I am about to purchase front camber adjusting plates for the front of my lowered 04 MCS. The product I like the most adjusts camber but not caster. Does it make sense? Or for the same $ buy a system that adjusts both? Is there ever a need to adjust caster? I will use this car for occasional street driving & autocrossing. Anyone install camber plates & then need to change caster & couldn't?

 

Most of the camber only plates are higher quality designs than the ones I've seen that do both.

My guess is that you'd know if you wanted/needed caster adjustment.

Unless there's a product out there that I haven't seen, I'd stick with a good quality camber-only design.

 

the ireland ones look interesting. and at only 275 bucks they seem like a steal?

 

I love my Ireland Street/Race plates... cheap, effective, and best of all, cheap. IMHO, they satisfy every requirement at half the price.

 

Messing with caster is much more tricky than camber. SAI and caster both affect returnability and steering response and therefore stability. I can't remember, but one typically aids high speed cornering stabilty while the other has a very close relationship to camber gain as a wheel turns in slow speed turns - aiding cornering grip in tight turns. I believe it is caster and SAI in that order. Too much of either will increase steering effort, increase kickback thru the steering, affects weight tranfer, pnuematic trail...basically a whole bunch of things I've long since forgotten about.

Just play with camber and have fun. The more geometry you play with, the less likely you are to be successful...and happy. Camber is very easy to grasp and understand.

 

to my thinking, the adjustability allows you to dial in both sides of the car to equal specs.

 

I never seem to remember that John. And to John's point, caster doesn't have to be far off for a nasty pull to one side to manifest.

 

I guess I was wondering if the ability to decrease caster for quick turn in on an autocross coarse & then return more positive caster for stability on the street was worth the effort? I do like the idea of adjusting caster to help with a slight pull, but normally that is bandading another problem like tire pull, incorrect camber split or brake drag.

 

I got the P&D (JLM) plates, they are camber/castor adjustable and they are one of the parts I'm proud of on my car. Not sure if he still produce them.

 

That will definately work up to a point afterwhich you may be fighting to get the wheel to turn back. Lots of caster will help wheels to return to center because caster, like SAI, lifts the car. The weight of the car returns the steering (simplified). At an extreme in the other direction - no caster - the wheels may not return well at all causing your car to stay in a locked position.

You'll have yo find a point where response is improved, but returnability or the lack of doesn't slow your steering response either. Make sense?

 

let me get this straight: if the steering axis were vertical, positive caster alone would function to steer the wheel straight but would not lift the car. (like casters on a rolling table or feathers on an arrow). Once you incline the steering axis back, any steering input in conjuction with postive caster will drop the car, right?

 

John,

Both raise the car because each cause the steering to travel along the face of a cone. Each contribute to different part of steering feel and grip. As I wrote above, I beleive SAI, among its other duties, contributes to tight cornering power and stability and caster contributes to high speed. The difference is more or less determined by steering angle. I wish I had a kinematics program - and someone to run it - just to see what all these things do in a what-if environment.

A caster wheel on a shopping kart has postive caster, but it is employed in a different way. The actual steering axis is vertical and sits above the wheel and forward of the center of the contact patch. Our car's caster is tilted to achieve placing the point of leverage out in front of the tire - same difference. The distance between the tire's center line and the point where caster intersects the ground in either case is called trail. Pneumatic trail is a condition that describes tire distortion and essentially increases trail/caster. Think od a cartoon where the car is speeding along and the tires are distorted into ovals - the contact patch actually moves backwards as speeds rise. This is also why domestic cars ran so little caster a while back as biased ply tires would distort in the same way. The day I saw Bugs Bunny driving a Caddy...

I was once part of an engineering forum. When I say engineering I mean the guys and gals engineering the cars we drive and many competition cars we see. SAI and caster were two intensely debated subjects. I was eventually thrown off the forum because I was found out to be a novice back yard type car guy, not an engineer.

 

meb,
As negative camber is increased SAI is also increased. But is it enough that a person would need Caster adjustment to compensate?

 

I'm not sure I understand??? You cannot compensate for SAI change with Caster in a way that will be outwardly meaningful. If I think about this for a moment...more negative camber will reshape the base of the SAI cone. (but because the cone is tilted due to caster, its new shape is not so simple to define) This may cause the body of the car to rise a bit more aiding returnability. However, there will be a point afterwhich the base grows so much it becomes flat - follow? The point where the strut attaches to the car is fixed. Moving the base of the cone farther and farther out begins to reduce the affect of raising the body.

If you are trying to determine the SAI's sweet spot (in isolation of everyhting else) as a way of keeping as much reternability as possible, but, increase turn in response by removing some caster...interesting, very interesting. The problem/question facing you is how do you determine the best grip vs returnability/stability? Seat of your pants is a good way, but this involves lots of time. A kinematics program could help you to theorize a narrower window, afterwhich you'll still need lots of seat of the pants time for adjusting.

Some of the subtleties in suspension design do not necessarily add up to big gains objectively, but may make your car feel better to you which will make YOU faster or more consistent.

Yes, adjusting camber also changes the SAI, which changes offset and also, front roll center. In the end, "everything affects everything else" is a great phrase to keep folded up in your pocket at times like these. It is very easy to get lost in a setup if you don't keep absolute track of where the changes occur.

As a follow up note, caster is a funny animal in some ways. I think it was phrased as a convenient conceit by an engineer I spoke with. Meaning, a front end that is properly designed and sorted out, does not require caster's band aid. It definately aids high speed stabilty at the expense of low speed responsiveness.

