DIY Corner Balance And Ride Height Adjustment - LotusTalk - The Lotus Cars Community
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post #1 of 140 (permalink) Old 08-24-2009, 11:01 PM Thread Starter
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DIY Corner Balance And Ride Height Adjustment

To properly corner balance your car, you need to have shocks with adjustable spring perches (i.e. Track Pack Bilsteins, Ohlins, Nitrons, etc.), and a set of weight scales. If you do this often enough, or are a car nut like me... you might buy your own set of scales; otherwise maybe you can borrow some from another nut.

The scales I have are from Longacre Racing; I've also purchased their roll-off levelers... that way I can compensate for my garage being about as level as the Arctic Sea during an episode of "The Deadliest Catch".

To level the scales, I use a contractor's laser level (Stanley makes a nice one for <$100). I set up the laser to be just slightly higher than the roll off levelers (10mm)... then I set each leveler to be an equal distance below the laser line by using the adjustable legs. I also try to adjust the legs so that the weight scales themselves are level on the leveler's platforms.

Now, since the weight scales are level, I can just measure the distance from the laser line to the car's chassis, adding the distance from the laser line to the top of the weight scale (in my case ~10mm).

Next concept... for those of you who might not be familiar with "corner balancing"... think of a four-legged table... if the legs aren't all the same length, the table will wobble. To fix the wobble, you can add a matchbook under one of the shorter legs (since it's harder to shorten a table leg than lengthen one). A car's suspension is similar... if there's a difference in the "height" of the corners, the car will not be as stable as if the heights match. The standard way to determine this is to compare the weight exerted on the left front + right rear wheels with the weight exerted on the right front + left rear wheels. With the scales I have, the "corner balance" is the ratio of the RF + LR weights divided by the total weight of the car. The goal is obviously 50&#37;.

In isolation, tightening a spring (by lowering the upper spring perch) will raise that corner and increase the weight it exerts on the scale... loosening a spring (by raising the upper spring perch) will lower that corner and decrease the weight it exerts on the scale.

So if your corner balance is off, what do you do? If your RF + LR weight is greater than your LF + RR weight, you have the following options:

1. Decrease the spring compression of the RF (move spring perch upward)
2. Decrease the spring compression of the LR (move spring perch upward)
3) Increase the spring compression of the LF (move spring perch downward)
4) Increase the spring compression of the RR (move spring perch downward)

or, some combination of the above...

So what combination should you use?

This is where ride heights come into play. If your ride height is good, and you don't want to change it... doing all four equally should leave your ride height unchanged. Doing 1+2 will probably lower the car at all four corners, doing 3+4 will probably raise the car at all four corners. Doing just 1) will lower the RF and raise the LR, doing just 2) will lower the LR and raise the RF, doing just 3) will raise the LF and lower the RR, and doing just 4) will raise the RR and lower the LF.

Let's say your corner balance is good and you want to change ride heights...

Moving spring perches upward or downward (to lower or raise height, respectively) on adjacent corners (i.e. LR+RR, or LR+LF) has a minimal affect on corner balance while affecting ride height at those corners.

Complicated? Well, a little bit. The best way to approach it is to take notes, make small adjustments, and be patient. See if the adjustment you made affected the ride height and corner balance in the way you expected... if not, figure out what you did wrong.

This is an admittedly terse description of how to corner balance and set ride height... I suppose I wasn't sure how much detail to get into. In any case, feel free to critique, ask questions, etc.

EDIT: Forgot this... very important... always ballast the car before doing any suspension measurement. If you track your car and drive alone, ballast for your weight. If you drive most often with a passenger, ballast for both you and a typical passenger. Also, inflate your tires to their "hot" pressures. You might also consider disconnecting one side of your front roll bar so it doesn't bias the front weights.

EDIT2: This post is more of an explanation of the concept of corner balancing... I'll try to put together a series of pictures documenting how I set up my workspace and proceed to set ride height and corner balance. More to come...

Last edited by apk919; 08-27-2009 at 10:55 PM. Reason: fixed minor details
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post #2 of 140 (permalink) Old 08-25-2009, 05:48 AM
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good stuff. I can attest to how this can make a big difference.

Last car I did was my Elan (elise hasn't adj perches), but I had to, iirc, roll the car back and forth to resume ride height after each adjustment.

