Corner-weight -> alignment?

Or vice versa? Or does it really even matter??? I’ll definitely set ride height first.

Car in question is my 90 STS Miata, which is the first car I’ve ever cared to corner weight. The spring rates are 800 lb/in front & 650 lb/in rear, so I definitely won’t be making any significant differences in ride height to get it balanced. 

They are kinda related. 

You make enough changes to the corner balance, you may change the alignment settings.  And vice-versa.

Honestly, I don't think corner-balancing is worth it unless you are after that nth degree more.  For a National-level car, oh yes, do it.  But for a street car, or racing at your local puddle, I don't think it's time/money well spent.

But that's just my opinion.

If you are an engineer-type of person who thinks to four decimal places, get it done.  If you're a construction worker who can smack it with a hammer and it's true enough to hang drywall, fuggetaboutit.

I've corner-balanced a number of Miata.  They are pretty dang good out of the box.

In reply to SkinnyG :

I already have adjustable sleeves on it, and it looks like I can get a set of scales for under $250, so I figure it’s worth the effort. I’ll give it a good garage alignment too, but then I’ll take it to a shop so they can get it more precise. 

If you cornerweight properly, the ride height and thus the alignment will be untouched. Make sure the car goes on the scales at the height and stance you want with the perches as close as possible to the same height side to side. That’ll get you pretty close. 

Then, when balancing, adjust all four corners at the same time and by the same amount. Remember, there’s no point in doing just one corner because you can’t add/subtract weight just on that one. All you can do is shift weight from one diagonal to the other. So you raise both perches on the light diagonal and lower the other two by the same amount. Do that, and the car’s stance/height/alignment won’t change at all. Remember to have the sways unhooked when you do this.

Cornerweighting can make a big difference to things like braking - a light corner will be more prone to lockup. 

Keith Tanner said:

If you cornerweight properly, the ride height and thus the alignment will be untouched. Make sure the car goes on the scales at the height and stance you want with the perches as close as possible to the same height side to side. That’ll get you pretty close. 

Then, when balancing, adjust all four corners at the same time and by the same amount. Remember, there’s no point in doing just one corner because you can’t add/subtract weight just on that one. All you can do is shift weight from one diagonal to the other. So you raise both perches on the light diagonal and lower the other two by the same amount. Do that, and the car’s stance/height/alignment won’t change at all. Remember to have the sways unhooked when you do this.

Cornerweighting can make a big difference to things like braking - a light corner will be more prone to lockup. 

What Keith said. The ideal situation is starting with a fresh install (your springs should be settled though, which takes time and use) where your shock/coilover lengths and preload amounts are exactly the same side to side. Get your alignment right first. Then you can go after getting the corner weights how you want. If you start here you shouldn't be too far off from ideal cross weight. I find it helps to record ride height at each corner as you go. This gives you more information about which adjustments to make so you can keep the car level. If you've done this carefully your ride heights won't change significantly and therefore your alignment will have changed insignificantly. It's still a good idea to back and check the alignment, especially if you had to make large changes earlier. Remember that this is an iterative process and changes you make in one step effect the other step. You must be prepared to back and make adjustments until you are satisfied. But all that said, I would not sacrifice the quality of my alignment for a better corner balance.

If you adjust all four corners at the same time as I described, there will not be any change in ride height at all. Cornerweighting should not affect alignment at all. Adjusting just one or two corners is never the right solution unless you specifically want to change ride height.

Well, if your car is a flexy wet noodle, I can see that you might get some ride height changes at each corner as the chassis flexes. That's the sort of car where you can't open the doors unless it's parked on a perfectly flat surface, though. 

I THINK gross alignment changes might make a subtle difference in corner weights, but we're talking theoretical amounts of each.

In reply to Keith Tanner :

Thanks Keith!

"  I Don't Know Why, But I do Know How ".     'Suitcase Jake' .  1963  

There are some things you need to make sure you do in order to get it right.  Put either a person the same weight as you in the passenger seat, or at least put something heavy in there.  Make sure you roll the car backwards and then forwards again after every alignment adjustment.  Bouncing the car once in a while to help settle the suspension in place will also help with ride height adjustments.  Make sure the car is sitting dead level before you corner weight.  Most garages have a pitch to them.  I have different height shims to go under all four of my scales and squares on the floor where they go.  This makes sure the car is level every time and the readings are accurate.

If your corner-weights are off the car will handle differently in left turns versus right turns.  You could get into a situation where the car understeers turning left and oversteers turning right.  That makes it awfully difficult to make setup adjustments.

Caster can change your corner weight HUGE so set all the alignment stuff before you do corner weights.  To properly set up scales you need to use archimedes level (water level) to make sure all the scale pads are at same height. 4 graduated cylinders with inter connecting hoses on on each pad add water and shim the ones with the lower level until their all the same height.

Does caster change corner weight even with the wheels straight? I can certainly see how it would with the wheels turned.

Depends on how it's adjusted. For example, if you have a macstrut car with caster/camber plates, you add caster by moving the top of the coilover rearward, which would also have a slight effect on ride height and therefore it could have a meaningful effect on corner weight. If you had a double-wishbone car where the coilover connects to the lower wishbone and you adjust caster by moving the upper wishbone rearward, caster wouldn't affect ride height or corner weight when the wheels are straight.

