Suspension Geometry maximums and problems

[StuwieP]

I've just been and had my wheels aligned - gave the specs I was after to the aligners, one recommended here. Can't recall the thread but essentially:
f: +5 caster, -1.1 camber, 1mm toe in
r:-1.5 camber and 2mm toe in

Anyway, 1 1/2hrs later, got the report back, told that -0.5 camber was the most that could be had out of the front suspension on one side (left I think). Other side matched (thankfully not left at -1.1 or whatever they felt like doing) and rears at -2 and -1.5 (left/right). caster was at 4/5 l/r, now both at ~4.3. Toe basically doubled (I suspect they looked at 1mm toe in and thought "this will be very non-pedestrian, he must want this on both sides, because he clearly hasn't got a clue what he wants, not like he just handed us his specs"): 2.5mm f and 3.7mm rear.
Not super happy right now. Car is numb, steering totally unresponsive. Drove over tram tracks, didn't move at all. Not even a twitch. That would be wonderful if I was driving a camry, but I'm not. It should hit me in the face and tell me to pay attention to the road.

What could be the cause of this inability to achieve what seems to be a quite conservative camber figure? i.e. what could cause the maximum achievable camber on the suspension arms to be -0.5? Aren't toe figures generally given as a total? (i don't want toe in on one side and toe out on the other, then I just have a steering wheel on a funny angle,so i just gave a total. Perhaps a communication breakdown on my part, I just assumed this) And further are there any reasons the caster figure couldn't be achieved?

Finally, contingent on my irritation being not totally misdirected, can someone recommend a good alignment specialist in Melbourne? For all that these guys are tyre specialists and doa good job there, apparently suspension (provided my car isn't the problem) isn't their thing. If my car is or could be the problem, any suggestions re. what could be done to fix this?

All my posts seem to run into essays, sorry.

Cheers
Stu

[M1474]

Standard ride height? I found the more caster I have, the less negative maximum camber.
Lower it.

[Magpie]

Possibly replace the camber bolts. I had a similar issue with mine that was solved by replacing them. However if you want to go -3 or greater on the camber you will need to change the arms and or have eccentric bushes installed.

Toe normally refers to TOTAL (as you said) toe so 2mm in should have got you 1mm in each side for a total of 2mm toe. Why so much toe anyway?

Where I have my alignment done they balast the car with the weight of the driver so that when they are making the settings they will be what you actually get Also they are happy for me to be there whilst they are doing the alignment so that the alignment can be discussed and I can see what they have done.

At the moment I'm restricted to about -2.4 camber on the front as the caster adjustment is causing a problem (it is not balanced beyond -2.4 on the front left). The person doing the alignment showed me what needs to be done to fix the problem (basically resetting the suspenssion arms). However I'm going down the path of replacing the arms so that I can get -3 or greater if ever needed.

When asking for the alignment tell them camber, toe and then caster in that order. Caster is not as important as the other settings (hopefully I will not get shot down for the caster comment).

[StuwieP]

standard ride height. All stock. sorry should have specified. Doesn't lowering the car = more negative camber because the a-arms move up towards the chassis? Or is it the other way around? Would be good if that were so but no cash=no suspension. Focus on getting roll bar + harnesses before fancy stuff like suspension

So the pursuit of +4.2-3 caster (despite my specifying 5) may have killed any chance of achieving -1 f camber without replacing pieces? Didn't even want so much caster anyway...
Would be nice to know my car isn't broken

I was using one of the suggested alignments in a thread here. suggested rear 2.4mm in for track. Only looking for 1mm on the fronts. Within mazda factory specs. Same as camber, not looking for anything drastic, -1.1 f, -1.5 r (not sure why rears were 0.5 degree out. Maybe some work is needed.
Either way next time I will take the time to be sure. write TOTAL <- like that next to my toe figures.

Any suggestions for dedicated alignment place in Melbourne? I'm inner SE suburbs. Next time I'd like to get at least close to the specs I ask for, rather than nothing at all (sorry, rear right wheel has correct camber. that's it.)

Thanks mate

Stu

[project.r.racing]

depends on what suspension shop you go do. some talk corners, some talk total. sounds like you have just been a victum of miscommunication.

and yes chasing caster will limit camber. best to chase the camber you want, then go with whatever maximum caster you can get. if you are unsure why they relate to each other on a double a-arm suspension, the google diagrams to understand why.

[93_Clubman]

Juffa recommends Bob Jane @ Morrabbin.

[StuwieP]

Re the toe - yep, communication is key. Problem was I wasn't there when the alignment was done, I could have seen what was happening and all would have been well in this case.

Re the camber; I had specified less (more?) caster (+5 not +4) not sure why they went (just) beyond factory specs for caster after I was specifically told over the phone if I supplied specs they wouldn't implement anything beyond factory limits. The biggest problem for me is that I really don't know enough about all this to be able to say what, if anything, was done wrong, certainly not enough to contradict the guys working there without the proper knowledge.

re caster angle, without seeing a diagram, wouldn't bringing the steering axis closer to upright limit the inboard movement of the upper a-arm, which would limit, naturally, being able to bring the upper part of the wheel further inboard (neg camber)? I don't think that made much sense but irrelevant. Me trying to wrap my head around it all.

Thanks for the help guys, looks like my questions have been answered for the most part. Everything else is between me and the shop.

Cheers
Stu

[NitroDann]

When I get home I'll post some links to help you understand, probably a good idea for a separate thread actually.

Dann

[Magpie]

try this http://www.fourcorks.com.au/cobra/wheelalign.html

[StuwieP]

Toe and camber are simple concepts for me to understand. I've read the 2nd piece on that link before.