I borrowed the scales from BMW CC NJ. Engine builder drove it, said it was most stable elan he'd driven. A friend w/unadjusted elan thought my speedometer was reading high @ speed; it wasn't.

In general (only), a 2 degree rake down in front is best for aerodynamics.

How far off was yours?

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post #3 of 140 (permalink) Old 08-25-2009, 07:18 AM
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Good continuation of the car setup posts, Andy We need to make some video tutorials

I was seriously thinking about making a simple/short vid for the DIY alignment... What do you say: you do the corner balance and I'll do the alignment vid?

IMO- Everyone that AX's or tracks their car would be well served by atleast doing their own alignments. If they have the shocks for the job and can swing the scales, same goes for corner balancing...

Happy driving!

Phil


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post #4 of 140 (permalink) Old 08-25-2009, 07:21 AM Thread Starter
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Quote:
Originally Posted by glb View Post
good stuff. I can attest to how this can make a big difference.

Last car I did was my Elan (elise hasn't adj perches), but I had to, iirc, roll the car back and forth to resume ride height after each adjustment.
Yes, good point... in addition to rolling it back and forth (which is another advantage of having roll-off levelers), you should bounce the car at each corner, and then roll it.

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Originally Posted by glb View Post
I borrowed the scales from BMW CC NJ. Engine builder drove it, said it was most stable elan he'd driven. A friend w/unadjusted elan thought my speedometer was reading high @ speed; it wasn't.

In general (only), a 2 degree rake down in front is best for aerodynamics.
Do you mean 2mm of rake or 2 of rake angle?

The points at which you measure ride height are the front jacking points (which are at the extreme front end of the aluminum chassis rails), and the side jacking points (which are at the extreme rear end of the aluminum chassis rails). The distance between these two points is about 1300mm. To get 2 of rake at distance of 1300mm would require (1300 * sin(2)) = 45mm of ride height difference.

I've heard from a number of sources that 5-10mm of ride height difference (higher in the back, of course) is optimal for the Elise/Exige body. 10mm equates to about 0.5 of rake.

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Originally Posted by glb View Post
How far off was yours?
Surprisingly enough, the corner balance on my Track Pack suspension was very close to 50% right from the factory (49.7%). Since our cars weigh around 2000 pounds, corner weights are around 400 pounds for the front corners and 600 pounds for the rear corners... so a ratio of 49.7% would imply an RF+LR weight of 994 pounds, or just 6 pounds short of perfect. While you could take your time to make it exactly 1000 pounds, a few tenths of a percent is close enough.

If you're changing suspensions, the best way to start off is to count threads on the spring perches... start off with the perches an equal number of threads from the top of the shock from side to side (LF=RF, LR=RR).
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post #5 of 140 (permalink) Old 08-25-2009, 07:27 AM
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In isolation, tightening a spring (by lowering the upper spring perch) will raise that corner and increase the weight it exerts on the scale... loosening a spring (by raising the upper spring perch) will lower that corner and decrease the weight it exerts on the scale.
I have never corner balanced a car, but this seems counter intuitive to me. Since I'm gearing up to get some ride height adjustable shocks, I'd like to make sure I understand what is involved.

First, adjusting the perch position doesn't actually tighten or loosen the spring, does it? It simply changes the position of the damper "plunger", no? I would think it would be bad for handling if the springs were compressed at different levels around the car. Am I wrong?

Second, lowering a corner should shift more weight onto it, not less. Intuitively, if I lift the corner of a table, it gets "lighter" the higher I go, not heavier.

Finally, if I "raise" the spring perch, it will shorten the overall shock length lowering, not raising, the car.

So, corner balancing a car is a trade off between ride height and weight distribution front to back. I may want more rake for aero reasons, but too much could exceed my target for weight balance.

Have I misunderstood something?

EDIT: And if anyone would care to discuss the pros/cons of controlling ride height other ways (e.g., the uprights from EliseParts) I'm all ears.
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post #6 of 140 (permalink) Old 08-25-2009, 07:29 AM
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Very excited about the thread. Buying DA shocks and planning on corner balancing with my buddy's scales in the next two week. Also likely going to do my own alignment.

I think the the DIY videos would be awesome! Look forward to seeing them!

