issue. The body may have shifted to cause the sag look and you corrected it with a spring change. Since you are going to weigh it, the measurements will tell what you have now so you can figure out what it was before your change. It is difficult to get correct weights one wheel at a time because of the added scale height vs the other wheel heights. I did mine one wheel at a time but blocked the three to the same height as the scales. It was time consuming and exhausting with all the jacking and reblocking.

I am going to have 4 scales and the pneumatic jack on the lift makes it very easy to repeatedly lower the entire front or rear for trial and error. Hopefully it will go as smooth in reality as I am thinking in my head it will go! Although it rarely does! haha

[NAZ]

Keep in mind that it's always better to roll the car onto the scales than to lift it and set it on the scales. When you roll it on, the suspension is at a stable height with no bind. When you set it on the scales you can't help but put the suspension in a bind. When the suspension travels through its arc the tires move laterally (in and out). Setting the car straight down puts a side load on the tires as the suspension tries to reach equilibrium as it squats when supporting the car's weight. Roll the car a couple of feet and the side load goes away. You can see this for yourself, simply jack the front of your car off the ground with a floor jack then lower it. Check the ride height, roll the car a few feet and check ride height again. Since you have IRS you should also see this phenomenon at the rear of the car as well.

[Gromit]

If you have access to 4 scales that is the way to go, make some filler ramps between the scales and beyond then roll the car back and fourth to let it settle yes the lift will help you make changes but you want the suspension to unload before you measure the weights

Good luck
Chris

[CraigS]

Yep my weights are way high. The pressure gauge stays at about 80-100 w/ no weight on it. I need to order a new gauge. It was reacting to changes normally though so I think that, although the absolute #s are high, the relationships are correct. McMaster Carr, here I come.

[Bob Cowan]

There's been a lot of talk about corner weights in the past, and rightfully so. If you're not racing, you don't need to be OCD-precise about it. But getting the weight and balance pretty close will make the car predictable and easy to drive.

Start by setting ride height. Jack the car up and adjust the collars so they're just touching the tops of the springs. Put it back on the ground and measure ride height. If you fold up some plastic bags and put them under the tires, they will slide around and eliminate bind. As you adjust ride height, move the collars the exact same distance on both sides. After final adjustments are done, you'll find that ride height will not be exactly the same on both sides, it will be about 1/8-1/4" or so different, and that's OK.

Now put the car on the scales. You'll probably find that the corners weights are very close to where they should be. Not exactly perfect, but very close. On my MkII, the numbers were so close to perfect, I didn't touch it after that.

As you adjust your corners, make small changes. If you make big changes, you can make the numbers look good. But the suspension will actually be all out of whack, and it will have evil handling.

If your floor is not flat, you can place boards under the scales to prop them up and create a flat measuring area. Cut up squares of 1/4" plywood to make shims, and use a laser level on the highest area to measure off of. If you scales are not accurate, don't even waste your time. Just set your ride height like I described above, and move on.

[Jeff Kleiner]

Scott and I have already talked---for anyone I haven't talked to just listen to Bob

Jeff

[GoDadGo]

Hey Gang,

I really think everybody is over thinking this issue for their Street Driven Masterpieces.

All I did was jack the car up from the front end (In The Middle Using My Jack Spreader) and leveled the car from left to right by adjusting the rear springs. Then I jacked the car up again, but this time from the rear (Again Lifting From The The Middle) and leveled the front. Then I took it to the next level by repeating the process a few times until my ride height was at 4.5" Front & 4.75" Rear.

When we scaled it my car, minus the body, we found that it was pretty much 50/50 left to right and 50/50 front to back. Understand that my center of gravity is further forward than most, because my engine is about 6"-7" forward and only 1" to the right of center compared to the typical Ford Builds plus my pig of a transmission assembly tips the scales at nearly 200lbs. (146 lbs Trans, 28 lbs flywheel, plus the Clutch & Pressure Plate Assembly)

While I don't know how the car will ultimately handle, I focused on simply leveling the car and the corner weights seemed to take care of themselves. Maybe not knowing what I was doing really helped since I started with a couple of levels and a couple of floor jacks before my pal brought over his fancy scaling system.

Re-level the car and all or at least most will be right with the world.

Steve

[wareaglescott]

Hey Gang,

I really think everybody is over thinking this issue for their Street Driven Masterpieces.

All I did was jack the car up from the front end (In The Middle Using My Jack Spreader) and leveled the car from left to right by adjusting the rear springs. Then I jacked the car up again, but this time from the rear (Again Lifting From The The Middle) and leveled the front. Then I took it to the next level by repeating the process a few times until my ride height was at 4.5" Front & 4.75" Rear.