Edit: Thinking about that a little more, there would still be a slight effect, since adjusting caster causes the hub to move in an arc above the lower wishbone. Zero caster would have the lowest ride height and greater amounts of caster would increase ride height a tiny bit. It would have far less effect than the macstrut + adjustable top mount setup though.

I think the best way to do it is rough alignment, then corner weights, then fine alignment. High-end race shops will repeat this for an entire work day to give you a super-accurate corner weighting & alignment for big $$$$.

Noob question here, but would you want to corner weight with the driver in the car and also with a typical fuel load? Or empty and no driver? I would imagine you want to balance the car as it would be driven, correct?

TheRX7Project said:

Noob question here, but would you want to corner weight with the driver in the car and also with a typical fuel load? Or empty and no driver? I would imagine you want to balance the car as it would be driven, correct?

That's right, the closer to race conditions the better.

(Usually they put weights in the driver's seat to simulate the driver)

Keith Tanner said:

Does caster change corner weight even with the wheels straight? I can certainly see how it would with the wheels turned.

In the case of my Miata, it would depend on a couple factors: Are the LCA bolts perfectly level? Does the arc described by the position of the upper & lower ball joints cause the hub to move vertically as the LCA is moved for caster adjustment? Those could cause corner weight changes, especially since with my 800 lb/in front springs a 1/8” change in ride height could shift 100lbs.

I'm going to have to spend some time with a pencil drawing this out Or maybe even try it to see how much we're talking about. I've spent time on the scales before testing things that I understood to be true but wanted to see for myself. Things like raising the ride height at one end and seeing what happens to the cross rates (nothing) or the effects of bad tire pressures. It's an educational way to spend time in the shop.

However, if the changes are symmetrical (ie, add 3* of caster on each side) you should see very little change in cross rates. If you put the car on the scales without even a rough alignment, I can see how you'd run into trouble afterwards.

When cornerweighting, you want the car in your "ideal" state. Driver (or equivalent), representative amount of fuel (especially if the tank is offset), tire pressures set, etc. Shocks should be set to full soft, sways should be disconnected. Keep in mind that there's a difference between a bunch of sandbags in the driver's seat and an actual person, as the driver will not typically be in a fetal position. Legs are heavy and they'll be extended. This is fine attention to detail, but if you're going to do it you might as well do it right.

When i was dwarf car racing i would put weight where my mass was when in the car. I figured it out by setting a scale under my butt and one under my feet and reached out my ands to the distance and height of the steering wheel i then took plastic tubs (laundry soap buckets)  and filled them with cement to the same number and placed one in the seat and the smaller one in front of the pedals. I also had a certain "settling ritual" where i would walk around the car and apply a load to each knerf bar and bumper with my foot, letting the car bonce back up and settle.  Always did the same three three pushes on each. I could see 4-5 lbs difference if not done in the same order or number of pushes. Now that 4- lbs is not a lot but car and driver were right at 1255lbs with 1250 being min weight after the race.  I liked to set my car with mid race fuel level as that's where i wanted to be the strongest.

 Really you Guy's?  800 lb. springs in the front of a Miata.  Dude that's all we ran on a HIGH Bank Oval with a 3000 lb car, That thing can't be working ,  But Chassis Flex will make you do stuff that ends up taking away control. Pete I can Be way Wrong but ya May as well Be on Bump Stops.  A Chassis that has travel can By the action of Movement Transfer weight During the run making Inside tires even heavier and attaining more grip,  but the spring must allow jounce and rebound to Let the sway bar do it's Job. 

For Instance, this is round track so it's only to show Massive weight transfer available;  car weigh's 3000 pounds,front is 51% rear 49%, now left side weight is 52% here is what I want to show ... 800 pound springs in front ,even spring rate  side to side, rear is only 225 on the left rear and 200 right side no sway bar in rear and front bar was almost 7/8". the thing is the car had 3" travel all around and sometimes 3.5 +" in the left rear,  Travel is Good 

motion ratio, 800lbs is the spring rate, not the wheel rate

You cannot simply compare spring rates from one vehicle to another as the motion ratios can be wildly different.

The reason you see Miatas with 800 lb springs is because they're faster around the track than Miatas with softer springs. And they have chassis rigidity and wheel travel. I've been running 750/500 on my track Miata for years, and it's softer than some of the others. I'll bet the Supermiata running this weekend at UTCC is over 1000 up front, and it's going to be hard to catch.

Keith Tanner said:

If you adjust all four corners at the same time as I described, there will not be any change in ride height at all. Cornerweighting should not affect alignment at all. Adjusting just one or two corners is never the right solution unless you specifically want to change ride height.

Well, if your car is a flexy wet noodle, I can see that you might get some ride height changes at each corner as the chassis flexes. That's the sort of car where you can't open the doors unless it's parked on a perfectly flat surface, though. 

I THINK gross alignment changes might make a subtle difference in corner weights, but we're talking theoretical amounts of each.

I rarely adjust more than two corners at a time but my car is so close to balanced that I make adjustments in 1/6 or 1/3 increments of a turn at a time. Each adjustment makes probably less than 1/16 of an inch of ride height, which for my car I'm happy with.