05' Elise - REV400, PPE Header, Quaife LSD, Ohlins, BOE Silent Touch, LETSLA, ACT HDSS, Fidanza flywheel, BOE CAB Intake, BOE Catch Can, V2 Fuel Tank, V2 Steering Arms, BWR sway bar, ForcedFed CF splitter, Manly's engine mounts, All Mesh Grilles, Volk CE28 wheels
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post #7 of 140 (permalink) Old 08-25-2009, 07:29 AM Thread Starter
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Originally Posted by turbophil View Post
Good continuation of the car setup posts, Andy We need to make some video tutorials

I was seriously thinking about making a simple/short vid for the DIY alignment... What do you say: you do the corner balance and I'll do the alignment vid?

IMO- Everyone that AX's or tracks their car would be well served by atleast doing their own alignments. If they have the shocks for the job and can swing the scales, same goes for corner balancing...

Happy driving!

Phil
Thanks Phil... I usually take a bunch of photos whenever I do work on the car... maybe I can find enough of the corner balancing work to add some visual aids.
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post #8 of 140 (permalink) Old 08-25-2009, 07:43 AM Thread Starter
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Quote:
Originally Posted by Lotus-Position View Post
I have never corner balanced a car, but this seems counter intuitive to me. Since I'm gearing up to get some ride height adjustable shocks, I'd like to make sure I understand what is involved.

First, adjusting the perch position doesn't actually tighten or loosen the spring, does it? It simply changes the position of the damper "plunger", no? I would think it would be bad for handling if the springs were compressed at different levels around the car. Am I wrong?

Second, lowering a corner should shift more weight onto it, not less. Intuitively, if I lift the corner of a table, it gets "lighter" the higher I go, not heavier.

Finally, if I "raise" the spring perch, it will shorten the overall shock length lowering, not raising, the car.

So, corner balancing a car is a trade off between ride height and weight distribution front to back. I may want more rake for aero reasons, but too much could exceed my target for weight balance.

Have I misunderstood something?

EDIT: And if anyone would care to discuss the pros/cons of controlling ride height other ways (e.g., the uprights from EliseParts) I'm all ears.
See the picture of the shocks below...

The perch (gold ring near the "Nitron" logo) controls the spring's "preload"... that is, how much compression the spring is already under when the suspension is at full droop (equal to the free length of the shock absorber). When a spring is preloaded, it takes more force to compress (f = kx for a linear spring), hence it will reach a given amount of force at a shorter amount of shock compression. Less compression from full droop equals a longer shock length, and therefore a higher ride height.

"Lowering" a corner in isolation actually reduces the weight on it... the other corners try to compensate for the reduced spring force at that corner. Think of shortening just one adjustable foot of a washing machine... does that increase or decrease the weight on that foot (i.e. the foot becomes easier to turn as you shorten it)?

Also, you can change rake without altering corner balance... just move adjacent spring perches equally (say, lowering the front heights equally) and in theory your corner balance should stay very close to the same.

EDIT: It should be noted that not all cars use the same method for setting ride height... but this is typical for cars with fixed suspension pickup points and coil-over shocks. Changing the uprights can certainly change ride height, but it will not allow fine adjustment or corner balancing.
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Last edited by apk919; 08-25-2009 at 11:28 AM. Reason: spelling
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post #9 of 140 (permalink) Old 08-25-2009, 08:11 AM
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Andy, this is great as usual. You really have this down with a nice set up. Really appreciate your help checking out my car. At some point I would like to make some adjustments to my car as the rear outer toe links are rotated. Therefore, I would imagine resetting these to where they need to be would change the toe.
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post #10 of 140 (permalink) Old 08-25-2009, 08:33 AM Thread Starter
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Andy, this is great as usual. You really have this down with a nice set up. Really appreciate your help checking out my car. At some point I would like to make some adjustments to my car as the rear outer toe links are rotated. Therefore, I would imagine resetting these to where they need to be would change the toe.
Thanks Paul! Yes, if the two toe link joints need to be reoriented, it will likely change the toe.
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post #11 of 140 (permalink) Old 08-25-2009, 11:17 AM
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Do you mean 2mm of rake or 2 of rake angle?