 

Meb: I've always understood as you explained it, but brainfart susceptible that I am, is seems like the wheel would rise as it rotates around that cone, thus lowering the chassis. Imagine a very extreme steering axis angle, almost horizontal, where my point is maybe more clear?

 

If I understand John; yes, I think you would be corect if the car were sitting in sand. On blacktop the ground pushes back with equal force causing the body to rise. Now I'm not sure I'm making any sense...let me go clear my head and I'l come back with a reason...or not.


...I'm back...John I understand. My answer is I agree with you, the car should fall, counter to almost everything I've read. The reason may lay with the number of degrees for a given vehicle, and, what happens on one wheel may not happen to the other. The inside wheel may actually lower while the outside remains at some constant creating the "rising condition". It's relative to what moves and what does not. I typically observed this in my mind as the car's body rising - and this is written in many manuals. However, one side may actually lower...very interesting. I love this stuff...and I was thinking I was getting board today.

...back again...if one side of the car rises and the other remains the same, I would expect to see lots of instability...what do you think? I think I'm full of it...gotta go look at some notes when I get home.

In any event, you'll find a bunch of learned folks who think lots of caster is a good thing and perhaps as meany who find it unnecessary. Depends upon the application I guess...and how big your arms are.

 

As I understand it Caster will cause the car to both rise & fall. If you turn the steering wheel to the rt. {with a car having positive caster} the rt. side spindle will try to drop. It cant drop because the ground doesn't let it, so the car rises on the rt. side. At the same time the left spindle is raising letting the car lower on the left side. SAI on the other hand should tend to raise both sides of the car at the same time as the spindle on both sides are rotating downward. A car that has a lot of SAI doesn't need as much caster to help the steering wheel return to the straight ahead possition.

 

...and correct you are. I dusted off 20 year old notes.

I want to add here regarding my note above about caster being a "convenient conceit"; That is one engineer's opinion based upon an ideal. We're not dealing with an ideal. There are plenty of folks who believe the added camber gain benefit from caster is a great thing.

BLIZZ, I'm sure you'll follow this path, but experiment with caution. Turn-in response must be wickedly quick for autoXing, but not at the expense of grip. I had a caster camber kit on my 99 Si and eventually removed it. The difference in turn-in responce is quite noticable...I think I added 3 degrees. This was a band-aid for Honda's typically light and dull feeling steering.

 

meb
In talking with you & thinking about my original question, I think I have an answer. The vehicle manufacturers in recent years have relied more on SAI than Caster to make their cars handle correctly.{partly because of the construction & type of suspension used}. But the amount of SAI needed is much more in comparison than Caster to arive at the same effect. So my thought is that another 2 degrees of SAI is a small enough percentage of total SAI that I would not have to compensate with a Caster change. I quess I will just have to see what happens in practice instead of theory. Thanks for your imput.

 

If your car is lowered you'll also be correcting roll couple by adding more negative camber. So essentially, you'll be able to achieve many things with one adjustment; better SAI and a better roll center relationship with the center of gravity.

Some folks damn a Mac strut for its packaging efficiency, it's not nearly as perfect as a Short and Long Arm suspension. But, it is far simpler to work on...good results come with less pain. SLA suspensions can be very tricky.

Good luck,

Michael

 

Blizz,

I'm not sure now about one side raising and the other lowering. My notes really aren't that clear after another read.

The spindles definately move thru arcs. But the effects of caster are also complicated by SAI and camber. jlm tried to imagine a positive caster value with zero SAI...I wonder...that might produce a different effect. In theory, if you imagine a chopper with a really long fork with the wheel turned to one side, the spindal drops on the inside but raises on the outside - in an extreme case the wheel would be flat on the ground.

Caster works in a straight line by leveraging the car's weight at a point ahead of the tire. In a turn, one tire scrubs the inside shoulder while the other scrubs the outside causing an aligning torque.

An easy way to determine what's happening with the mini is to simply measure body movement straight ahead vs lock to lock.

 

think this one over: if the "camber" of the steering axis was zero, but the axis was inclined back, the body would lift on turning no matter which way the wheel turned or which side of the car. As you make that "camber" negative, the wheel turning inward (left wheel/right turn) would arc up, lowering that corner of the car, but the wheel turning out (right wheel turning right) would arc down, raising that corner.

as far as the steering return to straight due to caster, a very thin tire would behave the same way as a fatter one.

 

Try making a simple prop to help see whats happening. Take a piece of steel welding rod {or something else like a wire or straightend out paper clip} bend a lower section @ 90 degrees to make an L shape. Now hold the rod staight up {verticle, no camber,caster or sai}with the shorter leg of the L on the bottom, turn therod in your fingers & watch the lower portion {spindle}, it doesn't raise or lower as it turns. Now if you tilt the top of the rod back towards you {positive caster}, and spin the rod in your fingers you will see the lower portion rise & fall from horizontal possition as it turns through its axis. You could also put the rod back to verticle & then tilt the top of the rod to your rt.{simulating positive sai & negative camber on the left wheel} watch the lower portion {spindle} as you rotate the rod in your hand. What do you think? Does that help? I hope you could follow my ramblings.

 

 

Imagine also a condition where the tires do not scrub while being turned - that they actually move the car instead. If you plot 12:00 at the top of the tire and 6:00 at the bottom - a vertical line - an outside turning tire with positive caster and zero SAI/camber will actually roll back on itself and drop relative to a mean axle line.

The character of the steering knuckle provides all the clues.