Have now read it 4-5 times, still having trouble with caster. I understand the concepts of trail and how caster is measured. I already thought that caster (only, didn't know bout the directional stability thing - useful to have) increased - camber on the outside wheel during cornering / as the wheel is turned (presumably there is a gain in + camber on the inner wheel equal to the - gain) but didn't know how - and I'm still having trouble visualising that, even with various diagrams. I think I haven't a sufficient grasp of the steering mechanism to quite comprehend the system's physical movement, even if I grasp the results. The problem with that is I don't quite see how it interferes with negative camber, but I will accept that it does and leave it to the experts.

Anyway, again thanks for the help (and amazingly prompt replies). Dan if you want to start a "how suspension works" thread that involves some useful diagrams and theory (not NASCAR, please!) I'm all for that but for now I think my curiosity is satiated.

Cheers
Stu.

[gslender]

Caster is hard to visualise.

Think of the front wheels as having no suspension, but steering. The axis it rotates to steer is the Y axis. This y axis is mentally straight up and down. Vertical. The wheel turns left or right around the Y axis.

Now, if we rotated or twisted the Y axis 90 degrees, the wheels would now poke out at the top or bottom of the car when ever we steered in maximum lock (instead of left and right). This is an extreme example of how caster (moving towards 90 degrees in the Y axis) adds or removes camber depending how which way we steer (and if you add caster in the right direction)

Caster is normally only a few degrees, but you should now see how it would add to camber when turning.

I've always asked for max caster and then max camber. This should suit track or spirited driving.

G

[StuwieP]

That helped. A clearer iteration of the same information everywhere else. Thanks.

max caster is more +? I've got (currently) +4.3 which, aside from being outside factory tolerances, which the shop assured me they wouldn't do even if I asked (and I didn't) seems to be more like minimum achievable caster - closest to 0.

Basically the plan is for a road car which can go on the track without ruining the outside shoulders of a set of tyres completely, and also giving me a bit more grip through corners, hence going for only moderate camber targets, which haven't been attained up front (due to the stock height suspension and low - is it low or high?- caster angle, perhaps?) and have been overdone at the rear.

Still struggling. too much information and far too many "?" from me not helping.

Cheers
Stu

[gslender]

I'd put it down to going to a lazy suspension or tyre shop. A good alignment can take nearly an hour to do correctly. They should charge you close to $100 to do it right. If you are paying $50 or less then they have to be rushing.

Caster effects camber and so on, so getting one right requires redoing the other etc. It isn't a K Mart or Bob Jane tyre mart job, but often that's where it gets done... When buying tyres.

Also, the MX5 has caster adjustment, very few cars do, and most shops would rarely need to adjust for that, and that again can be why it is over looked.

Ask good mechanics around where you live who they would recommend - they would probably know if you don't get someone here volunteer.

I've found that http://www.fulcrumsuspensions.com.au/ are very good.

G

[NitroDann]

Its because both the camber eccentric bolt and the castor bolt are on the lower arm.

In the lower photo the black part represents the front subframe, with the front of the car to the top.

Only the right hand side suspension mounts and control arms are shown to simplify it.



The purple arm is the lower arm, the yellow is the upper.

The yellow upper arm is not able to be adjusted, as such all of the mounting points and the tip where it joins the hub are cannot be adjusted.

The purple lower arm can be adjusted by turning camber bolts, located at the inner side where they join with the subframe (little black rectangles)

You can see that the yellow upper arm is offset from the purple arm where they meet the hub. The fact that it is closer to the subframe shows the camber, and the fact that it is further back is the castor.

To adjust camber the front camber bolt is turned moving the purple arms tip in and outward, however it pivots on the rear subframe mount, the only other place the lower arm is attached. NOTE: because it pivots, the outer tip will not move straight in and out but in an arc.

Seeing the shape of the arms and how they are mounted you can clearly see how moving the front (top in picture) attachment point in and out will affect camber and the rear most attachment point will move the tip where the lower arm meets the hub forwards and backwards in an arc and affect the relationship the upper and lower arm has.

Because the camber and castor adjustments move the arm in an arc, maximim castor will actually have the lower arm move a little closer to the subframe, and therefor lower maximum camber.

The following image shows the lower arm moved forward by pushing the rearmost section away from the subframe. the blac dot shows its original position, the thin red arc shows the arc that the arm has travelled (and can travel in) and the distance between the blue lines shows the camber you have lost.



Hope that helped and didnt hinder.

Thanks,
Dann

EDIT: Sorry I was typing and retyping this between the last 5 posts, so this was supposed to go after your last reply to me.

[StuwieP]

haha thank you for the effort Dan. It's good to see how the two interact; until then I only understood each part as an independent actor. I really need to go watch the alignment guys do it to fully grasp it. But paint is good in the interim.

Essentially, by your diagram, there will be a specific point at which you can gain maximum camber, and then as caster increases or decreases, camber adjustment wll be lost.

For reference, when people say "maximum caster" does this refer to high positive values (around 7 degrees, eg), or low positive (around 4)? I'm looking for 5, as suggested on this forum (somewhere... sorry, not sure). 5+ seems as though it sits somewhere in the middle.

I don't know that they were lazy. Some of this is down to miscommunication. I think that the owner (my dad knows him, has had his cars done there, never problems but he's also never really cared enough to go down this route, trusted them to do the job to suit the car, but one is dedicated track, the other road) knows his stuff but they're always busy, and everyone else, perhaps less so... I wasn't paying $50 or less, and it took over an hour. I haven't got much $ to spare so at the moment it seems wasted. Partly annoyed at myself for not being more on the ball.

Cheers
Stu