The points at which you measure ride height are the front jacking points (which are at the extreme front end of the aluminum chassis rails), and the side jacking points (which are at the extreme rear end of the aluminum chassis rails). The distance between these two points is about 1300mm. To get 2 of rake at distance of 1300mm would require (1300 * sin(2)) = 45mm of ride height difference.

I've heard from a number of sources that 5-10mm of ride height difference (higher in the back, of course) is optimal for the Elise/Exige body. 10mm equates to about 0.5 of rake.

I thought of that while I was typing, but this pc of info is from decades ago and I honestly can't remember: 2 degrees, 2%, 2 mm, 2 feet????

Suffice to say that a little lower in frt is "a good thing", as per Martha Stewart.

05 elise (BOE Rev300 supercharged, SSRs, shift tower mods, Multivex; HID hi/low beams); 05 Corolla XRS. Past '72 Elan Sprint (I restored), Lotus 7 w/X-flow, TT Supra, Bugeye Sprite, BMW 2002 & 2002tii, '65 GTO.

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post #12 of 140 (permalink) Old 08-25-2009, 11:45 AM
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Good continuation of the car setup posts, Andy We need to make some video tutorials

I was seriously thinking about making a simple/short vid for the DIY alignment... What do you say: you do the corner balance and I'll do the alignment vid?

IMO- Everyone that AX's or tracks their car would be well served by atleast doing their own alignments. If they have the shocks for the job and can swing the scales, same goes for corner balancing...

Happy driving!

Phil
I would defiantly be interested in a video to show DIY alignments. Is this something a novice mechanic can do?

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post #13 of 140 (permalink) Old 08-25-2009, 11:55 AM
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I would defiantly be interested in a video to show DIY alignments. Is this something a novice mechanic can do?
Yep- If you can remove the wheels from the car and own a 19mm and 12mm wrench you can do the alignment. There are a couple other very helpful items that are pretty inexpensive to add, but that could be part of the tutorial...

If not a video, I'm sure I could do a step by step with pics... Andy's corner balancing is the more difficult operation, IMO. A vid with some verbal explanation would probably be even more helpful for that operation...

Phil


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2011 Pearl White Evora, BOE Skunk Works 6 SPD 435WHP || 2014 Black Evora Skunk Works IPS 390WHP|| 2011 White Evora Skunk Works IPS 390WHP || 2006 CO Elise, Rev400, Steet Car

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post #14 of 140 (permalink) Old 08-25-2009, 12:07 PM
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Is the alignment you are talking about the string one I have heard about. I have no idea what it is but have heard this method is pretty easy.

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post #15 of 140 (permalink) Old 08-25-2009, 12:11 PM Thread Starter
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Step #1: Preparing The Environment

To measure ride height and corner weights properly, you have to have a suitable environment to get accurate measurements. If you happen to have a work surface as smooth as a billiard table... I'm jealous. If you're like the rest of us, your garage floor is graded in at least one direction for water drainage, and probably not very flat.

You also need a large enough area to put a floor jack under the car, and take off the wheels if necessary. An open two car garage is more than sufficient.

Start by pulling your car into the garage and parking it in the position where you'd like to work on it. Take some tape and mark the position of each tire. Drive the car back out.

This is what my garage looks like:



Now place the scale platforms directly over the outlines of each tire (the scales are usually labeled for position: RF, LR, etc). You have to make sure that their surfaces are level, and they are all at the same height.

That's where the laser level in the picture above comes in. The laser projects a plane of laser light that's just about perfectly level... I'm using a precision paint can () to get the laser's height just a little higher than where I want the weight scales to be.

Now I take a plastic cap to which I've attached a piece of blue tape. I've marked a line 10mm from the bottom of the cap. The goal is to set the height of each platform so that it is 10mm below the laser line, and that each scale surface is level.



Once I've got that done, I marked the position of two of the legs of each the platforms so I can easily repeat the procedure without all the prep work.

To start working on the car, you drive the car back onto the taped marks, jack up each side one at a time, and slide the scale platforms underneath so their feet line up with the black marks. You're almost ready to start measuring...
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post #16 of 140 (permalink) Old 08-25-2009, 12:12 PM
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Turbophil just read your signature. My Lotus is my first car I have really tried wrenching on. So far its has been the basics but with help from this forum it has been easy, fun, and most of all rewarding!
I am enjoying this car more then anything else I have owned and part of it is the fact I am doing things myself. People like yourself have been the reason for my success.
I applaud everyone here for the detailed instructions and the great pictures to help show us novices how to wrench on our cars!