When we scaled it my car, minus the body, we found that it was pretty much 50/50 left to right and 50/50 front to back. Understand that my center of gravity is further forward than most, because my engine is about 6"-7" forward and only 1" to the right of center compared to the typical Ford Builds plus my pig of a transmission assembly tips the scales at nearly 200lbs. (146 lbs Trans, 28 lbs flywheel, plus the Clutch & Pressure Plate Assembly)

While I don't know how the car will ultimately handle, I focused on simply leveling the car and the corner weights seemed to take care of themselves. Maybe not knowing what I was doing really helped since I started with a couple of levels and a couple of floor jacks before my pal brought over his fancy scaling system.

Re-level the car and all or at least most will be right with the world.

Steve

You are right Steve in that if i just went back to how it was I would be fine for my street driving.
Mainly after 1700 miles now I miss the build aspect and like tinkering with stuff. Pre build I anticipated much more continuos maintenance time required to keep the car running good. The reality to this point is the coyote is so darn reliable it is pretty much just get in and go whenever I desire.

When I made the first adjustment it resulted in some undesirable characteristics on hard accelerations that did not previously exist so I know by seat of the pants feel that what I will do will make a difference. I figure since I have the scales available I might as well go all in and learn a little more about an area of the car I previously knew little to nothing about.

Some guys here drive these things to the limit and all this really matters. The majority of us never reach that limit and are pretty much all guilty of going over the top in a lot of areas. Huge difference between what is actually needed and what we actually do that exceeds the need. It is fun though so why not.

[GoDadGo]

You are right Steve in that if i just went back to how it was I would be fine for my street driving.
Mainly after 1700 miles now I miss the build aspect and like tinkering with stuff. Pre build I anticipated much more continuos maintenance time required to keep the car running good. The reality to this point is the coyote is so darn reliable it is pretty much just get in and go whenever I desire.

When I made the first adjustment it resulted in some undesirable characteristics on hard accelerations that did not previously exist so I know by seat of the pants feel that what I will do will make a difference. I figure since I have the scales available I might as well go all in and learn a little more about an area of the car I previously knew little to nothing about.

Some guys here drive these things to the limit and all this really matters. The majority of us never reach that limit and are pretty much all guilty of going over the top in a lot of areas. Huge difference between what is actually needed and what we actually do that exceeds the need. It is fun though so why not.

Scott,

Excellent Points plus I need to keep in mind that your car Is WAY, WAY, WAY More Complex than mine just from the suspension set up alone. Scaling will likely be necessary since you've got sway bars front and rear plus the I.R.S. set up as opposed to my 3-link solid axle rear with only a front sway bar to contend with.

Steve

PS: If you are bored, make your last stop at N.O.L.A. one day and come swing wrenches at Camp Go-Dad-Go!

[Duke]

Here's mine after adjustments:

:23psi, swaybars attached, 1/4 take fuel, #140lbs driver ballast:

:619 : 544:
:677 : 670:

(2,510 total, 46.3%F/53.6%R, 51.6%L, 48.3%R)

:23psi, swaybars off, 1/4 take fuel, #140lbs driver ballast:

:600 : 562:
:695 : 652:

[CraigS]

Duke the second set of #s are great.

[wareaglescott]

Here are my results I posted in my build thread.


I have a local buddy with some scales so he let me borrow them.



Here are the initial readings:


Total weight was 2468 pounds. This was with about 1/2 tank of gas. As you can see the rears had quite a large difference which validated my theory on the right rear having more weight on it causing it to have better traction.

I made a series of adjustments. Very easily accomplished thanks to the lift and pneumatic jack. I had it up and down about 10 times. I would lower it onto the wood blocks and roll it forward onto the scales each time. I also did a series of adjustments with 190lbs of dumb bells in the drivers seat. About half my rides I have someone with me.

Here are the numbers after I finished the adjustments:


I am very pleased how that worked out. I took it on a test drive and the straight line traction on hard launches seems much improved. Honestly with my street driving I am so far away from the handling limits of the car I don't think it will really make a noticeable difference on cornering. I am sure if I were at the limit it would be noticeable. I do enjoy hard accelerations though and am very happy with that improvement.

[GoDadGo]

Scott,

Did you have to make any adjustments to the sway bars or just the coil over springs?
Also, I am surprised that you have so much weight on the front, but I can only assume that the Coyote is a pretty hefty mill.
It seems to be a bit further forward compared to the 302 & 351 SBF builds.
Glad you figured the issue out.

Steve

[Railroad]

Nicely done!