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post #17 of 140 (permalink) Old 08-25-2009, 12:43 PM Thread Starter
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Step #2: Measuring Ride Height And Corner Weights

Once you've placed your car over the marks, jacked it up and placed the scales underneath, you're almost ready to take measurements. Now is a good time to ballast your car... place weight in the driver's and passenger's seats equivalent to the weight you're expecting to carry. For track work, you probably want your body weight in the driver's seat. I use weight plates and barbells...

Also, inflate your tires to hot pressures. When in doubt, 5 psi above cold temps is a good guess (but depends on driving style and tire choices).

Since I have "roll-off" platforms... I first roll the car to the front of the platform, and off the weight scale itself. Make sure at least one of your platforms has front and back stops... you don't want the car to roll completely off the platform!

If it's a wireless scale system, turn it on... otherwise attach the signal wires from the scale's computer to each corner, making sure you attach the right wires to the right scales. Since the car is not on the scales, you can zero out the weight platform.

Now roll the car back onto the actual scales. This is what it should look like:



You can now read your corner weights...



To measure ride heights, I use the cap with the 10mm line drawn on it to calibrate the height of the scales. Since the scales measure weight by deforming slightly, they will no longer be exactly 10mm below the laser line... so I drew additional lines on the cap at 11mm and 12mm. For each corner of the car, place the cap on the scale next to the tire... and note how far below the laser line the surface of the scale is.

Now, use a tape measure to measure the distance from the chassis rail to the laser line:



Add the corresponding offset for that corner to get the true ride height (i.e. if the LF chassis rail is 110mm above the laser line, and the LF scale is 11mm below, the LF ride height is 110 + 11 = 121mm.

You've now measured corner weights and ride heights. Next step: how to adjust them...

Last edited by apk919; 08-25-2009 at 12:50 PM.
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post #18 of 140 (permalink) Old 08-25-2009, 06:59 PM
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A little while ago I made up a spreadsheet that is useful for those interested in the subject of corner balancing. After you enter the four corner weights in the appropriate cells it tells you everything (I think) you'd want to know including the optimal corner weights for your car. You can also see what shifting weight around in the car does to the corner weights. I'd be happy to e-mail it to anyone who PMs me for a copy. (And if anyone has any suggestions on how to improve it please let me know.)

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post #19 of 140 (permalink) Old 08-25-2009, 08:35 PM Thread Starter
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Step #3: Adjusting Ride Height And Corner Balance

If you know your ride heights and corner weights, the next step is to determine what needs to be changed. While you can try to hit your target ride heights and hit the optimal 50&#37; corner balance at the same time, it's easier to focus on one of the two goals at a time. Which first? I'd go with the one that's furthest from your target settings.

If your within a few tenths of a percent of perfect corner balance, I'd work with the ride heights first. If you're way off on corner balance... it's best to work toward getting that sorted first.

Let's say you're way off on corner balance (ignore this step if you're not). To keep the math simple let's say that your ballasted car weighs 2100 pounds, your target ride height is 130mm, and your measured corner weights and ride heights are:

<b>corner: weight, height</b>
LF: 420#, 132mm
RF: 400#, 130mm
LR: 680#, 130mm
RR: 600#, 128mm

Your cross weight (RF+LR / total) is (400 + 680) / 2100 = 51.4%. You need to decrease the weight on the RF and LR corners, and increase the weight on the LF and RR corners. To decrease the weight on a corner, reduce the spring's preload in that corner. To do that you must rotate the upper spring perch CCW. To increase the weight on a corner, increase the spring's preload in that corner (by rotating the upper spring perch CW).

Since the RF and LR are close to target ride height, I'd leave them alone for now and go with increasing the preload on the LF and RR springs. How do you change preload?

You'll need a lug nut wrench, a jackstand, and the spring perch spanners that usually come with adjustable height shocks (and with the Track Pack). While I recommend using the supplied spanners, there really are times when you can't get them to engage the perches because of space limitations. For that reason I use a set of drift pins with diameters equal to the holes drilled in the spring perches. It's also useful to have a permanent marker in a bright color (red is good). A little red paint can be used too.

In this case we'll start with the LF spring. Jack up the left side of the car high enough to remove the LF tire, and place the jackstand under the appropriate support point. Lower the car so it rests on the jackstand. Now remove the LF tire.

You'll see something like this (Track Pack shock shown):



The Track Pack shock shown above has two threaded collars... the lower one is the actual spring perch, the top one is a locking collar. You must loosen the locking collar before moving the perch collar. Some shocks don't have a locking collar... there is just the spring perch. Before you move the perch, mark the side facing you with the marker or paint. It will help you keep track of how much you've turned it. You may even want to put a distinctive mark over each "hole" in the collar (1,2,3 or A,B,C, etc) as you rotate it.

Since we're going to increase the preload, we need to turn the perch CW (like tightening a nut). How much do you turn it? That's a tough question to answer, and will be different for different types and rates of springs. I generally only tighten or loosen one turn at a time unless I'm making a major adjustment. YMMV. Note how much you've turned it... it'll help you decide how much to turn it next time if you need to readjust. After adjusting, if the perch has a locking collar, tighten it back down on the perch. It doesn't need to be very tight, just snug. Put the wheel back on and snug the lug nuts. No need to torque them to spec yet... just snug. Jack up the car and remove the jackstand. Lower the car back onto the scales.

Now do the same thing for the RR corner. Remember to place the jackstand at an appropriate place (yes, that means you probably have to remove the diffuser... while it changes the weight of the car slightly it has no effect on the corner balance since it's symmetrical to the centerline of the car).

RR spring perch (Nitron DA shown):



When you've increased the preload on the LF and RR springs, remeasure the corner balance. Bounce the car by hand and roll it on and off the scales to remove suspension binding.

You should see that the cross weight, RF+LR has decreased. Is it 50% yet? No? Add more preload to the LF and RR springs. Is it under 50%? Take a little preload out of the LF and RR springs. Are you close to 50%? Nice work.

Step 3 to be continued...

Last edited by apk919; 08-28-2009 at 02:41 PM. Reason: Posted better picture
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post #20 of 140 (permalink) Old 08-25-2009, 09:01 PM Thread Starter
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Step #3 (cont.): Adjusting Ride Height And Corner Balance

At this point you're fairly close to ideal corner balance (either by adjustment or by luck), and you want to adjust ride height.

If you did adjust corner balance, remeasure your ride height. Again... bounce the corners and roll the car off and on the scales.

Let's say your measurements are now thus:

<b>corner: weight, height</b>
LF: 430#, 132mm
RF: 390#, 130mm
LR: 660#, 130mm
RR: 620#, 128mm

So your corner balance is perfect: (390 + 660) / 2100 = 50.0&#37;

But your LF is high and your RR is low. What do you do? If you increase the preload on one corner, and decrease the preload on the diagonal corner an equal amount, the former corner will increase it's ride height and the latter corner will decrease it's ride height... and corner balance will not be affected significantly. In this case you want to decrease the preload on the LF corner and increase on the RR corner.

You might try one turn of decrease on the LF and one turn of increase on the RR. Take notes and remeasure your ride height. You should see that the LF height is lower and the RR height is higher, with minimal effect on the RF and LR heights. As before, if you're still not at your goal, tweak the corners a little more, if you've overshot, back off a little.

If instead your measurements look like this:

<b>corner: weight, height</b>
LF: 430#, 132mm
RF: 390#, 132mm
LR: 660#, 130mm
RR: 620#, 130mm

You want to lower the front ride heights without affecting the corner balance. Reducing the preload on both front springs will lower the front end without affecting the corner balance.

And lastly, if your measurements look like this:

<b>corner: weight, height</b>
LF: 430#, 130mm
RF: 390#, 128mm
LR: 660#, 130mm
RR: 620#, 128mm

You want to raise the right side heights without affecting the corner balance. Increasing the preload on the right side springs will raise the right side without appreciable altering the corner balance.

You can obviously have combinations of the above three conditions... if you're daring, you can try to solve the ride heights in one shot... or attack one mismatch at a time.

Step 3 will be continued...
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Last edited by apk919; 08-25-2009 at 11:06 PM.
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